Physiology 4

Question 1

what is the main function of the collecting duct?

Answer 1

To concentrate urine by reabsorbing water.

Question 2

Which hormone controls the permeability of the collecting duct?

Answer 2

ADH - vasopressin.

Question 3

where is vasopressin created and stored?

Answer 3

Created - hypothalamus

stored - posterior pituitary

Question 4

What is the half life of vasopressin?

Answer 4

10 minutes

Question 5

What controls vasopressin release?

Answer 5

Osmolarity

Question 6

How is osmolarity levels measured?

Answer 6

via the osmoreceptor cells in the brain

Question 7

What happens in hyperosmolarity?

Answer 7

the osmoreceptors in the brain shrink, sending neurological signals to the hypothalamus to secrete ADH.

Question 8

what happens in hypo-osmolarity?

Answer 8

the osmoreceptors swell, so no signals are sent to produce ADH.

Question 9

how does ADH affect the collecting duct?

Answer 9

It travels through the blood and binds to cAMP on the basal membrane, cAMP then causes vesicles to migrate to the luminal cell membrane where they fuse, they are full of aquaporins, allowing water into the cell and into the interstitium.

Question 10

Where does the water go after the interstitium?

Answer 10

It is reabsorbed by the vasa recta?

Question 11

how many aquaporins are on the basal membrane?

Answer 11

this number is fixed, the water reabsorption is controlled by the vesicle containing aquaporins on the luminal side.

Question 12

What affect does ADH have on urea?

Answer 12

An increase in ADH stimulates reabsorption of urea.

Question 13

How is urea reabsorbed?

Answer 13

The reabsorption of water increases the concentration of the urea in the collecting duct, so it moves out of the collecting duct - down its concentration gradient.

Question 14

How does urea maintain interstitial gradient?

Answer 14

The urea maintains osmolarity, ensuring that water is still reabsorbed.

Question 15

how is urea reabsorbed into the blood?

Answer 15

By the vasa recta.

Question 16

What causes suppression of ADH?

Answer 16

alcohol

Question 17

What causes an increase in ADH?

Answer 17

exercise, stress, pain, morphine

Question 18

Where are the baroreceptors?

Answer 18

in the aortic arch and carotid arteries, they monitor high pressure differences (like blood pressure)

Question 19

Where are the atrial receptors?

Answer 19

In the right and left atria, they are triggered by smaller changes in volume.

Question 20

What happens in decreased ECF volume?

Answer 20

The atrial receptors notice it, they reduce their effect on ADH (which is inhibitory) - this increases ADH release.

Question 21

What happens in increased ECF volume?

Answer 21

The atrial receptors increase firing, this increases the inhibitory effect on ADH.

Question 22

What is diabetes insipudis?

Answer 22

It is a lack of ADH - either ADH production is lacking or the body is insensitive to ADH.

Question 23

What is central diabetes insipidus?

Answer 23

A problem with the production of ADH.

Question 24

How is diabetes insipidus treated?

Answer 24

With ADH supplementation

Question 25

What is peripheral diabetes insipidus?

Answer 25

This is when the body becomes desensitised to ADH

Question 26

How is peripheral diabetes insipidus treated?

Answer 26

Usually by matching the output of urine with an input of water.

Question 27

What happens if theres an increase in osmolarity or decrease in ECF volume (requiring increased ADH) but theres too much urea?

Answer 27

The increase of water is the main goal, excess urea will be reabsorbed during this and will just be secreted at a later point.