Question

why do humans digest in two steps

Answer 1

The pancreas produces enzymes that help digest proteins, fats, and carbohydrates. ... These enzymes and bile travel through special channels (called ducts) directly into the small intestine, where they help to break down food.


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Answer 2

Hey Friend,___________________________________

solution:

The food eaten by us is acted upon by different digestive enzymes to break down it into simple absorb able forms. So basically the function of digestive enzymes is to increase the rate of breakdown and to break it into simple forms.

As we all  know digestion starts from mouth.And to the food entered starts acted upon by different digestive enzymes.


So let us now understand the function of some basic enzymes

Food entered the oral cavity is acted upon the enzyme salivary amylase or ptyalin .It is secreted by parotid . sub lingular and maxillary gland.The salivary amylase breaks starch into sugar.

the food further enters into esophagus and moves down by peristalsis movement.

The food further reached the stomach which is a J shaped bag structure.The stomach consists of mucous .HCL and enzyme pepsin.The HCL contributes for acidic medium in stomach which is required for the the enzyme pepsin to work.
Pepsin is responsible for digestion of protein.

The food then enters small intestine . the food in acted upon by bile juice andpancreatic enzymes. 

Bile juice creates an alkaline medium which is necessary for pancreatic enzyme to function. Bile juice emulsifies the fat globules.

Digestion is finally completed in the small intestine by pancreatic enzymes trypsin and lipase. Trypsin digests protein and fats are done by lipases. 
The small intestine then produces enzymes called lactase, sucrase and maltase, which break down the disaccharides into monosaccharides.
They convert the proteins into amino acids, carbohydrates into glucose and fats into fatty acids and glycerol. which are simple absorb able forms .
small intestine has small finger like projection called villi which absorb these since they are rich in blood vessels the nutrients are reached to other parts of body

The food then enters into large intestine where water is reabsorbed. the unwanted matter is finally thrown out by anus through rectum.
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Hope this helps you
 
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