The food taken into our mouth requires some kind of alteration before they can be absorbed into the blood stream.
Digestion is the process by which food molecules are broken down into various small substances that can be absorbed into the blood stream and assimilated into the cells for utilization. Digestion is mainly a chemical process brought about by the action of many enzymes.
The whole process of digestion takes place in the ALIMENTARY CANAL, which takes place in four major sections that is, the mouth, stomach, duodenum and small intestine.
The mouth: In the mouth, the food is mixed and softened with the saliva secreted by many enzymes and masticated and crushed into smaller particles by the teeth. Saliva contains mucin which lubricates the food and makes swallowing easier, it also provides an alkaline medium necessary for the action of ptyalin, an enzyme.
The stomach contains gastric juice which is acidic due to the presence o of hydrochloric acid [HCL].The hydrochloric acid performs three major functions viz:Stops the action of ptyalin from the mouth.
2.provides the acidic medium necessary for the action of rennin and pepsin in the stomach.
3.Destroys any bacteria that might have accompanied the food from the mouth.
From the stomach, the product of digestion are passed into the duodenum. The pancreatic juice from the pancreas is secreted into the duodenum and the bile from the liver are emptied into the duodenum through the bile duct. The bile does not contain any enzyme rather it emulsifies the fats or oils present in the chime.
The pancreatic juice on the other hand contains carbohydrate, protein, and fat splitting enzymes.
Amylase– converts starch to maltose
Trypsin– converts protein to peptides and peptones.
Lipase–converts fats to fatty acid glycerol.