Achieve Mastery of Medical Concepts

Study for medical school and boards with Lecturio

Gastrointestinal Secretions

The primary functions of the GI tract include the digestion Digestion Digestion refers to the process of the mechanical and chemical breakdown of food into smaller particles, which can then be absorbed and utilized by the body. Digestion and Absorption of food and the absorption Absorption Absorption involves the uptake of nutrient molecules and their transfer from the lumen of the GI tract across the enterocytes and into the interstitial space, where they can be taken up in the venous or lymphatic circulation. Digestion and Absorption of nutrients. Multiple organs in the GI system secrete various substances into the lumen to assist in digestion Digestion Digestion refers to the process of the mechanical and chemical breakdown of food into smaller particles, which can then be absorbed and utilized by the body. Digestion and Absorption and/or the regulation of GI function. The majority of digestive secretions come from the salivary glands Salivary glands The salivary glands are exocrine glands positioned in and around the oral cavity. These glands are responsible for secreting saliva into the mouth, which aids in digestion. There are 3 major paired salivary glands: the sublingual, submandibular, and parotid glands. Salivary Glands: Anatomy, stomach Stomach The stomach is a muscular sac in the upper left portion of the abdomen that plays a critical role in digestion. The stomach develops from the foregut and connects the esophagus with the duodenum. Structurally, the stomach is C-shaped and forms a greater and lesser curvature and is divided grossly into regions: the cardia, fundus, body, and pylorus. Stomach: Anatomy, pancreas Pancreas The pancreas lies mostly posterior to the stomach and extends across the posterior abdominal wall from the duodenum on the right to the spleen on the left. This organ has both exocrine and endocrine tissue. Pancreas: Anatomy, and gallbladder Gallbladder The gallbladder is a pear-shaped sac, located directly beneath the liver, that sits on top of the superior part of the duodenum. The primary functions of the gallbladder include concentrating and storing up to 50 mL of bile. Gallbladder and Biliary Tract: Anatomy, although the intestines secrete fluids and mucus too, which are critical in protecting their inner walls.

Last updated: Aug 4, 2022

Editorial responsibility: Stanley Oiseth, Lindsay Jones, Evelin Maza

Phases of Digestion

Digestion Digestion Digestion refers to the process of the mechanical and chemical breakdown of food into smaller particles, which can then be absorbed and utilized by the body. Digestion and Absorption is divided into 3 phases, namely cephalic, gastric, and intestinal.

Cephalic phase

  • Begins when the brain Brain The part of central nervous system that is contained within the skull (cranium). Arising from the neural tube, the embryonic brain is comprised of three major parts including prosencephalon (the forebrain); mesencephalon (the midbrain); and rhombencephalon (the hindbrain). The developed brain consists of cerebrum; cerebellum; and other structures in the brain stem. Nervous System: Anatomy, Structure, and Classification receives stimulatory sensory Sensory Neurons which conduct nerve impulses to the central nervous system. Nervous System: Histology inputs about food from the chemo- and mechanoreceptors located in the oral and nasal cavities
  • Sensory Sensory Neurons which conduct nerve impulses to the central nervous system. Nervous System: Histology inputs capable of stimulating gastric activity include:
    • Seeing, smelling, tasting, or thinking about food
    • Chewing and swallowing Swallowing The act of taking solids and liquids into the gastrointestinal tract through the mouth and throat. Gastrointestinal Motility
  • Induces higher brain Brain The part of central nervous system that is contained within the skull (cranium). Arising from the neural tube, the embryonic brain is comprised of three major parts including prosencephalon (the forebrain); mesencephalon (the midbrain); and rhombencephalon (the hindbrain). The developed brain consists of cerebrum; cerebellum; and other structures in the brain stem. Nervous System: Anatomy, Structure, and Classification centers to stimulate the dorsal vagal complex (DVC)
  • The vagus nerve Vagus nerve The 10th cranial nerve. The vagus is a mixed nerve which contains somatic afferents (from skin in back of the ear and the external auditory meatus), visceral afferents (from the pharynx, larynx, thorax, and abdomen), parasympathetic efferents (to the thorax and abdomen), and efferents to striated muscle (of the larynx and pharynx). Pharynx: Anatomy (parasympathetic) releases acetylcholine Acetylcholine A neurotransmitter found at neuromuscular junctions, autonomic ganglia, parasympathetic effector junctions, a subset of sympathetic effector junctions, and at many sites in the central nervous system. Receptors and Neurotransmitters of the CNS ( ACh ACh A neurotransmitter found at neuromuscular junctions, autonomic ganglia, parasympathetic effector junctions, a subset of sympathetic effector junctions, and at many sites in the central nervous system. Receptors and Neurotransmitters of the CNS), which leads to:
    • ↑ Salivary secretions
    • ↑ Gastric secretions ( HCl HCL Hairy cell leukemia (HCL) is a rare, chronic, B-cell leukemia characterized by the accumulation of small mature B lymphocytes that have “hair-like projections” visible on microscopy. The abnormal cells accumulate in the peripheral blood, bone marrow (causing fibrosis), and red pulp of the spleen, leading to cytopenias. Hairy Cell Leukemia, pepsinogen) → chemical digestion Digestion Digestion refers to the process of the mechanical and chemical breakdown of food into smaller particles, which can then be absorbed and utilized by the body. Digestion and Absorption
    • Gastric motility Gastric motility Gastrointestinal Motility → mechanical digestion Digestion Digestion refers to the process of the mechanical and chemical breakdown of food into smaller particles, which can then be absorbed and utilized by the body. Digestion and Absorption

Gastric phase

  • Begins when swallowed food enters the stomach Stomach The stomach is a muscular sac in the upper left portion of the abdomen that plays a critical role in digestion. The stomach develops from the foregut and connects the esophagus with the duodenum. Structurally, the stomach is C-shaped and forms a greater and lesser curvature and is divided grossly into regions: the cardia, fundus, body, and pylorus. Stomach: Anatomy
  • Stimuli include:
    • Chemical stimuli: e.g., the presence of proteins Proteins Linear polypeptides that are synthesized on ribosomes and may be further modified, crosslinked, cleaved, or assembled into complex proteins with several subunits. The specific sequence of amino acids determines the shape the polypeptide will take, during protein folding, and the function of the protein. Energy Homeostasis, peptides, and amino acids Amino acids Organic compounds that generally contain an amino (-NH2) and a carboxyl (-COOH) group. Twenty alpha-amino acids are the subunits which are polymerized to form proteins. Basics of Amino Acids
    • Mechanical stimuli: e.g., stretching
  • Stimuli trigger Trigger The type of signal that initiates the inspiratory phase by the ventilator Invasive Mechanical Ventilation several reflexes → ↑ gastric secretions and motility Motility The motor activity of the gastrointestinal tract. Gastrointestinal Motility
    • Short reflexes (local reflexes):
      • Contained within the enteric nervous system Enteric nervous system Two ganglionated neural plexuses in the gut wall which form one of the three major divisions of the autonomic nervous system. The enteric nervous system innervates the gastrointestinal tract, the pancreas, and the gallbladder. It contains sensory neurons, interneurons, and motor neurons. Thus the circuitry can autonomously sense the tension and the chemical environment in the gut and regulate blood vessel tone, motility, secretions, and fluid transport. The system is itself governed by the central nervous system and receives both parasympathetic and sympathetic innervation. Autonomic Nervous System: Anatomy (ENS)
      • Sensory Sensory Neurons which conduct nerve impulses to the central nervous system. Nervous System: Histology signals travel to cell bodies in the ENS (located within the gut wall).
      • ENS coordinates the response → sends out a signal via the ENS efferents → ACh ACh A neurotransmitter found at neuromuscular junctions, autonomic ganglia, parasympathetic effector junctions, a subset of sympathetic effector junctions, and at many sites in the central nervous system. Receptors and Neurotransmitters of the CNS stimulates ↑ gastric secretions and GI motility Motility The motor activity of the gastrointestinal tract. Gastrointestinal Motility
    • Long reflexes (vago-vagal reflexes):
      • Response is coordinated in the brain Brain The part of central nervous system that is contained within the skull (cranium). Arising from the neural tube, the embryonic brain is comprised of three major parts including prosencephalon (the forebrain); mesencephalon (the midbrain); and rhombencephalon (the hindbrain). The developed brain consists of cerebrum; cerebellum; and other structures in the brain stem. Nervous System: Anatomy, Structure, and Classification.
      • Sensory Sensory Neurons which conduct nerve impulses to the central nervous system. Nervous System: Histology signals are transmitted to vagus nerve Vagus nerve The 10th cranial nerve. The vagus is a mixed nerve which contains somatic afferents (from skin in back of the ear and the external auditory meatus), visceral afferents (from the pharynx, larynx, thorax, and abdomen), parasympathetic efferents (to the thorax and abdomen), and efferents to striated muscle (of the larynx and pharynx). Pharynx: Anatomy afferents → travels to the DVC in the medulla
      • DVC coordinates a response → sends out a signal via vagal nerve efferents to the stomach Stomach The stomach is a muscular sac in the upper left portion of the abdomen that plays a critical role in digestion. The stomach develops from the foregut and connects the esophagus with the duodenum. Structurally, the stomach is C-shaped and forms a greater and lesser curvature and is divided grossly into regions: the cardia, fundus, body, and pylorus. Stomach: Anatomy ACh ACh A neurotransmitter found at neuromuscular junctions, autonomic ganglia, parasympathetic effector junctions, a subset of sympathetic effector junctions, and at many sites in the central nervous system. Receptors and Neurotransmitters of the CNS stimulates gastric secretions and motility Motility The motor activity of the gastrointestinal tract. Gastrointestinal Motility
Neural regulation of gastric secretions

Neural regulation of gastric secretions:
The enteric nervous system Enteric nervous system Two ganglionated neural plexuses in the gut wall which form one of the three major divisions of the autonomic nervous system. The enteric nervous system innervates the gastrointestinal tract, the pancreas, and the gallbladder. It contains sensory neurons, interneurons, and motor neurons. Thus the circuitry can autonomously sense the tension and the chemical environment in the gut and regulate blood vessel tone, motility, secretions, and fluid transport. The system is itself governed by the central nervous system and receives both parasympathetic and sympathetic innervation. Autonomic Nervous System: Anatomy (ENS) reflex (also known as the short reflex) and the vaso-vagal reflex (also known as the long reflex) are shown.
GRP: gastrin-releasing peptide gastrin-releasing peptide Neuropeptide and gut hormone that helps regulate gastric acid secretion and motor function. Once released from nerves in the antrum of the stomach, the neuropeptide stimulates release of gastrin from the gastrin-secreting cells. Gastrointestinal Neural and Hormonal Signaling

Image by Lecturio.

Intestinal phase

  • Begins when food leaves the stomach Stomach The stomach is a muscular sac in the upper left portion of the abdomen that plays a critical role in digestion. The stomach develops from the foregut and connects the esophagus with the duodenum. Structurally, the stomach is C-shaped and forms a greater and lesser curvature and is divided grossly into regions: the cardia, fundus, body, and pylorus. Stomach: Anatomy and enters the duodenum Duodenum The shortest and widest portion of the small intestine adjacent to the pylorus of the stomach. It is named for having the length equal to about the width of 12 fingers. Small Intestine: Anatomy
  • Duodenum Duodenum The shortest and widest portion of the small intestine adjacent to the pylorus of the stomach. It is named for having the length equal to about the width of 12 fingers. Small Intestine: Anatomy:
    • Modulates gastric activity via hormones Hormones Hormones are messenger molecules that are synthesized in one part of the body and move through the bloodstream to exert specific regulatory effects on another part of the body. Hormones play critical roles in coordinating cellular activities throughout the body in response to the constant changes in both the internal and external environments. Hormones: Overview and Types and neural reflexes:
      • Initially, the signals stimulate gastric activity.
      • Soon, the signals inhibit gastric activity.
    • Secretes signaling molecules Signaling molecules Second Messengers (e.g., cholecystokinin) that stimulate secretions from the pancreas Pancreas The pancreas lies mostly posterior to the stomach and extends across the posterior abdominal wall from the duodenum on the right to the spleen on the left. This organ has both exocrine and endocrine tissue. Pancreas: Anatomy and gallbladder Gallbladder The gallbladder is a pear-shaped sac, located directly beneath the liver, that sits on top of the superior part of the duodenum. The primary functions of the gallbladder include concentrating and storing up to 50 mL of bile. Gallbladder and Biliary Tract: Anatomy
  • Absorption Absorption Absorption involves the uptake of nutrient molecules and their transfer from the lumen of the GI tract across the enterocytes and into the interstitial space, where they can be taken up in the venous or lymphatic circulation. Digestion and Absorption of nutrients begins.
Phases of digestion with their functional components

Phases of digestion Digestion Digestion refers to the process of the mechanical and chemical breakdown of food into smaller particles, which can then be absorbed and utilized by the body. Digestion and Absorption with their functional components

Image by Lecturio.

Salivary Secretions

Functions of salivary secretions

  • Protection of the oral cavity
  • Lubrication
  • Digestion of carbohydrates Digestion of carbohydrates Carbohydrates store energy and are used as a source of nutrition. To be used as energy by humans, most carbohydrates must be metabolized. Carbohydrate metabolism involves transforming complex starches into glucose, a monosaccharide that can subsequently be absorbed by the body. Digestion and Absorption of Carbohydrates and lipids Lipids Lipids are a diverse group of hydrophobic organic molecules, which include fats, oils, sterols, and waxes. Fatty Acids and Lipids

Salivary glands Salivary glands The salivary glands are exocrine glands positioned in and around the oral cavity. These glands are responsible for secreting saliva into the mouth, which aids in digestion. There are 3 major paired salivary glands: the sublingual, submandibular, and parotid glands. Salivary Glands: Anatomy

There are 3 primary salivary glands Salivary glands The salivary glands are exocrine glands positioned in and around the oral cavity. These glands are responsible for secreting saliva into the mouth, which aids in digestion. There are 3 major paired salivary glands: the sublingual, submandibular, and parotid glands. Salivary Glands: Anatomy (all with a tubuloacinar structure), which together produce a combination of serous and mucous secretions.

  • Parotid glands: serous secretion Secretion Coagulation Studies
  • Submandibular glands: both serous and mucous secretions
  • Sublingual glands: mainly mucous secretions, with a small serous component
Location of the three primary salivary glands

Location of the 3 primary salivary glands Salivary glands The salivary glands are exocrine glands positioned in and around the oral cavity. These glands are responsible for secreting saliva into the mouth, which aids in digestion. There are 3 major paired salivary glands: the sublingual, submandibular, and parotid glands. Salivary Glands: Anatomy:
Parotid, submandibular, and sublingual glands

Image by Lecturio.

Constituents of saliva Saliva The clear, viscous fluid secreted by the salivary glands and mucous glands of the mouth. It contains mucins, water, organic salts, and ptyalin. Salivary Glands: Anatomy

Saliva Saliva The clear, viscous fluid secreted by the salivary glands and mucous glands of the mouth. It contains mucins, water, organic salts, and ptyalin. Salivary Glands: Anatomy consists of:

  • Water
  • Mucus
  • Electrolytes Electrolytes Electrolytes are mineral salts that dissolve in water and dissociate into charged particles called ions, which can be either be positively (cations) or negatively (anions) charged. Electrolytes are distributed in the extracellular and intracellular compartments in different concentrations. Electrolytes are essential for various basic life-sustaining functions. Electrolytes:
    • K+: assists in the reabsorption of Na+ and water
    • HCO3: buffers Buffers A chemical system that functions to control the levels of specific ions in solution. When the level of hydrogen ion in solution is controlled the system is called a ph buffer. Acid-Base Balance acid
  • Enzymes Enzymes Enzymes are complex protein biocatalysts that accelerate chemical reactions without being consumed by them. Due to the body’s constant metabolic needs, the absence of enzymes would make life unsustainable, as reactions would occur too slowly without these molecules. Basics of Enzymes:
  • Antimicrobial agents:
    • Muramidase: lysozyme (an enzyme that can destroy cell walls of certain bacteria Bacteria Bacteria are prokaryotic single-celled microorganisms that are metabolically active and divide by binary fission. Some of these organisms play a significant role in the pathogenesis of diseases. Bacteriology)
    • Lactoferrin: binds iron Iron A metallic element with atomic symbol fe, atomic number 26, and atomic weight 55. 85. It is an essential constituent of hemoglobins; cytochromes; and iron-binding proteins. It plays a role in cellular redox reactions and in the transport of oxygen. Trace Elements, which helps prevent bacterial growth
    • IgA IgA Represents 15-20% of the human serum immunoglobulins, mostly as the 4-chain polymer in humans or dimer in other mammals. Secretory iga is the main immunoglobulin in secretions. Immunoglobulins: Types and Functions: immune mediator (secreted antibody)

Saliva Saliva The clear, viscous fluid secreted by the salivary glands and mucous glands of the mouth. It contains mucins, water, organic salts, and ptyalin. Salivary Glands: Anatomy production

Overview:

  • Saliva Saliva The clear, viscous fluid secreted by the salivary glands and mucous glands of the mouth. It contains mucins, water, organic salts, and ptyalin. Salivary Glands: Anatomy is produced by acinar cells in the salivary glands Salivary glands The salivary glands are exocrine glands positioned in and around the oral cavity. These glands are responsible for secreting saliva into the mouth, which aids in digestion. There are 3 major paired salivary glands: the sublingual, submandibular, and parotid glands. Salivary Glands: Anatomy as a filtrate.
  • Modified by ductal cells as it moves through the ducts
  • Salivary glands Salivary glands The salivary glands are exocrine glands positioned in and around the oral cavity. These glands are responsible for secreting saliva into the mouth, which aids in digestion. There are 3 major paired salivary glands: the sublingual, submandibular, and parotid glands. Salivary Glands: Anatomy secrete approximately 1‒1.5 L of saliva Saliva The clear, viscous fluid secreted by the salivary glands and mucous glands of the mouth. It contains mucins, water, organic salts, and ptyalin. Salivary Glands: Anatomy daily.
Diagram of ionic secretion by the acinar cells and their movement across the ductal cells

Diagram detailing the ionic secretion Secretion Coagulation Studies by acinar cells and their movement across ductal cells

Image by Lecturio.

Acinar cells:

Acinar cells secrete a filtrate containing Na+, K+, Cl, HCO3, water, and other substances.

  • Na+/K+ ATPase pump Pump ACES and RUSH: Resuscitation Ultrasound Protocols keeps:
    • K+ concentrated within acinar cells
    • Na+ concentrated in the interstitial space
  • Movement of Na+:
    • Na+ moves paracellularly to the acini lumen down its concentration gradient → Na+ is secreted in saliva Saliva The clear, viscous fluid secreted by the salivary glands and mucous glands of the mouth. It contains mucins, water, organic salts, and ptyalin. Salivary Glands: Anatomy
    • Brought into acinar cells via the Na+/Cl cotransporter on the basolateral membrane → Na+ is transported to the interstitial space with H+
  • Movement of water:
  • Movement of K+:
  • Movement of Cl, H+, and HCO3:
    • CO2 is produced during metabolism → CO2 combines with H2O → carbonic acid (H2CO3) → splits into H+ and HCO3
    • H+ and Na+ are transported into the interstitial space via the H+/Na+ cotransporter on the basolateral membrane.
    • HCO3 (from metabolism) and Cl (from the Na+/Cl basolateral cotransporter) are secreted via the HCO3/Cl cotransporter on the apical (lumenal) membrane
  • Produce and secrete other substances (e.g., mucin, enzymes Enzymes Enzymes are complex protein biocatalysts that accelerate chemical reactions without being consumed by them. Due to the body’s constant metabolic needs, the absence of enzymes would make life unsustainable, as reactions would occur too slowly without these molecules. Basics of Enzymes) into the acini
A diagram showing ion secretion by acinar cells

Diagram showing ion secretion Secretion Coagulation Studies by acinar cells:
In the acinar cells, Na+, K+, Cl, and HCO3 are filtered or secreted into the salivary fluid (note: Na+ and Cl are later reabsorbed by ductal cells).

Image by Lecturio.

Ductal cells:

Ductal cells modify the filtrate as it moves through the ducts, ultimately reabsorbing Na+ and Cl and secreting more K+ and HCO3.

  • Reabsorption of Na+ and secretion Secretion Coagulation Studies of K+:
    • Na+ and H+ are reabsorbed across the apical membrane via the Na+/H+ cotransporter.
    • Na+ is pumped out across the basolateral membrane into the interstitial space via the Na+/K+ ATPase pump Pump ACES and RUSH: Resuscitation Ultrasound Protocols.
    • H+ is recycled back into the lumen while K+ is secreted: H+ and K+ are moved across the apical membrane via the H+/K+ cotransporter.
  • Reabsorption of Cl and secretion Secretion Coagulation Studies of HCO3:
    • CO2 is produced during metabolism → CO2 combines with H2O → H2CO3 → splits into H+ and HCO3
    • HCO3 is exchanged for Cl on the apical membrane (HCO3 is secreted and Cl is reabsorbed into the ductal cell) via the HCO3/Cl countertransporter.
    • Cl is reabsorbed into the interstitial space via Cl channels Channels The Cell: Cell Membrane.
    • H+ (left over from the carbonic anhydrase Carbonic anhydrase A family of zinc-containing enzymes that catalyze the reversible hydration of carbon dioxide. They play an important role in the transport of carbon dioxide from the tissues to the lung. Carbonic Anhydrase Inhibitors reaction) is removed across the basolateral membrane via the H+/Na+ countertransporter (Na+ is moving down its concentration gradient into the cell).
  • As water is not reabsorbed (but some ions are), the resulting saliva Saliva The clear, viscous fluid secreted by the salivary glands and mucous glands of the mouth. It contains mucins, water, organic salts, and ptyalin. Salivary Glands: Anatomy is hypotonic Hypotonic Solutions that have a lesser osmotic pressure than a reference solution such as blood, plasma, or interstitial fluid. Renal Sodium and Water Regulation.
Ion transport by ductal cells

Diagram showing ion transport by ductal cells:
The Na+/H+ cotransporter reabsorbs Na+ and H+ from the salivary fluid. The Na+ is then pumped across the basolateral membrane by Na+/K+ ATPase, and K+ is brought into the cell. Next, H+ is recycled back into the lumen along with K+ via an H+/K+ cotransporter. The H+ is then used to reabsorb more Na+, whereas K+ remains in the saliva Saliva The clear, viscous fluid secreted by the salivary glands and mucous glands of the mouth. It contains mucins, water, organic salts, and ptyalin. Salivary Glands: Anatomy and is excreted. Chloride Chloride Inorganic compounds derived from hydrochloric acid that contain the Cl- ion. Electrolytes is reabsorbed, whereas HCO3 is excreted via the Cl/HCO3 exchanger on the apical membrane.

Image by Lecturio.

Control and regulation of salivary secretions

  • Involved in the cephalic phase of digestion Digestion Digestion refers to the process of the mechanical and chemical breakdown of food into smaller particles, which can then be absorbed and utilized by the body. Digestion and Absorption:
    • Sensory Sensory Neurons which conduct nerve impulses to the central nervous system. Nervous System: Histology input capable of stimulating salivation:
      • Thinking about food
      • Seeing, smelling, or tasting food
    • Induces higher brain Brain The part of central nervous system that is contained within the skull (cranium). Arising from the neural tube, the embryonic brain is comprised of three major parts including prosencephalon (the forebrain); mesencephalon (the midbrain); and rhombencephalon (the hindbrain). The developed brain consists of cerebrum; cerebellum; and other structures in the brain stem. Nervous System: Anatomy, Structure, and Classification centers to stimulate the ANS ANS The ans is a component of the peripheral nervous system that uses both afferent (sensory) and efferent (effector) neurons, which control the functioning of the internal organs and involuntary processes via connections with the CNS. The ans consists of the sympathetic and parasympathetic nervous systems. Autonomic Nervous System: Anatomy (primarily the parasympathetics)
  • Parasympathetic stimulation increases salivary secretions via:
    • ACh ACh A neurotransmitter found at neuromuscular junctions, autonomic ganglia, parasympathetic effector junctions, a subset of sympathetic effector junctions, and at many sites in the central nervous system. Receptors and Neurotransmitters of the CNS: increases salivary secretions
    • Vasoactive intestinal peptide Vasoactive intestinal peptide A highly basic, 28 amino acid neuropeptide released from intestinal mucosa. It has a wide range of biological actions affecting the cardiovascular, gastrointestinal, and respiratory systems and is neuroprotective. It binds special receptors. Gastrointestinal Neural and Hormonal Signaling ( VIP VIP A highly basic, 28 amino acid neuropeptide released from intestinal mucosa. It has a wide range of biological actions affecting the cardiovascular, gastrointestinal, and respiratory systems and is neuroprotective. It binds special receptors. Gastrointestinal Neural and Hormonal Signaling): increases blood flow Blood flow Blood flow refers to the movement of a certain volume of blood through the vasculature over a given unit of time (e.g., mL per minute). Vascular Resistance, Flow, and Mean Arterial Pressure to salivary glands Salivary glands The salivary glands are exocrine glands positioned in and around the oral cavity. These glands are responsible for secreting saliva into the mouth, which aids in digestion. There are 3 major paired salivary glands: the sublingual, submandibular, and parotid glands. Salivary Glands: Anatomy
  • Sympathetic stimulation: increases salivary secretions to a lesser degree via norepinephrine Norepinephrine Precursor of epinephrine that is secreted by the adrenal medulla and is a widespread central and autonomic neurotransmitter. Norepinephrine is the principal transmitter of most postganglionic sympathetic fibers, and of the diffuse projection system in the brain that arises from the locus ceruleus. Receptors and Neurotransmitters of the CNS release Release Release of a virus from the host cell following virus assembly and maturation. Egress can occur by host cell lysis, exocytosis, or budding through the plasma membrane. Virology

Clinical relevance of salivary secretions

Xerostomia Xerostomia Decreased salivary flow. Sjögren’s Syndrome, or dry mouth, is the clinical term used to identify impaired salivary secretion Secretion Coagulation Studies, which occurs commonly as part of Sjögren syndrome Sjögren Syndrome Rheumatoid Arthritis, as an adverse effect of some medications (such as antidepressants, antihypertensives Antihypertensives The 1st-line medication classes for hypertension include thiazide-like diuretics, angiotensin-converting enzyme inhibitors (ACEis), angiotensin II receptor blockers (ARBs), and calcium channel blockers (CCBS). Contraindications, adverse effects, and drug-to-drug interactions are agent specific. Hypertension Drugs, or anticholinergics Anticholinergics Anticholinergic drugs block the effect of the neurotransmitter acetylcholine at the muscarinic receptors in the central and peripheral nervous systems. Anticholinergic agents inhibit the parasympathetic nervous system, resulting in effects on the smooth muscle in the respiratory tract, vascular system, urinary tract, GI tract, and pupils of the eyes. Anticholinergic Drugs), and in individuals undergoing radiation Radiation Emission or propagation of acoustic waves (sound), electromagnetic energy waves (such as light; radio waves; gamma rays; or x-rays), or a stream of subatomic particles (such as electrons; neutrons; protons; or alpha particles). Osteosarcoma therapy for head and neck Neck The part of a human or animal body connecting the head to the rest of the body. Peritonsillar Abscess cancers.

Gastric Secretions

Functions of the stomach Stomach The stomach is a muscular sac in the upper left portion of the abdomen that plays a critical role in digestion. The stomach develops from the foregut and connects the esophagus with the duodenum. Structurally, the stomach is C-shaped and forms a greater and lesser curvature and is divided grossly into regions: the cardia, fundus, body, and pylorus. Stomach: Anatomy

  • Protecting the rest of the GI system by killing most microbes
  • Preparation of chyme Chyme Small Intestine: Anatomy for the small intestine Small intestine The small intestine is the longest part of the GI tract, extending from the pyloric orifice of the stomach to the ileocecal junction. The small intestine is the major organ responsible for chemical digestion and absorption of nutrients. It is divided into 3 segments: the duodenum, the jejunum, and the ileum. Small Intestine: Anatomy via:
    • Mechanical breakdown
    • Chemical digestion Digestion Digestion refers to the process of the mechanical and chemical breakdown of food into smaller particles, which can then be absorbed and utilized by the body. Digestion and Absorption by acid and pepsinogen
  • Absorption Absorption Absorption involves the uptake of nutrient molecules and their transfer from the lumen of the GI tract across the enterocytes and into the interstitial space, where they can be taken up in the venous or lymphatic circulation. Digestion and Absorption of lipophilic substances
  • Storage and gradual release Release Release of a virus from the host cell following virus assembly and maturation. Egress can occur by host cell lysis, exocytosis, or budding through the plasma membrane. Virology of material into the duodenum Duodenum The shortest and widest portion of the small intestine adjacent to the pylorus of the stomach. It is named for having the length equal to about the width of 12 fingers. Small Intestine: Anatomy (regulates food entering the small intestine Small intestine The small intestine is the longest part of the GI tract, extending from the pyloric orifice of the stomach to the ileocecal junction. The small intestine is the major organ responsible for chemical digestion and absorption of nutrients. It is divided into 3 segments: the duodenum, the jejunum, and the ileum. Small Intestine: Anatomy)

Gastric oxyntic glands: cells and their secretions

Gastric oxyntic glands are found below (and emptying into) the gastric pits. The glands contain numerous cell types, including:

  • Surface mucous cells Mucous cells Glandular Epithelium: Histology:
    • Line the gastric pits
    • Secrete bicarbonate Bicarbonate Inorganic salts that contain the -HCO3 radical. They are an important factor in determining the ph of the blood and the concentration of bicarbonate ions is regulated by the kidney. Levels in the blood are an index of the alkali reserve or buffering capacity. Electrolytes and insoluble mucus:
      • Form a protective barrier against the acidic environment of the stomach Stomach The stomach is a muscular sac in the upper left portion of the abdomen that plays a critical role in digestion. The stomach develops from the foregut and connects the esophagus with the duodenum. Structurally, the stomach is C-shaped and forms a greater and lesser curvature and is divided grossly into regions: the cardia, fundus, body, and pylorus. Stomach: Anatomy
      • Concentrate bicarbonate Bicarbonate Inorganic salts that contain the -HCO3 radical. They are an important factor in determining the ph of the blood and the concentration of bicarbonate ions is regulated by the kidney. Levels in the blood are an index of the alkali reserve or buffering capacity. Electrolytes in the mucus
  • Mucous neck Neck The part of a human or animal body connecting the head to the rest of the body. Peritonsillar Abscess cells:
    • Located in the neck Neck The part of a human or animal body connecting the head to the rest of the body. Peritonsillar Abscess of the glands where they join the gastric pits
    • Secrete soluble mucus
  • Stem cells:
    • Found between the pits and the entrance of the glands
    • Produce new cells to replace both surface mucous cells Mucous cells Glandular Epithelium: Histology in the pits and the glandular cells below
    • Stomach Stomach The stomach is a muscular sac in the upper left portion of the abdomen that plays a critical role in digestion. The stomach develops from the foregut and connects the esophagus with the duodenum. Structurally, the stomach is C-shaped and forms a greater and lesser curvature and is divided grossly into regions: the cardia, fundus, body, and pylorus. Stomach: Anatomy epithelial cells are replaced every 3‒6 days.
  • Parietal cells Parietal cells Rounded or pyramidal cells of the gastric glands. They secrete hydrochloric acid and produce gastric intrinsic factor, a glycoprotein that binds vitamin B12. Stomach: Anatomy:
    • Located in the lower-middle region of the glands
    • Secrete:
      • HCl HCL Hairy cell leukemia (HCL) is a rare, chronic, B-cell leukemia characterized by the accumulation of small mature B lymphocytes that have “hair-like projections” visible on microscopy. The abnormal cells accumulate in the peripheral blood, bone marrow (causing fibrosis), and red pulp of the spleen, leading to cytopenias. Hairy Cell Leukemia
      • Intrinsic factor Intrinsic factor A glycoprotein secreted by the cells of the gastric glands that is required for the absorption of vitamin B 12 (cyanocobalamin). Deficiency of intrinsic factor leads to vitamin B12 deficiency and anemia, pernicious. Gastritis: important for vitamin B12 Vitamin B12 A cobalt-containing coordination compound produced by intestinal microorganisms and found also in soil and water. Higher plants do not concentrate vitamin B 12 from the soil and so are a poor source of the substance as compared with animal tissues. Intrinsic factor is important for the assimilation of vitamin B 12. Folate and Vitamin B12 absorption Absorption Absorption involves the uptake of nutrient molecules and their transfer from the lumen of the GI tract across the enterocytes and into the interstitial space, where they can be taken up in the venous or lymphatic circulation. Digestion and Absorption
  • Chief cells Chief cells Epithelial cells that line the basal half of the gastric glands. Chief cells synthesize and export an inactive enzyme pepsinogen which is converted into the highly proteolytic enzyme pepsin in the acid environment of the stomach. Stomach: Anatomy:
    • Most numerous glandular cells
    • Located in the lower-middle region of the glands
    • Secrete:
      • Pepsinogen → converted to its active form pepsin Pepsin Pepsin breaks down proteins into proteoses, peptones, and large polypeptides. Proteins and Peptides by HCl HCL Hairy cell leukemia (HCL) is a rare, chronic, B-cell leukemia characterized by the accumulation of small mature B lymphocytes that have “hair-like projections” visible on microscopy. The abnormal cells accumulate in the peripheral blood, bone marrow (causing fibrosis), and red pulp of the spleen, leading to cytopenias. Hairy Cell Leukemia breaks down proteins Proteins Linear polypeptides that are synthesized on ribosomes and may be further modified, crosslinked, cleaved, or assembled into complex proteins with several subunits. The specific sequence of amino acids determines the shape the polypeptide will take, during protein folding, and the function of the protein. Energy Homeostasis
      • Gastric lipase Gastric lipase Digestion and Absorption → breaks down fats Fats The glyceryl esters of a fatty acid, or of a mixture of fatty acids. They are generally odorless, colorless, and tasteless if pure, but they may be flavored according to origin. Fats are insoluble in water, soluble in most organic solvents. They occur in animal and vegetable tissue and are generally obtained by boiling or by extraction under pressure. They are important in the diet (dietary fats) as a source of energy. Energy Homeostasis
  • Enteroendocrine cells:
    • Located in the base of the glands
    • D cells secrete somatostatin:
      • Inhibition of many secretions
      • Released in response to H+ (the natural way to “turn off” acid production)
    • G cells secrete gastrin:
      • Stimulates parietal cells Parietal cells Rounded or pyramidal cells of the gastric glands. They secrete hydrochloric acid and produce gastric intrinsic factor, a glycoprotein that binds vitamin B12. Stomach: Anatomy to secrete HCl HCL Hairy cell leukemia (HCL) is a rare, chronic, B-cell leukemia characterized by the accumulation of small mature B lymphocytes that have “hair-like projections” visible on microscopy. The abnormal cells accumulate in the peripheral blood, bone marrow (causing fibrosis), and red pulp of the spleen, leading to cytopenias. Hairy Cell Leukemia
      • Has trophic/growth effects on the GI mucosa
      • Released in response to proteins Proteins Linear polypeptides that are synthesized on ribosomes and may be further modified, crosslinked, cleaved, or assembled into complex proteins with several subunits. The specific sequence of amino acids determines the shape the polypeptide will take, during protein folding, and the function of the protein. Energy Homeostasis, peptides, and amino acids Amino acids Organic compounds that generally contain an amino (-NH2) and a carboxyl (-COOH) group. Twenty alpha-amino acids are the subunits which are polymerized to form proteins. Basics of Amino Acids
    • Enterochromaffin-like (ECL) cells secrete histamine (which stimulates parietal cells Parietal cells Rounded or pyramidal cells of the gastric glands. They secrete hydrochloric acid and produce gastric intrinsic factor, a glycoprotein that binds vitamin B12. Stomach: Anatomy to secrete HCl HCL Hairy cell leukemia (HCL) is a rare, chronic, B-cell leukemia characterized by the accumulation of small mature B lymphocytes that have “hair-like projections” visible on microscopy. The abnormal cells accumulate in the peripheral blood, bone marrow (causing fibrosis), and red pulp of the spleen, leading to cytopenias. Hairy Cell Leukemia).
    • Other chemical messengers secreted by enteroendocrine cells:
      • Substance P
      • VIP VIP A highly basic, 28 amino acid neuropeptide released from intestinal mucosa. It has a wide range of biological actions affecting the cardiovascular, gastrointestinal, and respiratory systems and is neuroprotective. It binds special receptors. Gastrointestinal Neural and Hormonal Signaling
      • Secretin
      • Neuropeptide Y

Production and secretion Secretion Coagulation Studies of acid in parietal cells Parietal cells Rounded or pyramidal cells of the gastric glands. They secrete hydrochloric acid and produce gastric intrinsic factor, a glycoprotein that binds vitamin B12. Stomach: Anatomy

  • Normal metabolism produces CO2 → combines with H2O → H2CO3 → splits into H+ + HCO3
  • H+ is pumped out to the lumen in exchange for K+ by H+/K+ ATPase:
    • 1 K+ molecule is brought into the cell.
    • K+ leaves the cell through the basolateral membrane down its concentration gradient through a K+ channel.
  • HCO3 is exchanged with Cl across the basolateral membrane:
    • HCO3 is moved into the interstitial space.
    • Cl is brought into the cell → moves into the lumen through its own channel
  • End result:
    • H+ and Cl are secreted into the lumen.
    • K+ and HCO3 are moved into the interstitial space.
Ion movement in parietal cells

Ion movement in parietal cells Parietal cells Rounded or pyramidal cells of the gastric glands. They secrete hydrochloric acid and produce gastric intrinsic factor, a glycoprotein that binds vitamin B12. Stomach: Anatomy:
Carbonic acid dissociates into H+ and HCO3. The H+ is exchanged for K+ in the apical membrane by H+/K+ ATPase. An HCO3 is exchanged for Cl in the basolateral membrane; Cl is then moved into the lumen.

Image by Lecturio.

Control and regulation of gastric secretions

Gastric secretions are heavily influenced by parasympathetic signaling via the vagus nerve Vagus nerve The 10th cranial nerve. The vagus is a mixed nerve which contains somatic afferents (from skin in back of the ear and the external auditory meatus), visceral afferents (from the pharynx, larynx, thorax, and abdomen), parasympathetic efferents (to the thorax and abdomen), and efferents to striated muscle (of the larynx and pharynx). Pharynx: Anatomy (cranial nerve X), which releases ACh ACh A neurotransmitter found at neuromuscular junctions, autonomic ganglia, parasympathetic effector junctions, a subset of sympathetic effector junctions, and at many sites in the central nervous system. Receptors and Neurotransmitters of the CNS that induces acid production by several pathways.

  • Production of secretions:
    • 40% in the cephalic phase
    • 50% in the gastric phase
    • 10% in the intestinal phase
  • HCl HCL Hairy cell leukemia (HCL) is a rare, chronic, B-cell leukemia characterized by the accumulation of small mature B lymphocytes that have “hair-like projections” visible on microscopy. The abnormal cells accumulate in the peripheral blood, bone marrow (causing fibrosis), and red pulp of the spleen, leading to cytopenias. Hairy Cell Leukemia secretion Secretion Coagulation Studies from parietal cells Parietal cells Rounded or pyramidal cells of the gastric glands. They secrete hydrochloric acid and produce gastric intrinsic factor, a glycoprotein that binds vitamin B12. Stomach: Anatomy is stimulated by:
    • ACh ACh A neurotransmitter found at neuromuscular junctions, autonomic ganglia, parasympathetic effector junctions, a subset of sympathetic effector junctions, and at many sites in the central nervous system. Receptors and Neurotransmitters of the CNS from the vagus and myenteric nerves (long and short reflex pathways, respectively)
    • Gastrin from G cells in the stomach Stomach The stomach is a muscular sac in the upper left portion of the abdomen that plays a critical role in digestion. The stomach develops from the foregut and connects the esophagus with the duodenum. Structurally, the stomach is C-shaped and forms a greater and lesser curvature and is divided grossly into regions: the cardia, fundus, body, and pylorus. Stomach: Anatomy
    • Histamine from ECL cells in the stomach Stomach The stomach is a muscular sac in the upper left portion of the abdomen that plays a critical role in digestion. The stomach develops from the foregut and connects the esophagus with the duodenum. Structurally, the stomach is C-shaped and forms a greater and lesser curvature and is divided grossly into regions: the cardia, fundus, body, and pylorus. Stomach: Anatomy
  • HCl HCL Hairy cell leukemia (HCL) is a rare, chronic, B-cell leukemia characterized by the accumulation of small mature B lymphocytes that have “hair-like projections” visible on microscopy. The abnormal cells accumulate in the peripheral blood, bone marrow (causing fibrosis), and red pulp of the spleen, leading to cytopenias. Hairy Cell Leukemia secretion Secretion Coagulation Studies is inhibited by:
    • Somatostatin
    • Prostaglandins Prostaglandins A group of compounds derived from unsaturated 20-carbon fatty acids, primarily arachidonic acid, via the cyclooxygenase pathway. They are extremely potent mediators of a diverse group of physiological processes. Eicosanoids

Acid-stimulation pathways

  • Direct pathway Direct Pathway Huntington Disease (direct activation of parietal cells Parietal cells Rounded or pyramidal cells of the gastric glands. They secrete hydrochloric acid and produce gastric intrinsic factor, a glycoprotein that binds vitamin B12. Stomach: Anatomy):
    • ACh ACh A neurotransmitter found at neuromuscular junctions, autonomic ganglia, parasympathetic effector junctions, a subset of sympathetic effector junctions, and at many sites in the central nervous system. Receptors and Neurotransmitters of the CNS stimulates the muscarinic (M3) receptors Receptors Receptors are proteins located either on the surface of or within a cell that can bind to signaling molecules known as ligands (e.g., hormones) and cause some type of response within the cell. Receptors of parietal cells Parietal cells Rounded or pyramidal cells of the gastric glands. They secrete hydrochloric acid and produce gastric intrinsic factor, a glycoprotein that binds vitamin B12. Stomach: Anatomy.
    • Activates Gq (a G protein)
    • Gq activates phospholipase C Phospholipase C A subclass of phospholipases that hydrolyze the phosphoester bond found in the third position of glycerophospholipids. Although the singular term phospholipase C specifically refers to an enzyme that catalyzes the hydrolysis of phosphatidylcholine, it is commonly used in the literature to refer to broad variety of enzymes that specifically catalyze the hydrolysis of phosphatidylinositols. Pseudomonas (PLC).
    • PLC cleaves phosphatidylinositol-4,5-bisphosphate (PIP2) to produce:
      • Inositol trisphosphate Inositol trisphosphate Intracellular messenger formed by the action of phospholipase C on phosphatidylinositol 4, 5-bisphosphate, which is one of the phospholipids that make up the cell membrane. Inositol 1, 4, 5-trisphosphate is released into the cytoplasm where it releases calcium ions from internal stores within the cell’s endoplasmic reticulum. These calcium ions stimulate the activity of B kinase or calmodulin. Second Messengers (IP3) → calcium Calcium A basic element found in nearly all tissues. It is a member of the alkaline earth family of metals with the atomic symbol ca, atomic number 20, and atomic weight 40. Calcium is the most abundant mineral in the body and combines with phosphorus to form calcium phosphate in the bones and teeth. It is essential for the normal functioning of nerves and muscles and plays a role in blood coagulation (as factor IV) and in many enzymatic processes. Electrolytes ( Ca CA Condylomata acuminata are a clinical manifestation of genital HPV infection. Condylomata acuminata are described as raised, pearly, flesh-colored, papular, cauliflower-like lesions seen in the anogenital region that may cause itching, pain, or bleeding. Condylomata Acuminata (Genital Warts)2+) release Release Release of a virus from the host cell following virus assembly and maturation. Egress can occur by host cell lysis, exocytosis, or budding through the plasma membrane. Virology from the ER
      • Diacylglycerol Diacylglycerol Second Messengers ( DAG DAG Second Messengers) → phosphorylation Phosphorylation The introduction of a phosphoryl group into a compound through the formation of an ester bond between the compound and a phosphorus moiety. Post-translational Protein Processing of protein kinase Protein kinase A family of enzymes that catalyze the conversion of ATP and a protein to adp and a phosphoprotein. Interferons (PK) C
    • Both Ca CA Condylomata acuminata are a clinical manifestation of genital HPV infection. Condylomata acuminata are described as raised, pearly, flesh-colored, papular, cauliflower-like lesions seen in the anogenital region that may cause itching, pain, or bleeding. Condylomata Acuminata (Genital Warts)2+ and PKC activate the H+/K+ ATPase to secrete H+.
  • Gastrin pathway:
    • ACh ACh A neurotransmitter found at neuromuscular junctions, autonomic ganglia, parasympathetic effector junctions, a subset of sympathetic effector junctions, and at many sites in the central nervous system. Receptors and Neurotransmitters of the CNS stimulates G cells to release Release Release of a virus from the host cell following virus assembly and maturation. Egress can occur by host cell lysis, exocytosis, or budding through the plasma membrane. Virology gastrin.
    • Gastrin activates cholecystokinin B receptors Receptors Receptors are proteins located either on the surface of or within a cell that can bind to signaling molecules known as ligands (e.g., hormones) and cause some type of response within the cell. Receptors on parietal cells Parietal cells Rounded or pyramidal cells of the gastric glands. They secrete hydrochloric acid and produce gastric intrinsic factor, a glycoprotein that binds vitamin B12. Stomach: Anatomy.
    • Cholecystokinin B activates PLC → cleaves PIP2 into IP3 + DAG DAG Second Messengers → ↑ Ca CA Condylomata acuminata are a clinical manifestation of genital HPV infection. Condylomata acuminata are described as raised, pearly, flesh-colored, papular, cauliflower-like lesions seen in the anogenital region that may cause itching, pain, or bleeding. Condylomata Acuminata (Genital Warts)2+ + PKC → ↑ H+/K+ ATPase activity
  • Histamine pathway:
    • ACh ACh A neurotransmitter found at neuromuscular junctions, autonomic ganglia, parasympathetic effector junctions, a subset of sympathetic effector junctions, and at many sites in the central nervous system. Receptors and Neurotransmitters of the CNS stimulates ECL cells to release Release Release of a virus from the host cell following virus assembly and maturation. Egress can occur by host cell lysis, exocytosis, or budding through the plasma membrane. Virology histamine.
    • Histamine activates H2 receptors Receptors Receptors are proteins located either on the surface of or within a cell that can bind to signaling molecules known as ligands (e.g., hormones) and cause some type of response within the cell. Receptors on parietal cells Parietal cells Rounded or pyramidal cells of the gastric glands. They secrete hydrochloric acid and produce gastric intrinsic factor, a glycoprotein that binds vitamin B12. Stomach: Anatomy.
    • H2 receptors Receptors Receptors are proteins located either on the surface of or within a cell that can bind to signaling molecules known as ligands (e.g., hormones) and cause some type of response within the cell. Receptors activate Gs (a G protein).
    • Gs activates adenylate cyclase (AC).
    • AC converts ATP to cAMP cAMP An adenine nucleotide containing one phosphate group which is esterified to both the 3′- and 5′-positions of the sugar moiety. It is a second messenger and a key intracellular regulator, functioning as a mediator of activity for a number of hormones, including epinephrine, glucagon, and acth. Phosphodiesterase Inhibitors.
    • cAMP cAMP An adenine nucleotide containing one phosphate group which is esterified to both the 3′- and 5′-positions of the sugar moiety. It is a second messenger and a key intracellular regulator, functioning as a mediator of activity for a number of hormones, including epinephrine, glucagon, and acth. Phosphodiesterase Inhibitors phosphorylates/activates PKA.
    • PKA stimulates H+/K+ ATPase to secrete H+.
  • The effects of these pathways are potentiating/synergistic in nature → ACh ACh A neurotransmitter found at neuromuscular junctions, autonomic ganglia, parasympathetic effector junctions, a subset of sympathetic effector junctions, and at many sites in the central nervous system. Receptors and Neurotransmitters of the CNS + gastrin + histamine activity simultaneously results in greater HCl HCL Hairy cell leukemia (HCL) is a rare, chronic, B-cell leukemia characterized by the accumulation of small mature B lymphocytes that have “hair-like projections” visible on microscopy. The abnormal cells accumulate in the peripheral blood, bone marrow (causing fibrosis), and red pulp of the spleen, leading to cytopenias. Hairy Cell Leukemia secretion Secretion Coagulation Studies than the sum of HCl HCL Hairy cell leukemia (HCL) is a rare, chronic, B-cell leukemia characterized by the accumulation of small mature B lymphocytes that have “hair-like projections” visible on microscopy. The abnormal cells accumulate in the peripheral blood, bone marrow (causing fibrosis), and red pulp of the spleen, leading to cytopenias. Hairy Cell Leukemia secretion Secretion Coagulation Studies if they each acted alone

Acid-inhibition pathways

Somatostatin and prostaglandins Prostaglandins A group of compounds derived from unsaturated 20-carbon fatty acids, primarily arachidonic acid, via the cyclooxygenase pathway. They are extremely potent mediators of a diverse group of physiological processes. Eicosanoids:

  • Somatostatin (released from D cells in the stomach Stomach The stomach is a muscular sac in the upper left portion of the abdomen that plays a critical role in digestion. The stomach develops from the foregut and connects the esophagus with the duodenum. Structurally, the stomach is C-shaped and forms a greater and lesser curvature and is divided grossly into regions: the cardia, fundus, body, and pylorus. Stomach: Anatomy) and prostaglandins Prostaglandins A group of compounds derived from unsaturated 20-carbon fatty acids, primarily arachidonic acid, via the cyclooxygenase pathway. They are extremely potent mediators of a diverse group of physiological processes. Eicosanoids activate the inhibitory Gi protein.
  • Gi inhibits AC → cAMP cAMP An adenine nucleotide containing one phosphate group which is esterified to both the 3′- and 5′-positions of the sugar moiety. It is a second messenger and a key intracellular regulator, functioning as a mediator of activity for a number of hormones, including epinephrine, glucagon, and acth. Phosphodiesterase Inhibitors levels fall → ↓ activation of PKA → ↓ H+/K+ ATPase activity

Clinical relevance of gastric secretions

  • GERD GERD Gastroesophageal reflux disease (GERD) occurs when the stomach acid frequently flows back into the esophagus. This backwash (acid reflux) can irritate the lining of the esophagus, causing symptoms such as retrosternal burning pain (heartburn). Gastroesophageal Reflux Disease (GERD): occurs when the stomach Stomach The stomach is a muscular sac in the upper left portion of the abdomen that plays a critical role in digestion. The stomach develops from the foregut and connects the esophagus with the duodenum. Structurally, the stomach is C-shaped and forms a greater and lesser curvature and is divided grossly into regions: the cardia, fundus, body, and pylorus. Stomach: Anatomy acid frequently flows back into the esophagus Esophagus The esophagus is a muscular tube-shaped organ of around 25 centimeters in length that connects the pharynx to the stomach. The organ extends from approximately the 6th cervical vertebra to the 11th thoracic vertebra and can be divided grossly into 3 parts: the cervical part, the thoracic part, and the abdominal part. Esophagus: Anatomy. The backwash (acid reflux) can irritate the lining of the esophagus Esophagus The esophagus is a muscular tube-shaped organ of around 25 centimeters in length that connects the pharynx to the stomach. The organ extends from approximately the 6th cervical vertebra to the 11th thoracic vertebra and can be divided grossly into 3 parts: the cervical part, the thoracic part, and the abdominal part. Esophagus: Anatomy, causing symptoms such as retrosternal burning pain Pain An unpleasant sensation induced by noxious stimuli which are detected by nerve endings of nociceptive neurons. Pain: Types and Pathways ( heartburn Heartburn Substernal pain or burning sensation, usually associated with regurgitation of gastric juice into the esophagus. Gastroesophageal Reflux Disease (GERD)) and may eventually lead to inflammation Inflammation Inflammation is a complex set of responses to infection and injury involving leukocytes as the principal cellular mediators in the body’s defense against pathogenic organisms. Inflammation is also seen as a response to tissue injury in the process of wound healing. The 5 cardinal signs of inflammation are pain, heat, redness, swelling, and loss of function. Inflammation ( esophagitis Esophagitis Esophagitis is the inflammation or irritation of the esophagus. The major types of esophagitis are medication-induced, infectious, eosinophilic, corrosive, and acid reflux. Patients typically present with odynophagia, dysphagia, and retrosternal chest pain. Esophagitis), metaplasia Metaplasia A condition in which there is a change of one adult cell type to another similar adult cell type. Cellular Adaptation (Barrett esophagus Esophagus The esophagus is a muscular tube-shaped organ of around 25 centimeters in length that connects the pharynx to the stomach. The organ extends from approximately the 6th cervical vertebra to the 11th thoracic vertebra and can be divided grossly into 3 parts: the cervical part, the thoracic part, and the abdominal part. Esophagus: Anatomy), and progression to esophageal cancer Esophageal cancer Esophageal cancer is 1 of the most common causes of cancer-related deaths worldwide. Nearly all esophageal cancers are either adenocarcinoma (commonly affecting the distal esophagus) or squamous cell carcinoma (affecting the proximal two-thirds of the esophagus). Esophageal Cancer. Uncomplicated GERD GERD Gastroesophageal reflux disease (GERD) occurs when the stomach acid frequently flows back into the esophagus. This backwash (acid reflux) can irritate the lining of the esophagus, causing symptoms such as retrosternal burning pain (heartburn). Gastroesophageal Reflux Disease (GERD) can be managed with lifestyle changes and over-the-counter medications.
  • Barrett esophagus Esophagus The esophagus is a muscular tube-shaped organ of around 25 centimeters in length that connects the pharynx to the stomach. The organ extends from approximately the 6th cervical vertebra to the 11th thoracic vertebra and can be divided grossly into 3 parts: the cervical part, the thoracic part, and the abdominal part. Esophagus: Anatomy: a condition characterized by metaplastic changes in the normal stratified squamous epithelium Epithelium The epithelium is a complex of specialized cellular organizations arranged into sheets and lining cavities and covering the surfaces of the body. The cells exhibit polarity, having an apical and a basal pole. Structures important for the epithelial integrity and function involve the basement membrane, the semipermeable sheet on which the cells rest, and interdigitations, as well as cellular junctions. Surface Epithelium: Histology of the esophagus Esophagus The esophagus is a muscular tube-shaped organ of around 25 centimeters in length that connects the pharynx to the stomach. The organ extends from approximately the 6th cervical vertebra to the 11th thoracic vertebra and can be divided grossly into 3 parts: the cervical part, the thoracic part, and the abdominal part. Esophagus: Anatomy to columnar epithelium Epithelium The epithelium is a complex of specialized cellular organizations arranged into sheets and lining cavities and covering the surfaces of the body. The cells exhibit polarity, having an apical and a basal pole. Structures important for the epithelial integrity and function involve the basement membrane, the semipermeable sheet on which the cells rest, and interdigitations, as well as cellular junctions. Surface Epithelium: Histology. The change is a consequence of chronic GERD GERD Gastroesophageal reflux disease (GERD) occurs when the stomach acid frequently flows back into the esophagus. This backwash (acid reflux) can irritate the lining of the esophagus, causing symptoms such as retrosternal burning pain (heartburn). Gastroesophageal Reflux Disease (GERD) and is considered premalignant.
  • Medications to reduce gastric acid Gastric acid Hydrochloric acid present in gastric juice. Gastroesophageal Reflux Disease (GERD) secretions: Drugs include proton pump Pump ACES and RUSH: Resuscitation Ultrasound Protocols inhibitors (PPIs) and H2 receptor Receptor Receptors are proteins located either on the surface of or within a cell that can bind to signaling molecules known as ligands (e.g., hormones) and cause some type of response within the cell. Receptors antagonists and are most commonly indicated in treating peptic ulcer disease Peptic ulcer disease Peptic ulcer disease (PUD) refers to the full-thickness ulcerations of duodenal or gastric mucosa. The ulcerations form when exposure to acid and digestive enzymes overcomes mucosal defense mechanisms. The most common etiologies include Helicobacter pylori (H. pylori) infection and prolonged use of non-steroidal anti-inflammatory drugs (NSAIDs). Peptic Ulcer Disease ( PUD PUD Peptic ulcer disease (PUD) refers to the full-thickness ulcerations of duodenal or gastric mucosa. The ulcerations form when exposure to acid and digestive enzymes overcomes mucosal defense mechanisms. The most common etiologies include Helicobacter pylori (H. pylori) infection and prolonged use of non-steroidal anti-inflammatory drugs (NSAIDs). Peptic Ulcer Disease), GERD GERD Gastroesophageal reflux disease (GERD) occurs when the stomach acid frequently flows back into the esophagus. This backwash (acid reflux) can irritate the lining of the esophagus, causing symptoms such as retrosternal burning pain (heartburn). Gastroesophageal Reflux Disease (GERD), and dyspepsia Dyspepsia Impaired digestion, especially after eating. Lactose Intolerance. The mechanism of action of PPIs in reducing gastric acid Gastric acid Hydrochloric acid present in gastric juice. Gastroesophageal Reflux Disease (GERD) is by inhibiting the H+/K+ ATPase in parietal cells Parietal cells Rounded or pyramidal cells of the gastric glands. They secrete hydrochloric acid and produce gastric intrinsic factor, a glycoprotein that binds vitamin B12. Stomach: Anatomy, whereas that of H2 blockers is by inhibiting the stimulatory effects of histamine on parietal cells Parietal cells Rounded or pyramidal cells of the gastric glands. They secrete hydrochloric acid and produce gastric intrinsic factor, a glycoprotein that binds vitamin B12. Stomach: Anatomy.
  • Zollinger-Ellison syndrome Zollinger-ellison syndrome A syndrome that is characterized by the triad of severe peptic ulcer, hypersecretion of gastric acid, and gastrin-producing tumors of the pancreas or other tissue (gastrinoma). This syndrome may be sporadic or be associated with multiple endocrine neoplasia type 1. Esophagitis (ZES): a gastrin-secreting tumor Tumor Inflammation (often malignant) arising from the pancreas Pancreas The pancreas lies mostly posterior to the stomach and extends across the posterior abdominal wall from the duodenum on the right to the spleen on the left. This organ has both exocrine and endocrine tissue. Pancreas: Anatomy, stomach Stomach The stomach is a muscular sac in the upper left portion of the abdomen that plays a critical role in digestion. The stomach develops from the foregut and connects the esophagus with the duodenum. Structurally, the stomach is C-shaped and forms a greater and lesser curvature and is divided grossly into regions: the cardia, fundus, body, and pylorus. Stomach: Anatomy, duodenum Duodenum The shortest and widest portion of the small intestine adjacent to the pylorus of the stomach. It is named for having the length equal to about the width of 12 fingers. Small Intestine: Anatomy, jejunum Jejunum The middle portion of the small intestine, between duodenum and ileum. It represents about 2/5 of the remaining portion of the small intestine below duodenum. Small Intestine: Anatomy, and/or lymph Lymph The interstitial fluid that is in the lymphatic system. Secondary Lymphatic Organs nodes, which is characterized by recurrent/refractory peptic ulcers, gastroesophageal reflux, and diarrhea Diarrhea Diarrhea is defined as ≥ 3 watery or loose stools in a 24-hour period. There are a multitude of etiologies, which can be classified based on the underlying mechanism of disease. The duration of symptoms (acute or chronic) and characteristics of the stools (e.g., watery, bloody, steatorrheic, mucoid) can help guide further diagnostic evaluation. Diarrhea. Diagnosis is based on elevated fasting serum gastrin levels. Treatment is with surgical resection of the tumor Tumor Inflammation and/or symptomatic management.

Pancreatic Secretions

Types of pancreatic tissue

There are 2 types of pancreatic tissues:

  • Exocrine (85% by mass Mass Three-dimensional lesion that occupies a space within the breast Imaging of the Breast):
    • Release Release Release of a virus from the host cell following virus assembly and maturation. Egress can occur by host cell lysis, exocytosis, or budding through the plasma membrane. Virology pancreatic enzymes Enzymes Enzymes are complex protein biocatalysts that accelerate chemical reactions without being consumed by them. Due to the body’s constant metabolic needs, the absence of enzymes would make life unsustainable, as reactions would occur too slowly without these molecules. Basics of Enzymes into the duodenum Duodenum The shortest and widest portion of the small intestine adjacent to the pylorus of the stomach. It is named for having the length equal to about the width of 12 fingers. Small Intestine: Anatomy
    • Arranged as clusters of acini draining into a ductal system → main and accessory pancreatic ducts → duodenum Duodenum The shortest and widest portion of the small intestine adjacent to the pylorus of the stomach. It is named for having the length equal to about the width of 12 fingers. Small Intestine: Anatomy
  • Endocrine:
    • Releases hormones Hormones Hormones are messenger molecules that are synthesized in one part of the body and move through the bloodstream to exert specific regulatory effects on another part of the body. Hormones play critical roles in coordinating cellular activities throughout the body in response to the constant changes in both the internal and external environments. Hormones: Overview and Types into the bloodstream
    • Cells are located in clusters known as islets.
    • α cells: secretion Secretion Coagulation Studies of glucagon
    • β cells: secretion Secretion Coagulation Studies of insulin Insulin Insulin is a peptide hormone that is produced by the beta cells of the pancreas. Insulin plays a role in metabolic functions such as glucose uptake, glycolysis, glycogenesis, lipogenesis, and protein synthesis. Exogenous insulin may be needed for individuals with diabetes mellitus, in whom there is a deficiency in endogenous insulin or increased insulin resistance. Insulin
    • 𝛿 cells: secretion Secretion Coagulation Studies of somatostatin
The pancreas with its two major tissue components

A drawing of the pancreas Pancreas The pancreas lies mostly posterior to the stomach and extends across the posterior abdominal wall from the duodenum on the right to the spleen on the left. This organ has both exocrine and endocrine tissue. Pancreas: Anatomy identifying its 2 major tissue components: the endocrine pancreas Pancreas The pancreas lies mostly posterior to the stomach and extends across the posterior abdominal wall from the duodenum on the right to the spleen on the left. This organ has both exocrine and endocrine tissue. Pancreas: Anatomy (islets of Langerhans or pancreatic islets) and exocrine pancreas Pancreas The pancreas lies mostly posterior to the stomach and extends across the posterior abdominal wall from the duodenum on the right to the spleen on the left. This organ has both exocrine and endocrine tissue. Pancreas: Anatomy (exocrine cells or pancreatic acini)

Image by Lecturio.

Exocrine pancreas Pancreas The pancreas lies mostly posterior to the stomach and extends across the posterior abdominal wall from the duodenum on the right to the spleen on the left. This organ has both exocrine and endocrine tissue. Pancreas: Anatomy secretions

The exocrine pancreas Pancreas The pancreas lies mostly posterior to the stomach and extends across the posterior abdominal wall from the duodenum on the right to the spleen on the left. This organ has both exocrine and endocrine tissue. Pancreas: Anatomy secretes a mixture known as pancreatic juice Pancreatic Juice The fluid containing digestive enzymes secreted by the pancreas in response to food in the duodenum. Pancreas: Anatomy, which contains water, enzymes Enzymes Enzymes are complex protein biocatalysts that accelerate chemical reactions without being consumed by them. Due to the body’s constant metabolic needs, the absence of enzymes would make life unsustainable, as reactions would occur too slowly without these molecules. Basics of Enzymes, zymogens (inactive proteins Proteins Linear polypeptides that are synthesized on ribosomes and may be further modified, crosslinked, cleaved, or assembled into complex proteins with several subunits. The specific sequence of amino acids determines the shape the polypeptide will take, during protein folding, and the function of the protein. Energy Homeostasis), HCO3, and electrolytes Electrolytes Electrolytes are mineral salts that dissolve in water and dissociate into charged particles called ions, which can be either be positively (cations) or negatively (anions) charged. Electrolytes are distributed in the extracellular and intracellular compartments in different concentrations. Electrolytes are essential for various basic life-sustaining functions. Electrolytes:

  • Buffer (neutralizes acid from the stomach Stomach The stomach is a muscular sac in the upper left portion of the abdomen that plays a critical role in digestion. The stomach develops from the foregut and connects the esophagus with the duodenum. Structurally, the stomach is C-shaped and forms a greater and lesser curvature and is divided grossly into regions: the cardia, fundus, body, and pylorus. Stomach: Anatomy): HCO3
  • For carbohydrate digestion Digestion Digestion refers to the process of the mechanical and chemical breakdown of food into smaller particles, which can then be absorbed and utilized by the body. Digestion and Absorption: pancreatic amylase Pancreatic Amylase A group of amylolytic enzymes that cleave starch, glycogen, and related alpha-1, 4-glucans. Pancreatic Parameters
  • For lipid digestion Digestion Digestion refers to the process of the mechanical and chemical breakdown of food into smaller particles, which can then be absorbed and utilized by the body. Digestion and Absorption:
    • Pancreatic lipase Pancreatic Lipase An enzyme of the hydrolase class that catalyzes the reaction of triacylglycerol and water to yield diacylglycerol and a fatty acid anion. It is produced by glands on the tongue and by the pancreas and initiates the digestion of dietary fats. Pancreatic Parameters
    • Phospholipase A2
    • Cholesterol Cholesterol The principal sterol of all higher animals, distributed in body tissues, especially the brain and spinal cord, and in animal fats and oils. Cholesterol Metabolism esterase
  • For protein and peptide digestion Digestion Digestion refers to the process of the mechanical and chemical breakdown of food into smaller particles, which can then be absorbed and utilized by the body. Digestion and Absorption (secreted primarily as zymogens):
    • Trypsinogen Trypsinogen The inactive proenzyme of trypsin secreted by the pancreas, activated in the duodenum via cleavage by enteropeptidase. Pancreatic Parameters → activated by enterokinase Enterokinase A specialized proteolytic enzyme secreted by intestinal cells. It converts trypsinogen into its active form trypsin by removing the N-terminal peptide. Digestion and Absorption (a glycoprotein bound to the brush border Brush border Tubular System) to trypsin Trypsin A serine endopeptidase that is formed from trypsinogen in the pancreas. It is converted into its active form by enteropeptidase in the small intestine. It catalyzes hydrolysis of the carboxyl group of either arginine or lysine. Proteins and Peptides
    • Chymotrypsinogen → activated by trypsin Trypsin A serine endopeptidase that is formed from trypsinogen in the pancreas. It is converted into its active form by enteropeptidase in the small intestine. It catalyzes hydrolysis of the carboxyl group of either arginine or lysine. Proteins and Peptides to chymotrypsin Chymotrypsin A serine endopeptidase secreted by the pancreas as its zymogen, chymotrypsinogen and carried in the pancreatic juice to the duodenum where it is activated by trypsin. It selectively cleaves aromatic amino acids on the carboxyl side. Pancreatic Parameters
    • Procarboxypeptidase → activated by trypsin Trypsin A serine endopeptidase that is formed from trypsinogen in the pancreas. It is converted into its active form by enteropeptidase in the small intestine. It catalyzes hydrolysis of the carboxyl group of either arginine or lysine. Proteins and Peptides to carboxypeptidase Carboxypeptidase Enzymes that act at a free c-terminus of a polypeptide to liberate a single amino acid residue. Pancreatic Parameters
    • Proelastase → activated by trypsin Trypsin A serine endopeptidase that is formed from trypsinogen in the pancreas. It is converted into its active form by enteropeptidase in the small intestine. It catalyzes hydrolysis of the carboxyl group of either arginine or lysine. Proteins and Peptides elastase Elastase A protease of broad specificity, obtained from dried pancreas. Molecular weight is approximately 25, 000. The enzyme breaks down elastin, the specific protein of elastic fibers, and digests other proteins such as fibrin, hemoglobin, and albumin. Proteins and Peptides
  • For nucleotide digestion Digestion Digestion refers to the process of the mechanical and chemical breakdown of food into smaller particles, which can then be absorbed and utilized by the body. Digestion and Absorption:

Ion concentrations in pancreatic juice Pancreatic Juice The fluid containing digestive enzymes secreted by the pancreas in response to food in the duodenum. Pancreas: Anatomy

  • HCO3:
    • Actively secreted: concentration in pancreatic juice Pancreatic Juice The fluid containing digestive enzymes secreted by the pancreas in response to food in the duodenum. Pancreas: Anatomy > that in plasma Plasma The residual portion of blood that is left after removal of blood cells by centrifugation without prior blood coagulation. Transfusion Products
    • Secretion Secretion Coagulation Studies increases as flow Flow Blood flows through the heart, arteries, capillaries, and veins in a closed, continuous circuit. Flow is the movement of volume per unit of time. Flow is affected by the pressure gradient and the resistance fluid encounters between 2 points. Vascular resistance is the opposition to flow, which is caused primarily by blood friction against vessel walls. Vascular Resistance, Flow, and Mean Arterial Pressure rate increases.
  • Cl:
    • Actively reabsorbed: concentration in pancreatic juice Pancreatic Juice The fluid containing digestive enzymes secreted by the pancreas in response to food in the duodenum. Pancreas: Anatomy < that in plasma Plasma The residual portion of blood that is left after removal of blood cells by centrifugation without prior blood coagulation. Transfusion Products
    • Reabsorption drops as flow Flow Blood flows through the heart, arteries, capillaries, and veins in a closed, continuous circuit. Flow is the movement of volume per unit of time. Flow is affected by the pressure gradient and the resistance fluid encounters between 2 points. Vascular resistance is the opposition to flow, which is caused primarily by blood friction against vessel walls. Vascular Resistance, Flow, and Mean Arterial Pressure rate increases.
  • Mechanism of HCO3 secretion Secretion Coagulation Studies and Cl reabsorption:
    • CO2 enters cells → combines with water to form H2CO3 → splits into H+ and HCO3
    • H+ is moved back across the basolateral membrane into the interstitial space via the H+/Na+ exchanger.
    • HCO3 is secreted across the apical membrane into the lumen via the HCO3/Cl exchanger.
    • Cl can be recycled back into the lumen through the Cl channel.
    • Na+ is removed from the cell to across the basolateral membrane via the Na+/K+ ATPase exchanger.
  • Na+ and K+ are neither actively secreted nor reabsorbed:
    • Concentration in pancreatic juice Pancreatic Juice The fluid containing digestive enzymes secreted by the pancreas in response to food in the duodenum. Pancreas: Anatomy is similar to that in the plasma Plasma The residual portion of blood that is left after removal of blood cells by centrifugation without prior blood coagulation. Transfusion Products.
    • Some Na+ moves paracellularly into the lumen.
    • Water follows Na+ into the lumen.

Control and regulation

Percentage of secretions produced:

  • 25% in the cephalic phase, stimulated primarily by ACh ACh A neurotransmitter found at neuromuscular junctions, autonomic ganglia, parasympathetic effector junctions, a subset of sympathetic effector junctions, and at many sites in the central nervous system. Receptors and Neurotransmitters of the CNS released from the vagus nerve Vagus nerve The 10th cranial nerve. The vagus is a mixed nerve which contains somatic afferents (from skin in back of the ear and the external auditory meatus), visceral afferents (from the pharynx, larynx, thorax, and abdomen), parasympathetic efferents (to the thorax and abdomen), and efferents to striated muscle (of the larynx and pharynx). Pharynx: Anatomy
  • 10% in the gastric phase, stimulated primarily by vago-vagal reflexes
  • 65% in the intestinal phase, stimulated by secretin and cholecystokinin, both of which are hormones Hormones Hormones are messenger molecules that are synthesized in one part of the body and move through the bloodstream to exert specific regulatory effects on another part of the body. Hormones play critical roles in coordinating cellular activities throughout the body in response to the constant changes in both the internal and external environments. Hormones: Overview and Types released in the duodenum Duodenum The shortest and widest portion of the small intestine adjacent to the pylorus of the stomach. It is named for having the length equal to about the width of 12 fingers. Small Intestine: Anatomy

Secretion Secretion Coagulation Studies stimulation:

  • Release Release Release of a virus from the host cell following virus assembly and maturation. Egress can occur by host cell lysis, exocytosis, or budding through the plasma membrane. Virology of secretin and cholecystokinin from the duodenum Duodenum The shortest and widest portion of the small intestine adjacent to the pylorus of the stomach. It is named for having the length equal to about the width of 12 fingers. Small Intestine: Anatomy:
    • Acidic content in the stomach Stomach The stomach is a muscular sac in the upper left portion of the abdomen that plays a critical role in digestion. The stomach develops from the foregut and connects the esophagus with the duodenum. Structurally, the stomach is C-shaped and forms a greater and lesser curvature and is divided grossly into regions: the cardia, fundus, body, and pylorus. Stomach: Anatomy induces the release Release Release of a virus from the host cell following virus assembly and maturation. Egress can occur by host cell lysis, exocytosis, or budding through the plasma membrane. Virology of secretin.
    • Amino acids Amino acids Organic compounds that generally contain an amino (-NH2) and a carboxyl (-COOH) group. Twenty alpha-amino acids are the subunits which are polymerized to form proteins. Basics of Amino Acids and fats Fats The glyceryl esters of a fatty acid, or of a mixture of fatty acids. They are generally odorless, colorless, and tasteless if pure, but they may be flavored according to origin. Fats are insoluble in water, soluble in most organic solvents. They occur in animal and vegetable tissue and are generally obtained by boiling or by extraction under pressure. They are important in the diet (dietary fats) as a source of energy. Energy Homeostasis induce the release Release Release of a virus from the host cell following virus assembly and maturation. Egress can occur by host cell lysis, exocytosis, or budding through the plasma membrane. Virology of cholecystokinin.
    • Secretin and cholecystokinin enter the bloodstream and are transported to the pancreas Pancreas The pancreas lies mostly posterior to the stomach and extends across the posterior abdominal wall from the duodenum on the right to the spleen on the left. This organ has both exocrine and endocrine tissue. Pancreas: Anatomy.
  • Neural stimulation:
    • Direct stimulation by the vagus nerve Vagus nerve The 10th cranial nerve. The vagus is a mixed nerve which contains somatic afferents (from skin in back of the ear and the external auditory meatus), visceral afferents (from the pharynx, larynx, thorax, and abdomen), parasympathetic efferents (to the thorax and abdomen), and efferents to striated muscle (of the larynx and pharynx). Pharynx: Anatomy ( ACh ACh A neurotransmitter found at neuromuscular junctions, autonomic ganglia, parasympathetic effector junctions, a subset of sympathetic effector junctions, and at many sites in the central nervous system. Receptors and Neurotransmitters of the CNS)
    • Stimulation via other neurotransmitters:
      • VIP VIP A highly basic, 28 amino acid neuropeptide released from intestinal mucosa. It has a wide range of biological actions affecting the cardiovascular, gastrointestinal, and respiratory systems and is neuroprotective. It binds special receptors. Gastrointestinal Neural and Hormonal Signaling
      • Gastrin-releasing peptide gastrin-releasing peptide Neuropeptide and gut hormone that helps regulate gastric acid secretion and motor function. Once released from nerves in the antrum of the stomach, the neuropeptide stimulates release of gastrin from the gastrin-secreting cells. Gastrointestinal Neural and Hormonal Signaling (GRP)
  • 2 major intracellular pathways trigger Trigger The type of signal that initiates the inspiratory phase by the ventilator Invasive Mechanical Ventilation the secretion Secretion Coagulation Studies of pancreatic juices:
    • ↑ In intracellular cAMP cAMP An adenine nucleotide containing one phosphate group which is esterified to both the 3′- and 5′-positions of the sugar moiety. It is a second messenger and a key intracellular regulator, functioning as a mediator of activity for a number of hormones, including epinephrine, glucagon, and acth. Phosphodiesterase Inhibitors, which is caused by:
      • Secretin
      • VIP VIP A highly basic, 28 amino acid neuropeptide released from intestinal mucosa. It has a wide range of biological actions affecting the cardiovascular, gastrointestinal, and respiratory systems and is neuroprotective. It binds special receptors. Gastrointestinal Neural and Hormonal Signaling
    • ↑ In intracellular Ca CA Condylomata acuminata are a clinical manifestation of genital HPV infection. Condylomata acuminata are described as raised, pearly, flesh-colored, papular, cauliflower-like lesions seen in the anogenital region that may cause itching, pain, or bleeding. Condylomata Acuminata (Genital Warts)2+:
      • ACh ACh A neurotransmitter found at neuromuscular junctions, autonomic ganglia, parasympathetic effector junctions, a subset of sympathetic effector junctions, and at many sites in the central nervous system. Receptors and Neurotransmitters of the CNS
      • Cholecystokinin
      • GRP
    • Both pathways result in phosphorylation Phosphorylation The introduction of a phosphoryl group into a compound through the formation of an ester bond between the compound and a phosphorus moiety. Post-translational Protein Processing of structural and regulatory proteins Proteins Linear polypeptides that are synthesized on ribosomes and may be further modified, crosslinked, cleaved, or assembled into complex proteins with several subunits. The specific sequence of amino acids determines the shape the polypeptide will take, during protein folding, and the function of the protein. Energy Homeostasis → induce docking and fusion of secretory granules → proteins Proteins Linear polypeptides that are synthesized on ribosomes and may be further modified, crosslinked, cleaved, or assembled into complex proteins with several subunits. The specific sequence of amino acids determines the shape the polypeptide will take, during protein folding, and the function of the protein. Energy Homeostasis are secreted into acini
Diagram of an exocrine pancreatic cell and its secretion-stimulation pathways

Diagram of an exocrine pancreatic cell and its secretion-stimulation pathways:
Note how vasoactive intestinal peptide Vasoactive intestinal peptide A highly basic, 28 amino acid neuropeptide released from intestinal mucosa. It has a wide range of biological actions affecting the cardiovascular, gastrointestinal, and respiratory systems and is neuroprotective. It binds special receptors. Gastrointestinal Neural and Hormonal Signaling ( VIP VIP A highly basic, 28 amino acid neuropeptide released from intestinal mucosa. It has a wide range of biological actions affecting the cardiovascular, gastrointestinal, and respiratory systems and is neuroprotective. It binds special receptors. Gastrointestinal Neural and Hormonal Signaling) and secretin increase the concentration of intracellular cAMP cAMP An adenine nucleotide containing one phosphate group which is esterified to both the 3′- and 5′-positions of the sugar moiety. It is a second messenger and a key intracellular regulator, functioning as a mediator of activity for a number of hormones, including epinephrine, glucagon, and acth. Phosphodiesterase Inhibitors, whereas gastrin-releasing peptide gastrin-releasing peptide Neuropeptide and gut hormone that helps regulate gastric acid secretion and motor function. Once released from nerves in the antrum of the stomach, the neuropeptide stimulates release of gastrin from the gastrin-secreting cells. Gastrointestinal Neural and Hormonal Signaling (GRP), acetylcholine Acetylcholine A neurotransmitter found at neuromuscular junctions, autonomic ganglia, parasympathetic effector junctions, a subset of sympathetic effector junctions, and at many sites in the central nervous system. Receptors and Neurotransmitters of the CNS ( ACh ACh A neurotransmitter found at neuromuscular junctions, autonomic ganglia, parasympathetic effector junctions, a subset of sympathetic effector junctions, and at many sites in the central nervous system. Receptors and Neurotransmitters of the CNS), and cholecystokinin (CCK) increase intracellular Ca CA Condylomata acuminata are a clinical manifestation of genital HPV infection. Condylomata acuminata are described as raised, pearly, flesh-colored, papular, cauliflower-like lesions seen in the anogenital region that may cause itching, pain, or bleeding. Condylomata Acuminata (Genital Warts)2+ concentrations. Both pathways result in phosphorylation Phosphorylation The introduction of a phosphoryl group into a compound through the formation of an ester bond between the compound and a phosphorus moiety. Post-translational Protein Processing of the structural and regulatory proteins Proteins Linear polypeptides that are synthesized on ribosomes and may be further modified, crosslinked, cleaved, or assembled into complex proteins with several subunits. The specific sequence of amino acids determines the shape the polypeptide will take, during protein folding, and the function of the protein. Energy Homeostasis, ultimately inducing docking and fusion of secretory granules that contain enzymes Enzymes Enzymes are complex protein biocatalysts that accelerate chemical reactions without being consumed by them. Due to the body’s constant metabolic needs, the absence of enzymes would make life unsustainable, as reactions would occur too slowly without these molecules. Basics of Enzymes.

Image by Lecturio.

Clinical relevance of pancreatic secretions

  • Acute pancreatitis Acute pancreatitis Acute pancreatitis is an inflammatory disease of the pancreas due to autodigestion. Common etiologies include gallstones and excessive alcohol use. Patients typically present with epigastric pain radiating to the back. Acute Pancreatitis: occurs when pancreatic enzymes Enzymes Enzymes are complex protein biocatalysts that accelerate chemical reactions without being consumed by them. Due to the body’s constant metabolic needs, the absence of enzymes would make life unsustainable, as reactions would occur too slowly without these molecules. Basics of Enzymes are retained within the pancreas Pancreas The pancreas lies mostly posterior to the stomach and extends across the posterior abdominal wall from the duodenum on the right to the spleen on the left. This organ has both exocrine and endocrine tissue. Pancreas: Anatomy, resulting in self-digestion. Acute pancreatitis Acute pancreatitis Acute pancreatitis is an inflammatory disease of the pancreas due to autodigestion. Common etiologies include gallstones and excessive alcohol use. Patients typically present with epigastric pain radiating to the back. Acute Pancreatitis can occur due to obstruction (e.g., gallstones Gallstones Cholelithiasis (gallstones) is the presence of stones in the gallbladder. Most gallstones are cholesterol stones, while the rest are composed of bilirubin (pigment stones) and other mixed components. Patients are commonly asymptomatic but may present with biliary colic (intermittent pain in the right upper quadrant). Cholelithiasis, cancer in the head of the pancreas Pancreas The pancreas lies mostly posterior to the stomach and extends across the posterior abdominal wall from the duodenum on the right to the spleen on the left. This organ has both exocrine and endocrine tissue. Pancreas: Anatomy) and can be seen in cases of cystic fibrosis Cystic fibrosis Cystic fibrosis is an autosomal recessive disorder caused by mutations in the gene CFTR. The mutations lead to dysfunction of chloride channels, which results in hyperviscous mucus and the accumulation of secretions. Common presentations include chronic respiratory infections, failure to thrive, and pancreatic insufficiency. Cystic Fibrosis.
  • Cystic fibrosis Cystic fibrosis Cystic fibrosis is an autosomal recessive disorder caused by mutations in the gene CFTR. The mutations lead to dysfunction of chloride channels, which results in hyperviscous mucus and the accumulation of secretions. Common presentations include chronic respiratory infections, failure to thrive, and pancreatic insufficiency. Cystic Fibrosis: an autosomal recessive Autosomal recessive Autosomal inheritance, both dominant and recessive, refers to the transmission of genes from the 22 autosomal chromosomes. Autosomal recessive diseases are only expressed when 2 copies of the recessive allele are inherited. Autosomal Recessive and Autosomal Dominant Inheritance disorder caused by mutations in the CFTR gene Gene A category of nucleic acid sequences that function as units of heredity and which code for the basic instructions for the development, reproduction, and maintenance of organisms. Basic Terms of Genetics. Mutations lead to dysfunction of the Cl channels Channels The Cell: Cell Membrane, resulting in the formation of hyperviscous mucus. Hyperviscous mucus obstructs the flow Flow Blood flows through the heart, arteries, capillaries, and veins in a closed, continuous circuit. Flow is the movement of volume per unit of time. Flow is affected by the pressure gradient and the resistance fluid encounters between 2 points. Vascular resistance is the opposition to flow, which is caused primarily by blood friction against vessel walls. Vascular Resistance, Flow, and Mean Arterial Pressure of pancreatic juice Pancreatic Juice The fluid containing digestive enzymes secreted by the pancreas in response to food in the duodenum. Pancreas: Anatomy and bile Bile An emulsifying agent produced in the liver and secreted into the duodenum. Its composition includes bile acids and salts; cholesterol; and electrolytes. It aids digestion of fats in the duodenum. Gallbladder and Biliary Tract: Anatomy in the GI tract, resulting in maldigestion Maldigestion Malabsorption involves many disorders in which there is an inability of the gut to absorb nutrients from dietary intake, potentially including water and/or electrolytes. A closely related term, maldigestion is the inability to break down large molecules of food into their smaller constituents. Malabsorption and maldigestion can affect macronutrients (fats, proteins, and carbohydrates), micronutrients (vitamins and minerals), or both. Malabsorption and Maldigestion, malabsorption Malabsorption General term for a group of malnutrition syndromes caused by failure of normal intestinal absorption of nutrients. Malabsorption and Maldigestion, and progressive liver Liver The liver is the largest gland in the human body. The liver is found in the superior right quadrant of the abdomen and weighs approximately 1.5 kilograms. Its main functions are detoxification, metabolism, nutrient storage (e.g., iron and vitamins), synthesis of coagulation factors, formation of bile, filtration, and storage of blood. Liver: Anatomy and pancreatic disease. Common presentations include chronic respiratory infections Infections Invasion of the host organism by microorganisms or their toxins or by parasites that can cause pathological conditions or diseases. Chronic Granulomatous Disease, failure to thrive Failure to Thrive Failure to thrive (FTT), or faltering growth, describes suboptimal weight gain and growth in children. The majority of cases are due to inadequate caloric intake; however, genetic, infectious, and oncological etiologies are also common. Failure to Thrive, and pancreatic insufficiency (due to loss of exocrine function).

Hepatobiliary Secretions (Bile)

Bile Bile An emulsifying agent produced in the liver and secreted into the duodenum. Its composition includes bile acids and salts; cholesterol; and electrolytes. It aids digestion of fats in the duodenum. Gallbladder and Biliary Tract: Anatomy

  • Synthesized by hepatocytes Hepatocytes The main structural component of the liver. They are specialized epithelial cells that are organized into interconnected plates called lobules. Liver: Anatomy
  • Transported to the gallbladder Gallbladder The gallbladder is a pear-shaped sac, located directly beneath the liver, that sits on top of the superior part of the duodenum. The primary functions of the gallbladder include concentrating and storing up to 50 mL of bile. Gallbladder and Biliary Tract: Anatomy (via the hepatic and cystic Cystic Fibrocystic Change ducts) for storage
  • Primary function: emulsification (rather than digestion Digestion Digestion refers to the process of the mechanical and chemical breakdown of food into smaller particles, which can then be absorbed and utilized by the body. Digestion and Absorption) of fats Fats The glyceryl esters of a fatty acid, or of a mixture of fatty acids. They are generally odorless, colorless, and tasteless if pure, but they may be flavored according to origin. Fats are insoluble in water, soluble in most organic solvents. They occur in animal and vegetable tissue and are generally obtained by boiling or by extraction under pressure. They are important in the diet (dietary fats) as a source of energy. Energy Homeostasis
Structure of the hepatobiliary tree

Structure of the hepatobiliary tree

Image by Lecturio.

Components of biliary secretions (i.e., bile Bile An emulsifying agent produced in the liver and secreted into the duodenum. Its composition includes bile acids and salts; cholesterol; and electrolytes. It aids digestion of fats in the duodenum. Gallbladder and Biliary Tract: Anatomy)

  • Bile salts Bile salts Steroid acids and salts. The primary bile acids are derived from cholesterol in the liver and usually conjugated with glycine or taurine. The secondary bile acids are further modified by bacteria in the intestine. They play an important role in the digestion and absorption of fat. They have also been used pharmacologically, especially in the treatment of gallstones. Cholelithiasis
  • Cholesterol Cholesterol The principal sterol of all higher animals, distributed in body tissues, especially the brain and spinal cord, and in animal fats and oils. Cholesterol Metabolism
  • Lecithin Lecithin A complex mixture of phospholipids; glycolipids; and triglycerides; with substantial amounts of phosphatidylcholines; phosphatidylethanolamines; and phosphatidylinositols, which are sometimes loosely termed as 1, 2-diacyl-3-phosphocholines. Lecithin is a component of the cell membrane and commercially extracted from soybeans and egg yolk. The emulsifying and surfactant properties are useful in food additives and for forming organogels (gels). Fatty Acids and Lipids
  • Bilirubin Bilirubin A bile pigment that is a degradation product of heme. Heme Metabolism
  • Ions

Bile Bile An emulsifying agent produced in the liver and secreted into the duodenum. Its composition includes bile acids and salts; cholesterol; and electrolytes. It aids digestion of fats in the duodenum. Gallbladder and Biliary Tract: Anatomy concentration in the gallbladder Gallbladder The gallbladder is a pear-shaped sac, located directly beneath the liver, that sits on top of the superior part of the duodenum. The primary functions of the gallbladder include concentrating and storing up to 50 mL of bile. Gallbladder and Biliary Tract: Anatomy

The primary function of the gallbladder Gallbladder The gallbladder is a pear-shaped sac, located directly beneath the liver, that sits on top of the superior part of the duodenum. The primary functions of the gallbladder include concentrating and storing up to 50 mL of bile. Gallbladder and Biliary Tract: Anatomy is the storage and concentration of bile Bile An emulsifying agent produced in the liver and secreted into the duodenum. Its composition includes bile acids and salts; cholesterol; and electrolytes. It aids digestion of fats in the duodenum. Gallbladder and Biliary Tract: Anatomy. Bile Bile An emulsifying agent produced in the liver and secreted into the duodenum. Its composition includes bile acids and salts; cholesterol; and electrolytes. It aids digestion of fats in the duodenum. Gallbladder and Biliary Tract: Anatomy can be concentrated in the gallbladder Gallbladder The gallbladder is a pear-shaped sac, located directly beneath the liver, that sits on top of the superior part of the duodenum. The primary functions of the gallbladder include concentrating and storing up to 50 mL of bile. Gallbladder and Biliary Tract: Anatomy by about 5%‒20% through dehydration Dehydration The condition that results from excessive loss of water from a living organism. Volume Depletion and Dehydration:

  • Na+:
    • Reabsorbed from the lumen in exchange for H+ via the Na+/H+ exchanger in the apical membrane
    • Na+ within the cell is then pumped across the basolateral membrane into the interstitial space in exchange for K+ via the Na+/K+ ATPase.
  • Cl:
    • Reabsorbed from the lumen in exchange for HCO3 via the HCO3/Cl exchanger in the apical membrane
    • Cl within the cell moves to the interstitial space through the Cl channels Channels The Cell: Cell Membrane in the basolateral membrane.
  • Water follows NaCl:
Mechanism of biliary concentration.

Mechanism of biliary concentration: Na+ is exchanged for H+ in the apical membrane and later exchanged for K+ in the basolateral membrane. Next, Cl is exchanged for HCO3 in the apical membrane and moves to the interstitial space through its own channels Channels The Cell: Cell Membrane. The concentration gradient that is produced induces the transcellular Transcellular The movement of one cell into, through, and out of another cell. Tubular System and paracellular Paracellular Renal Potassium Regulation movement of water.

Image by Lecturio.

Control and regulation

Bile Bile An emulsifying agent produced in the liver and secreted into the duodenum. Its composition includes bile acids and salts; cholesterol; and electrolytes. It aids digestion of fats in the duodenum. Gallbladder and Biliary Tract: Anatomy is continuously produced by the liver Liver The liver is the largest gland in the human body. The liver is found in the superior right quadrant of the abdomen and weighs approximately 1.5 kilograms. Its main functions are detoxification, metabolism, nutrient storage (e.g., iron and vitamins), synthesis of coagulation factors, formation of bile, filtration, and storage of blood. Liver: Anatomy; thus, regulation is via release Release Release of a virus from the host cell following virus assembly and maturation. Egress can occur by host cell lysis, exocytosis, or budding through the plasma membrane. Virology from the gallbladder Gallbladder The gallbladder is a pear-shaped sac, located directly beneath the liver, that sits on top of the superior part of the duodenum. The primary functions of the gallbladder include concentrating and storing up to 50 mL of bile. Gallbladder and Biliary Tract: Anatomy.

  • The primary mediator is cholecystokinin, which has 2 main effects:
    • Gallbladder Gallbladder The gallbladder is a pear-shaped sac, located directly beneath the liver, that sits on top of the superior part of the duodenum. The primary functions of the gallbladder include concentrating and storing up to 50 mL of bile. Gallbladder and Biliary Tract: Anatomy contraction
    • Relaxation of the sphincter of Oddi
  • Other regulators:
    • Vagus nerve Vagus nerve The 10th cranial nerve. The vagus is a mixed nerve which contains somatic afferents (from skin in back of the ear and the external auditory meatus), visceral afferents (from the pharynx, larynx, thorax, and abdomen), parasympathetic efferents (to the thorax and abdomen), and efferents to striated muscle (of the larynx and pharynx). Pharynx: Anatomy: weak stimulator of gallbladder Gallbladder The gallbladder is a pear-shaped sac, located directly beneath the liver, that sits on top of the superior part of the duodenum. The primary functions of the gallbladder include concentrating and storing up to 50 mL of bile. Gallbladder and Biliary Tract: Anatomy contraction
    • Inhibitors of bile Bile An emulsifying agent produced in the liver and secreted into the duodenum. Its composition includes bile acids and salts; cholesterol; and electrolytes. It aids digestion of fats in the duodenum. Gallbladder and Biliary Tract: Anatomy release Release Release of a virus from the host cell following virus assembly and maturation. Egress can occur by host cell lysis, exocytosis, or budding through the plasma membrane. Virology:
      • Somatostatin
      • Norepinephrine Norepinephrine Precursor of epinephrine that is secreted by the adrenal medulla and is a widespread central and autonomic neurotransmitter. Norepinephrine is the principal transmitter of most postganglionic sympathetic fibers, and of the diffuse projection system in the brain that arises from the locus ceruleus. Receptors and Neurotransmitters of the CNS

Intestinal Secretions

  • Intestines secrete about 1‒2 L of intestinal juice per day.
  • Secretions released into the lumen:
    • Mucus
    • Serous fluid
  • Functions of intestinal juice:
    • Protection of the intestinal walls
    • Regulation of GI function
    • Minimal secretions for digestive functions (i.e., secretions contain very few enzymes Enzymes Enzymes are complex protein biocatalysts that accelerate chemical reactions without being consumed by them. Due to the body’s constant metabolic needs, the absence of enzymes would make life unsustainable, as reactions would occur too slowly without these molecules. Basics of Enzymes)
  • Secretions released into the blood (i.e., hormonal signaling molecules Signaling molecules Second Messengers):
    • Secretin
    • Cholecystokinin
    • GIP GIP A gastrointestinal peptide hormone of about 43-amino acids. It is found to be a potent stimulator of insulin secretion and a relatively poor inhibitor of gatsric acid secretion. Gastrointestinal Neural and Hormonal Signaling
    • Motilin
    • Small amounts of gastrin

References

  1. Barrett, K.E. (2014). Chapter 3. Gastric secretion. Gastrointestinal physiology, 2e. New York, NY: The McGraw-Hill Companies. accessmedicine.mhmedical.com/content.aspx?aid=57850184
  2. Morton, D.A., Foreman, K.B., Albertine, K.H. (2019). Cranial nerves. The big picture: Gross anatomy, 2e. New York, NY: McGraw-Hill Education. accessmedicine.mhmedical.com/content.aspx?aid=1158277541
  3. Barrett, K.E. (2014). Chapter 4. Pancreatic and salivary secretion. Gastrointestinal physiology, 2e. New York, NY: The McGraw-Hill Companies. accessmedicine.mhmedical.com/content.aspx?aid=57850282
  4. Barrett, K.E. (2014). Chapter 11. Bile formation and secretion. Gastrointestinal physiology, 2e. New York, NY: The McGraw-Hill Companies. accessmedicine.mhmedical.com/content.aspx?aid=57850893
  5. Barrett, K.E. (2014). Chapter 7. Esophageal motility. Gastrointestinal physiology, 2e. New York, NY: The McGraw-Hill Companies. accessmedicine.mhmedical.com/content.aspx?aid=57850585
  6. Barrett, K.E. (2014). Chapter 8. Gastric motility. Gastrointestinal physiology, 2e. New York, NY: The McGraw-Hill Companies. accessmedicine.mhmedical.com/content.aspx?aid=57850653
  7. Barrett, K.E. (2014). Chapter 9. Intestinal motility. Gastrointestinal physiology, 2e. New York, NY: The McGraw-Hill Companies. accessmedicine.mhmedical.com/content.aspx?aid=57850727
  8. Saladin, K.S., Miller, L. (2004). Anatomy and physiology. (3rd Ed. Pp. 946-965).

USMLE™ is a joint program of the Federation of State Medical Boards (FSMB®) and National Board of Medical Examiners (NBME®). MCAT is a registered trademark of the Association of American Medical Colleges (AAMC). NCLEX®, NCLEX-RN®, and NCLEX-PN® are registered trademarks of the National Council of State Boards of Nursing, Inc (NCSBN®). None of the trademark holders are endorsed by nor affiliated with Lecturio.

Study on the Go

Lecturio Medical complements your studies with evidence-based learning strategies, video lectures, quiz questions, and more – all combined in one easy-to-use resource.

Learn even more with Lecturio:

Complement your med school studies with Lecturio’s all-in-one study companion, delivered with evidence-based learning strategies.

User Reviews

¡Hola!

Esta página está disponible en Español.

Details