Homeostasis: Osmoregulation

Question 1

Draw and label the structure of a kidney.

Answer 1

1. Cortex
2. Medulla
3. Renal artery
4. Renal vein
5. Ureter
6. Bladder
7. Urethra

Question 2

Draw and label the structure of a nephron.

Answer 2

1. The glomerulus
2. The proximal convoluted tube
3. The loop of Henle
4. The distal convoluted tube.
5. The collecting duct

Question 3

Describe how the glomerular filtrate is formed in the glomerulus?

Answer 3

1. The afferent arteriole has a wider lumen than the efferent arteriole, meaning that it has a higher hydrostatic pressure.
2. This forces small molecules like water, oxygen, and carbon dioxide through pores in the capillary endothelium.
3. They are then forced through the basement membrane and pores in the Bowmnes cause and into the tubule. This creates a solution called the glomerular filtrate.
4. Larger molecules like proteins are too big to fit through the pores so they remain in the blood.

Question 4

What happens in the PCT?

Answer 4

1. Glucose is reabsorbed back into the blood via facilitated diffusion and active transport.
2. Water is reabsorbed down a water potential gradient via osmosis.
3. Urea, excess ions and some water remain in the glomerular filtrate.

Question 5

How is the PCT adapted fie transport?

Answer 5

1. They have microvilli to increase the surface area for reabsorption.
2. They have a lot of carrier proteins for active transport and facilitated diffusion.
3. They have a lot of mitochondria to produce ATP and release the energy needed for active transport.

Question 6

How does the loop of Henle maintain a gradient of sodium ions between the medulla and itself?

Answer 6

1. The descending limb is permeable to water and impermeable to sodium ions. This means water can move out of the descending limb and into the medulla via osmosis. The sodium ions stay in the filtrate and build up at the junction between the ascending and descending limb.
2. At that junction, the concentration of sodium ions in the loop of Henle is higher compared to the medulla, so they diffuse out of the loop of Henle and into the medulla.
3. The ascending limb is impermeable to water, so there is no movement of water out of it via osmosis, but sodium ions can be actively transported from the loop of Henle to the medulla.
4. The increase in sodium ion concentration in the medulla decreases the water potential means that water can be reabsorbed by the descending limb and collecting ducts via osmosis.

Question 7

What happens in the DCT and collecting ducts?

Answer 7

Water moves out of the DCT and into the medulla via osmosis. The water is then reabsorbed into the blood via a set of capillaries.

Question 8

What controls the reabsorption of water into the blood in the DCt and collecting ducts?

Answer 8

ADH

Question 9

How does ADH control the reabsorption of water into the blood in the DCT and collecting ducts?

Answer 9

1. The ADH binds to receptors on the cell membrane of cells in the DCT and collecting ducts.
2. This triggers the increased inclusion of aquaporins into the cell membrane.
3. This means the permeability of the walls increases, as more water is reabsorbed into the blood.
4. The urine produced will be more concentrated.

Question 10

What is osmoregulation?

Answer 10

The control of the blood water levels.

Question 11

Why is osmoregulation important?

Answer 11

1. If the water potential of the blood is higher compared to the water potential of cells, then water will move into cells via osmosis, causing them to expand and burst.
2. If the opposite is the case, then water will be moved out of the cells via osmosis, causing them to shrivel up and die.

Question 12

How do osmoreceptors detect a change in water potential?

Answer 12

1. If there is little water in the blood, water will move out of the cells via osmosis, causing the cell volume of the osmoreceptors to decrease.
2. If there is too much water in the blood water will move into the osmoreceptors via osmosis causing the cell volume to increase

Question 13

How is a high water potential detected and brought back to normal levels?

Answer 13

1. The osmoreceptors in the hypothalamus detect an increase in pressure and send an electrical impulse down the sensory neuron to the posterior pituitary gland.
2. The pituitary gland decreases less ADH meaning the walls of the DCT and collecting ducts become less permeable.
3. This means less water is reabsorbed into the blood and the water potential in the blood decreases.
4. The urine produced will be less concentrated.

Question 14

How is a low water potential detected and brought back to normal levels?

Answer 14

1. The osmoreceptors in the hypothalamus detect a decrease in pressure and send an electrical impulse down the sensory neuron to the posterior pituitary gland.
2. The pituitary gland decreases more ADH meaning the walls of the DCT and collecting ducts become more permeable.
3. This means more water is reabsorbed into the blood and the water potential in the blood increases.
4. The urine produced will be more concentrated.