Regulation of Osmolarity Flashcards
What is water regulation controlled by?
ADH (Vasopressin)
What is ADH?
A polypeptide hormone
Where is ADH synthesised?
Supraoptic paraventricular nuclei of the hypothalamus
What part of the piuitary does ADH come from?
Posterior
What controls ADH secretion?
Plasma osmolarity
ECF volume
What do changes in volume of osmoreceptors result in?
Changes in osmoreceptor discharge (stretch sensitive ion channels)
What is the normal plasma osmolality?
280 - 290 mOsm/kg
What would an increase in osmolarity lead to?
H20 out of the cell
Cell shrinks/ sensitive ion channel activated
Increased neural discharge
Increased ADH secretion
What does a decreased osmolarity lead to?
H20 enters the cells
Cells swell
Decreased neural discharge
Decreased ADH secretion
What do the osmoreceptors detect?
Tonicity - not the osmolarity
What is tonicity?
Penetrating solutes concentration (e.g. glucose, urea)
Do solutes that penetrate membranes and move together with water produce any tonicity?
No
Where is the site of water regulation?
The collecting duct
What is the permeability of the collecting duct controlled by?
ADH
What does ADH stand for?
Anti diuretic hormone
How does ADH alter the permeability of the collecting duct?
Changes the amount of aquaporins (which allow water to pass through)
What happens if high ADH present?
H20 is able to leave the collecting duct
What happens if maximum ADH is presen?
Becomes highly concentrated at the tip of the medulla - produces a small volume of highly concentrated urine
How is H20 reabsorbed?
By the oncotic pressure of the vasa recta
Urea in the prescence of ADH
Movement of H20 out of the collecting ducts greatly concentrates the urea remaining in the ducts
Collecting duct membranes are relatively permeable to urea, particuarly towards medullary tips/
So as urea approaches these, there is an increasing tendency for these to move out down its concentration gradient - so it is reabsorbed
What does an increased ECF volume do to the ADH conc?
Decreases ADH
What does a decreased ECF volume do to the ADH conc?
Increases ADH
Where are low pressure receptors located?
Left and right atria
Great veins
What do low pressure receptors monitor?
The return of blood to the heart
The “fullness” of the circulation
