Control of blood water potential

Question 1

How does the body respond to a decrease in water potential?

Answer 1

-detected by osmoreceptors in the hypothalamus

-posterior pituitary gland secretes more ADH into the blood stream

-ADH attaches to receptors on the collecting duct

-ADH increases the permeability of the walls of the collecting duct → more water is reabsorbed into the tubules into the medulla and into the blood by osmosis

• (less water in urine) smaller volume of urine, more concentrated

Question 2

Describe the process of ultrafiltration

Answer 2

-the diameter of the efferent arteriole is smaller that the afferent arteriole

-build up of hydrostatic pressure in the glomerulus

-water, glucose and mineral ions are pushed out of the capillary into the renal capsule to form glomerulus filtrate

-through pores in the capillary endothelium, basement membrane and podocytes (act as filters)

-large proteins are too large so aren’t pushed out

-blood leaves via the efferent arteriole

Question 3

Describe the process of selective reabsorption of glucose and water in the PCT

Answer 3

1) sodium ions are actively transported out of PCT cells into the blood in the capillaries

2) due to the concentration gradient, sodium ions diffuse from the lumen of the PCT into the cells lining the PCT carrying a glucose molecule via a co transporter protein

3) higher concentration of glucose in PCT cells which diffuse out the PCT epithelial cells into the bloodstream

4) this is how ALL glucose is reabsorbed

Question 4

What are the adaptations of the proximal convoluted tubule?

Answer 4

microvilli → increase SA for reabsorption
lots of mitochondria → energy for active transport

Question 5

How is a sodium ion concentration gradient maintained in the loop of henle?

Answer 5

1) mitochondria in the walls of the cells provide energy to actively transport sodium ions out of the ascending limb

2) accumulation of sodium ions outside of the nephron into the medulla → lowers WP

3) so water diffuses of the descending limb by osmosis into the medulla then blood capillaries

4) at the base of the ascending limb some sodium ions are transported out by diffusion as there’s a very dilute solution ( high WP) due to all the water that has moved out

Question 6

How is water reabsorbed at the DCT and collecting duct?

Answer 6

1) due to all the sodium ions being actively transported out the loop of henle, when the filtrate reaches the DCT it’s very dilute

2) the filtrate moves into the DCT and collecting duct → this section of the medulla is very concentrated (low WP)

3) therefore water diffuses out the DCT and collecting duct

4) what remains is transported into urine

Question 7

descending limb

Answer 7

walls are much thinner
more permeable to water
water diffuses out into medulla then blood

Question 8

ascending limb

Answer 8

walls thicker
impermeable to water
sodium ions actively transported out nephron into the medulla