Kidneys and Kidney Failure

GCSE level Biology. Kidneys and Kidney Failure

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What Do The KIdneys Do?

The Kidneys Act As Filters Which Clean The Blood.

  • They remove Urea.
  • Adjust the Ions in the blood.
  • Adjust the water content of the blood.

-They remove Urea, which is a waste product and is poisonous. It is released into the bloodstream by the liver, and then the kidneys filter it out of the blood, and it is excreted in urine.

-Ions (like sodium) are brought into the body when you eat, and they are aborbed into the bloodstream. unbalanced Ion content can mean that the cells are taking in too much or too little water. Excess Ions are removed by the kidneys. (Some Ions are lost in sweat.)

-Water is lost in URINE, SWEAT, and BREATH. On a cold day (if not sweating) urine will be pale, dilute and there will be more of it. On a hot day (if sweating) there will be less urine, dark and concentrated.

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Ultrafiltration and Reabsorption


A high pressure is built up so water urea ions and sugar are squeezed out of the blood and into the bowmans capsule. Big molecules like proteins and blood cells are not allowed through the membranes. (see back for picture of a nephron.)


As this liquid then flows along the nephron, useful substances are reabsorbed into the blood. These are: sugar (active transport), sufficient Ions (active transport), and sufficient water.

Release of Wastes

The remaining substances continue out of the nephron, into the Ureta, and into the bladder as urine.

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Kidney Failure

If The Kidneys stop Working Properly, you can't control levels of ions and water in the body. There is a treatment, and a cure.


Has to be done regularly, (diagram on back) The dialysis fluid has the same concentration of ions and glucose as healthy blood. Only waste substances diffuse across the barrier. Patients have to have the treatment from three to four times a week, and it lasts for 3-4 hours.


Transplant is the only cure for kidney failure. Transplanted kidneys can come from the living or dead. The donor kidney can be rejected. Tissue types are taken into consideration and imuno- supressent drugs are taken. This means the patient has to be kept in sterile conditions for some time after the operation.

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