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 using ADH when body fluid osmolality is increased?

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 using ADH when body fluid osmolality is decreased ?

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 plasma osmolality?

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 13

Does urine osmolality go to 0?

Answer 13

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

Question 13

As plasma ADH increases, what happens to urinary osmolality?

Answer 13

It increases

Question 14

Describe the principal cell H2O model

Answer 14

-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 15

What protein channels aren’t regulated by ADH?

Answer 15

-AQP3
-AQP4

Question 16

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

Answer 16

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

Question 17

What is the effect of diabetes insipidus?

Answer 17

Create copious quantities of dilute urine

Question 18

Describe central diabetes insipidus and how it can be treated

Answer 18

-no release of ADH
-treatment - nasal spray desmopressin

Question 19

Describe nephrogenic diabetes insipidus and how it can be treated

Answer 19

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

Question 20

What is aldosterone?

Answer 20

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

Question 21

Where is aldosterone released from?

Answer 21

Cortex of adrenal gland by the layer zona glomerulosa

Question 22

What is aldosterone released in response to?

Answer 22

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

Question 23

What does aldosterone act on?

Answer 23

-late distal tubule
-cortical + medullary collecting duct

Question 24

What happens as a result of aldosterone?

Answer 24

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

Question 25

How does aldosterone act on principal cells?

Answer 25

-cytosolic mineralocorticoid receptor sits inside principal cell
-aldosterone diffuses across the membrane + binds to receptor
-moves to nucleus, then stimulates RNA transcription + protein synthesis
-makes more proteins involved in Na+ reabsorption + K+, H+ secretion

Question 26

At what level does aldosterone act at?

Answer 26

Acts at level of nucleus to promote transcription

Question 27

What is the net effect that aldosterone has on alpha intercalated cells?

Answer 27

-increased Na+ transport so:
-increased plasma Na+ content
-H2O increases, so ECF volume increases
-increased driving force for K+ secretion, so decreased plasma K+
-increased driving force for H+, so decreased plasma H+

Question 28

What is Pseudohypoaldosteronism?

Answer 28

-loss of response to aldosterone due to mineralocorticoid receptor mutations
-urinary Na+ loss but high aldosterone

Question 29

What does renin-angiotensin regulate?

Answer 29

-body fluid volume
-plasma Na+ and K+

Question 30

Where is renin released from?

Answer 30

Juxtaglomerular apparatus (JGA)

Question 31

Describe the renin-angiotensin cascade

Answer 31

-decreased ECF causes release of renin
-causes conversion of angiotensin to angiotensin I to angiotensin II
-active angiotensin II stimulates release of aldosterone from zona glomerulosa
-causes vasoconstriction at arterioles, increasing blood pressure

Question 32

What is the net effect of the renin-angiotensin cascade and how is it treated?

Answer 32

-increased plasma Na+ content + ECF volume
-results in increased blood pressure
-ACE1 inhibitors are blood pressure treatments