Physiology of the Small Intestine and Accessory Organs

Vocabulary flashcards covering the normal physiology, anatomy, and regulatory mechanisms of the small intestine and accessory digestive organs (pancreas, liver, and gallbladder).

Duodenum

The shortest, initial segment of the small intestine ($25\,\text{cm}$ long) extending from the pyloric sphincter of the stomach; contains openings for ducts delivering secretions from the liver and pancreas.

Jejunum

The middle segment of the small intestine ($2.5\,\text{m}$ in length) that serves as a primary site for nutrient digestion and absorption.

Ileum

The terminal segment of the small intestine ($3.5\,\text{m}$ long) that connects to the large intestine at the ileocecal junction.

Peyer patches

Aggregated lymphoid nodules situated in the mucosa and submucosa of the small intestine (predominantly the jejunum and ileum) that detect and fight intestinal infections.

Ileocecal junction

The anatomical connection between the ileum and the large intestine, composed of a ring of smooth muscle (ileocecal sphincter) and a one-way ileocecal valve.

Brush border enzymes

Digestive enzymes attached directly to the plasma membranes of absorptive intestinal cells (rather than secreted into the lumen), including disaccharidases and peptidases.

Exocrine pancreas

The digestive compartment of the pancreas comprising $99\%$ of its cells; secretes an enzyme- and bicarbonate-rich fluid into the duodenum via a duct system.

Endocrine pancreas

The hormonal compartment of the pancreas comprising $1\%$ of its cells; organized into islets containing $\alpha$-cells (glucagon), $\beta$-cells (insulin), and $\delta$-cells (somatostatin).

Acinar cells

Specialized exocrine cells of the pancreas that synthesize and secrete digestive enzymes and fluid into the pancreatic duct network.

Aqueous component of pancreatic juice

A fluid secreted at $200\text{ to }800\,\text{mL/day}$ rich in bicarbonate ($\text{pH} \approx 8$); neutralizes acidic gastric chyme entering the duodenum under the stimulation of secretin.

Enterokinase

A duodenal enzyme that converts the inactive zymogen trypsinogen into active trypsin, initiating the activation cascade of pancreatic proteolytic enzymes.

Pancreatic amylase

An active starch-digesting enzyme secreted by the pancreas; its detection in the systemic bloodstream serves as a clinical biomarker of pancreatic tissue damage.

Pancreatitis

Inflammation of the pancreas occurring when digestive enzymes are prematurely activated within pancreatic tissue, causing autodegradation; can be acute or chronic, commonly caused by gallstones or alcohol abuse.

Dual blood supply of the liver

The unique vascular arrangement where the liver receives $70\%$ of its blood flow from the hepatic portal vein (nutrient-rich, deoxygenated) and $30\%$ from the hepatic artery (oxygen-rich).

Portal triad

A microscopic structural unit located at each corner of a hexagonal liver lobule containing branches of the hepatic portal vein, hepatic artery, and hepatic duct.

Central vein

A blood vessel located at the center of each liver lobule that collects blood from hepatic sinusoids and unites with others to form hepatic veins that drain into the inferior vena cava.

Hepatocytes

The primary functional cells of the liver arranged in radiating hepatic cords; responsible for nutrient storage, plasma protein synthesis, bile production, and ammonia detoxification into urea.

Kupffer cells

Hepatic phagocytic cells lining the hepatic sinusoids that phagocytose bacteria, cellular debris, and worn-out erythrocytes and leukocytes.

Bile canaliculi

Microscopic channels situated between adjacent hepatocytes within hepatic cords that receive newly secreted bile and transport it toward interlobular bile ducts.

Common hepatic duct

A duct formed by the confluence of the right and left hepatic ducts draining bile from the lobes of the liver.

Common bile duct

A biliary conduit formed by the union of the common hepatic duct and the cystic duct from the gallbladder.

Hepatopancreatic ampulla

The dilated junction where the common bile duct and the main pancreatic duct merge, which empties into the duodenum at the major duodenal papilla.

Minor duodenal papilla

The duodenal opening through which the accessory pancreatic duct delivers pancreatic secretions independently into the gut lumen.

Gallbladder

A sac-like accessory organ on the underside of the liver that stores and concentrates hepatic bile by reabsorbing water and electrolytes.

Cholecystokinin (CCK)

A duodenal peptide hormone released in response to fat- and protein-rich chyme that triggers gallbladder contraction, pancreatic enzyme secretion, and relaxation of the sphincter of Oddi.

Secretin

A hormone released by the duodenum in response to acidic chyme that stimulates bicarbonate-rich fluid secretion from the pancreas and liver ductular cells.

Enterohepatic circulation

The recycling process in which over $90\%$ of bile salts secreted into the duodenum are reabsorbed in the ileum, returned via the portal circulation to the liver, and re-secreted.

Gallstones

Crystalline deposits formed in the gallbladder or biliary ducts when bile contains excessive cholesterol and insufficient bile salts to maintain solubility.

Jaundice

Yellowish discoloration of the skin and sclera caused by high systemic levels of bilirubin, often resulting from obstruction of the common bile duct by gallstones.