The kidneys filter out waste and control the balance between salts and acids within the body. Blood enters the kidneys through the renal artery and waste products are filtered out. The blood leaves the kidneys through the renal vein. The waste products leave the kidneys through the ureter. The ureter empties into the bladder. This link explains how the kidneys work - there are also some diagrams and videos. http://www.kidney.org.au/kidneydisease/howourkidneyswork/tabid/590/default.aspx (Will add to this as I go.) Wallflower
The kidney contains more than a million nephrons. Nephrons remove waste from the body. They also retain substances that are useful to the body - i.e. the body reabsorbs these substances. The nephron contains the glomerulus and a collection of tubes. The glomerulus is a system of intertwined capillaries. The glomerulus sits in the bowman's capsule (shaped like a cup.) The bowman's space is the area between the bowman's capsule and the glomerulus. Fluid that has passed through the glomerulus (the capillaries) collects in the bowman's space. This fluid is called filtrate. After leaving the glomerulus, the filtrate fluid passes through 4 parts of the nephron. Wastes are removed and useful substances are reabsorbed. The proximal convoluted tubule reabsorbs useful substances. The Loop of henle regulates the concentration of urine. The Distal convoluted tubule controls sodium, potassium and pH. The collecting duct controls water and sodium reabsorption. (See 3rd diagram in the link below - black and white image) http://anatomynotes.hubpages.com/hub/The-Urinary-System-How-the-Nephron-Works-in-Urine-Formation Wallflower
http://en.wikipedia.org/wiki/Metanephros I was doing some research last night on the development of the kidneys in human embryos. I was surprised to learn that the kidneys do not develop in the same manner as other major organs. For example, the brain that develops in the embryo, is the same organ that continues to grow into adulthood. This is also the case with the heart and other organs. According to the sites that I read, the kidneys do not develop like that. There is a first "version" (for want of a better word) and a second "version" before the embryo develops the kidney that will grow into adulthood (the third "version.") Pronephros - this is the first "version." It is a duct or tube. As the second "version" develops, this first one degenerates as the embryo continues to grow. Mesonephros - this is the second "version." It consists of a tube and a system of many vessels. This structure also links up to the blood supply - it is attached to the aorta (largest artery in the body) through smaller blood vessels. Metanephros - this is the third "version." A stalk grows out from the tube - this is called the "ureteric bud." The ureteric bud continues to grow and becomes the ureter (the tube that connects the kidney to the bladder.) The ureteric bud continues to grow further and forms the kidney that grows into adulthood. I was quite blown away (an expression meaning "to be amazed") by this. Curl my hair!!!!!! Wallflower
Forgot to add this scripture in the previous post: Psalms 139:13-16 - "For you yourself produced my kidneys; You kept me screened off in the belly of my mother. I shall laud you because in a fear-inspiring way I am wonderfully made. Your works are wonderful, as my soul is very well aware. My bones were not hidden from you when I was made in secret, when I was woven in the lowest parts of the earth. Your eyes saw even the embryo of me, and in your book all its parts were down in writing, as regards the days when they were formed and there was not yet one among them."