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 by facilitated diffusion and active transport via carrier proteins.
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. Descending limb: The descending limb is permeable to water so water moves out of the tubule and into the medulla via osmosis. The descending limb is impermeable to sodium ions so the concentration of sodium ions increases as you go down the tubule.
2. Ascending limb: It is impermeable to water so no water moves out of the tuble via osmosis. At the start of the limb the contraction of sodium ions is higher in the tubule compared to the medulla so sodium ions move out of the tubke via diffusion. Towards the end of the limb the concentration of sodium ions in the tubule is lower compared to the medulla so sodium ions move out of the tubule and into the medulla via active transport. The sodium ions decrease the water potential of the medulla, which allows water to be reabsorbed into the DCT 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 vesicles containing aquaporins to be inserted into the membrane.
3. This means the permeability of the walls increases, as more water moves out of the DCT and collecting ducts via osmosis and 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 the water potential and send an electrical impulse down the sensory neurone to the posterior pituitary gland.
2. The pituitary gland releases less ADH meaning the inclusion of aquaporins into the cell membranes of the cells of the DCT and collecting duct decreases.
3. This means the membrane becomes less permeable to water and less water is reabsorbed from the filtrate by osmosis.
4. The urine produced will have a larger volume and be more 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 water potential and send an electrical impulse to the posterior pituitary gland.
2. The gland releases more ADH which means more ADH binds to receptors on the cell surface membrane of the cells in the DCT and collecting duct.
3. The cell membrane become more permeable to water so more water is reabsorbed from the filtrate into the blood via osmosis.
4. The urine produced will have a smalle volume and be more concentrated.