Waste substances are either not reabsorbed at all, or only partially reabsorbed. Some molecules and ions are also secreted into the tubule by the epithelial cells and, together with waste products which remain in the filtrate, are excreted in the urine. The following diagram illustrates the blood supply to different parts of the nephron. High pressure within the glomerulus promotes the initial filtration of the blood plasma, and the network of vessels associated with the loop of Henle allows reabsorption of ions and water.
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Both kidneys are bean-shaped and about the size of an adult fist. Blood enters the kidneys through renal arteries. These arteries branch into tiny capillaries that interact with urinary structures inside the kidneys namely the nephrons. Here the blood is filtered. Waste is removed and vital substances are reabsorbed back into the bloodstream. The filtered blood leaves through the renal veins. Each kidney consists of an outer renal cortex, an inner renal medulla, and a renal pelvis.
Blood is filtered in the renal cortex. The renal medulla contains the renal pyramids, where urine formation takes place. A tough, fibrous , connective tissue renal capsule closely envelopes each kidney and provides support for the soft tissue that is inside. In the adult, each kidney is approximately 3 cm thick, 6 cm wide, and 12 cm long.
It is roughly bean-shaped with an indentation, called the hilum , on the medial side. The hilum leads to a large cavity , called the renal sinus , within the kidney.
The ureter and renal vein leave the kidney, and the renal artery enters the kidney at the hilum. The outer, reddish region, next to the capsule , is the renal cortex. This surrounds a darker reddish-brown region called the renal medulla. The renal medulla consists of a series of renal pyramids , which appear striated because they contain straight tubular structures and blood vessels. The kidneys are two bean-shaped organs, each about the size of a fist.
They are located just below the rib cage, one on each side of your spine. Healthy kidneys filter about a half cup of blood every minute, removing wastes and extra water to make urine. The urine flows from the kidneys to the bladder through two thin tubes of muscle called ureters, one on each side of your bladder.
Your bladder stores urine. Your kidneys, ureters, and bladder are part of your urinary tract. Your kidneys remove wastes and extra fluid from your body.
Your kidneys also remove acid that is produced by the cells of your body and maintain a healthy balance of water, salts, and minerals—such as sodium , calcium , phosphorus , and potassium —in your blood. Watch a video about what the kidneys do.
Each of your kidneys is made up of about a million filtering units called nephrons. Each nephron includes a filter, called the glomerulus , and a tubule.
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