What is Excretion?
Excretion is the process in which nitrogenous wastes are removed from the body. Substances that need to be excreted from the body include nitrogenous wastes, carbon dioxide, water, excess salts, water etc.
Kidneys play a major role in the process of excretion in humans. These are the bean-shaped structures located on either side of the backbone and protected by the last two ribs. Kidneys help in the elimination of wastes from the body in the form of urine.
Apart from kidneys, organs like lungs, liver, skin and sebaceous glands help in excretion.
Sweat glands are long tubular glands and are coiled at the ends. They are located in the dermis of the skin and help in maintaining the temperature of our body. During summers when it is too hot outside, sweat, which is a watery fluid containing lactic acid, urea, sodium chloride etc., is secreted from the sweat glands and helps in cooling of the body.
Our lungs are mainly concerned with respiration, but they help in removal of a large amount of carbon dioxide and water from our body through the air that we expire. Carbon dioxide is a waste product formed due to the oxidation of food. It is carried to the lungs by the blood. So it may also be considered as an organ that is involved in the process of excretion.
Next is the liver, which is the largest gland in our body. It secretes bilirubin, biliverdin, vitamins, drugs etc, which are substances containing bile. Bile pigments are produced by the breakdown of haemoglobin in the worn-out red blood cells in the liver. These are eliminated from the body and the organ thus helps in excretion. Liver also helps in the conversion of ammonia into less toxic urea.
There is another gland called the sebaceous gland, which eliminates substances like sterols, hydrocarbons and waxes through sebum. These glands are attached to the hair follicle.
Our lower intestinal tract also helps in the excretion by removing the waste products of digestion.