Regulation of osmolarity

Question 1

what hormone controls water regulation

Answer 1

ADH - vasopressin (anti diuretic hormone

Question 2

What stores ADH

Answer 2

posterior pituitary gland where it is then released into the blood stream

Question 3

Where is ADH synthesised

Answer 3

hypothalamus

Question 4

What controls ADH secretion

Answer 4

Plasma osmolarity

The higher the plasma osmolarity, the higher the rate of discharge of ADH secreting hormone and therefore greater release of ADH from the posterior pituitary

Question 5

What mediates the change in the neuronal discharge of ADHSH - ADH secreting hormone

Answer 5

Osmoreceptors in the anterior hypothalamus

Question 6

What is the effect of increased osmolarity on osmoreceptors

Answer 6

Increased plasma osmolarity means the water leaves the cell to try to dilute the plasma and achieve equilibrium which causes the cell to shrink which activates a stretch sensitive ion which causes increased ADH secretion due to increased neuronal discharge from the ion channels

Question 7

What does a change in the volume of an osmoreceptor do

Answer 7

Causes a change in the neuronal discharge by the osmoreceptor

Question 8

What is required to cause an increase in ADH with regards to increased osmolarity

Answer 8

An increase in tonicity - increase in non-permeable particles which cause an osmotic drag to balance them ie sodium chloride being followed by water
An example of something that can increase osmolarity but not tonicity is urea so ADH would not be released

Question 9

What does a higher concentration of solute require to be excreted

Answer 9

Would require higher volumes because there is a max concentration of urine at 1200-1400 mOsmoles/l

Question 10

What is the effect of ADH at the collecting duct

Answer 10

ADH binds to vasopressin recepotrs which activates Cyclic AMP (cAMP) secondary messenger signals - the effect of the signals makes storage vesicles bind to the luminal membrane - the cell inserts aquaporin channels into the apical membrane

Question 11

What does the aquaporin and ADH allow

Answer 11

It lets water move from the collecting duct lumen, into the collecting duct cell which is against the gradient, and then the water moves to the interstitial fluid to reach equilibrium due to the high osmolarity of the interstitial fluid - the vasa recta then reabsorbs the water

Question 12

What is the effect of maximal ADH

Answer 12

More water leaves the collecting duct lumen and gets reabsorbed so a small volume of highly concentrated urine is produced

Question 13

What happens in the absence of ADH

Answer 13

the collecting ducts are impermeable to water so the water cannot leave the collecting duct lumen and a large volume of dilute urine is excreted

Question 14

What is the function of urea

Answer 14

Urea has a tendency to move down it’s concentration gradient and leave the collecting duct to move to the interstitium - this is enhanced by the effect of ADH - urea plays an important part in the production of concentrated urine

Question 15

Where in the collecting duct is it most permeable to urea

Answer 15

The medullary tips

Question 16

What is the function of urea in an anti-diuresis (saving water)

Answer 16

The urea is retained in order to save water and reinforce the medullary gradient at the thin ascending loop of Henle by moving from the collecting duct to the interstitium - the urea is then reabsorbed by the vasa recta

Question 17

Why is it important that urea is reabsorbed after a diuresis is completed

Answer 17

because if the urea stayed in the interstitium it would exert an osmotic effect which would limit water entering the interstitium

Question 18

What is the relationship between ADH and ECF

Answer 18

Inversely proportional

Increase in ECF reduces ADH secretion
Decrease in ECF increased ADH secretion

Question 19

What are low pressure receptors and where are they located

Answer 19

Have a sense of the fullness of the circulation (volume receptors) which are located in the L and R atria and major veins

Question 20

What are high pressure receptors and where are they located

Answer 20

they measure high pressures during systole and are located at the carotid and aortic arch baroreceptors

Question 21

What happens when there is a moderate decrease in ECF volume

Answer 21

The atrial receptors (low pressure) are affected and they have an increased discharge which leads to ADH release increasing

Question 22

If volume changes enough to affect MBP (mean arterial blood pressure) what happens

Answer 22

Carotid and aortic receptors (high pressure) receptors cause an increase in ADH secretion

They are very important in haemorrhage where there is a rapid drop in blood volume and MBP

Even when moving from lying down to standing up causes an ADH release

Question 23

What cells are ADH secreting

Answer 23

Neurons which release multiple inputs to determine the ADH concentration

Question 24

What is the affect of alcohol on ADH

Answer 24

decreases ADH which decreases aquaporin channels in the collecting duct so more water is excreted and therefore a higher volume of a more diluted urine is secreted

Question 25

What is central diabetes insipidus

Answer 25

Issue with the synthesis of ADH in the hypothalamus

Question 26

What is peripheral diabetes insipidus

Answer 26

Collecting duct becomes insensitive to ADH

Question 27

What value of excreted urine classifies polyuria

Answer 27

more than 10L/day

Question 28

What is treatment for central diabetes insipidus

Answer 28

ADH

Question 29

Treatment for peripheral diabetes insipidus

Answer 29

Their collecting ducts are insensitive to ADH - it normally comes secondary to hypokalaemia or hypercalcaemia so correcting the ion disorder is the treatment