Regulation of osmolarity

Question 1

What is water regulation controlled by? Give some other names for this

Answer 1

ADH/vasopressin/arginine vasopressin

Question 2

Where is ADH synthesises?

Answer 2

supraoptic and paraventricular nuclei of the hypothalamus in the brain

Question 3

Where is ADH released from?

Answer 3

posterior pituitary

Question 4

Primary control of ADH secretion

Answer 4

plasma osmolarity

Question 5

Describe how an increase in plasma osmolarity leads to an increase in ADH secretion?

Answer 5

increase oncotic pressure
rate of discharge of ADH secreting neurons increased
ADH release increased

Question 6

How is the change in neuronal discharge of ADH mediated?

Answer 6

osmoreceptors

Question 7

Where are osmoreceptors found?

Answer 7

anterior hypothalamus close to the SO and PVN

Question 8

Is a high osmolarity high or low water concentration?

Answer 8

low

Question 9

Explain what happens to an osmoreceptor if osmolarity increases

Answer 9

water moves out of cell and shrinks

activate stretch sensitive ion channels which increases neuronal discharge and ADH secretion

Question 10

What kind of system is the ADH - plasma osmolarity system described as?

Answer 10

high gain

sensitive

Question 11

What must occur to cause an increase in ADH? (not just increase osmolarity)

Answer 11

increased TONICITY

Question 12

What is tonicity?

Answer 12

non penetrating particles which cause a movement of water

Question 13

Why do some solutes not exhibit tonicity?

Answer 13

solutes that can penetrate membranes move together with water and do not create an osmotic drag/tonicity

Question 14

Is urea or NaCl an ineffective osmole?

Answer 14

urea

Question 15

What 2 things is the amount of urine produced dependent on?

Answer 15

ADH

amount of solute to be excreted

Question 16

Why do hypertonic solutions eg seawater cause dehydration?

Answer 16

increase solute load to be excreted, increase urine flow and hence more water required to be excreted with solute than was ingested

Question 17

How does ADH increase permeability of the collecting duct?

Answer 17

bind to membrane receptor
activate cAMP
increase aquaporin uptake into apical membrane
water absorbed by osmosis into the blood

Question 18

What happens to water leaving the duct if ADH is max?

Answer 18

equilibrate with medullary interstitium and is highly concentrated at tip of medulla

Question 19

type of urine produced when ADH is max

Answer 19

small, highly concentrated

Question 20

What happens to the water when max ADH is present?

Answer 20

reabsorbed by vasa recta as oncotic pressure is high

Question 21

What happens when ADH Is absent? Why? Type of urine

Answer 21

CD impermeable to water
medullary gradient is ineffective
high amount, dilute urine

Question 22

What can concentration fall to when ADH absent?

Answer 22

30-50

Question 23

What does urea play an important role in?

Answer 23

production of highly concentrated urine

Question 24

What happens to urea in collecting duct if ADH is present?

Answer 24

greatly concentrates due to water out of CD

Question 25

Is the CD permeable or impermeable to urea? Where especially?

Answer 25

permeable | medullary tips

Question 26

What happens when urea reaches medullary tips?

Answer 26

moves out of CD - enhanced by ADH

Question 27

What happens when urea leaves collecting duct when ADH present?

Answer 27

reabsorbed into interstitium reinforce interstitial gradient at ascending loops of henle saves water and uraemia (vasa recta)

Question 28

Why is it important for urea to be reabsorbed by vasa recta?

Answer 28

if it remained in tubule would exert osmotic effect and hold onto water into tubule making rehydration difficult

Question 29

Is urea retention or water conservation more important?

Answer 29

water

Question 30

What is the 2nd thing which effects ADH secretion?

Answer 30

ECF volume

Question 31

What happens to ADH secretion as ECF volume increases and decreases

Answer 31

decreases, ADH increases

Question 32

Where are low pressure receptors found?

Answer 32

left and right atria and great veins

Question 33

What do the low pressure receptors monitor?

Answer 33

volume - Venous return to the heart and hence fullness of CVS

Question 34

Where are the high pressure receptors found?

Answer 34

carotid and aortic arch baroreceptors

Question 35

What receptors are affected most by a moderate decrease in ECF volume?

Answer 35

atrial receptors

Question 36

What is the relationship between the rate of ADH secretion and discharge of stretch in high and low pressure receptors?

Answer 36

inverse

Question 37

When will high pressure receptors contribute to changes in ADH secretion?

Answer 37

when MBP affected

Question 38

What kind of cells are ADH secreting cells?

Answer 38

neurons

Question 39

Importance of ADH secreting cells being neurones

Answer 39

integrate inputs

Question 40

What are some examples of things which increase ADH

Answer 40

pain, stress, emotion, nicotine, morphine, exercise

Question 41

What is an example of something which decreases ADH?

Answer 41

alcohol

Question 42

What is the cause of diabetes insipidus?

Answer 42

ADH deficiency

Question 43

Cause of central DI

Answer 43

hypothalamic areas secreting ADH affected eg tumour, meningitis, surgery

Question 44

Causes of peripheral DI

Answer 44

collecting duct insensitive to ADH | hypokalaemia, hyperkalaemia, genetic

Question 45

Symptoms of DI

Answer 45

large volumes of concentrated urine | polydipsia

Question 46

How is central DI treated?

Answer 46

ADH(AVP)

Question 47

How is peripheral DI treated?

Answer 47

usually due to hypokalaemia or hypercalcaemia so at this - will usually resolve cannot give ADH due to thirst mechanism