Small Intestine

The small intestine is the longest part of the GI tract, extending from the pyloric orifice 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 to the ileocecal junction. The small intestine is the major organ responsible for chemical digestion and absorption of nutrients. The small intestine is divided into 3 segments: the duodenum, the jejunum, and the ileum. Like the entire GI tract, the walls of the small intestine have several layers: an inner absorptive mucosal layer (which is made up of an 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, lamina propria, and muscularis mucosa) and submucosal, muscular, and serosal layers. The arterial supply to the small intestine is via branches of the superior mesenteric artery, and veins Veins Veins are tubular collections of cells, which transport deoxygenated blood and waste from the capillary beds back to the heart. Veins are classified into 3 types: small veins/venules, medium veins, and large veins. Each type contains 3 primary layers: tunica intima, tunica media, and tunica adventitia. Veins drain into the hepatic portal system. The small intestine is innervated by the ANS.

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Editorial responsibility: Stanley Oiseth, Lindsay Jones, Evelin Maza

Table of Contents

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Development

  • Embryologic origins:
    • Proximal duodenum (above the ampulla of Vater): develops from the foregut
    • Distal duodenum, jejunum, and ileum: develop from midgut
  • Development occurs primarily between the 5th and 10th weeks of fetal life
  • Ileum elongates rapidly → forms a U-shaped fold called the primary intestinal loop, which:
    • Grows around the developing superior mesenteric artery (its blood supply)
    • Herniates (protrudes) into the umbilical cord
    • Is connected to the yolk sac via the vitelline duct traveling through the umbilical cord
  • As the abdomen develops, the intestines return to the abdominal cavity
  • Undergoes a 270-degree counterclockwise rotation around the superior mesenteric artery ( SMA SMA Spinal muscular atrophy (SMA) is a spectrum of autosomal recessive syndromes characterized by progressive proximal muscle weakness and atrophy, possibly due to degeneration of the anterior horn cells in the spinal cord and motor nuclei in the lower brainstem. Spinal Muscular Atrophy (SMA))  → results in normal anatomic locations for the GI tract

Gross Anatomy

The small intestine is a long tubular structure in the abdomen that is responsible for approximately 90% of nutrient absorption.

General characteristics

  • Connects 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 at its proximal end to the colon Colon The large intestines constitute the last portion of the digestive system. The large intestine consists of the cecum, appendix, colon (with ascending, transverse, descending, and sigmoid segments), rectum, and anal canal. The primary function of the colon is to remove water and compact the stool prior to expulsion from the body via the rectum and anal canal. Colon, Cecum, and Appendix at its distal end
  • Average length: 6–7 m
  • Has 3 parts:
    1. Duodenum 
    2. Jejunum
    3. Ileum
  • Fills the majority of the mid and lower abdominal cavity
Small intestine and its parts

Small intestine and its parts

Image: “2417 Small IntestineN” by OpenStax College. License: CC BY 4.0

Duodenum

General characteristics and anatomic relations:

  • The 1st portion of the small intestines
  • Approximately 25 cm in length
  • C-shaped, curving around 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
  • Receives contents 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 at its proximal end
  • Empties contents into the jejunum at its distal end
  • Receives secretions from the pancreatic and bile ducts 

Parts of the duodenum:

The duodenum consists of 4 parts (from proximal to distal):

  • Superior: 
    • Begins at the pyloric valve (distalmost portion 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)
    • Located at spinal level L1
    • Intraperitoneal
    • Most duodenal ulcers occur in this part
  • Descending:
    • Located at spinal level L1–L3
    • Retroperitoneal (duodenum has moved posterior to the peritoneal membrane)
    • Contains connections 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 and bile duct via the major and minor duodenal papilla
    • Major duodenal papilla: 
      • Opening of the hepatopancreatic ampulla (i.e., ampulla of Vater, the combination of the common bile and main pancreatic ducts) into the duodenal lumen to allow entry of bile and pancreatic juice 
      • Papilla contains the hepatopancreatic sphincter (i.e., sphincter of Oddi), which regulates secretions
    • Minor duodenal papilla: 
      • Opening of the accessory pancreatic duct
      • Located just superior to the major papilla
      • Allows pancreatic juice to be released into the duodenum without bile
  • Transverse (sometimes referred to as the horizontal part): 
    • Located at spinal level L3
    • The longest section (10–12 cm)
    • Retroperitoneal
  • Ascending:
    • Located at spinal level L2–L3
    • Retroperitoneal
    • Terminates at the duodenojejunal flexure: 
      • Fixed to the posterior abdominal wall by the ligament of Treitz
      • Marks the end of the duodenum and beginning of the jejunum

Jejunum and ileum

The jejunum and ileum make up a majority of the small intestine as a long winding tube filling a large portion of the abdominal cavity. Both are completely intraperitoneal (within the peritoneal cavity).

  • Jejunum: 
    • Makes up the proximal ⅖ of the small intestine after the duodenum 
    • Approximately 2.5 m in length
    • Begins in the LUQ of the abdomen
    • Progresses inferiorly and medially
  • Ileum: 
    • Makes up the distal ⅗ of the small intestines 
    • Approximately 3.5 m in length
    • Primarily in the lower half of the abdomen
    • Ends at the ileocecal junction in the RLQ, where it empties into the cecum (1st portion of the large intestine Large intestine The large intestines constitute the last portion of the digestive system. The large intestine consists of the cecum, appendix, colon (with ascending, transverse, descending, and sigmoid segments), rectum, and anal canal. The primary function of the colon is to remove water and compact the stool prior to expulsion from the body via the rectum and anal canal. Colon, Cecum, and Appendix)
  • Mesentery: 
    • A fold of peritoneum Peritoneum The peritoneum is a serous membrane lining the abdominopelvic cavity. This lining is formed by connective tissue and originates from the mesoderm. The membrane lines both the abdominal walls (as parietal peritoneum) and all of the visceral organs (as visceral peritoneum). Peritoneum and Retroperitoneum that suspends the jejunum and ileum from the posterior abdominal cavity
    • Allows the jejunum and ileum significant mobility within the abdominal cavity
  • Transition between jejunum and ileum:
    • Gradual (as opposed to a discrete anatomic landmark)
    • Different segments are defined by differences in microscopic anatomy noted most prominently when comparing the proximal jejunum and the distal ileum

Microscopic Anatomy

Similar to other segments of the GI tract, the layers of the small intestinal wall (from the inner lumen outward) are mucosa → submucosa → muscular layer → serosa. The walls have several different types of folds.

Folds of the intestinal walls

Circular folds (known as plicae):

  • Large folds of intestinal wall projecting into the lumen
  • Contain both mucosa and submucosa
  • Permanent folds (i.e., not obliterated when the intestine is distended, which is different from rugae 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, which are obliterated as 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 distends)
  • Locations:
    • Begin approximately 6 cm into the duodenum
    • Most prominent in the jejunum
    • Decrease as you move farther down the ileum
  • Function: 
    • Mixes chyme 
    • ↑ Surface area required for:
      • Contact digestion
      • Absorption

Intestinal villi: 

  • Finger-like projections of the mucosa only ( 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 and lamina propria)
  • Location: off the entire lining of the small intestines, including off plicae folds
  • Function: significantly ↑ surface area
Layers and folds in the intestinal walls

Layers and folds in the intestinal walls

Image by Lecturio.

Layers of the intestinal walls

Mucosa:

  • Consists of 3 sublayers:
    1. Epithelium (innermost lining):
      • Enterocytes (also called absorptive cells): simple columnar cells primarily responsible for contact digestion and absorption
      • Goblet cells: secrete mucus
      • Enteroendocrine cells: secrete 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 into the blood
      • Cells are connected via tight junctions
      • Have a brush border: microvilli on the absorptive surface, which ↑ surface area and contain membrane-bound digestive 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 
    2. Lamina propria, which contains:
      • Vasculature: arterioles, veins Veins Veins are tubular collections of cells, which transport deoxygenated blood and waste from the capillary beds back to the heart. Veins are classified into 3 types: small veins/venules, medium veins, and large veins. Each type contains 3 primary layers: tunica intima, tunica media, and tunica adventitia. Veins, and capillary networks, which absorb a majority of the nutrients except for fats
      • Lymphatic vessels known as lacteals: absorb a majority of the fat and fat-soluble vitamins
    3. Muscularis mucosa: 
      • Thin layer of smooth muscle
      • Controls movement of the villi to ↑ mixing
  • Crypts of Lieberkuhn:
    • Pores at the base of the villi that open into tubular glands (similar to gastric glands)
    • Upper ½ contains enterocytes and goblet cells
    • Lower ½ contains:
      • Stem cells: replace enterocytes and goblet cells every 3–6 days 
      • Paneth cells: secrete defensins and lysozyme (which protect against bacterial infection)
    • Located throughout the small intestines
  • Peyer patches: 
    • Nodules of lymphatic tissue found within the lamina propria and submucosa
    • Most abundant in the ileum

Submucosa:

  • Loose connective tissue Connective tissue Connective tissues originate from embryonic mesenchyme and are present throughout the body except inside the brain and spinal cord. The main function of connective tissues is to provide structural support to organs. Connective tissues consist of cells and an extracellular matrix. Connective Tissue
  • Contains larger vessels
  • Brunner glands: 
    • Produce alkaline mucus that protects the mucosa from damage caused by 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 acid
    • Found only within the duodenum
  • Meissner plexus: 
    • Ganglia of the ANS
    • Control the muscularis mucosa (independently of the muscular layer of the intestines)

Muscular layer: 

The muscular layer is made up of 2 layers of smooth muscle that mix and move chyme along the tract.

  • Circular layer (inner layer)
  • Longitudinal layer (outer layer)
  • Auerbach (myenteric) plexus: 
    • Ganglia of the autonomic nervous system Autonomic nervous system 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, which controls the muscular layer
    • Located between the 2 layers of smooth muscle

Serosa: 

  • Made up of connective tissue Connective tissue Connective tissues originate from embryonic mesenchyme and are present throughout the body except inside the brain and spinal cord. The main function of connective tissues is to provide structural support to organs. Connective tissues consist of cells and an extracellular matrix. Connective Tissue
  • Joins with mesentery or peritoneum Peritoneum The peritoneum is a serous membrane lining the abdominopelvic cavity. This lining is formed by connective tissue and originates from the mesoderm. The membrane lines both the abdominal walls (as parietal peritoneum) and all of the visceral organs (as visceral peritoneum). Peritoneum and Retroperitoneum
Histology of the small intestine

Histology of the small intestine:
(a): The absorptive surface of the small intestine is vastly enlarged by the presence of circular folds, villi, and microvilli.
(b): Micrograph of the circular folds: Note that the folds contain both the mucosa and the submucosa.
(c): Micrograph of the villi: Note that the villi contain only the epithelial and lamina propria layers of the mucosa; the muscularis mucosa is visible as a “pink line” along the left edge of the slide.
(d): Electron micrograph of the microvilli: from left to right—light microscope, ×56; light microscope, ×508; electron microscope, ×196,000

Image: “Histology of the Small Intestine” by Phil Schatz. License: CC BY 4.0

Anatomic Differences between the Jejunum and Ileum

Characteristic differences between the jejunum and ileum are summarized in the table.

Table: Anatomic differences between the jejunum and ileum
Jejunum Ileum
Diameter 4 cm (at the most proximal end) 2 cm (at the most distal end)
Wall thickness Thicker Thinner
Fat in mesentery Less More
Circular folds Many, best developed Some in the proximal ileum, very few distally
Lymphoid tissue/Peyer patches Few Many

Neurovasculature

Arterial supply

  • Duodenum: superior and inferior pancreaticoduodenal arteries Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries
  • Jejunum and ileum: jejunal and ileal arteries Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries (branch off the SMA SMA Spinal muscular atrophy (SMA) is a spectrum of autosomal recessive syndromes characterized by progressive proximal muscle weakness and atrophy, possibly due to degeneration of the anterior horn cells in the spinal cord and motor nuclei in the lower brainstem. Spinal Muscular Atrophy (SMA))
    • Run within the mesentery from the SMA SMA Spinal muscular atrophy (SMA) is a spectrum of autosomal recessive syndromes characterized by progressive proximal muscle weakness and atrophy, possibly due to degeneration of the anterior horn cells in the spinal cord and motor nuclei in the lower brainstem. Spinal Muscular Atrophy (SMA) toward the intestines
    • Form anastomotic loops with each other, known as arcades 
    • Vasa recta: small straight arteries Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries off the arcades that supply the intestinal wall

Venous drainage

  • Veins running adjacent to the arterial supply
  • Drain into the superior mesenteric vein (SMV)
  • The SMV unites with the splenic vein to form the hepatic portal vein → brings nutrients absorbed through the gut to 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

Lymphatics

Lacteals within the intestinal villi drain into:

  • Pancreaticoduodenal nodes (duodenum only)
  • Superior mesenteric nodes (all 3 segments)

Innervation

The small intestine is innervated by the ANS.

Parasympathetic innervation (stimulatory): 

  • Posterior trunk of the vagus nerve
  • ↑ Secretions, motility, and blood flow
  • Relaxation of sphincters
Parasympathetic innervation of the gi tract

Parasympathetic innervation of the GI tract
CN: cranial nerve

Image by Lecturio.

Sympathetic innervation (inhibitory):

  • Greater, lesser, and least splanchnic nerves forming the superior mesenteric plexus around the SMA SMA Spinal muscular atrophy (SMA) is a spectrum of autosomal recessive syndromes characterized by progressive proximal muscle weakness and atrophy, possibly due to degeneration of the anterior horn cells in the spinal cord and motor nuclei in the lower brainstem. Spinal Muscular Atrophy (SMA)
  • Pass to small intestines via periarterial branches
  • ↓ Secretions, motility, and blood flow
Sympathetic innervation of the gi tract

Sympathetic innervation of the GI tract

Image by Lecturio.

Function

The small intestines are the primary site of chemical digestion and absorption of nutrients.

  • Receive:
    • Chyme 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
    • Pancreatic juice and 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
    • Bile
  • Secrete intestinal juice, which (along with the pancreatic juice and bile):
    • Neutralizes 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 acid
    • Digests nutrients ( carbohydrates Carbohydrates Carbohydrates are one of the 3 macronutrients, along with fats and proteins, serving as a source of energy to the body. These biomolecules store energy in the form of glycogen and starch, and play a role in defining the cellular structure (e.g., cellulose). Basics of Carbohydrates, fat, and proteins)
  • Primary site of nutrient absorption
  • Brush border of small intestines:
    • Contains additional digestive 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 required for contact digestion
    • ↑ Surface area for absorption of nutrients
  • Secrete 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 
  • Functions of intestinal motility:
    • Mix chyme with bile and digestive juices 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 and intestines
    • Churn chyme, bringing it into contact with the mucosa for contact digestion and absorption
    • Move contents toward the large intestine Large intestine The large intestines constitute the last portion of the digestive system. The large intestine consists of the cecum, appendix, colon (with ascending, transverse, descending, and sigmoid segments), rectum, and anal canal. The primary function of the colon is to remove water and compact the stool prior to expulsion from the body via the rectum and anal canal. Colon, Cecum, and Appendix

Clinical Relevance

  • Intestinal malrotation Intestinal malrotation Intestinal malrotation is a congenital anomaly that results from failure of the GI tract to undergo normal rotation around the mesenteric vessels during embryologic development. This condition can result in several anatomic patterns characterized by abnormal location and attachments of the abdominal cavity's intestines. Intestinal Malrotation: congenital GI anomaly that results from failure of the normal primitive gut rotation around mesenteric vessels during embryologic development. Intestinal malrotation Intestinal malrotation Intestinal malrotation is a congenital anomaly that results from failure of the GI tract to undergo normal rotation around the mesenteric vessels during embryologic development. This condition can result in several anatomic patterns characterized by abnormal location and attachments of the abdominal cavity's intestines. Intestinal Malrotation can result in a number of anatomic patterns characterized by abnormal location and attachments of the intestines within the abdominal cavity. These anomalies can be clinically silent or may present with a number of complications, the most catastrophic of which is midgut volvulus Volvulus A volvulus is the twisting or axial rotation of a portion of the bowel around its mesentery. The most common site of volvulus in adults is the colon; most frequently the sigmoid volvulus. Patients typically present with symptoms of bowel obstruction such as abdominal pain, distension, vomiting, and constipation/obstipation. Volvulus
  • Intussusception Intussusception Intussusception occurs when a part of the intestine (intussusceptum) telescopes into another part (intussuscipiens) of the intestine. The condition can cause obstruction and, if untreated, progress to bowel ischemia. Intussusception is most common in the pediatric population, but is occasionally encountered in adults. Intussusception: telescoping of the proximal part (intussusceptum) into a distal part (intussuscipiens) of the intestine. Intussusception Intussusception Intussusception occurs when a part of the intestine (intussusceptum) telescopes into another part (intussuscipiens) of the intestine. The condition can cause obstruction and, if untreated, progress to bowel ischemia. Intussusception is most common in the pediatric population, but is occasionally encountered in adults. Intussusception can cause obstruction and, if untreated, can progress to bowel ischemia. Intussusception Intussusception Intussusception occurs when a part of the intestine (intussusceptum) telescopes into another part (intussuscipiens) of the intestine. The condition can cause obstruction and, if untreated, progress to bowel ischemia. Intussusception is most common in the pediatric population, but is occasionally encountered in adults. Intussusception is most common in the pediatric population, but it is occasionally encountered in adults. The pediatric individual typically presents with acute cyclical abdominal pain Pain Pain has accompanied humans since they first existed, first lamented as the curse of existence and later understood as an adaptive mechanism that ensures survival. Pain is the most common symptomatic complaint and the main reason why people seek medical care. Physiology of Pain and vomiting, whereas adults present with symptoms of bowel obstruction. 
  • Meckel diverticulum: persistent remnant of the omphalomesenteric (vitelline) duct. Meckel diverticulum is usually located in the antimesenteric border of the ileum. The mucosal lining of the diverticulum may contain heterotopic mucosa (most commonly gastric). Although it is frequently asymptomatic, Meckel diverticulum can cause ulceration and present with lower GI bleeding. Other complications include diverticulitis and small bowel obstruction Small Bowel Obstruction Small bowel obstruction (SBO) is an interruption of the flow of the intraluminal contents through the small intestine, and is classified as mechanical (due to physical blockage) or functional (due to disruption of normal motility). The most common cause of SBO in the Western countries is post-surgical adhesions. Small bowel obstruction typically presents with nausea, vomiting, abdominal pain, distention, constipation, and/or obstipation. Small Bowel Obstruction
  • Small bowel obstruction: The normal passage of bowel contents is interrupted either because of a functional decrease in peristalsis or mechanical obstruction from intraluminal or extraluminal mechanical compression. The most common causes in developed countries include postsurgical adhesions, hernias, and malignancies. The most important clinical features include crampy abdominal pain Pain Pain has accompanied humans since they first existed, first lamented as the curse of existence and later understood as an adaptive mechanism that ensures survival. Pain is the most common symptomatic complaint and the main reason why people seek medical care. Physiology of Pain, obstipation (i.e., inability to pass flatus or stool), nausea, and vomiting.
  • Crohn’s disease: form of inflammatory bowel disease characterized by patchy transmural 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; any portion of the luminal GI tract can be involved, though the terminal ileum and proximal colon Colon The large intestines constitute the last portion of the digestive system. The large intestine consists of the cecum, appendix, colon (with ascending, transverse, descending, and sigmoid segments), rectum, and anal canal. The primary function of the colon is to remove water and compact the stool prior to expulsion from the body via the rectum and anal canal. Colon, Cecum, and Appendix are most commonly affected. The most important clinical features include crampy abdominal pain Pain Pain has accompanied humans since they first existed, first lamented as the curse of existence and later understood as an adaptive mechanism that ensures survival. Pain is the most common symptomatic complaint and the main reason why people seek medical care. Physiology of Pain, 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, fatigue, and weight loss. Complications include fistulas, phlegmon/abscess formation, and perianal disease.
  • Celiac disease Celiac disease Celiac disease (also known as celiac sprue or gluten enteropathy) is an autoimmune reaction to gliadin, which is a component of gluten. Celiac disease is closely associated with HLA-DQ2 and HLA-DQ8. The immune response is localized to the proximal small intestine and causes the characteristic histologic findings of villous atrophy, crypt hyperplasia, and intraepithelial lymphocytosis. Celiac Disease: also known as gluten-sensitive enteropathy. Celiac disease Celiac disease Celiac disease (also known as celiac sprue or gluten enteropathy) is an autoimmune reaction to gliadin, which is a component of gluten. Celiac disease is closely associated with HLA-DQ2 and HLA-DQ8. The immune response is localized to the proximal small intestine and causes the characteristic histologic findings of villous atrophy, crypt hyperplasia, and intraepithelial lymphocytosis. Celiac Disease is a common immune-mediated inflammatory disease of the small intestine caused by sensitivity to gliadin, a component of gluten. The most important clinical features include 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 with malabsorption Malabsorption 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, crampy abdominal pain Pain Pain has accompanied humans since they first existed, first lamented as the curse of existence and later understood as an adaptive mechanism that ensures survival. Pain is the most common symptomatic complaint and the main reason why people seek medical care. Physiology of Pain, and villous atrophy on histology.

References

  1. Collins, J., Nguyen, A. (2021). Anatomy, abdomen and pelvis, small intestine. StatPearls. Retrieved August 23, 2021, from https://www.statpearls.com/articlelibrary/viewarticle/32127/ 
  2. Saladin, K.S., Miller, L. (2004). Anatomy and Physiology, 3rd ed., pp. 964–965. McGraw-Hill Education.
  3. Peppercorn, M.A., Kane, S.V. (2020). Clinical manifestations, diagnosis, and prognosis of Crohn’s disease in adults. UpToDate. Retrieved August 20, 2021, from https://www.uptodate.com/contents/clinical-manifestations-diagnosis-and-prognosis-of-crohn-disease-in-adults
  4. Peppercorn, M.A., Kane, S.V. (2020). Clinical manifestations, diagnosis, and prognosis of ulcerative colitis in adults. UpToDate. Retrieved August 20, 2021, from https://www.uptodate.com/contents/clinical-manifestations-diagnosis-and-prognosis-of-ulcerative-colitis-in-adults
  5. Drake, R.L., et al. (Ed.) (2020). Regional anatomy. In Gray’s Anatomy for Students, 4th ed. Churchill Livingstone/Elsevier, pp. 309–315.
  6. Schuppan, D., Dieterich, W. (2020). Epidemiology, pathogenesis, and clinical manifestations of celiac disease in adults. UpToDate. Retrieved August 20, 2021, from https://www.uptodate.com/contents/epidemiology-pathogenesis-and-clinical-manifestations-of-celiac-disease-in-adults

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