16. Digestive System

Comprehensive vocabulary flashcards covering digestive system anatomy, monogastric vs. ruminant stomach structures, gastric cellular secretions, enteric functions, peritoneal attachments, and bilirubin metabolism.

Monogastric

An organism having a simple, single-chambered stomach, including animals such as dogs, cats, chickens, and pigs.

Hindgut Fermenters

Herbivorous animals, such as horses, rabbits, and rodents, that rely on microbial fermentation within an enlarged cecum and large colon to digest cellulose and fiber.

Amylase

A digestive enzyme present in saliva that initiates the chemical breakdown of dietary starches and sugars.

Epiglottis

A cartilaginous flap at the base of the tongue that closes over the larynx during deglutition to prevent food from entering the trachea and causing aspiration pneumonia.

Deglutition

The medical term for swallowing, divided into three progressive phases: the oral stage, pharyngeal stage, and esophageal stage.

Peristalsis

Involuntary, rhythmic waves of smooth muscle contraction and relaxation that propel ingested material along the gastrointestinal tract.

Cardia

The initial anatomical region of the monogastric stomach where the esophagus joins the gastric system.

Cardiac Sphincter

A muscular ring located at the junction between the esophagus and the cardia that regulates food entering the stomach and prevents acidic gastric contents from refluxing into the esophagus.

Fundus

The pouch-like upper section of the stomach adjacent to the cardia that expands to accommodate food and is densely lined with rugae.

Rugae

Continuous, expandable mucosal folds along the inner stomach lining that flatten out as the organ fills with food.

Corpus (Gastric Body)

The largest central section of the stomach that accounts for the majority of gastric volume and serves as the primary site of gastric digestion.

Pyloric Sphincter

The muscular valve at the terminal end of the stomach (pylorus) that regulates the outflow of chyme into the duodenum.

Parietal Cells

Gastric mucosal cells that secrete hydrogen ions ($H^+$) via a proton pump and chloride ions ($Cl^-$) into the gastric lumen to synthesize hydrochloric acid ($HCl$) without self-digesting the cell.

Chief Cells

Specialized cells of the gastric mucosa that secrete pepsinogen, an inactive proenzyme that converts to the protein-cleaving enzyme pepsin in the presence of acidic gastric juice.

G Cells

Endocrine cells within the stomach mucosa that secrete the peptide hormone gastrin to stimulate hydrochloric acid ($HCl$) production and regulate gastric emptying.

Goblet Cells

Mucus-secreting epithelial cells that create a thick protective mucoid barrier over the gastric lining, preventing chemical digestion by $HCl$ and pepsin.

Emesis (Vomiting)

The active, forceful evacuation of stomach contents mediated by abdominal muscular contractions and reverse peristalsis.

Regurgitation

The passive, backward expulsion of undigested oral and esophageal contents occurring without abdominal contractions or reverse peristalsis.

Plicae

Internal circular mucosal folds lining the small intestine that, alongside villi and microvilli, amplify the surface area available for nutrient absorption.

Chyme

The semi-fluid, acidic mass of partially digested food that passes from the stomach through the pylorus into the duodenum.

Secretin

A gastrointestinal hormone released by the duodenum that down-regulates stomach $HCl$ secretion and creates an alkaline intestinal environment suitable for pancreatic enzymes.

Jejunum

The middle and longest portion of the small intestine, acting as the primary site of nutrient absorption.

Peyer's Patches

Aggregated lymphoid nodules concentrated most heavily within the ileum that safeguard the intestine by identifying and neutralizing microbial pathogens.

Lacteals

Specialized lymphatic capillaries situated within intestinal villi that absorb dietary lipids and emulsified fats from the intestinal lumen.

Chyle

A milky-white fluid consisting of lymph and absorbed emulsified fats collected by intestinal lacteals during lipid digestion.

Mesentery

A continuous double fold of peritoneal membrane that suspends the intestines from the posterior abdominal wall, housing blood and lymphatic vessels that conduct blood to the liver for detoxification.

Greater Omentum

A large, apron-like peritoneal fold attached between the stomach and the parietal peritoneum that drapes over abdominal viscera.

Cecum

A blind pouch located at the ileocolic junction; it is vestigial or functionless in carnivores but serves as a fermentation chamber for cellulose and tough plant matter in herbivores.

Reticulorumen

The collective name for the first two communicating compartments of the ruminant stomach (reticulum and rumen), where symbiotic microflora digest cellulose through anaerobic fermentation without host-secreted enzymes.

Reticulum

The cranial compartment of the ruminant stomach, distinguished by an inner mucosal lining with a characteristic honeycomb-like appearance.

Omasum

The third ruminant stomach compartment, packed with prominent mucosal leaflets that absorb water and inorganic salts from the digesta.

Abomasum

The 'true stomach' of ruminants, which secretes gastric acid and digestive enzymes similarly to a monogastric stomach, driven by continuous motility.

Rumination

The digestive process in ruminants wherein fibrous forage is regurgitated from the reticulorumen back into the oral cavity for re-chewing and re-insalivation.

Eructation

The oral expelling of fermentation gases (principally carbon dioxide and methane) produced in the reticulorumen, commonly termed belching.

Biliary Tree

The ductal system that drains digestive secretions from the liver, gallbladder, and pancreas into the second portion of the duodenum via the ampulla of Vater.

Unconjugated Bilirubin

A lipid-soluble, water-insoluble yellow compound formed from heme oxidation during red blood cell destruction that circulates bound to protein until taken up by the liver.

Conjugated Bilirubin

The water-soluble form of bilirubin produced in hepatocytes by joining bilirubin with glucuronic acid, allowing it to be excreted in bile into the intestines.

Stercobilin

A brown pigment produced from the breakdown of conjugated bilirubin by intestinal bacteria that gives normal feces its characteristic color.

Urobilin

A yellow metabolite formed by intestinal bacteria, reabsorbed into the portal system, and excreted by the kidneys, giving normal urine its characteristic yellow tint.

Icterus (Jaundice)

A clinical state characterized by yellow discoloration of tissues, skin, and sclera caused by excess circulating unconjugated or total bilirubin.