Kidneys,Yum.

This is gonna be a pretty short post coz it's like 9pm and I can't be bothered to cover much.

Okay, first of all, the Kidneys are found in your lower back and are given blood via the renal artery, and blood is taken away by the renal vein.

There are a couple of main parts I need to know for the Kidneys -

I don't really need to know about that Adrenal Gland, but that's the best diagram I can get.

Inside the Medula are these things called Nephrons, where all the bad stuff is filtered out of the blood.

It looks like....

As you can see in the diagram, the Renal artery feeds into the glomerulus, which is a ball of tiny capillaries. The capillaries allow the molecules in the blood to filter out, accept for blood cells and protein, which are too big. Those molecules that have been filtered out go into a cup-sorta-thing called the Bowmans Capsule, and then through a tube that leads to the Loop of Henle.

Coiled around the Loop of Henle are more capillaries which reabsorb the useful stuff in the blood. This blood is 'clean' and can continue its journey through the body. However, stuff that isn't useful, like excess water and urea go into the collecting duct, and then out of the body through the ureter.

The kidneys also help to control the amount of water in the body. There's a special sensor in the brain that detects if the water content is too low. If it is, it sends a message to another part of the brain to start producing ADH (anti-diuretic hormone), which tells the kidneys to reabsorb more water. This means we produce less urine, but what we do produce is very concentrated and dark in colour. This usually happens in warm weather, as we sweat out water.

Something similar happens if there's too much water in the body. The brain is instructed to produce less ADH, so the kidneys stop reabsorbing so much water. This means we produce more urine, which is less concentrated and pale. This happens in cooler weather because we don't sweat.

The end :)