Urine formed through a combination of three basic process namelly; Glumerulus Ultra filtration， Selective Reabsorption，Selective secretion. These proceses described as shown bellow:-
1. Glumerulus Ultrafiltration
Glomerulus filtrate is the filtration of materials under high pressure due to the narrowness of blood capillaries. Blood pressure force water and many solutes from the blood vessels in the glomerulus into Bowman’s capsule. In filtration small molecules such as water, mineral salt (Na+, Cl-), glucose, amino acid, urea, uric acid, vitamin are allow to pass through the bowman’s capsule while large molecule such as Red blood cells, blood platelets, blood plasma are not filtered because the wall of the capillaries of glucose and bowman’s capsule have very small pore.
2. Selective Reabsoption; Selective reabsoption is the process whereby the essential components are reabsorbed back into the blood vessels, e.g. glucose, water,sodium. Most of water is reabsorbed in the collecting duct (it function as water conservation device). Water reabsorption takes place in the hypothalamus of the brain by detection of osmorecptor when the blood plasma becomes too concentrated.
When this happens , the hypothalamus signal the pituitary gland to release antidiuretic hormone (ADH) which make the distal convoluted tubule and collecting duct in the nephron more permeable so more water is reabsorbed into the blood. If the blood plasma is too dilute, the osmoreceptor in the hypothalamus part of the brain prevent the releasing of the ADH and cause distal convoluted tubule and collecting duct become less permeable to water, more dilute urine is produce.
The kidney regulate the blood salt under the influence of the hormone aldosterone, if the level of salt (Na+) decrease in the blood result in the releasing of aldosterone hormone to regulate the amount of salt in the blood and this hormone stimulate the distal convoluted tubule and collecting duct to reabsorbed Na+.
3. Tubular secretion; This is the active transport of unwanted substance from the blood into the distal convoluted tubule. The substance such as uric acid, hydrogen ion, ammonia and penicilium are eliminated from the tissue to the tubular, in the tubular in the region called distal tubule and removed as urine.