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Key Questions:

1. How do osmotic changes in fluids affect red blood cells?
   • If a red blood Cell is placed in water, water enters the Cell by osmosis. Because the membrane is quite weak the Cell will burst as the volume and therefore the pressure in the Cell increases. Red blood Cells shrink when placed in concentrated solutions of sugar as water moves out of them by osmosis.
2. (HT) How does ADH affect the permeability of the kidney tubules?
   • (HT) ADH increases the permeability of the kidney tubules (nephrons), causing them to reabsorb more water.
3. How does water from the lungs leave the body?
   • Water leaves the body via the lungs during exhalation.
4. (HT) What is the role of the hormone ADH?
   • (HT) ADH controls the level of water in the body by acting on the kidney tubules?
5. What is lost from the skin through sweat?
   • Water, ions and urea are lost from the skin in sweat.
6. (HT) How is water concentration controlled by ADH and what is this process controlled by?
   • (HT) ADH is released by the pituitary gland when the blood is too concentrated and it causes more water to be reabsorbed back into the blood from the kidney tubules. This is controlled by negative feedback.
7. Can we control loss through the lungs and skin?
   • There is no control over water, ion or urea loss by the lungs or skin.
8. How are people with kidney failure treated?
   • People who suffer from kidney failure may be treated by organ transplant or by using kidney dialysis. During dialysis ‘dirty’ blood (high in urea) is taken from a blood vessel in the arm, mixed with blood thinners to prevent clotting, and pumped into a dialysis machine. Inside the machine - separated by a partially permeable membrane the blood flows in the opposite direction to dialysis fluid, allowing exchange to occur between the two where a concentration gradient exists.
9. What is lost in urine?
   • Excess water, ions and urea are removed via the kidneys in the urine.
10. What happens to body cells if they lose of gain too much water?
    • If body Cells lose or gain too much water by osmosis they do not function efficiently.
11. (HT) Where do excess amino acids come from and how do we safely get rid of them?
    • (HT) The digestion of proteins from the diet results in excess amino acids which need to be excreted safely. In the liver these amino acids are deaminated to form ammonia. Ammonia is toxic and so it is immediately converted to urea for safe excretion.
12. What is the function of the kidneys?
    • The function of the kidneys is to maintain water balance by reabsorbing water from the blooodstream into the Cells until balance is restored.
13. How do the kidneys produce urine?
    • The kidneys produce urine by filtration of the blood and selective reabsorption of useful substances such as glucose, some ions and water.