Question

what is the process of digestion carbohydrate, fats, and proteins

Answer 1

Digestion of carbohydrates :- The digestion of starch begins in the mouth with the help of salivary amylase, it splits starch into oligosaccharides and 2 to 8 linked monosaccharides. Starch digestion continues until the amylase are inactivated by the acidic environment in the stomach. The salivary amylase requires pH of 6.75 to 7. carbohydrate digestion does not occur in the stomach.
Starchy food and other digestible carbohydrate which are not broken down into mouth are acted upon by pancreatic amylase in small intestine. After about 10 minutes of entering the starch entirely gets converted into the oligosaccharide mostly maltose.
Intestinal brush border enzymes further digest these products and produces monosaccharides. The most important brush border enzymes are dextrinase and glucoamylase which acts on oligosaccharide composed of more than three simple sugar and maltase, sucrase and lactase which hydrolyses maltose, sucrose and lactose respectively.
We know that the colon does not secrete digestive enzymes hence the digestion of carbohydrates end in small intestine.

Digestion of proteins :- protein digestion begins in the stomach when the pepsinogen secreted by chief cells gets activated to pepsin . Pepsin requires acidic pH of 1.5 to 2.5.
It cleaves the bonds involving the amino acids, tyrosine and phenylalanine so that the proteins are broken down into polypeptides and small number of free amino acids. Pepsin hydrolyses 10 to 15% of ingested proteins and is inactivated in duodenum due to high pH.
In small intestine trypsin and chymotrypsin secreted by the pancreas cleaves the protein into smaller peptides. The pancreatic and brush border enzyme carboxypeptidase splits off one amino acid at a time from the end of polypeptide chain that has carboxyl group. Aminopeptidase (one amino acid at a time) and dipeptidase liberates the final amino acid products.
Here the digestion of proteins ends.  

Digestion of fats :- The small intestine is essentially the sole site of lipid digestion because pancreases is the only significant source of fat digesting enzymes lipases. Neutral fats like triglycerides and triacylglycerol are most abundant fats in diet because triglycerides and their breakdown products are insoluble in water, fats need special pre-treatment with bile salts.
Triglycerides aggregate to form large fat globules . As the fat globules enters the duodenum they are coated with detergent like bile salts. Bile salts have both polar and non-polar, non-polar part attaches to the fat molecules and polar part allows allow them to repel each other and to interact with water. As a result the fat droplets are pulled off the large fat globules and aqueous suspension of fat droplets is formed. Emulsification does not break the bonds but it reduces the attraction between the fat molecules for wide dispersal. Due to which the more number of triglyceride molecules are exposed to the pancreatic amylase and are completely digested in small intestine
lipases catalyses the breakdown of fats by cleaving off the fatty acid chains which result in free fatty acids and monoglycerides. Fat soluble vitamins does not require digestion.