When food is indigested it is chew by the teeth breaking it down into smaller particles with a large surface are for enzymes to act. Chewing constitute physical digestion while enzymes action constitute chemical digestion. Food is also mixed with saliva produce from the salivary glands it help to moisten the food and it also help to lubricate it for easy swallowing.

                                                           The alkaline environment in the mouth permit salivary amylase or phyaline to start the digestion of starch by converting it to maltose.

                                                           The food is then rolled into bolus by the tongue and sent into the esophagus. The food in the esophagus move by peristalsis until it enter the stomach through the cardiac sphincter.

The presence food in the stomach stimulate the walls of the stomach and produces gastric juice. The oxntic cell covering the stomach linning secret hydrochloric acid which act on the food and mucus is secreted by the mucosa.

• Hydrochloric acid give the stomach an acidic medium suitable for protein enzymes it also kills pathogenic organism in the stomach.
• It also activate inactive pepsinogen to active pepsin
• HCL in an empty stomach will burn the linning of the stomach hence leading to gastric pains.
• The mucus secreted by the mucosa prevent the digestion of the stomach wall.
• Mucus also help to lubricate the food during physical digestion.
• The gastric juice produce from gastric glands contain the enzymes pepsinogen which is converted to active pepsin.
• Pepsin hydrolysis protein to polypeptides and  convert more molecules of pepsinogen to pepsin in a process known as autocatalysis.
• The inactive enzymes pro-renin, pro-rennin is produce in babies and is converted to active renin by HCL acid
• Running coagulate caesinogen into melt protein to casein which can be obligated by pepsin.
• The mixing reduce food size and the food is now.
• The chaining by the stomach walls causes small amount of chime to pass out through the pyrelic sphinter to the duodenum.

DIGESTION IN THE SMALL INTESTINE

The entering of acidic chime into the duodenum stimulate the duodenum wall to secret the hormone known as secretin.

                                                     Secretin triggers the pancreas and the gall bladder to secret pancreatic juices and biles respectively.

Bile perform the following function in digestion. It neutralizes the acidic chime from the stomach, providing and alkaline medium for the duodenal enzyme to act best.

It also help to emulsify fat emulsification fat is being change into liquid fat there by increasing the surface for enzyme action.

Bile also give faeces it color

It also slow down multiplication of bacteria. Pancreatic juice contain pancreatic lipase, pancreatic amylase  and trypsinogen.

Lipase act on fat and press it down to fatty acid and glycerol. Trypsinogen is converted to active trypsin by enterokinase produce by the walls of the duodenum. The walls of the duodenum add more mucus to the chime. The contraction and the relaxation of the muscles and duodenum mixing the mucus and the chime to form another liquid called chyle. The peristaltic action of the duodenum forces chyle in the next part of the intestine called ileum.

DIGESTION IN THE SMALL INTESTINE

 Lipase acts o fat and press it down to fatty acid and glycerol. In the ileum, digestion is completed and absorption follows. The ileum wall secrete many enzymes like sucrose, carboxy peptidase, maltase. Caboxy peptidase acts on peptides and break it down into amino acid, maltose breakdown maltose, sucrose breakdown glucose and fructose, lactase break down glucose and galactose at this stage digestion is complete.

ABSORPTION OF DIGESTED FOOD

Ileam is the main site for absorption even thus small quantities of water, salt etc . Molecules of digested food are directly absorbed by cell  lining the villi(villus). The molecules are rapidly remove by the blood. Amino acid, monossacharides are absorbed in to the blood capillaries.

                                                     This capillaries later unite to form the hepaticportal vein. Which carry blood to the level and later distribute it to the general circulation of the body.

Fatty acid and glycerol do not pass strait in to the blood stream but pass  instead into the lacteal villi.