Physiology of body fluid volume

Question 1

What is the osmolarity of the fluid leaving the loop of henle? What does this make it?

Answer 1

100 mosmol

hyposmotic

Question 2

What is the collecting duct bathed in?

Answer 2

progressively increasing concentrations of intersitial fluid as it descends through the medulla

Question 3

Where does hormone regulation of fluid and NaCl affect?

Answer 3

distal tubule and collecting duct

>95% of the ions in filtrate have been reabsorbed before this though

Question 4

What is the action of antidiuretic hormone?

Answer 4

increased water absorption

Question 5

What is the action of aldosterone?

Answer 5

increased Na absorption and increased H/K secretion

Question 6

What is the action of atrial natiuretic hormone?

Answer 6

decreased Na reabsorption

Question 7

What is the action of parathyroid hormone?

Answer 7

increased Ca reabsorption

decreased phosphate reabsorption

Question 8

What ions are transported in the early distal tubule?

Answer 8

Na, K and Cl

Question 9

What ions are transported in the late distal tubule?

Answer 9

Ca, Na and K REABSORBED

H SECRETED

Question 10

What are the characterisitics of the collecting duct in terms of water and ions?

Answer 10

early - permeable to ions

late - low ion permeability but high water and urea permeability

Question 11

What type of hormone is ADH?

Answer 11

neuropeptide - synthesised by nerve cells

Question 12

What happens when action potentials reach the ADH nerves?

Answer 12

ADH is released through Ca dependant exocytosis

Question 13

What type of ADH receptors does the basolateral membrane express?

Answer 13

type 2

Question 14

What happens when ADH binds to receptors?

Answer 14

cAMP increases which initiates the insertion of aquaporins (normally stored in vesicles) into the apical membranes of tubular cells

Question 15

What does decreased ADH cause?

Answer 15

aquaporins become internalised

Question 16

What is the purpose of aquaporins?

Answer 16

to create an equilibrium between the collecting duct fluid and tubular fluid

Question 17

Why would high volumes of urine come about due to the collecting duct?

Answer 17

in the collecting duct the membrane is impermeable to water so there is no water reabsorption

Question 18

Does ADH have an effect on salt reabsorption?

Answer 18

NO

Question 19

What does increased osmolarity trigger?

Answer 19

hypothalamic osmoreceptors -> hypothalamic neurons -> increased thirst

Question 20

What does decreased ECF volume trigger?

Answer 20

decreased arterial BP -> left atrial volume receptors activated -> hypothalamic neurones -> increased ADH and arterial vasodilation

Question 21

What are the two types of diabetes insipidus?

Answer 21

central - no ADH production

nephrogenic - produce ADH as normal but defect in Type 2 ADH receptors

Question 22

What stimulates ADH release?

Answer 22

nicotine

Question 23

What inhibits ADH release?

Answer 23

alcohol

Question 24

What does stimulation of stretch receptors in the upper GI tract cause?

Answer 24

feed forward initiation of ADH

Question 25

What is aldosterone secreted in response to?

Answer 25

increased K | decreased Na

Question 26

What is the role of aldosterone?

Answer 26

secrete K | reabsorb Na

Question 27

What would happen if there was no aldosterone?

Answer 27

tons of salt would be secreted from the body

Question 28

Should there be any K in the urine?

Answer 28

NO 90% of it is absorbed in proximal tubule rest is absorbed in distal

Question 29

Where is angiotensin converting enzyme expressed?

Answer 29

outside of endothelial cells

Question 30

What 3 things stimulate renin release?

Answer 30

1. reduced pressure in the efferent arteriole (low BP) 2. low salt - sensed by macula densa cells 3. increased sympathetic activity as a result of low BP - granular cells release renin and are innervated by sympathetic nervous system

Question 31

How does aldosterone increase the reabsorption of Na?

Answer 31

in the distal and collecting tubules, it increases the expression of sodium apical channels and basolateral sodium/potassium pump expression this is done by change in gene expression and therefore

Question 32

What is atrial naturetic peptide?

Answer 32

released by the heart and stored in atrial muscle cells

Question 33

When is ANP released?

Answer 33

when atrial muscle cells are stretched due to an increase in circulating plasma volume

Question 34

What does ANP do?

Answer 34

promotes excretion of Na and diuresis - which decreases plasma volume and BP

Question 35

What are the two reflexes that control micturition?

Answer 35

micturation reflex (can hold 250-400ml before stretch receptors are triggered) and voluntary control (tightening of external spinchter and pelvic diaphragm)