Extracellular fluid volume and sodium balance Flashcards
How is ECF volume regulated?
Regulation of body sodium content which is a vital function of kidneys
What is the effective circulating volume (ECV)?
Component of ECF which is perfusing tissues
What is ECV monitored by?
Low pressure baroreceptors
High pressure baroreceptors
CNS
Hepatic nervous system
What is ECV control dependent on?
Sodium balance
How is Na+ balance regulated?
Action of renal nerves
RAAS
Natriuretic peptides
What does the activation of the RAAS system result in?
Increase in blood pressure
decrease in salt and water excretion by the kidneys
What does severe haemorrhage cause?
Decreased renal perfusion -> elevated levels of renin in the blood
Where is renin synthesized and stored?
Granular cells
What is the stimulus for renin synthesis?
Wall tension - pulse pressure
What are granular cells?
Pressure sensitive cells
What does volume contraction cause?
increases renal sympathetic nerve activity
How do neural signals from vasomotor centre reach granular cells?
Renal sympathetic nerves
What do granular cells express?
Beta 1 adrenergic receptors
What stimulates these receptors?
Epinephrine or norephrine
What happens when beta 1 receptors are stimulated?
Induce renin secretion
What are the salt sensing cells in the JGA?
Macula densa cells
What does decreased renal perfusion cause?
Lower GFR and decreased filtered load of NaCl
What does decreased NaCl delivery cause?
Increased renin release
Are Ca2+ levels increased or decreased in granular cells during these mechanisms?
Decreased
What does elevated plasma levels result in?
Elevated angiotensin II levels
What does ANG2 produce?
Systemic vasoconstriction which increases TPR and increased BP
What does ANG2 stimulate?
The adrenal cortex to produce aldosterone
What does aldosterone stimulate?
Na+ reabsorption and K+ secretion from distal nephron
What diuretic drug blocks aldosterone?
Spironolactone
What does aldosterone bind to in principal cells?
Mineral corticoid receptors
What does aldosterone binding cause?
Conformational change that reveals nuclear localization signal
What does the nucleus promote after aldosterone binding?
Gene expression and synthesis of:
- NA+/K+ATPase pumps and K+ channels in BM
- ENaC channels and K+ channels in AM
- SGK1 which increases ENaC in AM and K+ channels
What happens when maximal concentration of aldosterone is reached?
Virtually no sodium excreted
What other factors increase aldosterone release?
Small increase in plasma K+
Decrease in plasma Na+
What are 5 other functions of ANG2?
Stimulates NaCl absorption in PCT
Vasoconstricts renal arterioles
Constricts mesangial cells
Increases thirst by acting on hypothalamus
Increases ADH secretion
Where is angiotensin mainly produced?
Liver
Where is ACE expressed?
Luminal surface of endothelial cells (particularly the lungs)
What blocks ANG?
ACE inhibitors and ANG2 receptor blockers
What is plasma concentration of ANG2 dependent on?
Plasma concentration of renin
What does increased atrial natriuretic peptide (ANP) levels cause?
Increased Na+ excretion
What do cardiac stretch receptors monitor?
Central volume
When are natriuretic peptides released?
When cardiac stretch receptors are distended
What do atrial myocytes release?
ANP
What do ventricular myocytes release?
BNP (brain)
What do NPs antagonize?
RAAS system
What 5 things do NPs cause?
Vasodilation of afferent and vasoconstriction of efferent arterioles
Inhibition of renin secretion
Inhibition of aldosterone secretion
Inhibition of NaCl reabsorption in CD
Inhibition of ADH secretion
