Humans have two kidneys at the back of the abdomen. Each receives blood from a renal artery, a branch of the aorta, and returns it through a renal vein to the vena cava. Urine leaves each kidney through a ureter to the bladder, and is released through the urethra.A kidney cut lengthways shows three regions:• the outer cortex, containing the Bowman's capsules and convoluted tubules
• the inner medulla, containing the loops of Henle and collecting ducts, arranged in cone-shaped pyramids
• the renal pelvis, a cavity that collects urine and leads into the ureter
2. proximal convoluted tubule, where most useful substances are reabsorbed
3. loop of Henle, with a descending and an ascending limb dipping into the medulla, which creates a high solute concentration in the medulla
4. distal convoluted tubule, where ion concentrations and pH are adjusted
5. collecting duct, shared by several nephrons, where water is reabsorbed as required before urine passes to the pelvisBlood reaches the glomerulus in an afferent arteriole and leaves in a narrower efferent arteriole, which then branches into capillaries around the tubules so that reabsorbed substances can return to the blood.So the kidney works in two stages: it filters small molecules out of the blood, then selectively reabsorbs what the body needs.
• the inner medulla, containing the loops of Henle and collecting ducts, arranged in cone-shaped pyramids
• the renal pelvis, a cavity that collects urine and leads into the ureter
2. proximal convoluted tubule, where most useful substances are reabsorbed
3. loop of Henle, with a descending and an ascending limb dipping into the medulla, which creates a high solute concentration in the medulla
4. distal convoluted tubule, where ion concentrations and pH are adjusted
5. collecting duct, shared by several nephrons, where water is reabsorbed as required before urine passes to the pelvisBlood reaches the glomerulus in an afferent arteriole and leaves in a narrower efferent arteriole, which then branches into capillaries around the tubules so that reabsorbed substances can return to the blood.So the kidney works in two stages: it filters small molecules out of the blood, then selectively reabsorbs what the body needs.