digestion 2

Chyme

Acidic (pH2)

Thin and watery

Fine particles of undigested material

Protein and polysaccharide breakdown fragments

Pepsin, intrinsic factor

The endocrine pancreas

Provides the main digestive fluid of the small intestine

• empties into duodenum via pancreatic duct/ common bile duct

• Acinar structure similar to salivary gland

Pancreatic secretion

Water

Enzymes

• all stored in inactive forms

Trypsin

Chymotrotrypsin

Amylase

Lipase

Nuclease

HCO3-

• neutralises acid in chyme

Control in pancreas

Gut hormones - secretion

The simulators factors are synergistic

HCO3 rich secretions

Parasympathetic nerves

• ACh

• VIP- vasoactive intestinal peptide

Enzyme activation cascade

Enterokinase- present in intestinal secretions

→ catalyses trypsinogen → trypsin

→ catalyses conversion of all other enzyme precursors to active forms

The liver

Receives all blood leaving the gastrointestinal tract

Produces bile (0.7-1.2 l day-1)

Produces many important plasma proteins

• albumin

• Clotting factors

A metabolic control centre

Stores

• carbohydrates

• Amino acids

• Fats

Monitors blood levels and stores and releases according

Can convert amino acids ( e.g. F → Y)

Can convert A acids to sugar

Liver looks after blood quality

Receives 28% resting cardiac output, accounts for 20% of resting O2 consumption

Destroys old RBC and breaks down haemoglobin

Purges blood of toxins and foreign components

An immune sentinel for material entering body from GI tract (kupfer cells)

Liver lobules

hepatic artery

Portal vein

Bile duct

Blood sinusoids

Hepatic vein

Bile cannaliculus

Bile

Digestive

• bile salts- emulsifying agents, aid absorption of fats (cholic acid, chenodeoxycholic acid)

Cholesterol, lecithin

Excretory

• bile pigments- breakdown products of haemoglobin

  biliverdin

  bilirubin

  converted to stercobilin

Control of the gall bladder

Parasympathetic nerves

• ACh

Cholecystokinin

• causes contraction of bladder

• Relaxation of sphincter of Oddi

Releases bile into duodenum