Chapter 23 Digestive System Study Guide

Vocabulary practice flashcards covering gross anatomy, microscopic structures, digestive physiology, neural controls, and hormonal mechanisms of the human digestive system.

Gastrointestinal (GI) Tract

The alimentary canal extending through the ventral body cavity; measures $30\,\text{feet}$ in a cadaver and is shorter in a living person due to muscle tone.

Peristalsis

Waves of contraction and relaxation of muscles in the organ wall that propel food through the digestive tract.

Segmentation

The back-and-forth mixing movements of the digestive tract that churn and mix food.

Mesentery

A double layer of peritoneum that provides blood vessels and nerves to the viscera, holds organs in place, and stores fat.

Retroperitoneal Organs

Organs situated outside the peritoneum, including the pancreas, duodenum, cecum, appendix, rectum, ascending and descending colon, kidneys, and adrenal glands.

Mucosa

The moist epithelial layer lining the lumen of the alimentary canal that secretes mucus, absorbs digestive end products, and protects against infectious disease.

Submucosa

A layer of connective tissue containing elastic fibers, blood and lymph vessels, lymph nodes, and nerves.

Muscularis Externa

Smooth muscle layer composed of an inner circular layer and an outer longitudinal layer responsible for peristalsis and segmentation.

Enteric Nervous System

The intrinsic nervous network of the digestive tract, known as the 'gut brain,' containing over $100\text{ million}$ neurons that regulate digestion.

Submucosal Nerve Plexus

An intrinsic nerve plexus located in the submucosa that regulates glandular secretions.

Myenteric Nerve Plexus

An intrinsic nerve plexus situated in the muscularis externa between the circular and longitudinal muscle layers that regulates motility, including peristalsis and segmentation.

Labial Frenulum

The median fold that connects the internal aspect of each lip to the gum.

Parotid Gland

The largest extrinsic salivary gland, located anterior to the ear between the masseter muscle and skin; its single duct opens into the vestibule next to the second upper molar.

Submandibular Gland

A medium-sized salivary gland positioned along the medial aspect of the mandibular body; its duct opens at the base of the lingual frenulum.

Sublingual Gland

The smallest extrinsic salivary gland, situated anterior to the submandibular gland beneath the tongue, emptying via $10\text{--}12$ ducts.

Dentin

A bone-like calcified tissue located deep to the enamel that forms the bulk of a tooth.

Deglutition

The process of swallowing, involving coordinated actions of the tongue, soft palate, pharynx, esophagus, and $22$ muscle groups.

Buccal Phase

The conscious, voluntary first phase of swallowing in which food is forced into the oropharynx by the tongue.

Pharyngeal-Esophageal Phase

The involuntary phase of swallowing controlled by the medulla, lower pons, and vagus nerve that directs food into the esophagus while sealing respiratory passages.

Parietal Cells

Secretory cells located in the middle region of gastric glands that produce hydrochloric acid ($\text{HCl}$) and intrinsic factor.

Chief Cells

Secretory cells located at the base of gastric glands that produce pepsinogen.

Cephalic Phase

The initial phase of gastric secretion occurring prior to food ingestion, triggered by the sight, aroma, taste, or thought of food; accounts for $30\text{--}50\%$ of the secretory response.

Gastric Phase

The secretory phase initiated when food enters the stomach, triggered by distension, stretch receptors, peptides, amino acids, and gastrin release; accounts for $40\text{--}50\%$ of secretion.

Intestinal Phase

The phase of gastric secretion occurring when partially digested food enters the small intestine, providing approximately $5\%$ of the secretory response.

Falciform Ligament

A fold of visceral peritoneum that separates the right and left liver lobes anteriorly and suspends the liver from the diaphragm and anterior abdominal wall.

Round Ligament (Ligamentum Teres)

The remnant of the fetal umbilical vein that extends along the inferior border of the falciform ligament on the inferior aspect of the liver.

Liver Lobules

Hexagonal structural and functional units of the liver composed of hepatocyte plates radiating from a central vein.

Portal Triad

A vascular cluster located at each corner of a liver lobule containing a bile duct, a hepatic artery branch, and a hepatic portal vein branch.

Hepatic Portal Circulation

A circulatory pathway that collects nutrient-rich venous blood from the digestive viscera and conveys it to the liver for metabolic processing and storage.

Bile Salts

Cholesterol derivatives present in bile that emulsify fats, promote fat and cholesterol absorption, and solubilize cholesterol.

Acinus

The smallest functional unit of the exocrine pancreas, made of secretory cell clusters containing zymogen granules filled with digestive enzymes.

Microvilli

Minute plasma membrane extensions on absorptive mucosal cells of the small intestine that create the brush border and increase surface area.

Gastrin

A digestive hormone secreted by stomach and duodenal mucosa that stimulates gastric secretions, motility, and ileocecal valve mass movements.

Secretin

A hormone produced by duodenal mucosa in response to acidic chyme that stimulates bicarbonate-rich pancreatic juice and bile secretion while decreasing gastric motility and secretions.

Cholecystokinin (CCK)

A duodenal hormone released in response to fatty chyme that triggers enzyme-rich pancreatic juice secretion, gallbladder contraction, and hepatopancreatic sphincter relaxation.

Somatostatin (GHIH)

An inhibitory hormone secreted by the stomach and intestinal mucosa that decreases gastric, pancreatic, and small intestine secretions and suppresses gallbladder contraction.

Teniae Coli

Three distinctive longitudinal bands of smooth muscle present in the muscularis externa of the large intestine.

Haustra

Pocket-like sacculations in the wall of the large intestine formed by the muscle tone of the teniae coli.

Gastroileal Reflex

A reflex triggered by stomach distension that opens the ileocecal sphincter to permit the passage of chyme from the small intestine into the large intestine.

Gastrocolic Reflex

A reflex initiated by stomach distension that drives mass movements of fecal contents from the colon into the rectum.

Chylomicrons

Lipoprotein droplets synthesized within intestinal cells from absorbed fatty acids and proteins, which are released by exocytosis into lacteals.