Unit 3 Biology - Kidneys

Key facts for B3 Kidney topic

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The kidneys have 2 jobs:

  • to get rid of toxics waste like urea as well as 
  • to adjust the amount of dissolved ions and water in the blood.

There are 3 stages involved in the kidneys function.

The sites where filtration takes place in the kidneys are called nephrons.

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  • Blood to be filtered is taken to the kidney by the renal artery. It then enters the glomerulus where a high pressure is built up which squeezes small molecules such as water, urea, ions and sugar out of the blood and into the Bowman's capsule, which encases the glomerulus. 
  • There are semi-permeable membranes between the glomerulus and the Bowman's capsule that act as filters, which means than large molecules like protein, platelets and red and white blood cells are not squeezed into the Bowman's capsule.   
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It's important the we don't lose some of the molecules in the liquid that enter the Bowman's capsule. So as the filtrate flows along the nephron useful substances are reabsorbed. However since there is a higher concentration of sugars, water and ions in the nephrons than in the blood, this has to be done by active transport. The filtered blood exits the kidneys through the renal vein.

What is reabsorbed?

  • All the sugars are reabsorbed
  • Sufficient ions
  • Sufficient water 
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Release of waste material

The new filtrate continues out of the nephron, into the ureter and down to be stored in the blood. It's now called urine. 

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Kidney Failure

Some people's kidneys do not work properly. This means that waste products like urea build up in the blood, you lose the ability to control the levels of ions and water in your body - if left untreated this can result in death.

There are 2 ways of dealing with kidney failure. One is to have dialysis: this involves machines doing the job of the kidneys. The other is having a kidney transplant

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How Does Dialysis Work?

  • Dialysis has to be done regularly to keep the concentration of dissolved substances in the blood at normal levels, and to remove waste substances
  • In a dialysis machine the person's blood flows alongside a selectively permeable barrier, surrounded by dialysis fluid. It's permeable to things like ions and waste substances, but not big molecules like proteins (just like the membranes in the kidney). 
  • The dialysis fr
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Kidney Transplants

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Pros and Cons of Kidney Dialysis and Kidney Transp

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