Regulation of Osmolality Flashcards
What type of hormone is ADH?
Polypeptide
Where is ADH released from?
Posterior pituitary
How is ADH secretion controlled?
Primarily by plasma osmolarity
How are changes in neuronal discharge mediated?
Osmoreceptors in the anterior hypothalamus
What happens when the osmolarity increases?
More water leaves the cell > cell shrinks > stretch sensitive ion channel activated > increased neural discharge > increased ADH secretion
What happens when the osmolarity decreases?
Water enters the cell > cells swell > decreased neural discharge > decreased ADH
What happens when there is an increase in osmolarity but not in tonicity?
It is ineffective at causing an increase in ADH
What is tonicity?
The relative concentration of solutes dissolved in solution: determines the direction and extent of the diffusion
What effect does changing urea concentration have on ADH release?
No effect: urea is an ineffective osmole
What factors affect the amount of urine produced?
ADH conc. and the amount of solute to be excreted
What happens when hypertonic solutions e.g. sea water are ingested?
It increases the solute load, increasing urine flow and leading to dehydration
Where is the site of water regulation?
Collecting duct
What effect does ADH have on the permeability of the collecting ducts to water?
It increases the permeability of the collecting duct to water by incorporating H2O channels (aquaporins) into the luminal membrane
What happens to the urine at maximal ADH conc.
A small amount of highly concentrated urine which contains less filtered water than of solute
What happens when ADH is absent?
The collecting ducts are impermeable to water so that the medullary interstitial gradient is ineffective in inducing water movement out of the collecting duct. Large amount of diluted urine is produced
What happens to urea in the presence of ADH?
As the water moves out of the collecting ducts the urea becomes concentrated
What happens to the late medullary collecting duct permeability to urea in presence of ADH?
It is greatly enhanced
What happens to urea when the ADH is high?
The urea will be reabsorbed from the collecting duct into the interstitium where it reinforces the interstitial gradient
Why is it important that urea is reabsorbed?
If it remained in the tubule it would exert an osmotic effect and hold the water in the tubule
How does ECF volume affect the ADH secretion?
It is an inverse relationship between ADH secretion and the stretch receptors in the low and high pressure receptors
Where are the low pressure receptors located?
L&R Atria and Great Veins
What are the high pressure receptors?
Carotid and aortic arch baroreceptors
Which receptors are primarily affected by moderate decreases?
Atrial receptors
What happens if the ECF volume changes enough to affect the MBP?
The carotid and aortic receptors will contribute to the ADH secretion
Is there an increase in ADH secretion when going from lying down to standing up?
Yes
Which stimuli increase ADH secretion?
Pain, emotion, stress, exercise, nicotine, morphine and traumatic surgery
Which stimulus decrease ADH secretion
Alcohol
What is diabetes inspipidus?
ADH deficiency
What is the clinical presentation of diabetes insipidus?
Polydipsia (increased drinking) and polyuria (increased urine volumes)
How is central diabetes insipidus treated?
Giving ADH
How is peripheral diabetes insipidus treated?
Cannot give ADH. Usually secondary to hypercalcaemia or hypokalaemia so treat the ion imbalance
