Digestive System Pathophysiology and Structural Function

A comprehensive master's-level vocabulary study set spanning digestive system anatomy, enteric physiology, adult gastrointestinal and hepatobiliary alterations, and pediatric congenital and acquired disorders.

Gastrointestinal Tract

The continuous muscular alimentary canal through which food travels, comprising the oral cavity, pharynx, esophagus, stomach, small intestine, colon, rectum, and anus.

Submucosal Plexus (Meissner Plexus)

An intrinsic enteric nerve network located within the muscularis mucosae that regulates local secretion and epithelial barrier functions.

Myenteric Plexus (Auerbach Plexus)

An intrinsic enteric nerve plexus situated between the inner circular and outer longitudinal layers of the muscularis externa that coordinates gastrointestinal motility.

Subserosal Plexus

An enteric nerve plexus located immediately beneath the serosal layer of the gastrointestinal tract wall.

Upper Esophageal Sphincter

A circular striated muscular ring formed by the cricopharyngeal muscle that prevents the entry of air into the esophagus during inspiration.

Gastric and Esophageal Sphincters

Specialized muscular rings including the lower esophageal sphincter (preventing gastric acid regurgitation into the esophagus) and the pyloric sphincter (controlling the exit of chyme from the stomach into the duodenum).

Parietal Cells

Specialized epithelial cells in the gastric glands responsible for secreting hydrochloric acid, intrinsic factor, and gastroferrin.

Chief Cells

Gastric gland secretory cells that synthesize and release pepsinogen, the zymogen precursor to the proteolytic enzyme pepsin.

G Cells

Endocrine cells situated in the gastric antrum that secrete the polypeptide hormone gastrin into the bloodstream to stimulate acid production.

Enterochromaffin-Like (ECL) Cells

Gastric mucosal cells that synthesize and release histamine, a potent paracrine stimulant of parietal cell acid secretion.

D Cells

Endocrine cells distributed in the gastric mucosa and pancreatic islets that secrete somatostatin to inhibit gastric acid secretion.

Gastroferrin

A gastric glycoprotein secreted by parietal cells that binds non-heme iron to facilitate its absorption within the small intestine.

Intrinsic Factor

A transport glycoprotein secreted by parietal cells that binds dietary vitamin $B_{12}$ to permit receptor-mediated absorption in the terminal ileum.

Crypts of Lieberkühn

Tubular invaginations located between intestinal villi containing columnar epithelial secretory cells and goblet cells that produce water, electrolytes, enzymes, and mucus.

Lacteals

Specialized central lymphatic capillaries within intestinal villi that absorb and transport emulsified dietary lipids packaged into chylomicrons.

Ileogastric Reflex

An inhibitory enteric reflex that suppresses gastric motility and emptying in response to distention of the ileum.

Intestinointestinal Reflex

A protective inhibitory reflex that suppresses intestinal peristalsis when any single intestinal segment is overdistended.

Gastroileal Reflex

A gastrointestinal reflex stimulated by gastric emptying that increases ileal motility and relaxes the ileocecal valve to empty the terminal ileum into the cecum.

Gastrocolic Reflex

A mass propulsion reflex occurring throughout the colon during or immediately following food intake, mediated by gastrin and cholecystokinin.

Defecation Reflex (Rectosphincteric Reflex)

A spinal and enteric reflex triggered by rectal distention that prompts involuntary relaxation of the internal anal sphincter and generates the urge to defecate.

Taenia Coli

Three distinct ribbons of outer longitudinal smooth muscle extending along the length of the colon.

Haustra

Pouch-like sacculations along the colon wall produced by the tonic gathering of the taenia coli and circular muscular contractions.

Glisson Capsule

The fibroelastic connective tissue capsule enveloping the liver, blood vessels, and intrahepatic biliary tree.

Kupffer Cells

Resident phagocytic tissue macrophages lining the hepatic sinusoids that play a central role in innate defense by removing bacteria and particulates.

Hepatic Stellate Cells

Perisinusoidal cells of the liver that store retinoids (vitamin A), regulate sinusoidal blood flow, and transform into collagen-producing myofibroblasts during fibrosis.

Pit Cells

Hepatic natural killer cells situated in the sinusoidal lumen that release interferon-$\gamma$ to provide antitumoral and antiviral surveillance.

Space of Disse

The perisinusoidal interstitial space situated between the sinusoidal endothelium and hepatocytes that drains lymph into the hepatic lymphatic channels.

Biliary and Pancreatic Ductal Anatomy

The ductal network where the common bile duct from the liver and gallbladder meets the pancreatic duct at the ampulla of Vater to empty bile and pancreatic juice into the duodenum.

Enterohepatic Circulation

The recycling loop wherein approximately $95\%$ of conjugated bile salts secreted into bile are reabsorbed in the terminal ileum and returned to the liver via portal blood.

Choleretic Agent

Any substance that stimulates the hepatocytes of the liver to produce and secrete bile, with circulating bile salts serving as the most potent physiological stimulus.

Enterokinase

A brush-border enzyme anchored in the duodenal mucosa that hydrolyzes trypsinogen to yield active trypsin, initiating the pancreatic enzyme cascade.

Retching

The rhythmic, involuntary spasmodic movement of the diaphragm, chest wall, and abdominal musculature that mimics vomiting without expelling gastric contents.

Projectile Vomiting

Spontaneous, forceful expulsion of gastric contents that occurs without preceding nausea or retching, often reflecting brainstem irritation or gastric outlet obstruction.

Osmotic Diarrhea

Excessive, large-volume diarrhea caused by the presence of nonabsorbable, osmotically active luminal solutes that draw water into the intestinal lumen and cease upon fasting.

Secretory Diarrhea

Large-volume diarrhea provoked by excessive mucosal secretion of fluid, chloride, or bicarbonate, or by inhibition of sodium absorption, which continues during fasting.

Parietal (Somatic) Pain

Local, sharp, and intense abdominal pain arising from irritation of the somatic nerve fibers of the parietal peritoneum.

Visceral Pain

Diffuse, poorly localized, and cramping abdominal discomfort originating from stretching, inflammation, or ischemia within the walls of abdominal organs.

Hematochezia

The passage of bright red, frank blood through the rectum, typically indicating lower gastrointestinal bleeding or massive upper gastrointestinal hemorrhage.

Melena

The evacuation of black, foul-smelling, tarry stools caused by the digestion and oxidation of hemoglobin from upper gastrointestinal bleeding.

Achalasia

A primary esophageal motility disorder characterized by loss of inhibitory ganglion cells in the myenteric plexus, leading to impaired peristalsis and failure of the lower esophageal sphincter to relax.

Gastroesophageal Reflux Disease (GERD)

A condition wherein gastric acid, pepsin, and bile reflux backward through an incompetent lower esophageal sphincter, causing esophagitis and mucosal damage.

Sliding Hiatal Hernia (Type I)

The most common anatomical hernia wherein the upper stomach and gastroesophageal junction slide upward through the diaphragmatic hiatus into the thoracic cavity.

Paraesophageal Hiatal Hernia (Type II)

A rolling hiatal hernia in which the greater curvature of the stomach herniates upward through a secondary opening in the diaphragm adjacent to the esophagus.

Succussion Splash

A sloshing sound heard on abdominal jarring during auscultation, indicative of retained fluid and gas associated with pyloric or gastric outlet obstruction.

Paralytic Ileus

A functional, nonmechanical bowel obstruction characterized by the failure of coordinated intestinal peristalsis, frequently following abdominal surgery.

Ogilvie Syndrome (Acute Colonic Pseudo-Obstruction)

Massive, nonmechanical autonomic dilatation of the cecum and colon observed in severely ill, bedridden, or elderly hospitalized patients.

Chronic Fundal Gastritis (Type A)

An autoimmune inflammatory disorder of the gastric corpus and fundus characterized by autoantibodies targeting parietal cells and intrinsic factor, producing gastric atrophy and pernicious anemia.

Chronic Antral Gastritis (Type B)

A nonimmune inflammatory disorder primarily localized to the gastric antrum, strongly associated with persistent Helicobacter pylori infection, NSAID exposure, and tobacco use.

Alkaline Reflux Gastritis

Inflammation of the gastric mucosa provoked by the retrograde reflux of alkaline bile and pancreatic secretions, characterized by unremitting epigastric burning that worsens postprandially and resists antacids.

Zollinger-Ellison Syndrome

A hypersecretory condition caused by a neuroendocrine gastrinoma that leads to autonomous hypergastrinemia, extreme gastric acid hypersecretion, and recalcitrant peptic ulcers.

Duodenal Ulcer

The most common peptic ulcer, classically presenting with epigastric pain $30\,\text{minutes}$ to $2\,\text{hours}$ postprandially or at night that is relieved by food or antacids.

Gastric Ulcer

A peptic ulcer localized to the stomach mucosa, characteristically in the antrum, presenting with burning epigastric pain immediately following food consumption and associated with anorexia and weight loss.

Curling Ulcer

An acute ischemic stress ulceration of the gastric or duodenal mucosa that develops in the setting of severe, extensive burn injury.

Cushing Ulcer

A severe, deep stress ulcer of the stomach or duodenum resulting from hypersecretion of gastric acid triggered by vagal nucleus stimulation following intracranial trauma or neurosurgery.

Dumping Syndrome

A postgastrectomy syndrome characterized by the rapid transit of hypertonic chyme into the proximal small intestine, producing early fluid shifts and vasomotor symptoms followed by late reactive hypoglycemia.

Pancreatic Insufficiency

Deficient exocrine pancreatic enzyme secretion (lipase, amylase, trypsin) resulting in maldigestion, profound fat malabsorption, steatorrhea, and weight loss.

Ulcerative Colitis

A chronic inflammatory bowel disease restricted to the mucosa and submucosa that originates in the rectum and spreads continuously throughout the colon without skip areas.

Crohn Disease

An idiopathic, granulomatous, transmural inflammatory disease that can affect any segment of the alimentary tract from mouth to anus, typically characterized by noncaseating granulomas and skip lesions.

Irritable Bowel Syndrome (IBS)

A disorder of gut-brain interaction characterized by recurrent abdominal pain associated with defecation or altered bowel consistency and frequency, occurring in the absence of identifiable structural disease.

Diverticulitis

The inflammatory, symptomatic complication of colonic diverticulosis characterized by localized microperforations, fever, leukocytosis, and left lower quadrant pain.

Portal Hypertension

Pathologic elevation of hydrostatic pressure within the portal venous system above $5\,\text{mmHg}$ (reference normal $3\text{--}5\,\text{mmHg}$), resulting from mechanical or sinusoidal vascular resistance.

Esophageal Varices

Dilated, thin-walled, tortuous collateral submucosal veins that form in the lower esophagus as a consequence of sustained portal hypertension, carrying a severe risk of lethal rupture.

Peripheral Arterial Vasodilation Theory

The accepted pathogenic model for ascites synthesis, asserting that portal hypertension induces splanchnic nitric oxide release, systemic arterial underfilling, and compensatory renal sodium and water avidity.

Hepatic Encephalopathy

A reversible neuropsychiatric complication of advanced liver failure and portosystemic shunting, manifested by sleep disturbances, cognitive decline, confusion, and asterixis due to systemic neurotoxin accumulation.

Asterixis

A classic flapping, involuntary motor tremor of the dorsiflexed wrists elicited in patients with hepatic encephalopathy.

Hepatorenal Syndrome (HRS)

Functional, oliguric renal failure occurring in decompensated cirrhosis with portal hypertension, driven by intense renal cortical vasoconstriction secondary to profound systemic arterial vasodilation.

Steatosis (Alcoholic Fatty Liver)

The initial, fully reversible morphological stage of alcoholic liver injury, defined by the accumulation of neutral lipid droplets within hepatocytes.

Primary Biliary Cholangitis

A chronic autoimmune liver disorder characterized by T cell-mediated destruction of interlobular, small intrahepatic bile ducts, leading to cholestasis, progressive fibrosis, and cirrhosis.

Secondary Biliary Cirrhosis

Chronic hepatic fibrosis and destruction resulting from prolonged, unrelieved mechanical obstruction of the extrahepatic common bile duct.

Cholelithiasis

The formation of calculi within the gallbladder lumen, classified predominantly into cholesterol stones, black pigment stones, and brown pigment stones.

Biliary Colic

Intermittent, severe visceral pain in the right hypochondrium or epigastrium caused by transient impaction of a gallstone within the cystic duct.

Cholecystitis

Acute or chronic inflammation of the gallbladder wall, typically developing when a gallstone persistently impacts the cystic duct, leading to wall ischemia, fever, and leukocytosis.

Acute Pancreatitis

Acute autodigestive inflammatory injury of the pancreatic parenchyma caused by premature intrapancreatic activation of proenzymes, clinically identified by severe epigastric pain and elevated serum lipase.

Whipple Procedure (Pancreaticoduodenectomy)

The standard surgical resection for pancreatic head adenocarcinoma, involving removal of the head of the pancreas, duodenum, distal stomach, gallbladder, and distal common bile duct.

Cleft Lip

A congenital craniofacial malformation resulting from incomplete embryonic fusion of the nasomedial and intermaxillary processes during the fourth week of development.

Cleft Palate

A congenital developmental defect characterized by the failure of the primary palatal shelves to fuse along the midline during the third month of gestation.

Esophageal Atresia

A congenital anomaly wherein the esophagus terminates prematurely in a blind mucosal pouch rather than forming a continuous conduit to the stomach.

Tracheoesophageal Fistula

An abnormal congenital fistula connecting the trachea and the esophagus, stemming from defective foregut septation and predisposing the infant to massive aspiration and respiratory distress.

Infantile Hypertrophic Pyloric Stenosis

A congenital narrowing of the gastric pyloric canal caused by muscular hypertrophy and hyperplasia of the circular pyloric sphincter, characteristically producing projectile nonbilious vomiting.

Ladd Bands

Abnormal peritoneal fibrous bands that form across the duodenum in intestinal malrotation, predisposing the neonate to duodenal obstruction and midgut volvulus.

Intestinal Volvulus

Torsion or twisting of an intestinal loop about its mesenteric vascular axis, resulting in luminal strangulation, mesenteric occlusion, bowel ischemia, and gangrene.

Meckel Diverticulum

The most common congenital anomaly of the digestive tract, caused by incomplete obliteration of the embryonic omphalomesenteric (vitelline) duct, classically following the 'rule of twos'.

Hirschsprung Disease (Congenital Aganglionic Megacolon)

A congenital bowel obstruction caused by failure of neural crest-derived enteric ganglion cells to migrate to the distal rectum and colon, producing functional distal obstruction and proximal megacolon.

Distal Intestinal Obstruction Syndrome (DIOS)

An obstructive syndrome in cystic fibrosis patients caused by the impaction of viscid, dehydrating mucofecal contents in the terminal ileum and cecum.

Intussusception

The telescoping or invagination of a proximal segment of intestine into an immediately downstream lumen (most commonly ileum into cecum), causing bowel ischemia and 'currant jelly' stools.

Cystic Fibrosis Digestive Triad

The classic pathophysiologic triad comprising exocrine pancreatic insufficiency, viscous respiratory mucus hypersecretion, and pathologically elevated sweat sodium and chloride concentrations.

Celiac Disease (Gluten-Sensitive Enteropathy)

A T cell-mediated autoimmune enteropathy triggered by ingested gluten (wheat, rye, barley) in genetically predisposed individuals expressing HLA-DQ2 or HLA-DQ8, resulting in intestinal villous blunting.

Dermatitis Herpetiformis

A chronic, pruritic, vesicular dermatosis linked to celiac disease that erupts symmetrically on the extensor surfaces of the elbows, knees, shoulders, and buttocks.

Kwashiorkor

A severe state of protein-energy malnutrition occurring when a child is weaned to a protein-deficient, high-starch diet, characterized by hypoproteinemia, generalized edema, distended abdomen, and fatty liver.

Marasmus

A severe form of protein-calorie malnutrition marked by non-selective starvation and universal nutrient deficit, characterized by extreme muscle and fat wasting without generalized edema.

Necrotizing Enterocolitis (NEC)

An acute ischemic and inflammatory necrosis of the bowel wall seen predominantly in premature neonates, characterized by mucosal breakdown, bacterial invasion, pneumatosis intestinalis, and perforation.

Kernicterus

A chronic, irreversible form of bilirubin neurotoxicity marked by the deposition of unconjugated, lipid-soluble bilirubin within basal ganglia and brainstem nuclei in neonates.

Biliary Atresia

A rare congenital disease defined by inflammatory destruction, fibrotic obliteration, and absence of the extrahepatic biliary system, presenting with persistent neonatal cholestasis and acholic stools.

Kasai Portoenterostomy

A corrective surgical hepatoportoenterostomy performed for infant biliary atresia to restore bile drainage by anastomosing a resected Roux-en-Y jejunal loop directly to the exposed hepatic porta.