Answer to Question #182807 in Cell Biology for Ara

Question #182807

For each of the following parts of the digestive system, describe what happens to this type of biomolecule. This may include physical and chemical changes. Name the enzymes which act on this type of biomolecule and tell where the biomolecule gets absorbed into the circulatory system.

Digestive system part Changes to biomolecule? Enzymes present?

Mouth 1. 2.

Salivary gland 3. 4.

Esophagus 5. 6.

Stomach 7. 8.

Gall bladder 9. 10.

Liver 11. 12.

Pancreas 13. 14.

Small intestine 15. 16.

Expert's answer

There are four major bio-molecules in nutrition; they are carbohydrates, lipids, proteins, and nucleic acids. Their availability in the body are of great importance ranging from proper organs function to survival. These biomolecules are availed or assimilated in the body after going through physical and chemical transformation in a process of digestion and absorption.

In the,

(a)  Mouth; mastication or chewing results in the physical breakdown of food by the action of teeth.

(b)  Salivary glands; presence of foods in the mouth triggers the release of saliva (contains mucus) that moistens the food and buffers the PH of the food. It (saliva) contains:

  • Lysozyme; which has antibacterial action.
  • Salivary amylase; converts starch in the food into disaccharides (maltose).
  • Enzyme lipase; produced by the tongue’s lining breaks down fats.

(c)   Esophagus; mainly involved in the movement of food particles from the oral cavity to the stomach by a process known as peristalsis, an involuntary activity triggered by swallowing action. The cardiac sphincter muscles at the stomach end act ac as valves that deters reflux of food. No digestion or enzymatic action takes place in the esophagus.

(d)  Stomach; here, large digestion of proteins takes place. Gastric juices are secreted here. The enzyme pepsin is involved in protein digestion under acidic conditions. Chemical digestion by churning action of the stomach by contraction and relaxation of smooth muscles resulting in “chyme”, a mixture of partially digested food and gastric juices. Small amounts of chyme are released into the stomach at a time; a movement regulated by hormones and muscular reflexes of the pyloric sphincter.

(e)   Gall bladder; a small organ that helps the liver in storing bile and concentration of bile salts which is then released into the small intestines for the digestion of lipids.

(f)   The liver; is the largest internal organ that helps in the digestion of fats and detoxification of blood. It produces bile juice needed for the breakdown of fats in the duodenum. It also processes the absorbed vitamins, fatty acids, and synthesis of protein plasma.

(g)  Pancreas; secretes bicarbonates that help to neutralize the acidic chyme and a variety of enzymes for the digestion of protein and carbohydrates. Such enzymes include:

  • Lipase; breakdown fats.
  • Protease; breakdown proteins.
  • Amylase;  breakdown starch into sugar for energy production.

(h) Small intestines; complete breakdown of fats and carbohydrates. It’s divided into 3 parts i.e. the duodenum, the jejunum, and the ileum. In the duodenum, the chyme mixes with the pancreatic juice, the alkaline solution rich in bicarbonates, that neutralizes the acidity of the chyme. The enzymes in the pancreatic juice, lipase, amylase, protease, help in the digestion of or breakdown of starches, disaccharides, proteins, and fats. Bile produced in the liver, containing bile salts makes the lipids accessible to water-soluble enzymes. The monosaccharides, amino acids, bile salts, vitamins, and other nutrients are absorbed in the (a)  ileum, part of the small intestines, by the cell linings (villi). Undigested food is sent to the colon from the ileum via peristaltic movement.

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