The stomach and beyond

Digestion part 2

The stomach• Smooth muscles mix food

(3-5 hours)• Acid secretion denatures

food• Digestive enzymes begin

to digest protein• (fat, carbohydrate to

lesser extent)• Chyme is formed (food is

liquefied); highly acidic

Very little absorption takes place

• Water, electrolytes, aspirin, alcohol

• Produces “intrinsic factor’ necessary for vitaminB12 absorption

Secretory structures of the stomach

• Cells in mucosa secrete:– Acid (parietal cells)– Mucus (goblet cells)– Pepsinogen (chief

cells)– hormones (G and D

cells)

Accessory organs: pancreas• Secretes digestive

enzymes into the small intestine– Pancreatic juice: amylase,

trypsin, lipase, etc.

• Secreted by acini (99% of pancreatic cells)

• Remaining 1% form islets of Langerhans and secrete insulin and glucagon

Liver and gall bladder

Diverse functions of liver

• Formation and secretion of bile• Metabolism of carbohydrates, lipids,

proteins• Formation of plasma proteins• Detoxification of blood• Storage of vitamins and minerals• Clearance of aged cells

Small intestine organization

Small intestine receives and produces secretions

• From pancreas and liver/gall bladder• Digestive enzymes

– Brush-border enzymes– Crypts of Lieberkühn

• Mucus– Goblet cells

• Hormones• Immune function

– Paneth cells

Large intestine

• Compaction of solid waste

• Bacterial breakdown of proteins; vitamin formation

• Absorption of water, ions, vitamins

• Defecation

Applications to health• Peptic ulcer- craterlike lesion caused by exposure to

gastric juices. • Vomiting- forcible expulsion of the contents of the upper

GI tract (stomach and duodenum).• Peritonitis- acute inflammation of the peritoneum.• Hepatitis- inflammation of the liver caused by viruses,

drugs, or chemicals.• Gallstones- crystallization of cholesterol due to

insufficient bile salts.• Appendicitis- inflammation of the appendix caused by an

obstruction of the lumen.