ECF Volume Regulation Flashcards
What is the water composition in the body?
ECF- 14L (plasma-3L, IF-11L)
ICF-28L
How is sodium regulated?
Low and high P receptors detect the blood pressure changes caused by the altered ECF volume.
How does the body try to raise the BP when ECF is reduced?
Reduced ECF means a reduced plasma volume so get a reduced stroke volume and cardiac output therefore the blood pressure decreases. This activates the sympathetic discharge from the carotid sinus which causes systemic vasoconstriction which increases the peripheral resistance. This works to increase the blood pressure.
How do the kidneys work to try to raise the BP when ECF is reduced?
The vasoconstriction triggered also affects the renal arteries. This causes an increase in renin which causes the reaction of angiotensin I to angiotensin II (rate limiting step) so that more NaCl and water are reabsorbed in the proximal tubule. Angiotensin II also triggers aldosterone release from the suprarenal gland which causes the distal tubule to also reabsorb more NaCl and water.
What effect does angiotensin have on blood vessels?
Effective vasoconstrictor
How is GFR affected by ECF volume change?
Autoregulation maintains GFR and the VC of afferent and efferent means little effect on GFR until volume depletion severe enough to cause considerable MBP. If GFR increases then the flow in the arterioles will also increase and this will be picked up by the macula densa and it constricts the afferent arteriole so that hydrostatic pressure increases therefore reducing the GFR back to normal.
What cells produce the hormone renin?
Juxtaglomerular cells
What five things affect renin release?
Increased Renin release when P in afferent arteriole at the level of the JG cells .
JG cells act as “renal baroreceptors”, less distension means increased secretion of renin. Intrinsic property, occurs if denervated.
Increased Sympathetic nerve activity causes increased renin release via Beta 1 effect.
Rate of renin secretion is inversely proportional to rate of delivery of NaCl at the macula densa (specialized distal tubule) Reduced NaCl delivery means more renin
Angiotensin II feeds back to inhibit renin.
ADH inhibits renin release (osmolarity control).
What is ANP and what does it do?
Atrial Natriuretic Peptide promotes Na+ excretion (counteracts aldosterone effect)
Has protective role in the retention of salt and water. The ANP is released from atrial cells and promotes the excretion of Sodium. (has no effect on potassium as this is regulated by aldosterone)
