Ch. 34 Berne and Levy: Control of Body Fluid Osmolality and Volume Flashcards
What are the 2 physiological regulators of ADH secretion?
1) osmolality of body fluids
2) volume and pressure of vascular system (hemodynamic)
During diuresis, ADH activity and production is ______ (low or high)
low
True or false: urea plays a major role in effecting ADH secretion
FALSE (urea is an ineffective osmole with respect to osmoreceptors)
When plasma osmolality INCREASES, ADH synthesis _________
INCREASES (want to save water to bring that plasma osmolality down)
What are the 3 actions of ADH?
1) INCREASE water permeability in the collecting duct
2) INCREASE medullary permeability of urea in collecting duct
3) stimulate NaCl reabsorption in the thick ascending limb and collecting duct
How does ADH affect the urea cycle?
INCREASES permeability of terminal portion of the inner medullary collecting duct to urea (INCREASES reabsorption of urea to increase osmolality of medulla)
True or False: fluid entering descending limb is isosmotic to plasma?
TRUE
Rank sections of the kidney in order of lowest to highest osmolality: outer medulla, inner medulla, cortex
cortex < outer medulla < inner medulla
What is known as the diluting segment and why is it called that?
the thick ascending limb - allows for active NaCl reabsorption
True or False: fluid leaving thick ascending limb is isosmotic to plasma
FALSE; it is hyposmotic
What effect do the distal tubule and collecting duct have on osmolality?
DECREASE it (further reabsorb NaCl)
What establishes the hyperosmotic medullary interstitial gradient?
counter current multiplier
Describe the steps that compromise the counter current multiplier
1) Water permeability of descending limb (passively moves out of tubule increasing osmo of tubular fluid)
2) Salt passively moves out of ascending limb, DT and CD
Where is the site of highest osmolality in tubular fluid
bend of loop of Henle
In the presence of ADH, what makes the urine concentrated, NaCl or urea?
urea
How is the hyperosmotic gradient maintained during antidiuresis when water is reabsorbed?
water is reabsorbed mostly from the cortex > outer medulla > inner medulla
What are the two most abundant species in the medulla?
NaCl and urea
Where is the only place along the nephron where urea can enter?
Descending limb of loop
Why is urea an ineffective osmole when it comes to driving water reabsorption?
inner medullary collecting duct is highly permeable to urea (especially in presence of ADH)
Therefore, urea just equilibrates tubular conc to interstitual conc.
Where does active salt pumping occur?
TAL, DT, CD
What happens to urine flow as vasa recta flow increases?
INCREASES
Which is greater, vasa recta water or salt?
salt
What is negative free water clearance?
Uosm > Posm (trapped water, think of it as negative (ie very little) water in the urine)
What are the 3 main chemical determinants of ECF osmolality?
Na, Cl, HCO3
What is ECV?
effective circulating volume (portion of ECF within vascular system that is effectively perfusing tissues)
What happens to ECV as arterial pressure and cardiac output increase?
INCREASES
How do the low-pressure sensors work to detect effective circulating volume?
cardiac stretch receptors on the venous side of circulation detect increased stretching (more volume) and secrete ANP which induces natriuresis
in cardiac atria and pulm vasculature
When cardiac stretch receptors are activated, what happens to sympathetic stimulation?
DECREASES, ADH decreases, water diuresis
Where are the high pressure sensors and how do they affect sympathetics?
aortic arch and carotid baroreceptors as well as JGA (detects slow tubular flow and decreases symp stim, increasing Na excretion)
DECREASE sympathetics
What are the other two sensors in addition to low and high pressure?
hepatic and CNS
How does sympathetic stimulation affect Na reabsorption?
INCREASES it
How does ANP affect GFR?
increases it (end goal of decreasing water and salt reabsorption to increase urine volume)
What are the three efferent effectors regulating ECV?
Two salt retention
1) renal symp nerves
2) renin-angiotensin-aldosterone
one salt excretion
3) ANP
What are the 3 factors important in stimulating renin secretion?
1) Perfusion pressure (increase perf pres, decrease renin)
2) Symp nerve activity (increase symp, increase renin)
3) Delivery of NaCl to macula densa (increase NaCl delivery, decrease renin?)
What is the enzymatic activity of renin?
converts angiotensinogen to AT1
What converts AT1 to AT2?
ACE (angiotensin converting enzyme)
What effect does AT2 have on ADH?
stimulates its release
What effect does AT2 have on aldosterone?
INCREASES release from the adrenal cortex
aldosterone then binds to receptors on the DT and CD and signals for production of new Na,K ATPase pumps which increases Na reabsorption and K+ secretion/excretion
What stimuli effect the release of ANP?
1) INCREASED ECF
2) INCREASED AP (left atrial pressure)
3) INCREASED VP (right atrial pressure)
basically, high pressure or too much volume (think, natriuertic wants to produce urine, wants to do that because there is too much volume)
How does ANP secretion effect renin, ADH, Na excretion, symp stim?
decreases renin
decreases ADH
increases Na excretion
decreases symps
What is euvolemia?
Na intake matches excretion
Where in the nephron does the 99% reabsorption of Na occur?
1) PT: 67%
2) TAL: 25%
3) DT: 4%
4) CD: 3%
What are the 3 integrated responses of the nephron to INCREASED ECV?
1) increased GFR
2) decreased Na reabsorption in PT
3) decreased Na+ reabsorption in CD
Why does an increase in ECV decrease Na reabsorption?
because Na in the interstitium pulls water and that continues to increase ECV
What are the two most common causes of edema in terms of Starling forces?
1) increased hydrostatic pressure
2) decreased oncotic pressure
