Digestion, absorption and assimilation of carbohydrates, lipids and proteins

Digestion, Absorption and Assimilation of Carbohydrates

Carbohydrates, once ingested, begin their digestion in the mouth where the enzyme amylase (produced by saliva glands) begins to break down starch into maltose, a simple sugar.
In the small intestine, pancreatic amylase continues the breakdown process, converting remaining starch into maltose.
The maltose then gets broken down into glucose by the enzyme maltase. This reaction occurs in the lining of the small intestine.
Glucose, a monosaccharide, is then absorbed through the wall of the small intestine via active transport.
Absorbed glucose is then transported via the bloodstream to cells throughout the body where it is assimilated and used as an energy source.

Digestion, Absorption and Assimilation of Lipids

Lipids or fats are primarily digested in the small intestine.
In the presence of bile, ingested lipids are emulsified or broken down into tiny droplets. This increases the surface area for lipase, a pancreatic enzyme, to work on.
Lipase then breaks these droplets down into glycerol and fatty acids.
These components are absorbed by the villi in the small intestine and transported to the cells of the body via the lymphatic system. There they are reassembled into fats and used for storage, insulation, or energy production.

Digestion, Absorption and Assimilation of Proteins

Proteins are digested primarily in the stomach and small intestine.
In the stomach, pepsin works in the highly acidic environment (enabled by gastric juice) to break down proteins into smaller chains known as polypeptides.
Polypeptides then reach the small intestine, where pancreatic enzymes such as trypsin convert them into even smaller peptides.
These peptides are then broken down into individual amino acids by dipeptidases which are located in the cells of the intestinal lining.
Once they are in the form of single amino acids, they can be absorbed through the small intestine wall via active transport and then transported via the bloodstream to cells.
Cells use these amino acids to build their own specific proteins for structure and function in a process known as protein synthesis.