Regulation Of Osmolarity Flashcards
Where is ADH synthesized ?
Supraoptic (SO) and paraventricular (PVN) nuclei of the hypothalamus
What is the half life of ADH and why is this important?
Half life of 10 mins so can be rapidly adjusted depending on the bodies need for water conservations
Does a high or low osmolarity of the plasma trigger ADH release?
Increased osmolarity = increased ADH release
Changes in the discharge of ADH are mediated by what receptors?
Osmoreceptors
What type of receptors are osmoreceptors?
Stretch sensitive ion channels
Describe how ADH causes water to move from the collecting duct into the vasa recta.
ADH binds to vasopressin receptors
This triggers cAMP second mesanger system which causes aquaporin 2 transporters to be inserted into apical membrane
H20 can pass through the cell and into the vasa recta capillaries
What is responsible for increasing the permeability of the collecting ducts to water?
Aquaporin 2 transporters inserted by activation of cAMP second messanger system by ADH
What is the main role of urea?
Concentration urine
At what part of the collecting ducts is urea particularly permeable?
Medullary tips
What enhances the permeability of the collecting ducts to urea?
ADH
Describe the role of urea in anti-diuresis.
In anti-diuresis with high levels of ADH, the collecting duct (particularly medullary tip) is permeable urea
Urea is reabsorbed from the collecting duct and reinforces the interstitial gradient in the ascending loop of henle
- uraemia occurs
If urea remained in the tubule = osmotic effect = retaining water in CD
If ECF increases, does ADH increase or decrease?
Decrease
What is responsible for ADH secretion?
Osmolarity
ECF
What are the low pressure receptors?
L and R atria and great veins (stretch receptors)
What are the high pressure receptors?
Aortic and carotid baroreceptors
What receptors primarily detect moderate decreases in ECF?
Aortic receptors
Via what nerve does low pressure receptors exert tonic inhibitory discharge of ADH?
Vagus nerve
Apart from osmolarity and ECF, what other stimuli can increase ADH release?
Pain Exercise Nicotine Morphine Emotion Traumatic surgery (inappropriate ADH secretion occurs)
Apart from osmolarity and ECF, what other factor can decrease ADH release?
Alcohol (suppresses ADH release)
What is diabetes insipidus?
ADH deficiency
What causes central and peripheral diabetes insipidus?
Central DI: hypothalamic areas synthesising ADH may become diseased due to tumours, meningitis or damaged during surgery
Peripheral DI: collecting duct may be insensitive to ADH
What is the difference in treatment of peripheral and central diabetes insipidus?
Central DI treat by giving ADH
Peripheral DI: cant give ADH as its important to retain thirst mechanism. Treat underlying ion imbalance i.e. hypercalcaemia/hypokalamia
