Sodium and Water Balance Flashcards
What are the sizes of the intracellular and extracellular fluid compartments compared to each other?
the intracellular compartment is double the size of the ECF
Why are the sizes of the compartments clinically significant?
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.
What are the concentraionts of sodium like in the ICF and ECF?
sodium in the blood is 140mmol/l whereas in the cells this is 4mmol/l
How do the concentrations of Na in the ICF and ECF compare with K?
potassium is the opposite, is very high in the ICF, but low in the ECF
What are the signs of a decreased ECF volume?
postural hypotension; increased HR; dry mucous membranes; decreased skin turgorl decreased consciousness; decreased urine output
What does mineralocorticoid activity refer to?
sodium retention in exchange for potassium and/or hydrogen ions
What is the main steroid with mineralocorticoid activity?
aldosterone
How does renin release lead to aldosterone production?
renin converts angiotensinogen to angiotensin 1 which is converted to angiotensin 2 which works on the adrenal gland to stimulate aldosterone production.
What are the effects of angiotensin 2?
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)
What controls water?
ADH
What is ADH released in response to?
osmotic and non-osmotic stimuli
What is ADH released from?
posterior pituitary
What is the other name for ADH?
arginine vasopressin
What are the 2 reasons for decreased sodium concentraion?
too little sodium or too much water
What are the 2 reasons for increased Na conc.?
too little water; too much sodium
What can too much water result from?
decreased excretion or increased intake
What causes decreased excretion of water?
SIADH
What hcauses increased intake of water?
compulsive water drinking
What can too little sodium be caused by?
increased sodium loss of decresed sodium intake
What are the options for increased sodium loss?
gut=obvious- vomiting and diarrhoae; skin- burns; kidneys eg adrenal insufficiency
What is too little water caused by?
increased water loss; decreased water intake
What causes increased water loss?
diabetes insipidus- problem with ADH secretion or action
What are the causes of too much sodium?
very rare- near drowning in sea; infants given high-salt feeds; some IV medications
What is Addison’s disease?
adrenal insufficiency
