kidneys

• kidneys


  filter blood from the renal arteries and produce urine as waste
• how do kidneys make urine?

  by taking waste products out of your blood
• kidney filtration


  substances are filtered out of the blood as it passes through the kidneys
• selective reabsorption


  the absorption of certain selected molecules (such as glucose, some ions and the right amount of water) back into the blood from the fluid in the nephron tubule
• what substances are removed from the body in urine?

  urea, ions and water
• why is urea removed from the body in urine?

  proteins (and the amino acids acids that they are broken down into) can't be stored by the body so any excess amino acids are converted into fats and carbohydrates, which cane be stored - this occurs in the liver and involves a process called deamination. ammonia is produced as a waste product from this process, which is toxic so it's converted to urea in the liver
• why are ions removed from the body in urine?

  ions such as sodium are taken into the body in food and the absorbed into the blood. if the ion (or water) content of the body is wrong, this could displace the balance between ions and water, meaning too much or too little water is drawn into cells by osmosis - having the wrong amount of water can damage cells or mean they don't work as well as normal. some ions are lost in sweat however this amount is not regulated, so the right balance of ions un the body must be maintained by the kidneys - the right amount is reabsorbed into the blood after filtration and the rest is removed from the the body in urine
• why is water removed from the body in urine?

  the body has to constantly balance the water coming in against the water going out. we lose water from the skin in sweat and from the lungs when breathing out. we can't control how much we lose in these ways, so the amount of water is balanced by the amount we consume and the amount removed by the kidneys in urine
• the concentration of urine is controlled by...

  a hormone
• what hormone controls urine concentration?

  anti-diuretic hormone (ADH), which is released into the bloodstream by the pituitary gland
• what happens when more ADH is released?

  kidney tubules reabsorb more water, little urine is produced and blood is returned to normal
• what happens when less ADH is released?

  kidney tubules reabsorb less water, more urine is produced and blood is returned to normal
• what happens if the kidneys do not work properly?

  waste substances build up in the blood and you lose your ability to control the levels of ions and water in your body, eventually resulting in death
• what do dialysis machines do?

  take over the role of failing kidneys and filter the blood
• dialysis treatment


  in a dialysis machine the person's blood flows between the partially permeable membrane, surrounded by dialysis fluid. these membranes are permeable to things like ions and waste substances but not big molecules like proteins (just like the membranes in the kidney)
• dialysis fluid


  the fluid used in dialysis and has the same concentration of dissolved ions and glucose as healthy blood - this means that useful dissolved ions and glucose won't be lost from the blood during dialysis and only waste substances (such as urea) and excess ions and water will diffuse across the barrier
• why must dialysis be done regularly?

  to keep the concentrations of dissolved substances in the blood at a normal level, and to remove waste substances. this often happens around three times a week and take 3-4 hours
• pros of dialysis


  can buy a patient with kidney failure valuable time until a donor organ is found
• cons of dialysis


  - requires carefully controlled diet

  - time consuming

  - may cause blood clots or infections

  - expensive for the NHS to run
• the only cure for kidney failure is...

  to have a kidney transplant
• where do healthy kidneys for kidney transplant come from?

  - people who have recently died and are on the organ donor register/carry a donor card

  - people who are still alive (as we have two kidneys) but there is a risk to the person donating the kidney
• pros of kidney transplant

  - no dialysis

  - liberal diet and fluid intake

  - feel better

  - can work

  - cheaper in the long run than dialysis
• cons of kidney transplant

  - long waiting lists

  - the kidney could be rejected

  - have to take immuno suppresants so you have a weak immune system and get ill often
• what happens when a kidney is rejected?

  the patients body's white blood cells in the immune system starts to attack the transplanted kidney. this happens when your immune system recognises the kidney as coming from a different person and thinks it's a hostile threat. the patient is treated with drugs t prevent this but it can still happen
• who cannot donate kidneys?

  people with heavy alcohol or recreational drug intake, anyone with obesity or serious medical conditions (such as high blood pressure, diabetes or AI