Physiology 1 GI tract and stomach

Accommodation and storage Mechanical and enzymatic breakdown Slow delivery of chyme to duodenum

The autonomic nervous system empty stomach = small volume

Mucus - lubricants Lipase Pepsin HCl - important in defence Intrinsic - for vitamin B12 absorption

“local hormones” Secreted from cells in the mucosa, but unlike hormones, the chemical acts locally on adjacent cells via the interstitial fluid

somatostatin inhibits gastrin release in the stomach

Salivary glands: mucus (lubrication), lipase (fat digestion) Gastric glands: HCl (denatures/activates), pepsin (proteins), mucus (protection) Pancreas: HCO₃⁻ (neutralises acid), enzymes (digest carbs, fats, proteins) Liver: bile salts (emulsify fats)

Endoderm - epithelium of the gut tube Mesoderm - surrounding muscle, connective tissue and mesenteries Ectoderm - innervation of the gut

by folding of sheets of cells in two directions 1)towards the midline along the cranial-caudal axis 2)towards the yolk sac at the cranial and caudal ends

from the pharynx to the 2nd part of duodenum

2nd part of the duodenum and 2/3 of the transverse colon

2/3 of the transverse colon to the anal canal

foregut - celiac artery midgut - superior mesenteric artery hindgut - inferior mesenteric artery

Type of food eaten determines rate of gastric emptying: carbohydrates>protein>fatty foods>indigestible solids injury hormones

The stomach muscles create their own contractions without needing nerve signals.Interstitial Cells of Cajal (ICC) help generate the rhythmic contractions.

stomach movements that are controlled by nerves and hormones. E.G Gastrin → increases stomach motility Cholecystokinin (CCK) → slows gastric emptying Secretin → reduces gastric motility

Negative feedback The duodenum detects acidic or fatty chyme and sends neural and hormonal signals that slow stomach emptying.

Segmentation(mixing contractions) Peristalsis Migrating motor complex(MMC) Mass movements

Circular smooth muscles contract in alternating segments, which mixes chyme with digestive enzymes and improves absorption rather than moving it forward.

wave-like contraction of circular and longitudinal smooth muscles that pushes chyme forward through the small intestine toward the large intestine.

a pattern of strong, rhythmic contractions that occur during fasting to sweep leftover food, bacteria, and secretions through the stomach and small intestine.

Bacterial fermentation Absorption of water and ions Elimination of waste Storage of waste and indigestible material

Segmental (Haustral) contractions: Mix colon contents; involve taenia coli. Peristalsis: Slow waves that move contents toward the anus; triggered by distension. Mass movements: Powerful contractions pushing feces from the colon to the rectum for evacuation.

Diarrhoea - frequent discharge of liquid faeces Constipation- difficulty/some constraint in opening/emptying bowel (hard faeces)

Transcellular - transport of solutes by a cell through a cell Paracellular - passage of solutes between cells through tight junctions