Endocrine Control of Fluid and Salt Balance

Question 1

what is the total body water content

Answer 1

0.6 x body weight = 42L

Question 2

what is the intracellular fluid content

Answer 2

0.4 x body weight = 28L

Question 3

what is the extracellular fluid content

Answer 3

0.2 x body weight = 14L

Question 4

what does the extracellular fluid subdivides into?

Answer 4

plasma - 1/4 of ECF = 3.5L

interstitial fluid - 3/4 of ECF = 10.5L

Question 5

what does ECF contains

Answer 5

Na+ 145 moles/L
K+ 4
Cl- 105
HCO3- 25

Question 6

approximate value of osmolarity

Answer 6

[Na+ + K+] x2 or 290-295 milliosmoles/L

Question 7

how much fluid do we take in as drinks

Answer 7

1200 ml/day

Question 8

how much fluid do we take in as food

Answer 8

1000ml/day

Question 9

how much water do we get form the catabolism of food

Answer 9

300ml/day

Question 10

how much water do we lose from lungs and skin

Answer 10

700ml/day

Question 11

how much water do we lose from sweat

Answer 11

100ml/day

Question 12

how much water do we loose from faecal loss

Answer 12

200ml/day

Question 13

how much water do we lose form urine

Answer 13

1500ml/day

Question 14

what is hypovolaemia

Answer 14

a decreased volume of circulating blood in the body.

Question 15

which receptors receive the decrease in the volume of circulating blood

Answer 15

baro-receptors, angiotensin II on subfornical area

Question 16

which receptors receive hypertonicity

Answer 16

osmoreceptors

Question 17

where do the signals from the baroreceptors and osmorecpetors go to?

Answer 17

hypothalamus

Question 18

what are the responses produced by the hypothalamus in response to hypertonicity and hypovalaemia

Answer 18

hypertonicity - thirst

hypokalaemia - vasopressin (ADH) release rom posterior pituitary

Question 19

what is the function of retention of sodium ion

Answer 19

to maintain extracellular volume

Question 20

how does an increase in extracellular volume influence renal loss

Answer 20

it enhances renal loss of sodium ion and hence a fall in volume after diuresis

Question 21

how does a decrease in extracellular volume influence the renal uptake of sodium ion

Answer 21

it enhances renal uptake of sodium ion and hence an increase in volume after antidiuresis

Question 22

fall in venous blood volume

Answer 22

1) general sympathetic discharge
2) constriction of the afferent arteriole
3) reduction in renal blood flow
4) reduction in glomerular filtration rate
5) reduction in sodium chloride presented to
distal convoluted tubule
6) conservation of sodium chloride

Question 23

fall in blood pressure in circulation

Answer 23

1) renal sympathetic nerve discharge - direct effect on renin releasing cells in afferent arteriole
2) reduced renal blood flow and glomerular filtration
3) reduced sodium chloride delivery detected by macula dense cells of the distal convoluted tubule
4) increased renin release
5) eventual increase sodium chloride reabsorption as well as reduced loss

Question 24

what converts angiotensinogen from liver secreted into circulation

Answer 24

plasma renin

Question 25

what does Angiotensin I in lungs and kidneys do

Answer 25

converts enzyme ACE in lung and renal endothelium

Question 26

functions of AT1 receptors

Answer 26

1) pressor effect on smooth muscle of arteries
2) acts on subfornical area to stimulate ADH production and thirst
3) actions on zona glomerulosa cells of adrenal cortex to produce aldosterone

Question 27

functions of aldosterone

Answer 27

increase Na+/K+ ATPase activity in distal tubule

increase sodium ion reabsorption

Question 28

what did de Wardener’s experiment confirmed?

Answer 28

existence of ANP

Question 29

what was done in the gardener’s experiment

Answer 29

1) an inflatable catheter inserted into the renal artery to stimulate reduced blood pressure
2) injection of maximal stimulatory dose of aldosterone

Question 30

what was the aim of de gardener’s experiment

Answer 30

intention to maximise sodium resorption in the distal convoluted tubuleq

Question 31

the site of atrial natriuretic peptide action

Answer 31

1) reduces arterial smooth muscle tone - reduces blood pressure
2) inhibits ADH release
3) inhibits renin release
4) reduces sodium ion absorption in distal convoluted tubule leads to natriuresis