Question

Where are each of our macronutrients (carbohydrates,proteinsand fats) chemically digested? Where does the process for each of them begin? Also note all locations in the GI tract that these processes continue (until each macronutrient has been broken down into components that our cells can absorb).

Answer 1

Answer:- In the intestine, carbohydrates, proteins and fats are digested where they are broken down into their basic units: carbohydrates within sugars. Proteins formed in amino acids. Fats converted into fatty acids and glycerol.

For carbohydrates:- Carbohydrates continue absorption in the mouth. The salivary enzyme amylase starts breakdown into maltose, a disaccharide, by food starches. No major absorption of carbohydrates takes place as the food bolus passes through the esophagus to the stomach.

Protein digestion occurs through the action of three main enzymes in the stomach and duodenum: pepsin, secreted by thestomach, and trypsin and chymotrypsin, secreted by pancreas.

The digestion of certain fats starts in the mouth, where lingual lipase allows short-chain lipids to break down into diglycerides. The fat found in the thesmall intestine induces the release of lipase from the pancreas and the conversion of fat into fatty acids by bile from the liver.

Fat digestion process:- The first phase in the digestion of triacylglycerols and phospholipids begins in the mouth, as lipids find saliva. First, the physical action of chewing combined with emulsifier activity enables the digestive enzymes to carry out their tasks.The digestion process is initiated by the enzyme lingual lipase, along with a tiny amount of phospholipid as an emulsifier. These actions contribute to greater accessibility of the fats to the digestive enzymes. Consequently, the fats are tiny droplets and detach from the watery ones.

In the stomach, triacylglycerols begin to break down into diglycerides and fatty acids through gastric lipase. Approximately 30 percent of triacylglycerols are converted into diglycerides and fatty acids within two to four hours of eating a meal.The churning and contractions of the stomach help disperse the fat molecules, while the diglycerides produced in this cycle serve as additional emulsifiers. Nonetheless, very little fat digestion occurs in the stomach even in the midst of all this operation.

When the contents of the stomach join the small intestine, a small obstacle is controlled by the digestive system, namely, to integrate the separated fats with its own watery fluids. The barrier is overcome by bile. Bile contains cholesterol-derived bile salts, lecithin, and substances and it functions when an emulsifier.It attracts and keeps on to fat while at the same time being attracted to and held on by water. Emulsification raises over a thousand times the surface area of lipids, rendering them more available to the digestive enzymes.

Fat-breaking enzymes work on triacylglycerols and diglycerides to extract fatty acids from their glycerol foundations while emulsifying the stomach contents. While pancreatic lipase enters the small intestine, it breaks down the fats into free fatty acids and monoglycerides.

Protein digestion process:- Protein digestion starts in the stomach with an enzyme action that we have heard about pepsin before. Pepsin is the stomach's active enzyme which digests proteins. Once pepsin acts on the protein molecule it breaks the bonds called peptide bonds which hold the protein molecule together.
So, you might think of pepsin as the enzyme breaking peptide bonds. If these bonds are broken you get amino acid chains, or polypeptides, linked together. Because we know that the prefix ' poly' means' many,' we can easily recall that many amino acid units are joined together by a polypeptide.Those polypeptides then pass into your small intestine, where additional enzymes can complete digestion.

Pancreatic enzymes that we previously heard about in the small intestine, including trypsin, chymotrypsin, and carboxypeptidase, really go to work breaking down the polypeptides. Such enzymes enter through the pancreatic duct into the duodenum.Such pancreatic enzymes are assisted by the enzymes on the brush line. We have learned previously that the brush line enzymes are special enzymes found on the small intestine microvilli which complete digestion.

The peptide bonds holding together the polypeptides tend to hydrolyze, or break down, resulting in smaller units called peptides. Peptides are simply defined as two or more bonded amino acids. Enzymes continue to break down amino acids into polypeptides and peptides.Since amino acids are very small, they can be absorbed into your bloodstream through the lining of the small intestine.

The cycle of digestion of carbohydrates:- The mechanical and chemical digestion of carbohydrates begins in the mouth. Chewing, also known as mastication, crumbles foods made from carbohydrates into smaller and smaller parts. In the oral cavity the salivary glands secrete saliva that coats the particles in the food. Saliva produces the amylase enzyme, salivary.This enzyme breaks the bonds between disaccharides, oligosaccharides, and starches, which are monomeric sugar units. The salivary amylase breaks down amyloseand amylopectin into smaller glucose chains, called maltose and dextrins. What improves their sweetness is the increased concentration of maltose in the mouth that results from the mechanical and chemical breakdown of starches in whole grains.Just about five per cent of starches in the mouth are broken down. (This is a good thing as more glucose in the mouth will result in more tooth decay.) Once carbohydrates enter the stomach no further chemical degradation occurs because the amylase enzyme does not work under acidic stomach conditions.But there is continuing mechanical breakdown— stomach's powerful peristaltic contractions mix the carbohydrates into the more standardized chyme mixture.

The chyme is slowly released into the upper part of the small intestine. After entry of the chyme into the small intestine, the pancreas releasespancreatic juice is released through a channel. This pancreatic juice contains the enzyme, pancreatic amylase, which starts breaking up dextrins into shorter and shorter carbohydrate chains once again.Hence the intestinal cells that hold the encoded villi enzymes. Collectively known as disaccharidase, these enzymes are sucrase, maltase, and lactase. Sucrase breaks up sucrose into the glucose and fructose groups.Maltase breaks the bond between the two units of maltose glucose and the bond between galactose and glucose is broken by lactase. When carbohydrates are chemically broken down into single units of sugar, they are then transported into the intestinal cells within.