regulation of sodium and water

Question 1

normal Na+ concentration in the ECF

Answer 1

135-145mM.

Question 2

How do losses/gains in ECF sodium affect the concentration of sodium and ECF volume

Answer 2

The concentration of sodium changes relatively little when sodium is lost or gained from the ECF, b/c sodium is usually in osmotic equilibrium. Thus losses or gains in ECF sodium actually cause greater changes in ECF volume than they do in sodium concentration

Question 3

How much does the ECF change in volume compared to the ECF sodium concentration from a gain of sodium

Answer 3

Due to the two-fold greater volume of the cellular over the ECF compartment, gains (or losses) of sodium from the ECF result in two-fold greater changes in ECF volume than they do in ECF sodium concentration.

Question 4

Sensors for sodium regulation

Answer 4

Since the ECF changes volume more than sodium concentration with addition/loss of sodium, sensors for sodium actually monitor changes in ECF volume. These measure mean arterial pressure of major arteries.

Question 5

2. describe the physiological feedback loop involved in the homeostasis of sodium concentration in the ECF.

Answer 5

Loss of ECF Na > shift of water from ECF to cells > decreased ECF volume (decreased MAP)> increased baroreceptor reflexes (arterial and intrarenal) > increased renin > increased angiotensin II > increased aldosterone synthesis/secretion by adrenal cortex > Na reabsorption in distal tubule and collecting duct > addition of ingested Na to ECF

Question 6

What components are monitored in regulation of ECF water levels

Answer 6

ECF volume and osmolarity

Question 7

3. describe the physiological feedback pathway for the regulation of water content in the ECF.

Answer 7

Severe sweating > Decreased ECF volume, decreased left atrial filling pressure and increased baroreceptor reflex to hypothalamus PLUS increased ECF osmolarity and increased activation of hypothalamic osmoreceptors > activation of ADH synthesizing neurons > increased secretion of ADH from post. pituitary > increased water reabsorption in late distal tubule and collecting duct > addition of ingested water to ECF

Question 8

Describe sweat tonicity

Answer 8

Normal sweat is hypotonic, thus severe sweating results in loss of hypotonic fluid which will cause the sweat to become hypertonic

Question 9

Describe changes in ADH secretion with changes in volume or osmolarity alone

Answer 9

Changes in ECF osmolarity cause monotonic, roughly linear changes in ADH levels in the plasma for osmolarity values both above and below normal. Changes in ECF volume have little effect on ADH levels, except when ECF volume falls severely

Question 10

4. identify the dominant pathway involved in water regulation during normal variations in volume and osmolarity.

Answer 10

Osmolarity is dominant and is sensitive to very small changes

Question 11

5. identify the dominant pathway involved in water regulation during severe hypovolemia.

Answer 11

Volume regulation is dominant when volume loss is severe (>10% volume reduction)

Question 12

6. describe the pathways involved in the regulation of ECF volume in a hypervolemic state by atrial natriuretic factor.

Answer 12

ECF volume expansion > increased atrial filling and distension > release of pro-ANP granules from cardiocytes > active ANP increases water and Na excretion by decreasing secretion of ADH, blocking ADH, decreasing renin release, blocking aldosterone action and dilating efferent, afferent arterioles

Question 13

Describe suppression of ADH

Answer 13

There is no suppression of ADH if volumes are above normal