DIGESTION IN HUMANS

 

 DIGESTION IN HUMANS

Digestion is the breakdown of complex food substances into simpler ones that the body can absorb.

There are five main stages involved in digestion. These are

Ø  Ingestion: The introduction of food into the body through the buccal cavity (mouth)

Ø  Digestion: The breakdown of complex food into simpler ones

Ø  Absorption: The movement of digested food into the bloodstream

Ø  Assimmilation: The use of digested food by the body and

Ø  Egestion: The removal of undigested food from the body.

DIGESTION AS IT OCCURS AT EACH PART OF THE BODY

Mouth: In the mouth, there are a lot of activities that go on. The teeth grinds food, the saliva softens it, the tongue rolls it into bolus for easy swallowing. The saliva is produced in the salivary glands. It contains the enzyme salivary amylase (ptyalin) which converts starch into maltose.

Oesophagus: Food is pushed through the gullet into the stomach through contraction and expansion (peristalsis)

Stomach: The stomach is a muscular sac that stores food for some time. In the stomach, the gastric gland secrets gastric juice that contains hydrochloric acid. The hydrochloric acid – Kill germs, stops the work of ptyalin and provides an acidic medium for rennin and pepsin to work. In the juice, the enzyme pepsin begins the digestion of proteins. It converts proteins into polypeptides. Rennin (found in infants) cuddles milk (convert it into caseinogens).

NB: Food remains in the stomach for 3 to 4 hours. (Food turns into chyme)

Duodenum: The duodenum is the first part of the small intestines. The liver and pancreas are attached to the duodenum. The liver produces bile – a liquid to emulsify fats – and it is stored by the gall bladder. The gall bladder release this fluid into the duodenum to emulsify fats (turn fats into tiny fatty droplets)

The pancreas produces pancreatic juice that contains the enzymes pancreatic amylase – converts extra starch into maltose, trypsin – converts proteins into polypeptides and polypeptides into peptides, and lipase for digestion of fats and oils into fatty acids and glycerol. Food in the small intestine is known as chyle

Illeum: This is the final place for digestion. In the ileum, the Succus entericus (intestinal juice) secreted by the intestinal glands contains the following enzymes – Lipase, Maltase – converts maltose into glucose, lactase – converts lactose into glucose and galactose, sucrase – converts sucrose into glucose and fructose, erepsin – converts peptides into amino acids. At the end, fatty acids, glycerol, glucose and amino acids are absorbed along with vitamins, minerals and water into the bloodstream. This is done through simple diffusion through the villi – (villus sing) a finger likeprojections in the ileum.

Large Intestine: The large intestine is made up of the colon, appendix, caecum and rectum.

Most of the liquid part of the undigested food is absorbed in the colon and caecum leaving a semi solid substance known as faeces. This is stored in the rectum. They are periodically released through the anus. This process is called egestion.