33 Renal Transport of Sodium and Chloride

Question 1

how does the kidney help to maintain the body’s extracellular fluid (ECF) volume?

Answer 1

by regulating the amount of sodium in the urine

Question 2

this ion is the most important contributor to the overall osmolality of the ECF?

Answer 2

Sodium and so wherever sodium goes water follows

Question 3

this reabsorbs the largest fraction of filtered Na+

Answer 3

proximal tubule

Question 4

what percent of the proximal tubule reabsorbs the largest fraction of filtered Na+?

Answer 4

67%

Question 5

what percent does the loop of Henle reabsorb?

Answer 5

25%

Question 6

what is the loop of Henle?

Answer 6

the classic distal tubule and collecting ducts reabsorb smaller fractions of filtered Na+

Question 7

The segments between the distal convoluted tubule and the cortical collecting tubule reabsorb what percent of the filtered Na+ load?

Answer 7

approximately 5%

Question 8

the medullary collecting duct reabsorbs what percent of the filtered Na+ load?

Answer 8

3%

Question 9

what is the effect of furosemide on sodium?

Answer 9

its a loop diuretic used to decrease sodium

Question 10

what part of the kidney carries the most concentrated urine? least concentrated?

Answer 10

thin descending loop of henle (tDLH); end of the thick ascending limb of henle’s loop (TAL) or beginning of distal convoluted tubule

Question 11

when does glucose start appearing in the blood?

Answer 11

170-180 mg/dl, sodium glucose cotransporters are saturated

Question 12

which of the tubules has the most ATP usage?

Answer 12

proximal tubule because its what sees what comes from the bowman space and passage of molecules reabsorbed back into the blood

Question 13

what is the effect of water reabsorption on the proximal tubule?

Answer 13

Na+ can move uphill from lumen to blood&raquo_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

Question 14

how does water move through the proximal tubule epithelium?

Answer 14

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

Question 15

in terms of water reabsorption and proximal tubule, why does the trans cellular route dominate?

Answer 15

due to presence of high density of AQP1 water channels on the apical and basolateral membranes

Question 16

in the absence of arginine vasopressin (AVP or antidiuretic hormone), what is the water permeability on the TAL and all downstream segments?

Answer 16

relatively low water permeability

Question 17

what is osmotic diuresis?

Answer 17

whatever you start from first filtration sites you can put out the same amount, i.e. 300 mOsm; using mannitol

Question 18

what is the regulation of the Na+ and Cl- transport based on?

Answer 18

Glomerulotubular balance

Renin-angiotensin aldosterone / Arginine vasopressin / Sympathetic Division of the Autonomic Nervous System

Five natriuretic humoral factors

Question 19

what are the effects of the regulation of the Na+ and Cl- transport?

Answer 19

(1) Glomerulotubular balance&raquo_space;> fractional Na+ reabsorption
(2) Renin-angiotensin aldosterone / Arginine vasopressin / Sympathetic Division of the Autonomic Nervous System&raquo_space;> increase Na+ reabsorption
(3) Five natriuretic humoral factors&raquo_space;> decrease Na+ reabsorption

Question 20

with glomerular balance, what happens if excessive Na+ loss contracts the extracellular fluid volume? what happens in response

Answer 20

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

Question 21

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?

Answer 21

only a factor of two

Question 22

what is circulatory shock?

Answer 22

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&raquo_space;> the final urine contains only traces of Na+

Question 23

how does the Renin-Angiotensin-Aldosterone work?

Answer 23

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&raquo_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

Question 24

Cellular Actions of Aldosterone?

Answer 24

Aldosterone binds to cytoplasmic mineralocorticoid receptors

Chronic exposure to aldosterone&raquo_space;> targeting of newly synthesized Na-K pumps to the basolateral membrane & amplification of the basolateral membrane area

Question 25

Sympathetic ANS

Answer 25

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

Question 26

Arginine Vasopressin

Answer 26

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

Question 27

ANP

Answer 27

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

Question 28

Prostaglandins and Bradykinin

Answer 28

Act through protein kinase C to inhibit Na+ reabsorption

Question 29

Dopamine

Answer 29

Causes renal vasodilation, which increases Na+ excretion & directly inhibits Na+ reabsorption at the level of tubule cells