Anatomy and Physiology: The Digestive System

Comprehensive vocabulary flashcards covering the anatomy, histology, secretions, motility patterns, and regulation of the human digestive system.

Digestion

The breakdown of food molecules through mechanical and chemical processes for absorption by the body.

Ingestion

The intake of food into the digestive tract through the mouth.

Absorption

The uptake of digestive nutrients into the blood.

Defecation

The storage and elimination of undigested material from the body.

Motility

Muscular contractions that break up food, mix it with enzymes, and move it along the gastrointestinal tract.

Mastication

The process of chewing food and mixing it with saliva to increase the surface area exposed to digestive enzymes.

Deglutition

The act of swallowing food, proceeding through a voluntary phase, an involuntary pharyngeal phase, and an involuntary oesophageal phase.

Peristalsis

Rhythmic wave-like muscular contractions (moving at a rate of $2\text{--}4\,\text{cm/s}$) where circular smooth muscle contracts behind a bolus and relaxes in front, followed by longitudinal muscle contraction.

Reverse Peristalsis

Vomiting; a process that causes a bolus to move in the opposite direction along the digestive tract.

Secretion

The process by which substances are produced and discharged from a cell, gland, or organ for excretion or a particular physiological function.

Brunner's Glands

Duodenal glands that secrete an alkaline fluid ($\text{pH } 8\text{--}8.9$, volume of approximately $200\,\text{mL/day}$) to protect the intestinal mucosa from acidic gastric chyme.

Gastrin

A gastrointestinal hormone secreted by G-cells that stimulates gastric acid ($\text{HCl}$) secretion and mucosal growth.

Secretin

A hormone released by the small intestine that stimulates pancreatic bicarbonate release and inhibits gastric acid secretion.

Cholecystokinin (CCK)

A gastrointestinal hormone stimulated by intestinal fatty acids and amino acids that triggers bile release and pancreatic enzyme secretion.

Gastric Inhibitory Peptide (GIP)

A hormone, also known as glucose-dependent insulinotropic peptide, that enhances insulin release.

Somatostatin

A peptide hormone secreted by D-cells that inhibits the secretion of gastrointestinal hormones and slows gastric emptying.

Parietal Cells

Epithelial cells within gastric glands that secrete hydrochloric acid ($\text{HCl}$) to lower pH and kill bacteria, as well as intrinsic factor.

Chief Cells

Cells in gastric glands that secrete the zymogen pepsinogen and gastric lipase.

Enterochromaffin-like (ECL) Cells

Gastric mucosal neuroendocrine cells that secrete histamine, which binds to $H_2$ receptors to stimulate acid production by parietal cells.

Intrinsic Factor

A substance secreted by gastric parietal cells essential for the absorption of vitamin $B_{12}$ in the ileum.

Gastric Rugae

Folds within the stomach mucosa and submucosa that increase surface area with the lumen and allow the stomach to stretch as food enters.

Cephalic Phase

The first phase of gastric secretion, triggered by the sight, smell, taste, or chewing of food via parasympathetic vagal stimulation, causing increased $\text{HCl}$ secretion.

Gastric Phase

The second phase of gastric secretion, stimulated by stomach distension, peptides, and rising pH via gastrin and neural reflexes, causing increased $\text{HCl}$ secretion.

Intestinal Phase

The regulatory phase triggered by distension, low pH ($<2$), or lipids in the duodenum, acting via secretin, CCK, somatostatin, and neural reflexes to decrease gastric secretions.

Plicae Circulares

Permanent circular folds of the small intestine mucosa and submucosa (also called valves of Kerckring) that increase absorption surface area.

Brush Border Enzymes

Digestive enzymes embedded in the microvillar membranes of absorptive enterocytes whose active sites face the chyme in the intestinal lumen.

Paneth Cells

Specialized secretory cells located at the base of intestinal crypts (of Lieberkühn) that secrete lysozyme and are capable of phagocytosis.

Segmentation

An intestinal motility pattern characterized by random ring-like constrictions (occurring $12\text{ times per minute}$ in the duodenum) that mix and churn chyme with digestive secretions.

Gastroileal Reflex

A gastrointestinal reflex triggered by food in the stomach that causes relaxation of the ileocecal valve and subsequent filling of the cecum.

Teniae Coli

Three ribbon-like bands of longitudinal smooth muscle fibers in the muscularis externa of the large intestine.

Haustra

Pouch-like segmentations of the colon wall created by the tonic contraction of the teniae coli.

Enterokinase

An intestinal brush border enzyme that converts the pancreatic zymogen trypsinogen into active trypsin.

Kupffer Cells

Resident liver macrophages that phagocytize worn-out and dying red and white blood cells as well as bacteria.

Enterohepatic Circulation

The recycling process in which bile acids/salts are reabsorbed in the ileum and transported via the portal vein back to the liver for resecretion.

Porta Hepatis

The entry and exit region on the inferior surface of the liver through which the hepatic portal vein, hepatic artery, and hepatic ducts travel.