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The Kidney

The kidney is one of the organs in the body. It carries out the following functions:

  • Removal of metabolic wastes that is excretion
  • Regulate the concentration of blood plasma and tissue fluid that is osmoregulation.
  • Regulation of ions in the body
  • Regulation pH of blood.

You have learnt that active transport and diffusion are two physiological rocesses by which the body absorbs materials. In this lesson you will learn how the kidney tubules reabsorb materials.

The illustration shows the structure of the human kidney

The kidney receives oxygenated blood through the renal artery. This blood is also rich in waste products of metabolism.

Enlarged section through the kidney showing nephrons

A branch of the renal artery, the afferent arteriole, carries blood into a capsule of the nephron called the bowman capsule. Here it branches and forms a ball-like structure of cappillaries called glomerulus. These rejoin to form the efferent arteriole that leaves the bowman capsule. The afferent arteriole that gets into the bowman capsule has a wider lumen than the efferent arteriole leaving it. This causes blood pressure to build up in the glomerulus.The high pressure forces the fluid part of the blood and materials of small sizes into the Bowmans capsule. This fluid is called glomerular filtrate. It contains water, urea, glucose, amino acids and salts. Large sized molecules are not filtered. They remain in the blood vessels. These include plasma proteins and blood cells.