Absorption, Assimilation and Egestion MCQ - Practice Questions & Answers

Quick Facts

Absorption of Digested Food

Absorption is the process by which the end products of digestion pass through the intestinal mucosa into the blood or lymph.
It is carried out by passive, active or facilitated transport mechanisms.
Small amounts of monosaccharides like glucose, amino acids and some electrolytes like chloride ions are generally absorbed by simple diffusion.
The passage of these substances into the blood depends upon the concentration gradients.
However, some substances like glucose and amino acids are absorbed with the help of carrier proteins.
This mechanism is called facilitated transport.
Transport of water depends upon the osmotic gradient.
Active transport occurs against the concentration gradient and hence requires energy
Various nutrients like amino acids, monosaccharides like glucose, electrolytes like Na+ are absorbed into the blood by this mechanism.
Fatty acids and glycerol being insoluble, cannot be absorbed into the blood.
They are first incorporated into small droplets called micelles which move into the intestinal mucosa.
They are re-formed into very small protein-coated fat globules called chylomicrons which are transported into the lymph vessels (lacteals) in the villi.
These lymph vessels ultimately release the absorbed substances into the bloodstream.
Absorption of substances takes place in different parts of the alimentary canal, like mouth, stomach, small intestine and large intestine.
However, maximum absorption occurs in the small intestine.

Summary of Absorption in Different Parts of the Digestive System:

Assimilation and Egestion

The absorbed substances finally reach the tissues which utilise them for their activities.
This process is called assimilation.
The digestive wastes, solidified into coherent faeces in the rectum initiate a neural reflex causing an urge or desire for its removal.
The egestion of faeces to the outside through the anal opening (defaecation) is a voluntary process and is carried out by a mass peristaltic movement.