"[These webpages] give a clear explanation on how the polymerase chain reaction works and why it is useful."
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.
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.
b) What is the difference in function between the ureter and the urethra?