33 Renal Transport of Sodium and Chloride Flashcards
how does the kidney help to maintain the body’s extracellular fluid (ECF) volume?
by regulating the amount of sodium in the urine
this ion is the most important contributor to the overall osmolality of the ECF?
Sodium and so wherever sodium goes water follows
this reabsorbs the largest fraction of filtered Na+
proximal tubule
what percent of the proximal tubule reabsorbs the largest fraction of filtered Na+?
67%
what percent does the loop of Henle reabsorb?
25%
what is the loop of Henle?
the classic distal tubule and collecting ducts reabsorb smaller fractions of filtered Na+
The segments between the distal convoluted tubule and the cortical collecting tubule reabsorb what percent of the filtered Na+ load?
approximately 5%
the medullary collecting duct reabsorbs what percent of the filtered Na+ load?
3%
what is the effect of furosemide on sodium?
its a loop diuretic used to decrease sodium
what part of the kidney carries the most concentrated urine? least concentrated?
thin descending loop of henle (tDLH); end of the thick ascending limb of henle’s loop (TAL) or beginning of distal convoluted tubule
when does glucose start appearing in the blood?
170-180 mg/dl, sodium glucose cotransporters are saturated
which of the tubules has the most ATP usage?
proximal tubule because its what sees what comes from the bowman space and passage of molecules reabsorbed back into the blood
what is the effect of water reabsorption on the proximal tubule?
Na+ can move uphill from lumen to blood»_space;> the movement of water is not active, but passively follows the reabsorption of Na+
the water permeability of the proximal-tubule epithelium to water is very high
how does water move through the proximal tubule epithelium?
via both trans- and para-cellular pathways.
Transcellular route dominates due to presence of high density of AQP1 water channels on the apical and basolateral membranes
in terms of water reabsorption and proximal tubule, why does the trans cellular route dominate?
due to presence of high density of AQP1 water channels on the apical and basolateral membranes
in the absence of arginine vasopressin (AVP or antidiuretic hormone), what is the water permeability on the TAL and all downstream segments?
relatively low water permeability
what is osmotic diuresis?
whatever you start from first filtration sites you can put out the same amount, i.e. 300 mOsm; using mannitol
what is the regulation of the Na+ and Cl- transport based on?
Glomerulotubular balance
Renin-angiotensin aldosterone / Arginine vasopressin / Sympathetic Division of the Autonomic Nervous System
Five natriuretic humoral factors
what are the effects of the regulation of the Na+ and Cl- transport?
(1) Glomerulotubular balance»_space;> fractional Na+ reabsorption
(2) Renin-angiotensin aldosterone / Arginine vasopressin / Sympathetic Division of the Autonomic Nervous System»_space;> increase Na+ reabsorption
(3) Five natriuretic humoral factors»_space;> decrease Na+ reabsorption
with glomerular balance, what happens if excessive Na+ loss contracts the extracellular fluid volume? what happens in response
the reduced renal perfusion pressure causes GFR to fall
In response, the proximal tubule excretes a constant fraction of Na+ and water, which corresponds to a smaller absolute amount
GT balance helps prevent additional Na+ and water loss
In contrast to GT balance in the proximal tubule, increasing flow by a factor of four in the distal nephron causes cumulative Na+ reabsorption to rise by how much?
only a factor of two
what is circulatory shock?
When GFR, and thus distal flow, acutely falls, as in circulatory shock, the proximal nephron reabsorbs a constant fraction of Na+, and delivers a lower absolute amount of Na+ to the distal convoluted tubule (GT balance)
as a result
Distal reabsorption lowers luminal [Na+] even further -under the influence of neural and humoral factors»_space;> the final urine contains only traces of Na+
how does the Renin-Angiotensin-Aldosterone work?
Aldosterone stimulates Na+ reabsorption by initial and cortical collecting tubules, and by medullary collecting ducts
Only 2-3% of the filtered Na+ load is under control by aldosterone
The lack of aldosterone (Addison’s disease) can lead to severe Na+ depletion»_space;> circulatory insufficiency
Aldosterone acts on the principal cells of the collecting ducts
Physiological increases in aldosterone concentration raise the product of number of channels and open probability
Cellular Actions of Aldosterone?
Aldosterone binds to cytoplasmic mineralocorticoid receptors
Chronic exposure to aldosterone»_space;> targeting of newly synthesized Na-K pumps to the basolateral membrane & amplification of the basolateral membrane area
Sympathetic ANS
Norepinephrine reduces renal blood flow & GFR
Proximal GT balance & the flow response of the distal nephron decreases Na+ excretion
Stimulates granular cells to release renin
Activates –adrenergic receptors on renal tubule cells increase Na+ reabsorption
Arginine Vasopressin
Renal effect of AVP is to produce urine with a high osmolality and thus retain water
AVP increases water permeability of the collecting tubules and ducts, allowing water to exit the tubule lumen and enter the hypertonic medullary interstitium
ANP
Increases GFR, increases cortical and medullary blood flow, decreases renin and AVP, to promote natriuresis (elimination of extra Na in the urine)
Directly inhibits Na+ transport in the inner medullary collecting duct
Prostaglandins and Bradykinin
Act through protein kinase C to inhibit Na+ reabsorption
Dopamine
Causes renal vasodilation, which increases Na+ excretion & directly inhibits Na+ reabsorption at the level of tubule cells
