Digestion & Absorption

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Digestion

a. The mouth: salivary alpha enzyme
chew food, perceive taste, moisten food with saliva, lubricate food with mucus, release starch –digesting (amylase) enzymes, initiate swallowing reflex - Enzyme: alpha amylase with cooked starch as substrate – starch digestion enzyme an enzyme that catalyses the breakdown of starch into sugar - The Functions of Saliva -

1. Moistens and lubricates food, permitting swallowing
2. Holds taste producing substances in solution and bring them in contact w/ taste buds 3. Dilutes acids and salts, protecting mucosa and teeth
4. Cleansing effect on teeth, gums and buccal mucosa
5. Amylase may be cleansing agent for oral cavity by digestion starch particles near or on teeth.

b. The Stomach: the role of HCL and pepsin
store, mix, dissolve and continue digestion of food, dissolve food particles with secretions, kill microorganisms with acid, release protein-digesting (pepsin) enzyme, lubricate and protect stomach surface with mucus, regulate emptying of dissolved food into small intestine, produc intrinsic factor for vitamin B-12 absorption - Pepsin: protein splitting enzyme

- Functions of HCL-
1. Enhances the conversion of pepsinogen to pepsin and provides a favorable pH for activity of pepsin 2. Reduces ferric iron to ferrous form
3. Sterilization of the gastric contents
4. Hydrolysis of some proteins and carbohydrates
5. Makes calcium more soluble
* Davenport theory of HCL production
- Phases of Gastric Secretion-
1. Nervous: gastric secretion elicited by sensory stimuli
2. Gastric: gastric secretory production with the presence of food in the stomach- probable distention effect 3. Humeral: postabsorptive state, role of gastrin and histamine Gastrin facilitates HCL production// histamine is a powerful stimulant of gastric secretion

c. The Pancreas: 췌장
Secrete sodium bicarbonate and enzymes for digesting carbohydrate, fat, and protein - Protein splitting enzymes; trysinogen and chymotripsinogen (zymogen forms), elastin and carboxypeptidases - Lipase: enzyme used to break down fats in food so they can be absorbed in the intestines - Amylase: an enzyme that to hydrolyse dietary starch into disaccharides and trisaccharides which are converted by other enzymes to glucose to supply the body with energy - Bicarbonate secretion; pancreas secretes bicarbonate in order to neutralize the highly acidic substance coming from the stomach (BASE)

d. The Gall bladder: 쓸개
Store, concentrate, and later release bile into the small intestine - Production of bile by the liver & storage in the gall bladder Bile is produced in the liver and it is stored and concentrated in the gallbladder. It is emptied into the small intestine through the common duct - Micelle formation

Micelle formation is essential for the absorption of fat-soluble vitamins and complicated lipids within the human body. Bile salts formed in the liver and secreted by the gall bladder allow micelles of fatty acids to form.  - Functions of Bile Salts-

1. Accelerate the action of pancreatic lipase
2. Aid in the emulsification of fats w/ their power of lowering surface tension; they tend to stabilize such emulsions 3. Facilitate fat absorption with micelle formation
4. Keep cholesterol in solution
5. Have choleretic action. The live is stimulated to secrete bile as long as bile salts are absorbed. This secretion apparently continues during fat digestion and the absorption of bile salt – fatty acid complex, exactly during the period necessary for such secretion 6. Stimulate intestinal motility

7. The chief vehicle for the excretion of excess cholesterol

e. Secretions of the small intestine
mix and propel contents, lubricate with mucus, digest and absorb most substances using enzymes made by the pancreas and small intestine - Enzymes: carbohydrate and protein splitting, nucleases
The small intestine secretes sucrase (breaks sucrose into glucose and fructose); maltase (breaks maltose into...
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