Physiology 4 Flashcards
what is the main function of the collecting duct?
To concentrate urine by reabsorbing water.
Which hormone controls the permeability of the collecting duct?
ADH - vasopressin.
where is vasopressin created and stored?
Created - hypothalamus
stored - posterior pituitary
What is the half life of vasopressin?
10 minutes
What controls vasopressin release?
Osmolarity
How is osmolarity levels measured?
via the osmoreceptor cells in the brain
What happens in hyperosmolarity?
the osmoreceptors in the brain shrink, sending neurological signals to the hypothalamus to secrete ADH.
what happens in hypo-osmolarity?
the osmoreceptors swell, so no signals are sent to produce ADH.
how does ADH affect the collecting duct?
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.
Where does the water go after the interstitium?
It is reabsorbed by the vasa recta?
how many aquaporins are on the basal membrane?
this number is fixed, the water reabsorption is controlled by the vesicle containing aquaporins on the luminal side.
What affect does ADH have on urea?
An increase in ADH stimulates reabsorption of urea.
How is urea reabsorbed?
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.
How does urea maintain interstitial gradient?
The urea maintains osmolarity, ensuring that water is still reabsorbed.
how is urea reabsorbed into the blood?
By the vasa recta.
What causes suppression of ADH?
alcohol
What causes an increase in ADH?
exercise, stress, pain, morphine
Where are the baroreceptors?
in the aortic arch and carotid arteries, they monitor high pressure differences (like blood pressure)
Where are the atrial receptors?
In the right and left atria, they are triggered by smaller changes in volume.
What happens in decreased ECF volume?
The atrial receptors notice it, they reduce their effect on ADH (which is inhibitory) - this increases ADH release.
What happens in increased ECF volume?
The atrial receptors increase firing, this increases the inhibitory effect on ADH.
What is diabetes insipudis?
It is a lack of ADH - either ADH production is lacking or the body is insensitive to ADH.
What is central diabetes insipidus?
A problem with the production of ADH.
How is diabetes insipidus treated?
With ADH supplementation
What is peripheral diabetes insipidus?
This is when the body becomes desensitised to ADH
How is peripheral diabetes insipidus treated?
Usually by matching the output of urine with an input of water.
What happens if theres an increase in osmolarity or decrease in ECF volume (requiring increased ADH) but theres too much urea?
The increase of water is the main goal, excess urea will be reabsorbed during this and will just be secreted at a later point.
