Flashcards in Disorders of Sodium Metabolism Deck (12):
1. Describe the differences between salt and water content in the body.
osmolality equilibrates between body compartments, sodium is restricted to the ECF and water moves to achieve equilibrium
2. Explain why the sodium ion determines the extracellular fluid volume.
Na+ stays in the ECF, so Na+ content of the ECF will either cause water to enter or exit this compartment and determine the ECF volume
3. Evaluate total body sodium content. What are the signs and symptoms of low sodium?
thirst (angiotensin II)
decreased urine output
skin turgor reduced
4. Describe sodium transport in the nephron. List the sodium channels located in each section of the nephron.
PCT: Na/H antiporter
Ascending Limb: NKCC channel
DCT: Na/Cl cotransporter
Cortical duct: ENaC (epithelium sodium channel)
5. Explain how the body regulates the sodium balance.
volume status is the major mediator of sodium balance
sympathetic system: vasoconstriction , reducing the amount of Na filtered; activates RAAS thru B2 receptors
Renin Angiotensin System: angiotensin II causes vasoconstriction, aldosterone causes reabsorption of salt and reabsorption of water
ANP: vasodilation in response to atrial stretch, can cause increased salt delivery as well as act as a direct inhibitor to sodium reabsorption
pressure natriuresis- increased systemic pressure causes loss of sodium
Changes in salt content manifest as changes in _____ volume.
extracellular volume effected by changes in salt content
Define effective circulating volume.
effective circulating volume refers to part of the ECF that is in the arterial bed
essentially the pressure perfusing the arterial baroreceptors in the carotid sinus and glomerular afferent arterials that the body uses to monitor volume status
Describe why patients with CHF retain water using effective circulating volume.
diminished cardiac output leads to reduced effective circulating volume which causes the system to retain Na+ and water despite appropriate volume (can lead to edema)
note in cirrhosis ECF volume is increased but plasma volume is decreased due to low albumin
If you were measuring Na+ and Cl- to determine fluid status, would you test serum concentration or urine concentration?
urine sodium and chloride (modulated by aldosterone) tell you about volume status, unlike serum sodium, they are markers of effective circulating volume
Is sunken fontanelle a symptom of sodium gain or loss and why?
sodium gain- expansion of the ECF causes fluid to leave the ICF, causing shrinkage of brain
How do you treat volume depletion?
administer isotonic fluids to maintain appropriate intravascular volume then address osmolarity