1 . Excretion is the process by which waste products and toxic materials are removed from the body of an organism.
2 . Excretory organs:
3 . The urinary system in man:
Fig.9.1 The urinary system in man.
Fig.9.2 The structure of the kidney.
4 . Lungs:
The lungs supply the body with oxygen, but they are also excretory organs because they get rid of carbon dioxide. They also lose a great deal of water vapour, but this loss is unavoidable and is not a method of controlling water content of the body.Kidneys:5. The kidneys remove urea and other nitrogenous waste from the blood. They also expel excess water, salts,
5 . Kidneys:
The kidneys remove urea and other nitrogenous waste from the blood. They also expel excess water, salts, hormones and drugs.
6 . Liver:
The liver breakdown haemoglobin to produce yellow/green bile pigment, bilirubin. Bilirubin is excreted with the bile into the small intestine and expelled with the faeces. The pigment undergoes changes in the intestine and is largely responsible for the brown colour of the faeces.
7 . Skin:
Sweat consists of water, with sodium chloride (salt) and traces of urea dissolved in it. These substances are excreted when we sweat. But, sweating is a response to rise in temperature and not a change in the blood composition. Therefore, skin is not an excretory organ.
8 . Kidney failure may result from an accident involving a drop in blood pressure, or from a disease of the kidneys. A dialysis machine is required to replace the function of the kidneys should the kidneys are damaged.