Regulation of EF Volume and NaCl Balance Flashcards
What is effective circulating volume?
portion of ECF volume that is effectively perfusing the tissues
not a measurable or distinct compartment
about 1.7% of TBW or 1% of body weight
What occurs in congestive heart failure in relation to fluid compartments?
low ECV due to reduced CO
Na and fluid retention –> increase ECF, but still no increase in ECV
What are the 4 ways to counteract decreases in effective circulating volume?
- Activation of RAAS
- baroreceptor reflex –> sympathetic stimulation
- increased ADH
- increased renal fluid retention via altered starlings forces in the peritubular capillaries
What do osmoreceptors sense, and what are their 2 functions?
sense changes in plasma osmolality
regulate ADH and thirst
What are the 2 sensors affecting ADH secretion?
Which is more sensitive?
osmoreceptors
baroreceptors
osmoreceptors are more sensitive!
How much does blood pressure need to fall for ADH to rise to compensate?
by 20%
How does decreases of sensed blood volume affect ADH?
sensitizes the osmoreceptor-ADH system, so that smaller changes of osmolality induce larger amounts of ADH
opposite for expansion –> desensitized
Which type of baroreceptor specifically affects ADH?
how?
cardiopulmonary baroreceptors
sense pressure in atria and pulmonary arteries –> hypothalamus –> ADH
also send afferent info to brainstem w/ arterial baroreceptors
What do arterial baroreceptors do?
sense pressures in aorta and carotid arteries –> afferent to brainstem vasomotor center –> autonomic efferents regulate TPR, cardiac performance, sympathetic drive to kidney, venous compliance
(cardiopulmonary baroreceptors can do the same thing in addition to signaling hypothalmus)
How do problems with sodium balance manifest?
as altered ECF volume –> signals baroreceptors –> RAAS/SNS/ANP –> urine Na excretion affected
How do problems with water balance manifest?
plama osmolality abnormality –> osmoreceptors sense –> hypothalamic osmoreceptors –> ADH –> urine osmolality/water retention and thirst
What is the effect of renal sympathetic nerve stimulation?
decreased GFR
increased renin secretion
increased sodium reabsorption along nephron
What are the effects of the Renin-Angiotensin-Aldosterone system on the kidney?
Angiotenin II –> Na reabsorption along nephron and ADH secretion
Aldosterone –> Na reabsorption in DT and CD and lesser degree in TAL
What effect do ANP, BNP, and Urodilatin have on the kidney?
increased GFR
decreased renin
decreased aldosterone (indirect via angiotensin II and direct on adrenal gland)
decreased NaCl and water reabsorption by CD
Decreased ADH and inhibition of its action of DT and CD
What are the 3 main causes for renin secretion?
- Perfusion pressure in afferent arterioles
- sympathetic nerve activity
- NaCl delivery to macula densa (tubuloglomerular feedback)
Where is the macula densa?
proximal part of distal tubule
What is the main action of ANP?
directly inhibits Na reabsorption in the distal parts of the nephron –> pee out more Na and H2O to lower blood volume
also inhibits renin secretion and acts on adrenal cortex to inhibit aldosterone
How is sodium reabsorbed in the early proximal tubule?
isoosmotic reabsorption
apical side: co-transported w/ glucose, AAs, Pi, lactate; exchanged for H+
Basolateral side: Na/K ATPase
Where do carbonic anhydrase inhibitors work, and what is their effect?
Act on the early PT
inhibit reabsorption of filtered HCO3 –> indirectly lead to decreased absorption of Na
How is Na reabsorbed in the late proximal tubule?
Filtered glucose, AAs, and HCO3- have been already absorbed
Na is reabsorbed with Cl-
How does an ECF volume contraction affect PCT reabsorption?
increases it
How does an ECF volume expansion affect PCT reabsorption?
decreases it
How is sodium reabsorbed in the TAL?
apical side: NKCC
basolateral side: Na-K ATPase
How is Na reabsorbed in the early distal tubule?
apical side: Na-Cl cotransporter
basolateral side: Na-K ATPase
Which type of cell in the collecting duct reabsorbs Na and H2O?
principal cells
