Sodium and Water Balance

Question 1

what hormone controls water balance and where is it secreted from

Answer 1

ADH(anti-diuretic hormone), secreted from posterior pituitary

Question 2

what class of hormones controls sodium balance and where is it secreted from

Answer 2

Steroids, secreted from adrenal glands

Question 3

describe the action of ADH

Answer 3

causes water reabsorption from the renal tubules, makes you pee less

Question 4

what affect does increased and decreased ADH have on urine

Answer 4

increased ADH = small volume conc. urine

decreased ADH = large volume dilute urine

Question 5

describe what urine osmolality is

Answer 5

a measure of the urine conc./dilution

Question 6

describe high and low osmolality in terms of urine

Answer 6

high osmolality = concentrated urine

low osmolality = dilute urine

Question 7

what is the effect of steroids on Na balance called and what does it refer to

Answer 7

mineralocorticoid activity, refers to Na reabsorption in renal tubules in exchange for K+/H+

Question 8

give 2 examples of steroids with mineralocorticoid activity

Answer 8

aldosterone(main one) and cortisol

Question 9

what affect does too much and too little mineralocorticoid have on the sodium balance

Answer 9

too much = sodium gain

too little = sodium loss

Question 10

what is the equation to calculate Na conc.

Answer 10

(mmol Na) / (1L H2O)

Question 11

what does hyponatraemia and hypernatraemia mean

Answer 11

hyponatraemia = low [Na]
hypernatraemia = high [Na]

Question 12

in terms of water and sodium what are the two ways in which hyponatraemia can occur

Answer 12

Na is too low

or H20 is too high

Question 13

in terms of water and sodium what are the two ways in which hypernatraemia can occur

Answer 13

Na is too high

or H20 is too low

Question 14

what is the [Na] in extracellular fluid compared to intracellular fluid

Answer 14

extracellular = 140 mmol/L
intracellular = 4mmol/L

Question 15

water is present in all body compartments, what does this mean in terms of water gain and loss

Answer 15

when water is lost or gained it is lost and gained from all tissues equally, not more in different compartments

Question 16

what compartment is sodium confined to and by what, and what does this mean for sodium loss/gain

Answer 16

confined to extracellular fluid(ECF), by Na/K ATP pump

so Na loss/gain is only in ECF

Question 17

considering water moves by osmosis describe how Na affects water movement

Answer 17

[Na] is vastly greater than anything else, so water follows Na
ie if you lose/gain Na, you lose/gain water

Question 18

when you lose/gain water due to sodium loss or gain, where is that water lost/added from/to

Answer 18

lost or added from/to the ECF, as that is where the sodium is confined to and lost/added from/to, and water follows sodium
(results in significant water gain/loss due to smaller volume of ECF)