K IDNEY STRUCTURE

T HE NEPHRON Nephron begins as a bowman's capsule in the cortex and leads to a highly coiled proximal convoluted tubule. This leads to the u shaped loop of henle which is in the medulla the ascending limb of the loop of henle leads to the distil convoluted tubule in the cortex which leads to the collecting duct.

U LTRA FILTRATION Blood flows into the glomerulus from the afferent arteriole the afferent arteriole is wider than efferent arteriole. Ensures blood in glomerulus is under increased pressure- higher than in the Bowman’s capsule providing the necessary hydrostatic filtration pressure. The filtration membrane is the basement membrane of glycoprotein's surrounding the endothelium and capillaries the inner layer of the bowman's capsule consists of podocytes which provide support for the membrane. Water and crystalloid solutes including urea are filtered from the blood into the bowman's capsule. Cells platelets and proteins with a molecular mass greater than do not pass through the undamaged filtration membrane. Hormones in the blood pass into the filtrate which allows urine analysis to test for pregnancy or misuse of anabolic steroids.

S ELECTIVE REABSORPTION Glucose, amino acids, vitamins and some ions are reabsorbed by the proximal convoluted tubule. Sodium ions are actively transported out of the PCT cells through the plasma membranes next to blood capillaries, so sodium diffuses into the cells from the filtrate via co transporter proteins, bringing glucose into the cells with the sodium ions. The PCT cells have microvilli to give a large surface are of contact with the filtrate and many mitochondria to provide ATP for active transport. Ions are absorbed from the filtrate by distil convoluted tubule cells

O VERVIEW OF THE NEPHRON

O SMOREGULATION The walls of the collecting duct can be made more or less permeable according to the needs of the body anti diuretic hormone from the posterior pituitary gland the collecting duct wall is more permeable to water which passes out of the filtrate by osmosis, the release of ADH is triggered by osmoreceptors in the hypothalamus. When there is little ADH present the collecting duct wall is impermeable to water