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Amino acid

The basic building blocks of proteins. There are twenty amino acids used, in different combinations, to make every protein required by the human body.


The tube through which urine flows from the bladder to the outside world.


The muscular organ in which urine is collected and stored.


Blood vessel(s) which carries blood away from the heart


The tube through which urine flows from the kidneys to the bladder.


A large organ in the upper abdomen which manufactures, stores and breaks down substances as required by the body


Blood vessel which carries blood to the heart

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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