Excretory system

EXCRETORY SYSTEM

There are a large number of chemical reactions that take place inside a living body, due to which a variety of waste products are being constantly produced inside.
The process of removal of wastes from the cells of living organisms is called excretion.
The organ system responsible for the removal of wastes is called the excretory system.

Excretion in Animals:

Animal wastes mainly include carbon dioxide (which is formed during respiration), wastes of the digestive system, and other wastes such as urea and uric acid.
Animals such as Amoeba, Paramoecium, Hydra, etc., do not have well-developed excretory system. They get rid of all kinds of body wastes by direct diffusion through the cell membranes.
Animals such as earthworms, insects, and leeches have tubular structures that help to get rid of body wastes.

Excretion in Humans:

(i) Through exhaled air

(ii) Through sweat

(iii) Through the kidney

(i) Through exhaled air:

(ii) Through sweat:

Our skin also acts as an excretory organ.
It has small outer openings called sweat pores.
Our body gets rid of a small quantity of urea, salts, and water through sweat secreted by the sweat glands present under the skin.
Sweating is important because it helps in regulating body temperature.
It helps to keep the body cool by losing body heat, as sweat evaporates off the skin.

(iii) Through the kidney:

A number of nitrogenous wastes such as urea and uric acid are formed inside our body.
Urea is a result of the combination of carbon dioxide and ammonia. It is excreted from the body in the form of pale yellowish- coloured liquid called urine.
Urine contains almost 95% water and rest 5% urea, uric acid, and minerals.
Formation of urine takes place inside the kidneys.
The human excretory system comprises:

A pair of reddish, bean-shaped organs called kidneys

Two tubes called ureters

A urinary bladder that stores urine

A urethra which passes out the urine

Human excretory system

Waste substances present in the blood are removed with the help of the kidney.
When blood enters the kidney, the useful substances are absorbed/filtered back into the blood.
Waste substances get dissolved in water and are removed as urine.
This absorption/filtration is done by the functional unit of the kidney called nephrons.
Urine thus formed is collected through the ureters into the urinary bladder.
Then, urine is passed out from the body through the opening at the end of the urethra.

Dialysis:

Kidneys work in pairs but they are so efficient that even if one is damaged one can lead a healthy life.
In case both the kidneys are damaged, a person can survive with the help of:

regular dialysis

a kidney transplant

Dialysis is a method for removing toxic substances from the blood with the help of a machine when the kidneys are unable to do so.
The dialysis machine is also called an artificial kidney.

Dialysis machine

Blood from an artery of the arm is led through the dialysis machine, where urea and excess salts are removed.
The blood is then led back to the patient's body through a vein.
In a kidney transplant, at least one of the diseased kidneys is replaced with a healthy kidney from a donor.

Excretion in Plants:

Carbon dioxide and oxygen:

Excess water:

Excessive salts:

Salts excreting out in the form of K⁺ ions

If there is a high level of salts present in water or in the soil, these usually get deposited in plants as crystals.

Gums, resins, and latex:

Many older plants get rid of their toxic wastes in the form of gum, resins, and latex.

In fact, we use these secretions to manufacture paints, varnishes, rubber, and adhesives.