Human Digestive System: Gastric Secretions, Small Intestine, and Large Intestine

Vocabulary practice flashcards covering gastric secretions, digestive enzymes, the structures of the small and large intestines, and nutrient absorption processes.

Gastrin

A regulatory hormone released into the blood circulation in response to stomach distention and the presence of amino acids and peptides; it stimulates powerful peristaltic waves to move chyme toward the relaxed pyloric sphincter to enter the duodenum.

Rennin (Chymosin)

An enzyme secreted in infants that converts soluble milk protein caseinogen into insoluble casein, which is subsequently digested by pepsin.

Serotonin (Gastric Inhibitory Polypeptide)

A substance that inhibits gastric acid secretions in the stomach.

Duodenum

The first part of the small intestine, measuring approximately $25\,\text{cm}$ in length, which receives digestive secretions from the pancreas and liver (gall bladder).

Cholecystokinin (CCK)

A hormone released by duodenal endocrine cells in response to fatty acids that stimulates contractions of the gall bladder smooth muscles, releasing bile into the duodenum via the common bile duct.

Secretin

A hormone stimulated by acidic chyme in the duodenum and transported via circulation to the liver to stimulate the release of bicarbonate ions into bile, neutralizing acidity.

Pancreatic Amylase

A pancreatic enzyme that hydrolyses remaining starch into the disaccharide maltose.

Pancreatic Lipase

A pancreatic enzyme that hydrolyses dietary fats into fatty acids and glycerol.

Enterokinase

An enzyme secreted by the intestinal glands that converts the inactive pancreatic proenzyme trypsinogen into active trypsin.

Trypsinogen

An inactive proenzyme produced by the pancreas that is activated to trypsin by enterokinase, which then converts proteins into polypeptides.

Chymotrypsinogen

An inactive pancreatic zymogen that is activated into chymotrypsin by the action of trypsin.

Bile Salts

Components of bile (specifically sodium taurocholate and sodium glycocholate) that emulsify fats into small droplets to provide a large surface area for lipase action.

Bile Pigments

Non-enzymatic waste excretions in bile consisting of yellow-brown bilirubin and greenish biliverdin.

Jejunum

The middle section of the small intestine, measuring about $2.5\,\text{m}$ long, where the digestion of proteins, carbohydrates, and fats is completed.

Chyle

A watery emulsion formed in the jejunum when chyme is acted upon by intestinal digestive enzymes.

Ileum

The terminal and longest part of the small intestine, measuring approximately $3.6\,\text{m}$ long, serving as the major site of nutrient absorption.

Plicae Circulares

Circular internal mucosal folds along the wall of the small intestine that increase the surface area available for nutrient absorption.

Lacteal

A central lymphatic capillary situated within an intestinal villus that absorbs processed fat globules known as chylomicrons.

Chylomicrons

Small globules formed within intestinal epithelial cells from recombined fats mixed with cholesterol and proteins, which enter lacteals for transport to the thoracic duct.

Hepatic Portal Vein

The blood vessel formed by the confluence of intestinal blood capillaries that delivers absorbed amino acids and monosaccharides directly to the liver.

Large Intestine

A portion of the alimentary canal measuring about $1.5\,\text{m}$ long and $6.5\,\text{cm}$ wide, functioning in water and electrolyte reabsorption, vitamin synthesis, and faeces formation.

Caecum

The blind pouch of the large intestine situated in the lower right abdominal cavity that receives undigested material through the ileocecal valve and reabsorbs water and salts.

Vermiform Appendix

A blind tube measuring approximately $18\,\text{cm}$ in length attached to the caecum that functions primarily as a vestigial organ.

Colon

The section of the large intestine consisting of ascending, transverse, descending, and sigmoid portions; it reabsorbs water, salts, and vitamins and harbors symbiotic bacteria such as Lactobacillus.

Rectum

A straight, muscular tube extending from the termination of the sigmoid colon to the anus, guarded by sphincter valves to regulate defecation and egestion.