Digestion: MDCAT Notes and MCQs
Alimentary canal & functions
| Part | Secretion / function |
|---|---|
| Mouth (oral cavity) | Mastication; 3 pairs of salivary glands (parotid, submandibular, sublingual) → saliva ≈ 1.5 L/day with salivary amylase (ptyalin): starch → maltose; mucus lubricates; lysozyme. |
| Pharynx & oesophagus | Swallowing; food moved by peristalsis; no digestion. |
| Stomach | Gastric glands: parietal (oxyntic) cells → HCl (kills microbes, activates pepsinogen, pH ≈ 2); chief (peptic/zymogen) cells → pepsinogen → pepsin (proteins → peptides); mucous cells → mucus. Hormone gastrin stimulates gastric juice. Food becomes chyme. |
| Small intestine (duodenum, jejunum, ileum) | Completes digestion and absorbs nutrients; villi & microvilli increase surface area; lacteals absorb fats. Intestinal enzymes: maltase, sucrase, lactase, peptidases, lipase. |
| Large intestine (caecum, appendix, colon, rectum) | Absorbs water and salts; bacteria make vitamin K; forms and stores faeces. |
Associated glands
- Liver (largest gland): produces bile (stored in gall bladder). Bile has no enzymes; bile salts emulsify fats and neutralize acid chyme. Liver also stores glycogen, deaminates amino acids (urea), detoxifies, makes plasma proteins.
- Pancreas (mixed gland): pancreatic juice (alkaline, HCO3−) with trypsin (secreted as trypsinogen, activated by enterokinase), pancreatic amylase, lipase (fats → fatty acids + glycerol), nucleases. Islets of Langerhans → insulin, glucagon.
Hormonal control
Gastrin (stomach) → gastric secretion. Secretin (duodenum) → pancreatic bicarbonate (first hormone discovered — Bayliss & Starling, 1902). Cholecystokinin (CCK) → gall bladder contraction & pancreatic enzymes.
PMDC learning outcomes for this unit
- Human digestive system: 14.1 Describe the parts of human digestive system
- Human digestive system: 14.2 Explain the functions of the main parts of the digestive system including associated structures and glands