The Digestive System and Nutrition

Vocabulary flashcards covering key terms and concepts from the lecture notes on the digestive system.

Alimentary canal

A tube with two openings that forms the gastrointestinal tract; most animals have one.

Ingestion

The intake of food into the digestive tract.

Digestion

Mechanical and chemical breakdown of food into a form usable by the body.

Absorption

Uptake of nutrient molecules into epithelial cells of the digestive tract and then into the blood or lymph.

Compaction

Absorbing water and consolidating the indigestible residue into feces.

Defecation

Elimination of feces from the digestive tract.

Oral cavity

Mouth; ingestion, tasting, mastication, beginning of chemical digestion, swallowing, speech, respiration.

Bolus

A chewed and moistened mass of food prepared for swallowing.

Mastication

Chewing; mechanical digestion that fragments food and increases surface area.

Saliva

Watery oral secretion that moistens food and begins digestion; contains enzymes, mucus, electrolytes, and antibodies.

Salivary amylase

Enzyme in saliva that begins digestion of starch.

Lingual lipase

Enzyme in saliva that digests fats; active in the mouth.

IgA (Immunoglobulin A)

Antibody present in saliva providing mucosal immune protection.

Lysozyme

Antibacterial enzyme found in saliva.

Mucus (in saliva)

Glycoproteins (mucins) that bind and lubricate food for swallowing.

Major salivary glands

Larger glands with ducts and acini; produce most saliva (about 1–1.5 L/day), stimulated by parasympathetic nerves.

Intrinsic (minor) salivary glands

Dispersed glands in the mouth; keep mouth moist; secrete mucus and serous saliva.

Deglutition

Swallowing; complex process coordinated by the swallowing center in the medulla.

Oral phase

Voluntary phase of swallowing; bolus formation and oral propulsion.

Pharyngeal phase

Involuntary phase; soft palate and tongue root block nasal entry; airway protection.

Esophageal phase

Involuntary phase; peristalsis moves bolus to the stomach.

Esophagus

Muscular tube that transports food from the pharynx to the stomach via peristalsis.

Stomach

Muscular sac; mechanically digests, liquefies, and begins chemical digestion; produces chyme and intrinsic factor.

Gastric juice

Gastric secretions (2–3 L/day) including water, HCl, pepsin, mucus, and enzymes.

Hydrochloric acid (HCl)

Acidic gastric secretion that denatures proteins, activates enzymes, and aids digestion.

Pepsinogen

Zymogen secreted by chief cells; activated to pepsin by HCl.

Pepsin

Active protease that digests proteins.

Gastric lipase

Lipase secreted by chief cells; digests fats in the stomach.

Parietal cells

Stomach cells that secrete HCl and intrinsic factor; use H+/K+-ATPase.

Intrinsic factor

Glycoprotein required for vitamin B12 absorption in the small intestine.

Chief cells

Stomach cells that secrete pepsinogen and gastric lipase.

Mucous neck cells

Secret mucus and bicarbonate to protect the stomach lining.

G cells

Enteroendocrine cells that secrete gastrin, regulating digestion.

Enteroendocrine cells

Hormone-secreting cells in the stomach (and elsewhere) that regulate digestion.

Gastrin

Hormone that stimulates gastric acid secretion and motility; released by G cells.

Bile

Digestive fluid produced by the liver that emulsifies fats; contains bile salts, pigments, and acids; stored in the gallbladder.

Gallbladder

Stores and concentrates bile; releases bile into the duodenum.

Liver

Versatile organ with roles in metabolism, bile production, detoxification, storage, and synthesis of plasma proteins.

Hepatic portal vein

Blood vessel that carries nutrient-rich blood from the GI tract to the liver for processing.

Hepatocyte

Liver cell performing most metabolic, synthetic, and detoxification tasks.

Bile salts

Amphipathic compounds derived from cholesterol that emulsify fats.

Chylomicrons

Lipoprotein particles formed in enterocytes to transport dietary triglycerides via the lymph system.

VLDL (Very-Low-Density Lipoprotein)

Lipoprotein carrying endogenous triglycerides from the liver to tissues; becomes IDL/LDL.

LDL (Low-Density Lipoprotein)

Lipoprotein that delivers cholesterol to tissues; can be taken up by the liver via receptors.

HDL (High-Density Lipoprotein)

Lipoprotein that scavenges cholesterol from tissues to bring it to the liver.

Apolipoproteins

Protein components of lipoproteins (e.g., apo-B48, apo-B100, apo-C, apo-E).

Lipoprotein lipase

Enzyme that hydrolyzes triglycerides in lipoproteins at capillary walls.

Enterocytes

Absorptive cells of the small intestine with microvilli and brush border enzymes.

Brush border enzymes

Digestive enzymes on the microvilli of enterocytes (e.g., dextrinase, glucoamylase, maltase, sucrase, lactase, aminopeptidase, dipeptidase).

SGLT1

Sodium-glucose cotransporter; takes up glucose and galactose with Na+ entry into enterocytes.

GLUT2

Glucose transporter on enterocytes; facilitates glucose movement into blood.

Duodenum

First section of the small intestine where chyme mixes with bile and pancreatic juice.

Jejunum

Middle section of the small intestine; primary site of nutrient absorption.

Ileum

Distal small intestine; vitamin B12 absorption and bile acid reabsorption occur here.

Brunner’s glands

Duodenal submucosal glands that secrete alkaline mucus to protect the duodenum and aid digestion.

Carbohydrate digestion

Begins in the mouth with salivary amylase and finishes with brush border and pancreatic enzymes to glucose.

Protein digestion

Begins with pepsin in the stomach; continued by pancreatic proteases and brush border enzymes.

Lipid digestion

Digestion of triglycerides by lipases; emulsified by bile salts; absorbed as micelles and reassembled into triglycerides.

Micelles

Aggregates of bile salts and lipids that transport lipids to enterocyte membranes for absorption.

Chylomicron remnants

Remnants of chylomicrons after lipoprotein lipase activity, cleared by the liver.