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Kidneys Relating Structure to Function
There are two pairs of kidneys located in the abdominal cavity (small of the back) • They are dark red organs shaped like kidney beans. • The right kidney is slightly lower than the left kidney because of the large area occupied by the liver • Each kidney is supplied with oxygenated (dirty)blood by the renal artery. Deoxygenated (clean) blood leaves via the renal vein.
Cortex Medulla Pyramids Pelvis Renal Vein Renal Artery Ureter
Internal Structure • A longitudinal section through the kidney shows several layers: • A thin outer fibrous layer which is protective • Beneath this layer lies the cortex a smooth textured layer (location of the Bowman’s capsule) • Under the cortex is the medulla. Within the medulla are the triangular structures termed the pyramids. They are striated in appearance. Striations are due to the presence of straight tubules) • All these tubes drain into the renal pelvis, situated on the concave side of each kidney.
The nephron is a long tube which runs from the cortex into the medulla and back again before joining another tube called the collecting duct. • The nephron starts as a small cup shaped structure called the Bowman’s capsule (found in the cortex) • Leading from the capsule is the proximal convoluted tubule. • It descends as the loop of Henle and then doubles back into the cortex to become the distal convoluted tubule.
Ultra filtration • The afferent arteriole has a larger diameter (bore) than the efferent arteriole this offers resistance to the flow of blood. • The blood pressure in the glomerulus is higher than the renal artery. • The membranes of the glomerulus and Bowman’s capsule are permeable to small molecules and ions but impermeable to large protein molecules and red blood cells. • This forces some of the plasma and all the substances dissolved in it into the kidney tubule.
Osmoregulation • This is the regulation of the concentration of blood plasma and body fluids. • Organisms gain water in several ways: • By osmosis • In food and drink • As a product of respiration • Organisms loose water in several ways; • In urine • By evaporation • By osmosis • Exhaling