The kidney

What are the main functions of the kidneys?

• Removal of urea (from excess amino acids).

• Regulation of ion concentration (e.g., sodium, potassium).

• Regulation of water content (osmoregulation).

What is urea and how is it made?

Urea is a waste product from the breakdown of excess amino acids in the liver (deamination).

How is urea removed from the body?

Carried in the blood → filtered in kidneys → excreted in urine.

What are the functional units of the kidney?

Nephrons.

What are the main stages in a nephron?

1. Ultrafiltration → blood is filtered under pressure in the glomerulus.

2. Selective reabsorption → useful substances (glucose, ions, water) reabsorbed in tubules.

3. Excretion → excess water, ions, and urea form urine.

What is osmoregulation?

The control of water balance in the body.

Which hormone controls water balance?

ADH (Antidiuretic Hormone) from the pituitary gland.

How does ADH affect the kidney?

Increases the permeability of kidney tubules so more water is reabsorbed into the blood.

How is ADH controlled?

By negative feedback:

• Too little water → more ADH → more reabsorption → concentrated urine.

• Too much water → less ADH → less reabsorption → dilute urine.

What are the two main treatments for kidney failure?

Dialysis and kidney transplant.

How does dialysis work?

Blood is passed through a dialysis machine where waste products and excess ions diffuse into dialysis fluid.

What are pros and cons of kidney transplants?

• ✅ Long-term solution, no regular dialysis needed.

• ❌ Risk of rejection, immunosuppressant drugs needed, limited donor organs.

Is there a required practical on the kidney?

No direct kidney RP, but kidney knowledge links to osmosis practicals (potato in solutions).