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Homeostasis - kidneys and water balance

Age range 14-16

Kidney - structure and function

Your kidneys are complex organs. They regulate the amount of water lost from the body and get rid of waste products, especially urea. Urea is made when any excess amino acids are broken down in your liver. The amino acids come from protein you have eaten.
About 180 litres of water filters through your kidneys every day, but only about 1.5 litres finally leaves your body as urine.

Where are the kidneys?

Your kidneys are just under your ribcage above the small of your back. The blood arrives through the renal artery and leaves in the renal vein. The kidneys produce urine which is carried to the bladder along the ureter. The urine is kept in the bladder until you urinate. The muscular sphincters relax and let urine out of the body through the urethra. The diagram below shows the structure of the kidneys and their position in your body.

Question 1

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a) What are the main functions of the kidney?

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b) What is the difference in function between the ureter and the urethra?

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c) i. About how much water is processed by the kidney daily?

ii. What percentage leaves the body as urine?

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Amino acid
The small molecules which are built up into long chains to make proteins
Artery
Blood vessel which carries blood away from the heart
Bladder
The muscular organ in which urine is collected and stored
Liver
Large organ in the abdomen which carries out many functions in the body including breaking down excess amino acids and making urea as a waste product.
Organ
A collection of tissues specialised to carry out a particular function in the body
Urea
The poisonous waste compound produced when excess amino acids are broken down in your liver
Ureter
The tube through which urine flows from the kidneys to the bladder
Urethra
The tube through which urine flows from the bladder to the outside world
Urine
The liquid which leaves your body through the urethra. It contains water, salts urea and other chemicals
Vein
Blood vessel which carries blood to the heart