1. SF Biology II1 Digestion & Absorption Water and ions Carbohydrate (CHO) Protein Fat Vocabulary: trypsin/ogen, enterokinase, proteolytic, chylomicron, chyme, micelle

2. SF Biology II2 Digestion & Absorption GENERAL PRINCIPLES Breakdown of complex molecules – Enzymes (pH) Absorption into gut cells – Mechanism of absorption – Active [energy] – Passive [no direct energy ] – carriers

3. SF Biology II3 Bulk flow of liquid in gut Input –Ingestion ~ 2 litres per day –Secretion (gut) ~ 7 litres/day Output –Faeces ~100 ml/day Conclude ~ 9 litres/day absorbed

4. SF Biology II4 Absorption of Water Passive Osmotic gradient –Due to Na + [active] ‘Leaky’ tight junctions (paracellular) –Regulated ~95% absorption in small intestine

5. SF Biology II5 Carbohydrate (CHO) Digestion

6. SF Biology II6 Carbohydrate (CHO) Digestion

7. SF Biology II7 CHO Digestion — Summary Polysaccharides to disaccharides (gut amylases) Disaccharides to monosaccharides (brush border) –Glucose, galactose enter cells by energy-dependent secondary active transport i.e. ‘piggy-back on Na + gradient (active)

8. SF Biology II8 Carbohydrate Absorption Glucose, galactose enter capillaries down concentration gradient Fructose enters capillaries via passive carrier mediated transport

9. SF Biology II9 Protein Digestion Essentially similar to CHO Proteins to peptides –Gastric pepsinogen –Activated by HCl AND pepsin –Pancreatic proteases (trypsin)

10. SF Biology II10 Protein Digestion contd Essentially similar to CHO Peptides to amino acids (brush border) Absorbed by secondary active transport –Depends on Na + transport

11. SF Biology II11 Pancreas Endocrine –Insulin,glucagon Exocrine –Enzymes (acini) –Bicarbonate (ducts)

12. SF Biology II12 Digestion and Absorption of Fat Emulsification by bile salts Pancreatic lipase Micelles are water- soluble

13. SF Biology II13 Digestion and Absorption of Fat Monoglycerides and FFA enter cells by diffusion Triglyceride synthesis Add protein Chylomicrons To lacteal (lymph)

14. SF Biology II14 Fat Digestion & Absorption Fat to triglycerides (pancreatic lipase) Bile salts emulsify (surface area) Bile salts — micelles containing monoglycerides and free fatty acids (FFA) Enter passively Triglyceride synthesis — chylomicrons Exocytosis and thence to lacteals

15. SF Biology II15 3. Regulation of Digestive Function Neural mechanisms Humoral [hormonal] mechanisms Control of movement Control of secretions Acts to maintain contents of gut