The primary functions of the GI tract are 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 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, which require coordinated contractions of the smooth muscles Smooth muscles Unstriated and unstriped muscle, one of the muscles of the internal organs, blood vessels, hair follicles, etc. Contractile elements are elongated, usually spindle-shaped cells with centrally located nuclei. Smooth muscle fibers are bound together into sheets or bundles by reticular fibers and frequently elastic nets are also abundant. Muscle Tissue: Histology present in the GI tract. Peristaltic waves, segmentation contractions, and the migrating motor Motor Neurons which send impulses peripherally to activate muscles or secretory cells. Nervous System: Histology complex are all important contraction patterns that help to mix contents, get them in contact with the intestinal walls (where they are further digested by brush-border 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 and absorbed into the enterocytes), and propel material down the tract at appropriate times and in appropriate amounts.
Last updated: 20 Dec, 2021
GI motility refers to the contraction of smooth muscle within the walls of the GI tract, which:
Coordination
Coordination
Cerebellar Disorders of smooth muscle in peristalsis:
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) causes constriction of the muscle just behind the foodstuff, while NO and
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) cause relaxation ahead of it. This creates a
pressure gradient
Pressure gradient
Vascular Resistance, Flow, and Mean Arterial Pressure, forcing the food downward. Nerves from the enteric
nervous system
Nervous system
The nervous system is a small and complex system that consists of an intricate network of neural cells (or neurons) and even more glial cells (for support and insulation). It is divided according to its anatomical components as well as its functional characteristics. The brain and spinal cord are referred to as the central nervous system, and the branches of nerves from these structures are referred to as the peripheral nervous system.
Nervous System: Anatomy, Structure, and Classification (with input from the autonomic
nervous system
Nervous system
The nervous system is a small and complex system that consists of an intricate network of neural cells (or neurons) and even more glial cells (for support and insulation). It is divided according to its anatomical components as well as its functional characteristics. The brain and spinal cord are referred to as the central nervous system, and the branches of nerves from these structures are referred to as the peripheral nervous system.
Nervous System: Anatomy, Structure, and Classification), coordinate the wave of constriction and relaxation.
Segmentation contractions 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:
Note how the subsequent contraction achieves mixing of contents and enough increase in pressure to overcome the relaxed pyloric sphincter.
GI motility is controlled primarily via the parasympathetic nervous system Nervous system The nervous system is a small and complex system that consists of an intricate network of neural cells (or neurons) and even more glial cells (for support and insulation). It is divided according to its anatomical components as well as its functional characteristics. The brain and spinal cord are referred to as the central nervous system, and the branches of nerves from these structures are referred to as the peripheral nervous system. Nervous System: Anatomy, Structure, and Classification (PNS) and the ENS.
A specialized portion of 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 located within the walls of the GI tract
Consists of:
Structure of the intestinal walls:
The
Meissner plexus
Meissner plexus
One of two ganglionated neural networks which together form the enteric nervous system. The submucous (Meissner’s) plexus is in the connective tissue of the submucosa. Its neurons innervate the epithelium, blood vessels, endocrine cells, other submucosal ganglia, and myenteric ganglia, and play an important role in regulating ion and water transport.
Gastrointestinal Neural and Hormonal Signaling is located within the submucosa, and the
Auerbach plexus
Auerbach plexus
One of two ganglionated neural networks which together form the enteric nervous system. The myenteric (Auerbach’s) plexus is located between the longitudinal and circular muscle layers of the gut. Its neurons project to the circular muscle, to other myenteric ganglia, to submucosal ganglia, or directly to the epithelium, and play an important role in regulating and patterning gut motility.
Gastrointestinal Neural and Hormonal Signaling (also known as the
myenteric plexus
Myenteric plexus
One of two ganglionated neural networks which together form the enteric nervous system. The myenteric (Auerbach’s) plexus is located between the longitudinal and circular muscle layers of the gut. Its neurons project to the circular muscle, to other myenteric ganglia, to submucosal ganglia, or directly to the epithelium, and play an important role in regulating and patterning gut motility.
Gastrointestinal Neural and Hormonal Signaling) is located between the circular and longitudinal muscular layers.
Function: local control of GI function
Schematic depiction of slow electrical waves and how they
affect
Affect
The feeling-tone accompaniment of an idea or mental representation. It is the most direct psychic derivative of instinct and the psychic representative of the various bodily changes by means of which instincts manifest themselves.
Psychiatric Assessment smooth
muscle tone
Muscle tone
The state of activity or tension of a muscle beyond that related to its physical properties, that is, its active resistance to stretch. In skeletal muscle, tonus is dependent upon efferent innervation.
Skeletal Muscle Contraction:
If the peak of the wave reaches the
threshold
Threshold
Minimum voltage necessary to generate an action potential (an all-or-none response)
Skeletal Muscle Contraction required for an
action potential
Action Potential
Abrupt changes in the membrane potential that sweep along the cell membrane of excitable cells in response to excitation stimuli.
Membrane Potential (seen as a vertical spike in the
membrane potential
Membrane potential
The membrane potential is the difference in electric charge between the interior and the exterior of a cell. All living cells maintain a potential difference across the membrane thanks to the insulating properties of their plasma membranes (PMs) and the selective transport of ions across this membrane by transporters.
Membrane Potential), muscle contraction occurs. When action potentials occur back to back in smooth muscle (Stimulated panel), contractions are stronger. If
threshold
Threshold
Minimum voltage necessary to generate an action potential (an all-or-none response)
Skeletal Muscle Contraction is not reached (Inhibited panel), contractions do not occur.
Swallowing (also called deglutition) is a complex process involving > 22 muscles in the mouth, pharynx Pharynx The pharynx is a component of the digestive system that lies posterior to the nasal cavity, oral cavity, and larynx. The pharynx can be divided into the oropharynx, nasopharynx, and laryngopharynx. Pharyngeal muscles play an integral role in vital processes such as breathing, swallowing, and speaking. Pharynx: Anatomy, and 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, which moves food in the mouth through the upper esophageal sphincter Upper esophageal sphincter The structure at the pharyngoesophageal junction consisting chiefly of the cricopharyngeus muscle. It normally occludes the lumen of the esophagus, except during swallowing. Esophagus: Anatomy and 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.
Swallowing:
First, the
tongue
Tongue
The tongue, on the other hand, is a complex muscular structure that permits tasting and facilitates the process of mastication and communication. The blood supply of the tongue originates from the external carotid artery, and the innervation is through cranial nerves.
Lips and Tongue: Anatomy compresses the food against the hard
palate
Palate
The palate is the structure that forms the roof of the mouth and floor of the nasal cavity. This structure is divided into soft and hard palates.
Palate: Anatomy (note the
glottis
Glottis
The vocal apparatus of the larynx, situated in the middle section of the larynx. Glottis consists of the vocal folds and an opening (rima glottidis) between the folds.
Larynx: Anatomy is open). Next, the
tongue
Tongue
The tongue, on the other hand, is a complex muscular structure that permits tasting and facilitates the process of mastication and communication. The blood supply of the tongue originates from the external carotid artery, and the innervation is through cranial nerves.
Lips and Tongue: Anatomy forces the bolus to the back of the mouth; the soft
palate
Palate
The palate is the structure that forms the roof of the mouth and floor of the nasal cavity. This structure is divided into soft and hard palates.
Palate: Anatomy closes off the
nasopharynx
Nasopharynx
The top portion of the pharynx situated posterior to the nose and superior to the soft palate. The nasopharynx is the posterior extension of the nasal cavities and has a respiratory function.
Pharynx: Anatomy. Finally, as the foodstuff is forced downwards, the
epiglottis
Epiglottis
A thin leaf-shaped cartilage that is covered with laryngeal mucosa and situated posterior to the root of the tongue and hyoid bone. During swallowing, the epiglottis folds back over the larynx inlet thus prevents foods from entering the airway.
Larynx: Anatomy is pulled forwards, closing the
glottis
Glottis
The vocal apparatus of the larynx, situated in the middle section of the larynx. Glottis consists of the vocal folds and an opening (rima glottidis) between the folds.
Larynx: Anatomy (
airway
Airway
ABCDE Assessment), and the
upper esophageal sphincter
Upper esophageal sphincter
The structure at the pharyngoesophageal junction consisting chiefly of the cricopharyngeus muscle. It normally occludes the lumen of the esophagus, except during swallowing.
Esophagus: Anatomy relaxes, letting food 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. Peristaltic waves move the food down towards 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.
Innervation 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:
Note how the swallowing center integrates striated and smooth muscle activity.
Regions 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 and their functions:
In the body 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, the
interstitial cells of Cajal
Interstitial cells of Cajal
C-kit positive cells related to smooth muscle cells that are intercalated between the autonomic nerves and the effector smooth muscle cells of the gastrointestinal tract. Different phenotypic classes play roles as pacemakers, mediators of neural inputs, and mechanosensors.
Gastrointestinal Neural and Hormonal Signaling are the
pacemaker
Pacemaker
A device designed to stimulate, by electric impulses, contraction of the heart muscles. It may be temporary (external) or permanent (internal or internal-external).
Bradyarrhythmias cells triggering
regular
Regular
Insulin peristaltic movements.
Mixes chyme Chyme Small Intestine: Anatomy:
A graph showing the waves of the migrating
motor
Motor
Neurons which send impulses peripherally to activate muscles or secretory cells.
Nervous System: Histology complex during fasting:
The red dotted line shows the
phase 3
Phase 3
Skin: Structure and Functions waves.
The rectum Rectum The rectum and anal canal are the most terminal parts of the lower GI tract/large intestine that form a functional unit and control defecation. Fecal continence is maintained by several important anatomic structures including rectal folds, anal valves, the sling-like puborectalis muscle, and internal and external anal sphincters. Rectum and Anal Canal: Anatomy contains stretch 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 that stimulate the defecation reflex when the rectum Rectum The rectum and anal canal are the most terminal parts of the lower GI tract/large intestine that form a functional unit and control defecation. Fecal continence is maintained by several important anatomic structures including rectal folds, anal valves, the sling-like puborectalis muscle, and internal and external anal sphincters. Rectum and Anal Canal: Anatomy begins to fill with feces.
The defecation reflex:
1. Feces stretch the
rectum
Rectum
The rectum and anal canal are the most terminal parts of the lower GI tract/large intestine that form a functional unit and control defecation. Fecal continence is maintained by several important anatomic structures including rectal folds, anal valves, the sling-like puborectalis muscle, and internal and external anal sphincters.
Rectum and Anal Canal: Anatomy and stimulate the stretch
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, transmitting the signal to the
spinal cord
Spinal cord
The spinal cord is the major conduction pathway connecting the brain to the body; it is part of the CNS. In cross section, the spinal cord is divided into an H-shaped area of gray matter (consisting of synapsing neuronal cell bodies) and a surrounding area of white matter (consisting of ascending and descending tracts of myelinated axons).
Spinal Cord: Anatomy.
2. A spinal reflex sends parasympathetic
motor
Motor
Neurons which send impulses peripherally to activate muscles or secretory cells.
Nervous System: Histology signals to the myenteric nerve plexus, resulting in contraction of the
smooth muscles
Smooth muscles
Unstriated and unstriped muscle, one of the muscles of the internal organs, blood vessels, hair follicles, etc. Contractile elements are elongated, usually spindle-shaped cells with centrally located nuclei. Smooth muscle fibers are bound together into sheets or bundles by reticular fibers and frequently elastic nets are also abundant.
Muscle Tissue: Histology within the
rectum
Rectum
The rectum and anal canal are the most terminal parts of the lower GI tract/large intestine that form a functional unit and control defecation. Fecal continence is maintained by several important anatomic structures including rectal folds, anal valves, the sling-like puborectalis muscle, and internal and external anal sphincters.
Rectum and Anal Canal: Anatomy and pushing feces downward.
3. The same spinal reflex also sends parasympathetic
motor
Motor
Neurons which send impulses peripherally to activate muscles or secretory cells.
Nervous System: Histology signals to relax the
internal anal sphincter
Internal anal sphincter
Rectum and Anal Canal: Anatomy.
4. Voluntary impulses from 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 prevent defecation by keeping the
external anal sphincter
External anal sphincter
Rectum and Anal Canal: Anatomy contracted. Defecation will occur if voluntary signals allow the
external anal sphincter
External anal sphincter
Rectum and Anal Canal: Anatomy to relax.