Homeostatic Regulation of Na

Question 1

2 things that can happen to the extracellular compartment if the number of sodium ions in the body increases

Answer 1

Extracellular compartment can increase in osmolarity

Extracellular compartment will increase in size as water is added to preserve the osmolarity

Question 2

Effective circulating volume

Answer 2

Basically the blood volume
It is a fixed fraction of the total extracellular volume
This statement changes in disease states

Question 3

Where are low pressure sensors in the body?

Answer 3

Atria, ventricles (R) and pulmonary circulation

Question 4

Where are high pressure sensors in the body?

Answer 4

Carotid artery
Aortic arch
Renal arteries

Question 5

Low pressure sensors

location, stimulation, response

Answer 5

Located in areas of lower BP (atria, RV, pulmonary circulation) where changes in blood volume do not cause large changes in blood pressure
Stimulus: increasing pressure/stretch
Response: inhibition of ADH, release of ANP and BNP

Question 6

Low pressure sensors sense _____

High pressure sensors sense ____

Answer 6

Low: stretch/increasing pressure (volume)
High: decrease in arterial pressure (pressure)

Question 7

Net effect of low pressure sensor activation

Answer 7

Increases blood volume here suggests increased ECFV so it is sensed as an increase in total body salt and water
Decrease in ADH allows more water excretion
ANP and BNP allow more natriuresis
Shrink blood volume

Question 8

High levels of BNP suggest what disease?

Answer 8

Congestive heart failure

Question 9

High pressure sensors

location, stimulation, response

Answer 9

Stretch receptors in the carotid artery, aortic arch and arterioles of the kidney, that are more sensitive to pressure than volume
Stimulus: decrease in arterial pressure
Response: increase in sympathetic NS activity, increase ADH release, activate RAAS, inhibit ANP

Question 10

What physiologic effects does increased sympathetic NS activity (from decreased circulating volume) have?

Answer 10

Increase HR, CO
Increase vascular tone
Decrease GFR
Increase renin secretion
Increase renal Na reabsorption
Overally: decrease renal Na excretion to raise the effective circulating volume

Question 11

Sodium handling: filtration across the glomerular basement membrane

Answer 11

NaCl is in solution and is freely filtered across the BM

[Na] at the start of the proximal tubule = serum [Na]

Question 12

Sodium handling: proximal tubule

Answer 12

The cells themselves are almost completely free of Na because of the basal Na/K ATPase
60% of filtered Na is reabsorbed here
Mostly via the Na/H antiporter, Na/glucose co-transporter, or Na/AA co-transporter
This is not a site for potent diuretics (a lot of time to reabsorb later)
Further down a Cl gradient is established and NaCl can be passively reabsorbed
At the end the [Na] is the same as plasam

Question 13

Sodium handling: loop of henle

Answer 13

Important site for reabsorption of ~25% of filtered Na, but less water
Powered by basolateral Na/K ATPase
Na/K/2 Cl symporter brings ions in with concentration gradient (but needs ATP)

Question 14

Loop diuretics inhibit what channel

Answer 14

NKCC2

Used when ECF volume overload is suspected

Question 15

Sodium handling: distal tubule

Answer 15

Early part reabsorbed NaCl without water

Na/Cl symporter is the main channel

Question 16

Thiazide diuretics inhibit what channel

Answer 16

The Na/Cl symporter (NCC)

Not as potent as loop diuretics but are commonly used to treat hypertension

Question 17

2 main sites that Na can be excreted from

Answer 17

Loop of Henle

DCT

Question 18

Sodium handling: collecting duct/tubule

Answer 18

Principal cells carry out NaCl reabsorption via an ENaC

Site of action of aldosterone (increase Na reabsorption in exchange for K excretion)

Question 19

Aldosterone antagonists

Answer 19

K sparing diuretics

Inhibit the cells in the collecting duct that exchange Na for K

Question 20

Main prostaglandin in the kidney

Answer 20

PGI2

Question 21

Effect of prostaglandins on the kidney

Answer 21

Afferent arteriolar vasodilation and natriuresis
In response to Na conserving and vasoconstricting stimuli
In healthy subjects, there is little or no basal PGI2 synthesis

Question 22

Renal effects of ANPs

Answer 22

Increased GFR
Natriuresis (K sparing)
Antagonism of almost all actions of the RAAS

Question 23

Uroguanylin

Answer 23

Gut natriuretic peptide
Produced in the intestine in response to salt intake
Reduced renal Na reabsorption, helping to compensate for the ingestion of dietary Na
Not yet a target for intervention

Question 24

Increased ANP and BNP from an increased effective circulating volume causes…

Answer 24

Increased GFR
Decreased renin secretion
Decreased aldosterone secretion
Decreased Na reabsorption
Overall: Increased Na and H2O excretion