How the body loses water, filtration and selective reabsorption, the role of ADH, and how dialysis compares with a kidney transplant. Biology only content.
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1.Why must water content of the body be controlled?
If cells lose or gain too much water by osmosis they do not function efficiently, and may shrink or burst.
2.Name three ways water is lost from the body.
Through the lungs when breathing out, through the skin in sweat, and in urine from the kidneys.
3.Which water losses cannot be controlled?
Loss through the lungs and through sweating. Only the loss in urine is controlled.
4.What else is lost in sweat besides water?
Ions such as sodium and chloride.
5.What is the function of the kidneys?
To produce urine by filtering the blood and selectively reabsorbing what the body needs.
6.What is filtration in the kidney?
Blood is filtered under pressure so that water, glucose, ions and urea pass out of the blood, while proteins and blood cells stay behind.
7.What is selective reabsorption?
Useful substances are taken back into the blood from the filtrate, including all the glucose and the right amounts of water and ions.
8.Why is all the glucose reabsorbed?
Glucose is needed for respiration, so none of it should be wasted in urine.
9.What is left in the urine after reabsorption?
Excess water, excess ions and urea.
10.Where does urea come from?
The liver breaks down excess amino acids into ammonia, which is converted into urea.
11.What is deamination?
The breakdown of excess amino acids in the liver, producing ammonia.
12.Why is ammonia converted into urea?
Ammonia is toxic, so it is converted into the far less toxic urea for safe transport and excretion.
13.Which hormone controls water reabsorption?
ADH, antidiuretic hormone.
14.Which gland releases ADH?
The pituitary gland.
15.What happens if the blood is too concentrated?
More ADH is released, so the kidney tubules become more permeable and more water is reabsorbed into the blood.
16.What happens if the blood is too dilute?
Less ADH is released, less water is reabsorbed, and a larger volume of dilute urine is produced.
17.Why is ADH control described as negative feedback?
A change in the water content of the blood triggers a response that reverses it and returns the level to normal.
18.What happens if a person's kidneys fail?
Waste substances build up in the blood and they will die unless treated by dialysis or a transplant.
19.How does dialysis work?
Blood flows between partially permeable membranes surrounded by dialysis fluid, so waste and excess substances diffuse out while useful ones stay.
20.Why does dialysis fluid contain glucose and normal ion levels?
So there is no concentration gradient for glucose and useful ions, and they are not lost from the blood.
21.Give two disadvantages of dialysis.
It must be done regularly for several hours at a time, and it restricts diet and normal life between sessions.
22.Give an advantage of a kidney transplant over dialysis.
The patient can lead a normal life without regular treatment sessions.
23.Give two disadvantages of a kidney transplant.
Donor organs are in short supply, and the kidney may be rejected so immunosuppressant drugs must be taken.
24.Why might a transplanted kidney be rejected?
The immune system recognises the antigens on the donor organ as foreign and attacks it.
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