Question

name the product formed after complete digestion of carbohydrates protein and fest in the small intestine

Answer 1

Carbohydrates
Like everything else you eat carbohydrates technically begin their digestion with the mechanical breakdown that happens in the mouth. Unlike the other two major macronutrients, Carbohydrates also begin their "chemical" digestion in the mouth. In case you haven't been paying attention, your mouth is filled with a watery liquid called saliva. Among many other things, saliva contains an enzyme known as salivary amylase. This enzyme is responsible for breaking down larger sugars into the kind of single ring sugars used in basic metabolism, the most common example being sucrose which can be split yielding some glucose – which is why there are some foods such as saltine crackers, white rice, and a lot of breads which seem to get sweeter the longer you chew them.

After exposure to salivary amylase in the mouth carbohydrates are swallowed and dropped down to the stomach where they are exposed to HCl which usually helps free sugars from other larger polymers and proteins which are more susceptible to denaturing. While in the stomach, any free glucose is transported into the bloodstream with a sort of secondary active transport – the high concentration of sodium in the stomach compared to the bloodstream provides enough of a gradient to transport glucose (and conveniently enough several water molecules). This is the basic principle that makes Gatorade and other sports drink effective, the presence of both electrolytes including sodium and sugar or glucose they allow all three of those ingredients to begin entering the bloodstream directly from the stomach which does not usually transport or absorb water. Water is usually absorbed in the small intestine and mostly in the large intestine.

Gradually the sphincter at the bottom of the stomach opens up and drops the mashed up food including our carbohydrates that were not transported out of the stomach into the small intestine. Immediately the pH is raised because the small intestine is not coated with mucus to protect itself from HCl like the stomach cells are. The cells of the small intestine form structures to increase the surface area which appears little tentacles or kind of like carpeting. On this incredibly dense surface area cells are joined together by tight junctions and form an impermeable layer. The tight junctions divide the cells in half with one side filled with transport proteins and digestive enzymes and the other side filled with complementary transport proteins to move collected and digested materials from the inside of the small intestine to the bloodstream.

Proteins
Proteins follow along just about the same path as carbohydrates but of course are less affected by the salivary amylase before they drop in the stomach. In the stomach proteins experience and unwinding which we refer to as denaturing which destroys their functions and increases the surface area available to enzymes. The stomach itself has cells that release enzymes that break down peptides, a.k.a. proteins. These enzymes are actually very dangerous since they are capable of breaking down cell organelles or enzymes or pretty much anything else. These cells protect themselves by creating an inactive form of the enzyme which can only be activated by a low pH. When this inactive form reacts with HCl it activates the enzyme and the combination of denaturing in the enzyme begin to separate proteins into their individual amino acids.

Same song and dance happens and they are dropped into the small intestine where a similar but different set of enzymes and transporters finishes the digestion and moves the and amino acids into either the bloodstream or their own metabolic processes for further processing.