Digestion of food:

Deglution: Swallowing of food also called deglution, passage of food bolus from buccal cavity to stomach.

A) Digestion of carbohydrates:

In buccal cavity 30% starch get digested:

In small intestine:

Remaining carbohydrates is digested by intestinal amylase.

(B) Digestion of protein:

(In stomach & small intestine)

Stomach → occurs 2 changes:

(A) Mechanical change	(B) Chemical change
Wall of stomach undergoes muscular contration & breaks the food & mixes it with gastric juice.	Here food get mixed with gastric juice which  is secreted by gastric glands.

 

i) Hcl:

• Kills bacteria in food.   
• Stops the action of salivary amylase.
• Activates propepsin to Pepsin.
•  Produces acidic PH for protein synthesis.
•  Softens the food.
• Denaturates the protein to make action of enzymes easy.

(ii)   Pro-pepsin → Activated by HCL into pepsin.

Activated pepsin activates other propepsin itself called autocatalytic activation.

(iii)  Pro-renin → Activated by HCl into rennin.

Para casein + calcium   ----à Calcium-paracaseinate (curd)

[The acidic mixture of gastric juice & semi digested food in stomach is called chime.]

(i) Pancreatic juice:-Has 3 inactive proteases. Tripsinogen, chymotripsinogen & procarboxy peptidase.

(ii) Intestinal juice: Has 2 digestive proteases → amino – di – peptidases. and  one  non – digestive protease (enterokinase).

(1) Amino peptidases →

C) Digestion of fats:  By lipase.

In small intestine bile, pancreatic & intestind juice undergoes fat’s digestion.

(i) Bile:-It has 2 salts (codicene glycocholate & sodium tacrocholate which breaks large fat droplets into small ones

It increases the surface are which further increases lipase action on fats.

(ii) Pancreatic juice:- Has pancreatic lipase.

(iii) Intestinal fuice:- Has intestinal lipase that connects remaining tri, di – glycerides into glycerol, fatly acids, monoflycerides

During food digestion in small intestine:  It receives 3 juices to form a basic emulsion called chyle.

D) Digestion of nucleic acids:

Pancreatic juice & intestinal juice works on them in small intestine.

(i) Pancreatic juice:-

(ii) Intestinal juice:-

Nucleosides → Nitrogenous base + pentose sugar