Question

You decide to eat a given food. Discuss the various biological steps that will take place in your body to extract the necessary nutrients like amino acids, glucose, and fatty acids from the food and make them available to the body cells.

Answer 1

The proteins, lipids, and carbohydrates that make up most of the food we eat must be broken down into smaller molecules before our cells can use them. Digestive process starts the moment you chew food, which breaks food into smaller particles by the process of chewing which involves mechanical digestion, carbohydrate digestion begins in the mouth itself, The saliva secreted from your salivary glands moistens food as it's chewed. Saliva releases an enzyme called amylase, which breaks carbohydrates into sugars. Once in your stomach, food stays in the upper portion for only around a half hour so carbohydrates can be further digested by amylase. The digestion of protein starts in the stomach, where HCl and pepsin break proteins into smaller polypeptides. After, the food moves to the lower section of your stomach gastric enzymes can break down proteins, after this  pepsin, hydrochloric acid and stomach movement work together to create chyme, which is moved into the small intestine.

Once the food is in the small intestine, pancreatic amylase digest carbohydrates, after this, the brush border enzyme α-dextrinase starts working on α-dextrin, breaking off one glucose unit at a time.Brush border enzyme involved are,  Sucrase which  splits sucrose into one molecule of fructose and one molecule of glucose; maltase breaks down maltose and maltotriose into two and three glucose molecules, and lactase breaks down lactose into one molecule of glucose and one molecule of galactose.  Chemical digestion in the small intestine is continued by pancreatic enzymes, including chymotrypsin and trypsin, simaltenously the cells of the brush border secrete enzymes such as aminopeptidase and dipeptidase, which further break down peptide chains. This results in molecules small enough to enter the bloodstream. All  lipid digestion occurs in the small intestine, Bile contains bile salts, which act as an emulsifier of lipids. This breaks the large fat droplets into smaller droplets that are then easier for the fat-digesting enzyme pancreatic lipase to digest  Pancreatic lipase breaks down each triglyceride into two free fatty acids and a monoglyceride.

Absorption :  All carbohydrates are absorbed in the form of monosaccharides (glucose). Glucose, are absorbed across the membrane of the small intestine and transported to the liver where they are either used by the liver, or further distributed to the rest of the body, The excess glucose is stored as glycogen by the liver and is released when the body requires it this process is known as glycolysis, some amount of glucose are stored in skeletal muscles and adipose cells and remaining glucose molesules are transported into the bloodstream, glucose is transported by  secondary active transport or facilitated diffusion, remaing carbohydrates which are not absorbrsed moves into large intestine to be expelled out of the body.

Proteins, after they enter the absorptive epithelial cells, they are broken down into their amino acids before leaving the cell and entering the capillary blood via diffusion.

Lipid Absorption, most of the lipids are absorbed in the small intestine. Short-chain fatty acids are relatively water soluble and can enter the absorptive cells (enterocytes) directly, by the process of simple diffusion and moved into the blood stream