Digestion

1
Digestion Absorption

• Water and ions
• Carbohydrate (CHO)
• Protein
• Fat
• Vocabulary trypsin/ogen, enterokinase,
  proteolytic, chylomicron,
• chyme, micelle

2
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
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
Absorption of Water

• Passive
• Osmotic gradient
• Due to Na active
• Leaky tight junctions (paracellular)
• Regulated
• 95 absorption in small intestine

5
Carbohydrate (CHO) Digestion
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Carbohydrate (CHO) Digestion
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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
Carbohydrate Absorption

• Glucose, galactose enter capillaries down
  concentration gradient
• Fructose enters capillaries via passive carrier
  mediated transport

9
Protein Digestion

• Essentially similar to CHO
• Proteins to peptides
• Gastric pepsinogen
• Activated by HCl AND pepsin
• Pancreatic proteases (trypsin)

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Protein Digestion contd

• Essentially similar to CHO
• Peptides to amino acids (brush border)
• Absorbed by secondary active transport
• Depends on Na transport

11
Pancreas

• Endocrine
• Insulin,glucagon
• Exocrine
• Enzymes (acini)
• Bicarbonate (ducts)

12
Digestion and Absorption of Fat

• Emulsification by bile salts
• Pancreatic lipase
• Micelles are water-soluble

13
Digestion and Absorption of Fat

• Monoglycerides and FFA enter cells by diffusion
• Triglyceride synthesis
• Add protein
• Chylomicrons
• To lacteal (lymph)

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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

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3. Regulation of Digestive Function

• Neural mechanisms
• Humoral hormonal mechanisms
• Control of movement
• Control of secretions
• Acts to maintain contents of gut