Lesson 9: Maintaining water/ nitrogen balance

Question 1

Why is it important (in terms of cells) for the body to keep the level of water in the blood as constant as possible?

Answer 1

• Too little water: cells will lose too much water.
• Too much water: cells will gain too much water.
• If body cells gain/ lose too much water (by osmosis) they do not function efficiently.

Question 2

What are the 3 ways we can lose water (urea, ions) from our bodies?

Answer 2

1.) Water leaves the body via the lungs (during exhalation.)
2.) Water, ions and urea are lost from the skin in sweat.
3.) Excess water, ions, urea are removed via the kidneys in the urine.

Question 3

Can the body control how much water/ ions/ urea are lost through exhalation and sweating? What CAN it control if not?

Answer 3

• There is no control over water, ion or urea loss by the lungs or skin.
• The amount/ volume of ions/ water/ urea released in urine can be controlled depending on the amount of these substances in the body.

Question 4

What happens to the excess of amino acids in the blood after someone has eaten a high- protein meal?

Answer 4

• These amino acids need to be EXCRETED SAFELY.
• Liver: amino acids deaminated to form ammonia.
• Ammonia is TOXIC! and so needs to be immediately converted to urea for safe excretion.

Question 5

How do the kidneys produce urine?

Answer 5

• Filtration of the blood.
• Selective reabsorption of useful substances (ie. glucose, some ions, water.)
• EXCESS ions, EXCESS water and urea are released in urine.

Question 6

What effect does ADH have on kidney tubules?

Answer 6

• If the blood is too concentrated (not enough water), ADH is released by pirturitary gland.
• ADH makes the kidney tubules more permeable - causing more water to be reabsorbed back into the blood from the kidney tubules.

Question 7

How might people with kideny failure be treated?

Answer 7

• Organ transplant
• Using kidney dialysis.

Question 8

How does kidney dialysis work?

Answer 8

1.) Patient’s blood (containing excess ion, urea, excess water) will pass through a semi- permeable membrane.
2.) Urea, ions, water pass through the semi- permeable membrane to the dialysis fluid.
3.) Dialysis fluid contains the NORMAL concentrations for water/ ions but doesn’t contain any urea.
4.) So urea (from the patient’s blood) diffuses into the dialysis fluid - down the concentration gradient.
5.) Excess water and ions (from patient’s blood) will diffuse into the dialysis fluid.
6.) Urea is removed/ concentrations of water and glucose in the patient’s blood will return to normal.

Question 9

Why is dialysis fluid constantly refreshed?

Answer 9

• To ensure there is always a large enough concentration gradient for all of the pateint’s urea/ excess ions and excess water to diffuse from their blood to the dialysis fluid.

Question 10

Give 2 disadvantages of kidney dialsyis.

Answer 10

1.) Expensive in the long-term.
2.) Inconvinient: frequent treatments/ controlled diet.

Question 11

Why does kidney dialysis require a controlled diet?

Answer 11

• To ensure the patient isn’t producing too much urea that would be difficult to remove by dialysis.

Question 12

Give 1 advantage of kidney dialysis in comparison to a kidney transplant.

Answer 12

• There is a large supply of dialysis machines.
• However (TRANSPLANT): there is a shortage of kidney donors.

Question 13

What is a big issue with doing a kidney transplant?

Answer 13

• Their body might reject the organ.
• They have to take immunospressants for their WHOLE lives + immunosupressants are dangerous to use.

Question 14

Give 2 advantages of a kidney transplant.

Answer 14

1.) Allows the patient to lead a normal life.
2.) Only expensive initially.