Sodium Handling by the Kidney - Hausman Flashcards
Diagram of water and electrolyte absorption in sections of the nephron
Where is water absorption isoosmotic?
Where is the most water reabsorped in the kidney?
Where is tubular fluid hyperosmotic?
Where is tubular fluid hypoosmotic?
Proximal tubule- reabsorb 60-90% of water, freely permeable to water. Water moves from osmotic forces to outside higher soulte concentrations.
Bottom of Henle loop is hyperosmotic: tonicity of medulla is 1200mosm/kg and pulls water out of tubule.
The distal nephron is hypoosmotic because Na is permeable and water is not in the ascending loop of Henle (water is diluted)
Fluid becomes concentrated again and hyperosmotic in the distal tubule with ADH, but water is excreted without ADH as the CCD is impermeable to water.
When is ADH secretion normally ceased?
What is the max concentration of urine at max ADH secretion?
Plasma osmolarity below 275 mosm/kg
Plasma Na+ below 135 meq/l
Urine can become as hypoosmotic as 50 mosm/kg with a max. water excretory capacity of more than 10 l/day
With a lot of hypovolemia and ADH secretion urine osmolarlity can get up to 1200 mosm/kg
Aquaporins
Where are they found?
When are they activated?
AQP2 located on the luminal side of CCD cells allows H20 to enter the cell
ADH presence activates cAMP on the basolateral side –> acquaporin movement to membrane
When ADH removed, aquaporins moved back into cell
What are the components of urine volume?
What is free water clearance?
Urine volume = isoosmotic osmolal clearance + free water clearance
Free water is created a lot by furosemide (and diuretics)
If reabsorbing free water: free water is negative (V = Cosm - CH20, can happen with SIADH, adrenal insufficiency and hypothyroidism)
Liddle Syndrome Pathophysiology
Problem with ENaC (Epithelial sodium channels). ENaC should be endocytosed out of hte apical membrane when aldosterone is low and resorption is not needed. But in ENaC here is stuck in the epithelial membrane regardless of aldosterone presence. Resorbs all sodium and pumps out too much K+.
Results in hypertension and hypokalemia.
