Key Definitions Glossary

Term	Definition	NEET Relevance
Alimentary canal	The continuous muscular tube from mouth to anus through which food travels	Framework for all digestive processes
Amylase	Enzyme that hydrolyses α-1,4-glycosidic bonds in starch/glycogen to produce maltose and limit dextrins	Two types: salivary (pH 6.8) and pancreatic (pH 7–8)
Bile	Alkaline secretion produced by the liver, stored in the gallbladder, containing bile salts, bilirubin, cholesterol. Contains NO enzymes	Most-tested NEET fact: emulsification only
Bile salts	Amphipathic molecules in bile (sodium salts of bile acids) that emulsify dietary fats by reducing surface tension	Distinguish from digestive enzymes (bile salts ≠ enzymes)
Bolus	Moistened, chewed ball of food formed in the mouth and swallowed	First mechanical and chemical processing unit
Brush border	Dense layer of microvilli on the apical surface of small intestinal enterocytes; site of brush border enzymes	~600-fold surface area amplification
Carboxypeptidase	Pancreatic exopeptidase (from procarboxypeptidase) that cleaves amino acids from C-terminal end of peptides	Cleaves from C-terminal end; activated by trypsin
Chylomicrons	Lipoprotein particles formed in enterocytes containing triglycerides, cholesterol, phospholipids, and apoprotein B48	Vehicle for fat transport from lacteals to bloodstream
Chyme	Semi-fluid, acidic mixture produced by gastric digestion and mechanical churning; released through pyloric sphincter	Triggers secretin, CCK, GIP when entering duodenum
Dipeptidase	Brush border enzyme that cleaves dipeptides into two amino acids	Final step in protein digestion
Emulsification	Physical process of breaking large fat globules into smaller droplets, increasing surface area for lipase; performed by bile salts	NOT enzymatic — this is the key NEET distinction
Enterokinase	Enzyme secreted by DUODENAL MUCOSA (NOT pancreas) that converts trypsinogen → trypsin, initiating proenzyme cascade	Source = duodenal mucosa; most tested cascade initiator
Gastrin	Peptide hormone from G-cells of pyloric stomach; stimulates HCl and pepsinogen secretion	Triggered by food/proteins in stomach
GIP	Gastric Inhibitory Peptide; from K-cells of duodenum; inhibits gastric acid; stimulates insulin (incretin)	GIP = inhibits Gastric + stimulates Insulin
Haustra	Sacculations (outpocketings) of the large intestinal wall	Characteristic structural feature of large intestine
Jaundice	Yellowing of skin and sclera due to excess bilirubin in blood	Liver failure or bile duct obstruction
Kwashiorkor	PEM from protein deficiency (adequate calories); oedema, distended belly, skin lesions	Protein deficiency → low albumin → oedema
Lactase	Brush border enzyme; converts lactose → glucose + galactose	Deficiency → lactose intolerance
Lacteals	Lymph capillaries in each intestinal villus; absorb chylomicrons	Fats → lacteals (not blood capillaries)
Marasmus	PEM from total calorie + protein deficiency; severe wasting; NO oedema	Total starvation → wasting
Microvilli	Sub-cellular finger-like projections on enterocyte apical surface; form brush border	With villi → ~600-fold surface area amplification
Peristalsis	Wave-like muscular contractions of alimentary canal that propel food forward	Coordinated by enteric nervous system (ENS)
Pepsin	Active gastric protease; from chief cells (as pepsinogen); activated by HCl; pH optimum 1.5–2.0	Activated by HCl; initial protein digestion
Pyloric sphincter	Muscular valve at stomach-duodenum junction; controls chyme release into duodenum	Regulates gastric emptying rate
Rugae	Mucosal folds in the stomach; allow stomach expansion	Characteristic feature of the stomach
Secretin	Hormone from S-cells of duodenal mucosa; triggered by acid; stimulates pancreatic bicarbonate	Triggered by acid; produces bicarbonate (not enzymes)
SGLT	Sodium-Glucose Linked Transporter; secondary active transport co-transporting $Na^{+}$ and glucose on brush border	Mechanism of glucose absorption; basis for ORS
CCK	Cholecystokinin; from I-cells of duodenal mucosa; triggered by fats + amino acids; stimulates bile + pancreatic enzymes	Dual action: bile release + pancreatic enzyme secretion
Trypsin	Active pancreatic protease; from trypsinogen; activated by enterokinase; master activator of all other proenzymes	Trypsin = master activator
Villi	Finger-like mucosal projections in small intestine; increase surface area	Macroscopic surface area amplification in SI