Introduction and definition of terms:
The kidneys are the main organs in the urinary system. They filter waste products out of blood from the renal artery. These are then excreted. Useful solutes are reabsorbed into the blood. They also have a major homeostatic role in the body, and help to control the water content (osmoregulation) and pH of the blood.
Homeostasis is the maintenance of a constant internal environment within a living organism.
Excretion is the removal from the body of waste products made in the cells during metabolism.
Osmoregulation is the homeostatic control of body water. Water intake needs to balance with water loss.
Urea is instantly converted …show more content…
This is joined to a collecting duct, which carries urine through the medulla to the pelvis of the kidney.
Each Bowman's capsule is supplied with blood by an afferent arteriole. It branches inside the Bowman's capsule to form a knot of capillaries, the glomerulus. These join up again to form the efferent arteriole, which take blood away from the Bowman's capsule. The afferent arteriole is much wider than the efferent arteriole; this means that pressure is built up.
Ultrafiltration involves the filtering (under pressure) of small molecules out of the blood and into the Bowman's capsule. The blood entering the glomerulus is separated from the space inside the Bowman's capsule, by two cell layers and a basement membrane.
* The first layer is the endothelium of the capillary. In the glomerulus, this single layer of cells has thousands of gaps.
* The basement membrane between the two cell layers is composed of glycoprotein and collagen fibres. Its mesh-like structure acts as the filter during ultrafiltration.
* The second layer makes up the wall of the Bowman's capsule. …show more content…
This is facilitated diffusion. All this results in the surrounding blood having a relatively high solute concentration. So a large amount of water passes out of the filtrate in the proximal convoluted tubule, back into the blood by osmosis.
Reabsorption of water in the loop of Henle and collecting duct:
The loop of Henle is a hairpin loop that runs deep into the medulla and then turns and goes back to the cortex again. The function of the loop of Henle is to create an area of high solute concentration deep in the medulla. The collecting duct of each nephron pass through this area and so a lot of water can be reabsorbed from the collecting ducts by osmosis. Concentrated urine can be produced as a result. The ascending limb is more permeable to salts and less permeable to water. As the filtrate moves up, sodium and chloride ions move out passively at first and are actively pumped out of into the surrounding tissue. This causes water to pass out of the descending limb by osmosis. As a result the filtrate becomes more concentrated as it passes down