Quiz, block 2- Renal system Flashcards
How does the Loop of Henle and CD play a role in the countercurrent multiplier system?
Loop of Henle and CD keep a progressively hyperosmotic Na+ gradient deep into the medulla to allow for reabsorption/retention of water within the interstitial fluid space. Hence, water won’t be excreted.
what organ is most responsible for maintaining acid-base homeostasis?
kidney!
what are two reflex receptors that control body Na+?
- arterial baroreceptors in the CV system
2. sensors in kidney that monitor the filtered load of Na+
what are the consequences of low total body Na+?
- results in low ECF volume
- low plasma volume
- low arterial and venous blood pressure
what’s the obligatory water loss volume and define it?
0.46L/day (minimal amount or urine- water loss- that you need to form to carry wastes away.
how is the concentrated urine gradient (hyperosmotic fluid) formed?
- in juxtamedullary nephrons, NaCl are actively pumped out of ascending limb of loop of Henle into interstitial fluid that surrounds the loop. Water would follow Na+ into the IS fluid and get retained there/can’t exit the loop b/c it’s impermeable to it.
- -the effect is multiplied by the countercurrent flow through the loops. this concentrates the renal medullary interstitium to a maximum of about 1400 mOsmol. - UREA also get trapped in the interstitium
- VASA RECTA (blood supply of renal medulla) has a counter current construction that prevents the “washing out” of Na+ conc gradient (prevent blood from carrying off Na+ with it).
how is urine concentration affected by high blood ADH levels?
high ADH levels- water diffuses out of filtrate medullary CDs into the renal medullary interstitial space, producing a small volume of hyperosmotic/concentrated urine when one is thirsty. then water enters the capillaries of the renal medulla to be carried away in venous blood.
how is urine concentration affected by low blood ADH levels?
both the cortical and medullary CDs are impermeable to water, so water is not reabsorbed as the filtrate flows through the CD, and a large volume of hypoosmotic urine is formed (lots of water in urine).
what are the two corrective reflexes in response to low BLOOD PRESSURE?
- control of GFR.
the reflexes are set into motion by CV baroreceptors, thus regulating the mean systemic arterial pressure (MAP), simultaneously achieves regulation of total body Na+ - control of Na+ reabsorption (more important regulation than of GFR) via hormonal control (aldosterone)
Describe the direct effect of controlling GFR as one of the corrective reflexes in response to low blood pressure.
low plasma volume (possibly due to low total body Na+, thus water).
- leads to LOW arterial blood pressure that results in a decreased net glomerular filtration pressure, that decreased GFR
- > decreased Na+ and water excreted
- > bp rises
Describe the INdirect effect of controlling GFR as one of the corrective reflexes in response to low blood pressure.
Low plasma volume (possible due to low total body Na+, thus water). leads to LOW arterial blood pressure.
-this increase activity in SYMPATHETIC nerves to kidneys (motor pathway).
-constricts AFFERENT arterioles of kidney to decrease net glomerular filtration pressure.
Also:
hormonal control of secretion of angiotensin and ADH decrease net glomerular filtration pressure as well.
–> both result in decrease GFR, which decrease Na+ and water excretion.
- bp rises!
what plasma protein get secreted by the liver?
angiotensinogen (At’n)
what does the kidney secrete, and its function?
renin that breaks angiotensinogen into angiotensin I.
renin, an enzyme, secreted by the juxtaglomerular cells (JG cells), part of the JG apparatus of the kidney.
what does the walls of lung capillary secrete?
angiotensin-converting enzyme (ACE or converting enzyme) that convert angiotensin I into angiotensin II.
what organ does angiotensin II act on?
AT II leaves the blood and signals the adrenal cortex to secrete aldosterone to tell kidney to increase reabsorption of Na+
what organ secretes aldosterone and what is the function of that hormone?
adrenal cortex secretes aldosterone and other steroids.
aldosterone- increase Na+ reabsorption rate in the CD and late distal tubule.
in absence of aldosterone,
how much of total filtered Na+ is reabsorbed in the proximal tubule, in the loop of Henle and first part of distal tubule? where does most of unregulated reabsorption occur at?
65% (not regulated) of total filtered Na+ is reabsorbed in the proximal tubule,
with another 30-32% reabsorbed in the loop of Henle and first part of distal tubule (regulated?).
**most reabsorption occurs early and not regulated
at high plasma levels of aldosterone,
how much of filtered Na+ is reabsorbed in the proximal tubule. Complete reabsorption of the last 4% occur at the late DT and CD.
nearly 100% of filtered Na+ is reabsorbed, with the remaining Na+ being reabsorbed in the late DT and CD.
Complete reabsorption of the last 4%
what are the 3 inputs that JG cells receive to increase renin secretion?
Renin is secreted by JG cells. JG cells receive 3 inputs that activate it.
1. Stimulation of sympathetic nerves to the JG cells in kidneys. Sympathetic nerves- activated by the baroreceptor reflex that was discussed in low blood pressure scenario.
- baroreceptors within the kidney that get activated by DECREASED stretch resulting from decreased blood pressure within the kidney
* less stretch: activate baroreceptors. - paracrine factors released from macula densa. This is in response to a decreased volume and/or conc. of Na+ in tubular fluid flowing past the macula densa cells.
what effect does increased Na+ in the body leads to regulation of arterial blood pressure?
cause water to be reabsorbed and also due to osmotic considerations.
this reabsorbed water plus retained Na+ –> increases ECF volume (thus plasma volume). This plays an important role in long-term regulation of arterial blood pressure.
what is the function of the cardiac hormone? its function?
atrial natriuretic peptide (ANP) decreases Na+ reabsorption by directly inhibiting aldosterone secretion.
what are the 3 ways that plasma ANP increase Na+ excretion under condition of high plasma volume, so less Na+ are present in plasma (thus lower plasma volume)?
- kidney tubules decrease Na+ reabsorption
- kidney vessels: dilate the afferent arterioles and constrict efferent arterioles. this damn up blood and increase bp or increase GFR
- inhibit adrenal cortex from secreting more aldosterone, which increase Na+ excretion
how is water regulated?
unlike Na+, which stays in the ECF when added to the body, water distributes throughout all the body fluid compartments w/ 2/3 entering the intracellular comparment. Thus, pure water (w/o Na+) gains or losses only slightly influence BLOOD PRESSURE (and thus baroreceptors).
what’s involved in water excretion reflexes?
there are reflexes that alter water excretion without altering sodium excretion. this reflex is:
a. initiated by sensory receptors in the hypothalamus called OSMORECEPTORS that detect ECF osmolarity level.
b. mediated by posterior pituitary hormone, ADH
how are hypothalamic osmoreceptors respond to high ECF osmolarity via control of ADH secretion rate?
they are neurons that increase their frequency of action potentials when they shrink. they shrink when ECF osmolarity is ABOVE NORMAL, which causes water to be pulled out of the cells and into the ECF by osmosis.
-osmoreceptors synapse on neurons that have cell bodies in the hypothalamus and have axons that travel down into and release ADH from the posterior pituitary.
what are steps following ingestion of excess distilled water?
this decrease ECF osmolarity
–> leads to inhibition of (decrease firing) by hypothalamic osmoreceptors
–> decrease ADH secretion from posterior pituitary
–> decrease plasma ADH
–> decrease permeability of renal collecting ducts to water
–> decrease water reabsorption
INCREASE water excretion (more water end up in urine)