Control of Blood Water Potential

Question 1

What is osmoregulation?

Answer 1

Osmoregulation is the control of the water potential of the blood.

Question 2

What are the key processes in control of blood water potential?

Answer 2

1) Ultrafiltration: formation of glomerular filtrate.
2) Selective reabsorption: reabsorption of useful substances, such as glucose, amino acids and ions.
3) Osmoregulation: reabsorption of water.

Question 3

What is the process of ultrafiltration?

Answer 3

Efferent arteriole is smaller in diameter than the afferent arteriole so the hydrostatic pressure in glomerular capillaries increase. Small molecules are forced through a 3-layer filter into the Bowman’s capsule.

Question 4

What passes through during ultrafiltration?

Answer 4

Glucose, water, urea, amino acids, ions, XS vitamins.

Question 5

What is the process of selective reabsorption?

Answer 5

Co-transport with Na+ ions in the lining of the ileum. This reabsorption lowers the water potential of blood, so water moves out of PCT into the capillaries by osmosis.

Question 6

What is the process of osmoregulation?

Answer 6

1) At the top of the ascending limb, Na+ ions are pumped into the medulla by active transport. The ascending limb is impermeable to water, so water remains in the tubule which lowers the water potential in the medulla.
2) This causes water to move out of the descending limb by osmosis. Descending limb is not permeable to ions so the filtrate becomes more concentrated.
3) At the bottom of the ascending limb, Na+ ions diffuse into the medulla which further lowers the water potential in the medulla.