Egestion

Intoduction

Egestion is the process of elimination of faeces from the alimentary canal is called egestion or defecation. The egestion of feces to the outside through the anal opening (defaecation) is a voluntary process and is carried out by a mass peristaltic movement. In infants, the defecation occurs by reflex action without the voluntary control of the external anal sphincter. 

Nutrition

Nutrition is the sum of all those activities which are concerned with ingestion; digestion; absorption of digested food; oxidation of simple food to produce energy and egestion. The process of nutrition involves following steps:

 I. Ingestion: Intake of food.

II. Digestion: Breaking of complex food components into simple soluble components. 

III. Absorption: Passing of digested food through the wall of the small intestine into the blood or lymph.

IV. Assimilation: Use of simple food components in the synthesis of complex components in different body cells.

V. Egestion: Elimination of undigested food as faeces.

Digestion

Digestion is classified into two main types of the basis of site of digestion of food : 

1. Intracellular digestion 

2. Intracellular Digestion.

The intracellular digestion is more efficient; an alimentary canal shows regional differentiation in which different parts are specialised differently to perform different functions. So showing physiological division of labour.

(a) Ingressive zone. It is involved with intake and mastication of food and includes mouth, lips, buccal cavity, teeth, tongue etc. 

(b) Progressive zone. It is for conduction and early digestion and includes pharynx, oesophagus and stomach.

(c) Degressive zone. It is an area of final digestion and absorption of food. It includes the small intestine. 

(d) Egressive zone. It is to temporarily store the faeces and finally their expulsion to outside through the anus. It includes the large intestine (rectum, anus etc.).

Mechanism of Egestion

It involves the formation of feces, temporary storage and finally expelling out of the body through anus and is called egestion or defecation or evacuation. The undigested food along with water and excess of digestive enzymes enter the large intestine. In man, the caecum is vestigial. Colon absorbs the water and concentrates the undigested food into feces. It also helps in active absorption of Na+ ions and certain drugs.

 Mucus of goblet cells adheres the undigested food particles into faeces. It also transports excess of certain ions like calcium, magnesium, iron and phosphorus from blood into the large intestine to egest out with faeces. The undigested food is moved backward by peristaltic rush movements called bowel movements. The faeces are temporarily stored in rectum where more water is reabsorbed. Expansion of rectum initiates a neural reflex which expels the faeces through the anus and involves the coordinated contraction of muscles of large intestine, abdominal muscles and diaphragm and relaxation of anal sphincters. Egestion is partly voluntary and partly involuntary.

The faeces are formed of water (75%) and solid matter (25%) which is further formed of undigested roughage (30%), fats (20%), inorganic matter (15%), proteins (3%) and bacteria (3%). Brown colour of faeces is due to stercobilinogen and stercobilin.

Biological Significance of Egestion

Waste disposal by unicellular and multicellular organisms is vital to their health and to the continuance of life. Animals must take in (ingest) energy-containing chemical compounds, extract a portion of the energy to power their life processes, and dispose of the unusable material or by-products formed during the energy-extraction process. Egestion is a vital process in humans and animals as it is the means to dispose of the undigested food from the system. 

Egestion Disorders

When the fecal material is delayed over a prolonged period of time, it may harden from water absorption. The evacuation of feces may turn out to be difficult or straining. The condition is referred to as constipation. Conversely, when the fecal material still contains excess liquid when evacuated too fast and frequently the condition is referred to as diarrhea.

Conclusion

Henceforth this unit helps us to learn more about egestion, mechanism and its significance. We learn the difference between excretion and egestion. The process by which metabolic waste products are eliminated (totally or partially) from the body of animals is called excretion. It is different from egestion, which is the discharge of undigested food materials from the body.