Regulation of osmolarity Flashcards
What is water regulation controlled by? Give some other names for this
ADH/vasopressin/arginine vasopressin
Where is ADH synthesises?
supraoptic and paraventricular nuclei of the hypothalamus in the brain
Where is ADH released from?
posterior pituitary
Primary control of ADH secretion
plasma osmolarity
Describe how an increase in plasma osmolarity leads to an increase in ADH secretion?
increase oncotic pressure
rate of discharge of ADH secreting neurons increased
ADH release increased
How is the change in neuronal discharge of ADH mediated?
osmoreceptors
Where are osmoreceptors found?
anterior hypothalamus close to the SO and PVN
Is a high osmolarity high or low water concentration?
low
Explain what happens to an osmoreceptor if osmolarity increases
water moves out of cell and shrinks
activate stretch sensitive ion channels which increases neuronal discharge and ADH secretion
What kind of system is the ADH - plasma osmolarity system described as?
high gain
sensitive
What must occur to cause an increase in ADH? (not just increase osmolarity)
increased TONICITY
What is tonicity?
non penetrating particles which cause a movement of water
Why do some solutes not exhibit tonicity?
solutes that can penetrate membranes move together with water and do not create an osmotic drag/tonicity
Is urea or NaCl an ineffective osmole?
urea
What 2 things is the amount of urine produced dependent on?
ADH
amount of solute to be excreted
Why do hypertonic solutions eg seawater cause dehydration?
increase solute load to be excreted, increase urine flow and hence more water required to be excreted with solute than was ingested
How does ADH increase permeability of the collecting duct?
bind to membrane receptor
activate cAMP
increase aquaporin uptake into apical membrane
water absorbed by osmosis into the blood
What happens to water leaving the duct if ADH is max?
equilibrate with medullary interstitium and is highly concentrated at tip of medulla
type of urine produced when ADH is max
small, highly concentrated
What happens to the water when max ADH is present?
reabsorbed by vasa recta as oncotic pressure is high
What happens when ADH Is absent? Why? Type of urine
CD impermeable to water
medullary gradient is ineffective
high amount, dilute urine
What can concentration fall to when ADH absent?
30-50
What does urea play an important role in?
production of highly concentrated urine
What happens to urea in collecting duct if ADH is present?
greatly concentrates due to water out of CD
Is the CD permeable or impermeable to urea? Where especially?
permeable
medullary tips
What happens when urea reaches medullary tips?
moves out of CD - enhanced by ADH
What happens when urea leaves collecting duct when ADH present?
reabsorbed into interstitium
reinforce interstitial gradient at ascending loops of henle
saves water and uraemia (vasa recta)
Why is it important for urea to be reabsorbed by vasa recta?
if it remained in tubule would exert osmotic effect and hold onto water into tubule making rehydration difficult
Is urea retention or water conservation more important?
water
What is the 2nd thing which effects ADH secretion?
ECF volume
What happens to ADH secretion as ECF volume increases and decreases
decreases, ADH increases
Where are low pressure receptors found?
left and right atria and great veins
What do the low pressure receptors monitor?
volume - Venous return to the heart and hence fullness of CVS
Where are the high pressure receptors found?
carotid and aortic arch baroreceptors
What receptors are affected most by a moderate decrease in ECF volume?
atrial receptors
What is the relationship between the rate of ADH secretion and discharge of stretch in high and low pressure receptors?
inverse
When will high pressure receptors contribute to changes in ADH secretion?
when MBP affected
What kind of cells are ADH secreting cells?
neurons
Importance of ADH secreting cells being neurones
integrate inputs
What are some examples of things which increase ADH
pain, stress, emotion, nicotine, morphine, exercise
What is an example of something which decreases ADH?
alcohol
What is the cause of diabetes insipidus?
ADH deficiency
Cause of central DI
hypothalamic areas secreting ADH affected eg tumour, meningitis, surgery
Causes of peripheral DI
collecting duct insensitive to ADH
hypokalaemia, hyperkalaemia, genetic
Symptoms of DI
large volumes of concentrated urine
polydipsia
How is central DI treated?
ADH(AVP)
How is peripheral DI treated?
usually due to hypokalaemia or hypercalcaemia so at this - will usually resolve
cannot give ADH due to thirst mechanism
