The renal artery carries blood into the kidneys, which once there is filtered by nephrons. The waste filtered by these nephrons is combined with water to make urine. As the urine is produced it drains out of a tube called the ureter and collects in the bladder. Once your bladder is about half way fill your body signals you that you have to urinate. The urine exits your body through a tube called the urethra.
So to summarize:
1. Blood flows through renal artery to kidneys.
2. Waste is filtered out of the blood by nephrons.
3. Water is mixed with the waste collected.
4. The result is urine that is drained through the ureter into the bladder.
5. When your bladder is half full your body thinks "pee!"
6. When you pee it exits out your body through the urethra.
Human kidney is an organ which performs many vital functions of the body. The most important of this is the production of urine. This involves separation of and removal of various waste material from the blood. There are a pair of kidneys that lie below the middle of the back on each side of the spine.
The human kidney consists of three layers. In order of their location from outside to inside these are called cortex, medulla, and pelvis. The blood to be purified enters the medula. In medula and cortex the blood arteries carrying the blood branch into increasingly smaller arteries. These arteries lead the blood to tiny blood filtration units called nephrons located at the end of each branch of the arteries. In a normal adult there are about 2 million nephrons capable of filtering about 190 liters of blood daily.
A nephron consists of various parts including parts - a network of tiny blood vessels, the glomerulus, Bowman's capsule surrounding the glomerulus, convoluted tubule, and collecting tuble. Pressure forces much of the fluid portion of the blood (blood plasma) through the glomerulus and into Bowman's capsule. The resulting fluid called tubular fluid, which contains water and dissolved chemicals, then passes into the convoluted tubule. The remaining blood in the glomerulus flows into small vessels called capillaries, which surround the convoluted tubule. As the tubular fluid flows through the tubule, substances needed by the body are absorbed by the cells of the tubule wall. These substances rejoin the blood in the capillaries. The capillaries return the blood to the heart by way of the renal vein.
Substances not absorbed in the tubule are wastes that the body needs to get rid of. These are secreted into the tubular fluid by the tubular cells of the kidney. These various substances, which include ammonia, urea, uric acid, and excess water, make up urine. The urine passes from the convoluted tubules into larger collecting tubules and then into the pelvis layer of the kidney.This urine collects in the bladder to be passed out periodically.
The kidney follows a series of steps to do that. First, the renal artery directs the blood into the kidney. The renal artery divides into smaller branches which have a tiny knot at the end. This knot of vessels is called glomerulus. Surrounding it there is a cup shaped structure called the Bowman's capsule. It is a part of the nephron, which then follows into a series of convoluted tubules, loop of Henle and collecting duct. Due to the pressure in the glomerulus, the blood plasma is caused to leak into the bowmans capsule. All the contents in the blood plasma except the red blood cells and some proteins remain (as they are too big to enter through the small holes). Even the needed substances such as glucose and others also pass into the capsule. This is called ultrafiltration. In the first convoluted tubule, the renal vein absorbs the glucose and then much of the water, and other needy substances. Urea and other nitrogenous waste are not absorbed by the renal vein. It then passes through the loop of Henle (a U shaped structure) into the collecting duct (where much of water is absorbed). The contents in the collecting duct are emptied into the pelvis of the kidney and passes down through the ureter into the uriniary bladder. Then as the spincher muscle relaxes, the urine passes out.