The Kidneys

Question 1

How do the kidneys make urine?

Answer 1

By taking waste products (and other unwanted substances) out of your blood.

Question 2

What happens to substances as it passes through the kidneys?

Answer 2

They are filtered out of the blood.

Question 3

What is the process of substances being filtered out of the blood called?

Answer 3

Filtration.

Question 4

What happens after filtration? What is this process called?

Answer 4

Useful substances like glucose, some ions and the right amount of water are then absorbed back into the blood. This process is called selective reabsorption.

Question 5

What substances are removed from the body in urine?

Answer 5

1. Urea
   1) Proteins (and the amino 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 can be stored. This occurs in the liver and involves a process called deamination.
   2) Ammonia is produced as a waste product from this process.
   3) Ammonia is toxic so it’s converted to urea in the liver. Urea is then transported into the kidneys, where it’s filtered out of the blood and excreted from the body in urine.
2. Ions
   1) Ions such as sodium are taken into the body in food and then absorbed into the blood.
   2) If the ion (or water) content of the body is wrong, this could upset 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.
   3) Some ions are lost in sweat. However, this amount is not regulated, so the right balance of ions in the body must be maintained by the kidneys. The right amount of ions is reabsorbed into the blood after filtration and the rest is removed from the body in urine.
3. Water
   1) The body has to constantly balance the water coming in against the water going out.
   2) We lose water from the skin in sweat and from the lungs when breathing out.
   3) 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.

Question 6

What hormone controls the concentration of urine? Where is it released into and by what?

Answer 6

Anti-diuretic hormone (ADH). This is released into the bloodstream by the pituitary gland.

Question 7

How is it known how much ADH is needed?

Answer 7

The brain monitors the water content of the blood and instructs the pituitary gland to release ADH into the blood according to how much is needed.

Question 8

What is the whole process of water content regulation controlled by?

Answer 8

Negative feedback. This means that if the water content gets too high or too low a mechanism will be triggered that brings it back to normal.

1. A receptor in the brain detects that the water content is too high/low.
2. The coordination centre in the brain receives the information and coordinates a response.
3. The pituitary gland releases less/more ADH, so less/more water is reabsorbed from the kidney tubules.