PHYSIOLOGY OF DIGESTION

Food - omnivorous.
Digestion - Intercellular.

(i) Mechanical - by chewing, deglutinationm, churnning, peristalais. Under control of medulla oblongeta. (ii) Chemical - by hydrolases enzymes.

It can be studied in following steps -

DIGESTION IN BUCCAL CAVITY

1. Digestion starts in buccal cavity.
2. In buccal cavity food is masticated and mixed well with saliva.
3. About 30% starch of food is converted into maltose in buccal cavity.
4. Digestion of fats and carbohydrates do not take place in buccal cavity.
5. Saliva contains - mucus, lysozymes, ptyalin or salivary amylase and electrolytes such as Na+, K+, Cl- and HCO .
6. In buccal cavity pH is slightly acidic (6.8 pH).
7. Starch ^{sali var y amylase} fi Maltose +lim it dextrins

DIGESTION IN OESOPHAGUS

1. No digestive juice is secreted in the oesoophagus, onlymucus is secreted. Action of salivary amylase continues.

DIGESTION IN STOMACH

1. Fundic glands of stomach secrete digestive enzymes, HCl and mucus.
2. In stomach mainly digestion of proteins takes place.
3. Protein digesting enzymes are secreted in proenzyme form.
4. No carbohydrate splitting enzyme is secreted in stomach.
5. Gastric glands of stomach secrete gastric juice.
6. Gastric juice contain HCl & digestive enzymes.
7. In stomach pH is highly acidic (1.3 to 2.3 pH).
8. 
9. HCl in stomach kills bacteria present in food and activates pepsinogen.
10. HCl present in stomach inactivates salivary amylase and stops action on carbohydrates.
11. Gastrin hormone secreted from G-cells of gastric epithelium stimulates secretion of HCl.
12. Enterogastrone secreted from epithelium of duodenum inhibits secretion of gastric juice.

DIGESTION IN SMALL INTESTINE

1. It receives bile juice and pencreatic juice.
2. Hepatocrine stimulates bile juice for synthesis.
3. CCK stimulates contraction of gall bladder.
4. Secretin (discovered by Beylis & Sturling) & pancreozymine stimulate pancreatic juice.
5. First bile juice reacts on food.
6. In bile juice -  89% H O,  11% Others [Mucous, Incorganic, Bile juice (Sodium or Potassium taurocholate and glycholate), Bile pigment, Cholesterol, Lecithin, pH 7.7 - 8.6]
7. Total amount 500 - 1000 ml / 24 Hr.
8. Bile salts are helpful in imulsification particles of imulsified lipid are micellus or chitomicellus (.1 - .5m)
9. The reaction is known as saponification.
10. Bile salts are helpful in absorption of Vit. A, D, E & K.
11. Bile pigment, cholesterol & lecithin are excretory.

PANCREATIC JUICE - COMPLETE JUICE

1. 98.5% H O,  1.5% Others [Inorganic salts, Mucous, Chemotrypsinogen, Carboxypeptidase, Aminopeptidase, Trypsinogen,  Amylase, Maltase, Isomaltase, Limit Dextrinase, Lipase or steapsine, Cholesterol esterase, Polynucleotidase, pH 8.0]
2. Total amount - 500 - 800 ml / 24 hrs.
3. 
4. Now food is termed as chyle.
5. Endopeptidase react with peptide bond.
6. Glycosidase for Carb. digestion.
7. Here food gets succus entericus stimulated by enterokrinine harmone.
8. It's consists of - 98.5% H O, 1.5% Others [Mucous, Inorganic salts, Erapsin, Maltase, Isomaltase, Limit Dextrinase, Sucrase, Lectase, Lipase, Polynucleotidase, Phasphotase, Nucleosidase]
9. 

DIGESTION OF CELLULOSE

1. No vertebrate secretes any enzyme for digestion of cellulose.
2. In all herbivores digestion of cellulose takes place with the help of symbiotic bacteria and protozoans present in the alimentary canal.
3. In ruminants like cow, buffalo, goat, camel etc. symbiotic bacteria and protozoans are found in compound stomach.
4. In ruminants digestion of cellulose takes place in the compound stomach.
5. In other herbivores like rabbit and horse, digestion of cellulose takes place in caecum.
6. After digestion cellulose is converted into sugars.