ADD Body fluid homeostasis

Question 1

Where are antidiuretic hormones released from?

Answer 1

Posterior pituitary gland

Question 2

How is vasopressin released?

Answer 2

Sits in vesicles where it waits for signal to be fused with the presynaptic membrane where it’s secreted

Question 3

Where is the signal that initiates the release of antidiuretic hormones released from?

Answer 3

Neurosecretory neurons

Question 4

What does ADH do?

Answer 4

-regulates body fluid osmolality
-conserves H2O by reducing urinary losses

Question 5

How is blood plasma concentration returned to normal when body fluid osmolality is increased using ADH?

Answer 5

-increased blood fluid osmolality
-causes increased plasma conc.
-so increased ADH
-so less water lost in urine
-plasma conc. returned to normal

Question 6

How is blood plasma concentration returned to normal when body fluid osmolality is decreased using ADH?

Answer 6

-decreased body fluid osmolality
-causes decreased plasma conc.
-so decreased ADH
-so more water lost in urine
-plasma conc. returned to normal

Question 7

Where do hypothalamic osmoreceptors sit?

Answer 7

Sub-optic + paraventricular nuclei

Question 8

How sensitive are hypothalamic osmoreceptors?

Answer 8

-very
-detect changes of +- 3 mosmol/kg H2O
-normal range = 280-300 mosmol/kg H2O

Question 9

What are hypothalamic osmoreceptors stimulated by and what is their response?

Answer 9

-stimulated by increased osmolality
-release ADH from posterior pituitary
-feeling of thirts

Question 10

What causes an increased osmolality plasma?

Answer 10

-solute ingestion or H2O deficiency
-stress + drugs (nicotine, ecstasy)

Question 11

What causes a decreased osmolality plasma?

Answer 11

-excessive fluid ingestion
-alcohol

Question 12

At normal plasma osmolality, is there ADH circulating?

Answer 12

Yes

Question 14

Does urine osmolality go to 0?

Answer 14

-no
-we can never not produce urine
-always have to excrete waste products of metabolism

Question 14

As plasma ADH increases, what happens to urinary osmolality?

Answer 14

It increases

Question 15

Describe the principal cell H2O model

Answer 15

-ADH binds to V2 receptor, initiating signalling cascade
-activates PKA creating active PKA
-phosphorylates proteins in vesicle membranes
-causes vesicles containing AQP2 H2O channels to fuse with principal cell membrane
-more AQP2 channels in membrane

Question 16

What protein channels aren’t regulated by ADH?

Answer 16

-AQP3
-AQP4

Question 17

What does having more AQP2 channels in the apical membrane of principal cells lead to?

Answer 17

-increased H2O reabsorption
-dilution of plasma
-fall in body fluid osmolality
-fast response - around 15 mins

Question 18

What is the effect of diabetes insipidus?

Answer 18

Create copious quantities of dilute urine

Question 19

Describe central diabetes insipidus and how it can be treated

Answer 19

-no release of ADH
-treatment - nasal spray desmopressin

Question 20

Describe nephrogenic diabetes insipidus and how it can be treated

Answer 20

-no response to ADH
-caused by gene mutations in the genes coding for V2 receptors or AQP2 channels
-range of treatments

Question 21

What is aldosterone?

Answer 21

-classed as a mineralocorticoid
-regulates plasma Na+ content, K+ content + body fluid volume

Question 22

Where is aldosterone released from?

Answer 22

Cortex of adrenal gland by the layer zona glomerulosa

Question 23

What is aldosterone released in response to?

Answer 23

-increased plasma K+
-decreased plasma Na+ –> usually maintained by osmoregulation (ADH)
-decreased ECF volume - in conjunction with renin-angiotensin system

Question 24

What does aldosterone act on?

Answer 24

-late distal tubule
-cortical + medullary collecting duct

Question 25

What happens as a result of aldosterone?

Answer 25

-increased Na+ reabsorption, causing increased H2O reabsorption
-increased secretion of K+ and H+