Nephrons

structure

glomerulus, Bowman’s (renal) capsule, proximal convoluted tubule, distal convoluted tubule, loop of Henle, collecting duct

glomerulus

‘knot’ of capillaries

tubules function

allow transportation of filtrate to and from the Loop of Henle

collecting duct function

collects urine and passes to the ureter

nephron structure diagram

nephron function

site of 3 processes of the kidneys: ultrafiltration - removing substances from the blood

selective reabsorption - reabsorbing the substances the body needs

urine formation - substances which are not reabsorbed travel as urine along the nephron to the collecting ducts where the waste travels to the bladder

counter current multiplier mechanism

allows concentrated urine to be produced e.g. animals with longer loops of Henle - such as desert animals

in loop of Henle

descending limb - permeable to water. Water leaves the nephron by osmosis and is reabsorbed. As much water as the body needs is reabsorbed here

ascending limb - permeable to ions. Because the tissue around the loop has a high concentration of water, Na+ and Cl- ions diffuse out of the nephron. Concentration of salt in the ascending limb decreases further up the limb. Towards the top, some Na+ and Cl- are actively pumped out of the nephron

distal convoluted tubule - where final reabsorption of ions and water occurs to adjust water balance. ADH has an effect on the amount of water reabsorbed here

where does ultrafiltration occur?

in the renal capsule

ultrafiltration process

blood enters via the renal artery and flow through many capillaries under high pressure (renal capsule)

specialised cells called podocytes make up the basement membrane, leaving small gaps. Here, small molecules and ions are squeezed out of the blood by the pressure and into the nephron. Larger molecules e.g. proteins stay in the blood

where does selective reabsorption occur?

mostly in the proximal convoluted tubule

selective reabsorption process

in the proximal convoluted tubule, simple ions, amino acids and glucose diffuse into the blood via channel proteins

some larger molecules are reabsorbed by endocytosis

loop of Henle is important in reabsorption of water and salt

ADH increases the amount of water reabsorbed in the kidneys. Released from the pituitary gland to maintain homeostasis