Control Of Extracellular Fluid Flashcards
Na+ regulation responds primarily to changes in _____________
Blood volume
Water regulation responds to changes in _________ and _________ of ECF
Osmolarity
Volume
Na+ retention entails loss of ____
K+
What are the 2 ways that aldosterone can be activated/
- Angiotensin II
- K+ plasma concentrations increase (remember that aldosterone will stimulate Na+ reabsorption, which will entail K+ loss)
Aldosterone binds to the intracellular _______________ receptor in __________ cells
Mineralocorticoid
Principal
What does spironolactone do?
Binds to the mineralocorticoid receptor and prevents aldosterone from having an effect
What are the effects of aldosterone?
It stimulates transcription, resulting in up-regulation of:
Apical ENaCs
apical K+ channels
Na+,K+ ATPase
Mitochondrial metabolism
H+ ATPase
What are the effects of angiotensin II?
Vasoconstrictor
Activates aldosterone
Stimulates Na+/H+ exchange in proximal tubule (NHE antiport)
Makes you thirsty
Overall- salt retention and elevation of BP
What is a dipsogen?
Stimulates thirst
What hormone regulates the levels of Angiotensin II?
Renin
What cells release renin?
Granular cells (aka juxtaglomerular cells)
What 3 mechanisms can stimulate renin release?
- Intrarenal barorecpetors in the granular cells of JGA respond to stretch in afferent arterioles (Low BP=HiGh renin release)
- Macula Densa senses flow to the distal tubule (NaCl levels) and will cause renin release if GFR is too low
- Renal Sympathetic Nerves near granular cells will increase renin release via stimulation of β receptors
How does renin release lead to angiotensin II floating around?
Renin cleaves angiotensinogen floating around in the blood to make angiotensin I, and then the whole ACE to angiotensin II thing
Where does atrial natriuretic peptide come from?
Atria of the heart
When do the atria release ANP?
When BP is high
What effect does ANP have on the kidney?
- Increases GFR
2. Decreases NaCl reabsorption by the CD
How does ANP increase GFR (and thus, the filtered load of NaCl)?
Dilates the afferent arteriole and constricts the efferent arteriole
How does ANP decrease NaCl reabsorption by the Collecting Duct?
- Directly inhibits secretion of renin and aldosterone
2. Directly inhibits Na+ uptake by medullary CD
What is the most important hormone regulating water balance?
ADH
Where does ADH come from?
Pituitary gland
What cauwses the release of ADH from the pituitary ?
Increased plasma osmolality
Plasma volume decreases
Does ADH have an effect on NaCl excretion?
Very little
Which is the primary controller of ADH release: plasma osmolality or plasma volume
Plasma osmolality
What is the average osmolarity of the body?
290 mOsm/L
If your plasma volume changes just a little, will ADH get released?
No you need a pretty significant loss of plasma volume (about 10%)
Will a teeny tiny change in plasma osmolarity cause release of ADH?
Yes
If you drink a ton of water will you release ADH?
No, and the collecting duct permeability to H2O will be diminished, so you will lose H2O in your pee
How could a decrease in plasma volume lead to an indirect release of ADH?
SNS detects lower plasma volume-> SNS activity-> renin secretion -> aldosterone -> renal sodium conservation -> increased plasma osmolarity -> ADH release
If you drink a ton of water, your urine volume will increase. Will you also be peeing out a lot of solutes?
No, the amount of solute excretion will remain relatively constant
What is clearance?
The ml/min of blood plasma cleared of a given substance
What is Osmolar Clearance?
The ml/min of blood plasma cleared of osmotically active particles
How do you calculate osmolar clearance?
(Uosm)(V)
_____________
Posm
Uosm = osmolarity of Urine
Posm- osmolarity of plasma
What is a normal Osmolar clearance?
1-2 ml/min
What does it mean if your Cosm (osmolar clearance) decreases?
You are not getting rid of enough solutes
-POSITIVE osmolar balance = gaining osmoles and water and progressing towards edema
What can cause a reduced Cosm?
Decreased GFR
Increased Aldosterone (inapp. Reabsorption of sodium)
Kidney disease that decreases kidney’s ability to eliminate solute
If someone develops edema, do you think their Cosm went up or down?
Down.
Reduced Cosm= not getting rid of enough solutes
What effect will diuretics have on Cosm?
Increased. Will cause you to “dump” osmolytes and ECF will decrease
What kinds of things can cause an increased Cosm?
Diuretics
Reduced aldosterone
Kidney disease that prevent normal reabsorption
