Sodium and Water Balance

Question 1

What are the sizes of the intracellular and extracellular fluid compartments compared to each other?

Answer 1

the intracellular compartment is double the size of the ECF

Question 2

Why are the sizes of the compartments clinically significant?

Answer 2

water loss is distributed across compartments so the cinical signs of water overload or deficit are muted or dilluted- you can lose a lot of water without being clinically dehydrated.

Question 3

What are the concentraionts of sodium like in the ICF and ECF?

Answer 3

sodium in the blood is 140mmol/l whereas in the cells this is 4mmol/l

Question 4

How do the concentrations of Na in the ICF and ECF compare with K?

Answer 4

potassium is the opposite, is very high in the ICF, but low in the ECF

Question 5

What are the signs of a decreased ECF volume?

Answer 5

postural hypotension; increased HR; dry mucous membranes; decreased skin turgorl decreased consciousness; decreased urine output

Question 6

What does mineralocorticoid activity refer to?

Answer 6

sodium retention in exchange for potassium and/or hydrogen ions

Question 7

What is the main steroid with mineralocorticoid activity?

Answer 7

aldosterone

Question 8

How does renin release lead to aldosterone production?

Answer 8

renin converts angiotensinogen to angiotensin 1 which is converted to angiotensin 2 which works on the adrenal gland to stimulate aldosterone production.

Question 9

What are the effects of angiotensin 2?

Answer 9

cardiac and vascular hypertrophy; sympathetic stimulation; causes thirst and acts on pituitary to increase ADH, works on adrenal cortex to release aldosterone–increased blood volume (sodium retention)

Question 10

What controls water?

Answer 10

ADH

Question 11

What is ADH released in response to?

Answer 11

osmotic and non-osmotic stimuli

Question 12

What is ADH released from?

Answer 12

posterior pituitary

Question 13

What is the other name for ADH?

Answer 13

arginine vasopressin

Question 14

What are the 2 reasons for decreased sodium concentraion?

Answer 14

too little sodium or too much water

Question 15

What are the 2 reasons for increased Na conc.?

Answer 15

too little water; too much sodium

Question 16

What can too much water result from?

Answer 16

decreased excretion or increased intake

Question 17

What causes decreased excretion of water?

Answer 17

SIADH

Question 18

What hcauses increased intake of water?

Answer 18

compulsive water drinking

Question 19

What can too little sodium be caused by?

Answer 19

increased sodium loss of decresed sodium intake

Question 20

What are the options for increased sodium loss?

Answer 20

gut=obvious- vomiting and diarrhoae; skin- burns; kidneys eg adrenal insufficiency

Question 21

What is too little water caused by?

Answer 21

increased water loss; decreased water intake

Question 22

What causes increased water loss?

Answer 22

diabetes insipidus- problem with ADH secretion or action

Question 23

What are the causes of too much sodium?

Answer 23

very rare- near drowning in sea; infants given high-salt feeds; some IV medications

Question 24

What is Addison’s disease?

Answer 24

adrenal insufficiency

Question 25

What causes excessive pigmentation in Addison’s disease?

Answer 25

excess ACTH from pituitary (adrenal corticotrophic hormone- to try make more aldosterone) which is degraded into MSH- melanocyte stimulating hormone

Question 26

What are non-osmotic stimuli for ADH release?

Answer 26

hypovolaemia/hypotension; pain; N and V

Question 27

What causes diabetes insipidus?

Answer 27

there is disruption of the pituitary or infundibulum so patient cant secrete ADH from post. pituitary

Question 28

Why do you get high sodium conc. in diabetes insipidus?

Answer 28

no ADH so lose lots of water, but not sodium, so sodsium conc. goes up

Question 29

What does hypovolaemia in hyponatraemia indicate?

Answer 29

too little sodium

Question 30

What does oedema signify?

Answer 30

circulatin volume depletion

Question 31

What should be measured if adrenal insufficiency is suspected?

Answer 31

cortisol and ACTH