Chapter 6- Excretion

6.1 Excretion

Cells produce a range of excretory products (waste materials) that must be removed. Toxic substances must also be removed
Urea is produced in the liver from the breakdown of amino acids. It is carried to the kidneys and filtered into the blood
The kidneys contain filters which allow dissolved materials to pass through under pressure (protein molecules and blood cells are too big)
Useful substances (eg. sugar) and filtered and pass back into the blood. Most filtered water is reabsorbed.
Urine is produced (containing urea, salts, water and chemicals) and is passed down ureters to the bladder for storage
The water and solute balance of the body needs to be kept constant. Water is lost through breathing, sweating and through faeces. When we are short of water, the kidneys reabsorb more water and produce less urine
If kidneys fail, urea, toxins and water build in the blood, and can be fatal
Dialysis machines mimic the role of kidneys (haemodialysis) and treat kidney failure
The patient's blood flows into the machine and dialysis fluid is separated by a membrane, useful substances go in and harmful ones removed from blood
Other treatments include kidney transplant or peritoneal dialysis (where fluid is inserted into the abdominal cavity)

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