Carbohydrate digestion and absorption involve both mechanical (chewing) and chemical (enzymatic) process of digestion.
How carbohydrates are digesting?
Carbohydrates of a monosaccharide group do not require to digest and can be absorbed directly. On the other hand, disaccharides and polysaccharides needs to be digest into simple sugar before it has absorbed by the body.
Carbohydrate digestion in the mouth
The digestion process of carbohydrates begins in the mouth. Chewing (mechanical digestion of mastication) breaks down food into smaller particles followed by bio-chemical (by enzyme amylase or ptyalin secreted by parotid glands) digestion can take place faster and bio-chemical) digestion to break down polysaccharides.
- Teeth help to masticate (by chewing) food into smaller particles that can easily be digested by the enzymes.
- Tongue helps the teeth to grind food into smaller particles and helps to push the masticated food to stomach through the esophagus.
- Salivary gland secretes enzyme amylase, which bio-chemically break down polysaccharides (starch) into disaccharides (maltose).
- Bicarbonate ions in saliva behave as buffer and maintain a pH of 6.5 to 7.5.
- Mucous secreted by the salivary gland helps lubricate and hold masticated foods together in a clump called a bolus.
Stomach Carbohydrate digestion
The enzyme amylase or ptyalin presents in the masticated food from the mouth continue its breakdown of carbohydrate in the stomach, until the stomach pH reaches acidic. Acidic pH deactivates the enzyme amylase.
There is no more digestion of carbohydrate take place in the stomach once the pH reach acidic that deactivates amylase. In the stomach, before the pH becomes acidic almost 35% of the starches (polysaccharides) are broken down into maltose and isomaltose (disaccharide an isomer of maltose).
Small intestine Carbohydrate absorption
The food chyme from the stomach reaches the duodenum for further breakdown and absorption of carbohydrates.
In the duodenum, pancreatic juice is secret and mixes with the stomach chyme. The pancreatic juice contains large quantities of amylase that breakdown polysaccharides into maltose (disaccharides) then break down even further into simple sugars (monosaccharide) by the enzymes in the small intestine cell linings. These simple sugars (glucose, fructose, and galactose) then absorbing by the small intestinal figure like projection called villi.
The absorbed glucose is transport to the liver and further dumped into the blood stream for the body-cells energy needs.
Glucose metabolism by Pancreas
Glucoregulation – Insulin and Glucose level in the body: Gluco-regulation is the regulation of steady levels of glucose in the blood & body. The hormone "Insulin" plays a vital role in the utilization of glucose by the body cells.
Glucose cannot enter the muscle cells, once there is no insulin in the blood stream.
- Once the blood-glucose level rises to certain level
- Then it is a sense by the pancreas, and it starts releasing insulin into the blood stream.
- Once the insulin is available in the blood steam, it is considering as the signal to the muscle’s cells to start absorbing the glucose from the blood.
- Once the blood-glucose level drops below a certain level, then insulin secretion too stopped and the muscle cells to stop absorption of glucose.
- The muscle’s cell start burning the glucose received from the blood for its energy needs.
Glucose Metabolism by the Liver
The glucose absorbed by the small intestine that is taking to be liver via the bloodstream. Liver distribute it to the body cells or stored the unused excess glucose for future requirements. Thus, the liver manages blood-glucose levels to provide sufficient energy for the body cells.
The excess unused glucose is converts to glycogen and stores in the liver in response to the insulin (hormone) this process called glycogenolysis. Likewise, if blood-sugar levels drop between meals or during fasting, the glycogen is converting back to glucose in response to the hormone glucagon. If the stored glycogen level in the liver is exhausted; then the hormone glucagon will trigger the breakdown of amino acids (protein) or glycerol (fats) to form glucose; this process is called gluconeogenesis (a process that results in the generation of glucose from non-carbohydrate source).