Kidneys in Mammals
Kidneys within mammals are responsible for filtering out any harmful or detrimental waste that forms within our bodies and needs to be expelled. Through the use of both active and passive transport of materials within the kidney; blood can be filtered so that the good materials can be separated from the bad materials. Therefore the bad materials can be collected within the bladder and excreted from the body as urine. The main toxin which is naturally formed within the body is Urea and Uric acids. However water and salt concentrations within the body can also be regulated through the kidneys. First of all how does the body form much of these bad materials?
Due to the fact that amino acids cannot be biologically stored by mammals, excess amino acids need to be broken down into components which can either be stored within the organism or excreted. This is how Urea and uric acids come about and is called deamination. Within mammals, deamination takes place within the liver and involves removing Nitrogen from the amino acids. When this occurs, both a carbohydrate (glycogen) and a waste (urea) is formed and are then sent off to the repective parts of the body. Glycogen is stored as a carbohydrate where as urea is excreted from the organism via the urinary tract and the kidneys.
Structure of the Kidney
Commonly referred to as the jellybeans of the body, the two human kidneys are about the size of human fists and rest just below the ribcage on either side of the spinal column. The Renal artery delivers blood to the bean like structure while the Renal vein takes blood back to the heart. Another tube by the name of the Ureter takes the fluid of bad materials (urine) which the kidney has formed, away from the main organ towards the bladder. The inside of the kidney is composed of three main sections. The Pelvis (middle) a white structure for the collection of urine. The Medulla (one 'layer' out from the pelvis) which consists of several lobes lying around the circumference of the pelvis. The cortex is the most-red layer of the kidney (two 'layers' out from the pelvis) which is red due to the vast network of capillaries which it contains. Millions of tiny structures called nephrons can be found within both the Medulla and Cortex layers of the kidney. These are the places where material exchange occurs between the blood and forming urine. The majority of the nephron lies in the cortex, wrapped around capillaries which includes much of the Renal Capsule (consisting of Bowman's Capsule and the Glomerulous), the Proximal Convoluted tuble and the Distal Convoluted Tubule. The Loop of Henle dips down into the Medulla connecting both convoluted tubules while the collecting duct which travels from the Distal Convoluted Tubule to the pelvis, generally lies in the Medulla. As blood travels along the capillaries near the nephron, passive and active transport occurs between the nephron tubules and capillaries.