9.5 Digestion in the Small and Large Intestines

9.5 Digestion in the Small and Large Intestines Pages 412-420

Small intestine • Site of digestion of carbohydrates, lipids and protein • Food passes through in 3-5 hours

Dimensions of Small Intestine • Diameter 2.5 cm • 7 m long

Sections

Duodenum • First section • 25-30 cm • Digestive enzymes added • Acid is neutralized

Jejunum • Digestion and absorption

ileum • absorption

Villi and microvilli • Finger-like projections increase the surface area for absorption

Where the food goes • Sugars, amino acids, water-soluble vitamins and minerals go into capillaries • Fats go into lacteal  lymphatic system bloodstream

Chemical Digestion • Pyloric sphincter regulates movement of chyme into the small intestine

Pancreas • Produces digestive enzymes which pass through pancreatic duct. Ex. more amylase for carbs • Produces insulin

Cholesystokinin, CCK, from duodenum lining prompts pancreas to secrete

Secretin Prosecretin secretin acid Functions - stimulates liver to secrete bile - stimulates pancreas to secrete enzymes -stimulates pancreas to secrete HCO3- - change in pH inactivates pepsin -regulates rate

trypsinogen enterokinase trypsinogen trypsin Further digests long-chain protein into short-chain protein Enzmes: carboxypeptidase and erepsin break protein segments down into amino acids

Fats • Too big for enzyme lipase • Bile emulsifies fats…micelles

Liver • Liver detoxifies blood, • Glycogen manufacture and storage, vitamins • Produces bile

Absorption • Simple Diffusion • Fascilitated Diffusion • Osmosis • Active Transport

Large intestine • 1.5 m in length • 7.6 cm diameter Cecum, colon, rectum and anus Colon: ascendingtransversedescending sigmoid Rectum: last 20 cm

Functions of large intestine • Absorbs water (20L per day) • Vitamins B and K, and Na+ and Cl- • 4-72 hours • 500 species of bacteria (gas)

Cellulose and Fibre • Bulk • Full-feeling lasts longer

Anus • Defecation reflex-eliminated feces • 1st sphincter, the internal anal sphincter is a smooth muscle (involuntary) • 2nd sphincter, the external anal sphincter is made of skeletal muscle and is voluntary • Both muscles must be relaxed for defecation to happen

Endoscopy • Light, lens and camera • Through anus, mouth or opening in the abdomen • Diagnosis: biopsy • Treatment: surgery

9.5 Digestion in the Small and Large Intestines