Egestion is the expulsion of undigested food materials from the body through the anus or cell vacuoles. It is a voluntary movement which takes place in complex species through the anus and through cell vacuoles in simple unicellular organisms. It is often confused with the term excretion, which is the removal of nitrogenous waste from the body via sweat, urine, etc.
Process of egestion in complex species
Substances that cannot be digested pass into the colon, where minerals and ions are reabsorbed. After absorption of nutrients, the leftover food particles are stored in the rectal ampulla. As the food particles, now called faeces, keep collecting in the rectum, the rectal wall expands, and just when there is enough of the faeces, the internal and external sphincters in the anus relax and contract, respectively. This movement sends a signal to the brain, causing an urge to defecate.
In this way, the fecal material keeps collecting in the ampulla, and the next peristaltic movement acts again.
- If the urge to defecate is not acted upon instantly, the fecal material goes back to the colon, where it absorbs more water. The feces hardens and becomes difficult to expel in the next round. This condition leads to constipation.
- Due to malabsorption activities, the feces is sometimes watery and runny, a condition known as diarrhoea.
Process of egestion in simple species
In simple, unicellular organisms such as amoeba, unwanted waste is eliminated by cell vacuoles. They form vacuoles from the unwanted materials and fuse with the cell membrane. The cell membrane then ruptures, throwing out the waste to the outside.
Egestion in plants
Plants do not undergo egestion as they do not have any digestive system. They undergo excretion from stomata and hydathodes.
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What is meant by ingestion and egestion?
Ingestion is the uptake of food, and egestion is the elimination of unwanted food from the body.
What are egestion and excretion?
Egestion is the elimination of unwanted foods, whereas excretion is the removal of nitrogenous waste from the body.
How is egestion done in amoeba?
In amoebae, egestion or the expulsion of unwanted substances takes place through cell vacuoles which attach with the cell membrane and throw the waste out of their body.
What is holozoic nutrition?
Holozoic nutrition is characterised by the internalisation and internal processing of food materials.