Regulation of ECF Volume and NaCl Balance

Question 1

What ion is the primarily involved in long-term regulation of ECF volume?

Answer 1

Na+

Question 2

What is primarily involved in long-term regulation of ECF osmotic balance?

Answer 2

Water

Question 3

Effective circulatory volume (ECV)

Answer 3

Portion of ECF vol. that is in the arterial system under pressure and is perfusing tissues.
Not measurable.
Approx. 0.7 L of vascular vol. forms the ECV.

Question 4

CHF

Answer 4

Low ECV due to decreased CO.

Na+ and fluid retention causing edema.

Question 5

Decreasing the ECV is counteracted in 4 ways:

Answer 5

1. • RAAS
2. Stimulate SNS via baroreceptors.
3. Increase ADH
4. Increase renal fluid retention by altering the Starling forces in peritubular capillaries.

Question 6

What is the most important non-osmotic stimulus of ADH release?

Answer 6

Decreased BP

Question 7

Effect of small changes in ADH?

Large ones?

Answer 7

Small changes (5%-10%) have little effect.
Larger changes (20%) ADH rises to a level beyond what is necessary to maintain antidiuresis.

Question 8

Stressed volume on osmolality and ADH release

Answer 8

The body can become sensitize so that smaller changes in osm induce larger amts of ADH release.
If body sense vol expansion, there is a higher threshold for release of ADH and a less vigorous response to hyperosmolarity.

Question 9

Arterial baroreceptors

Answer 9

Sense pressures in aorta and carotid to send info to brainstem which regulates BP via autonomics.

Question 10

CP baroreceptors

Answer 10

Sense pressures in the atria and pulmonary as. Also send affarent info in parallel w/ arterial baroreceptors.

Question 11

Which baroreceptors have a greater impact on hypothalamus (i.e. ADH)?

Answer 11

CP baroreceptors

Question 12

Intrarenal receptors

Answer 12

Major role in RAAS system.

Question 13

Problems w/ water balance typically manifest as:

Answer 13

Altered plasma osmolality (changes in Na+).

Question 14

ECF volume
Sensed:
Sensor:
Effector:
Affected:

Answer 14

Sensed: ECV
Sensor: Arterial and cardiac baroreceptors
Effector: Ang II/aldosterone/SNS/ANP
Affected: Urine Na excretion

Question 15

Plasma osm
Sensed:
Sensor:
Effector:
Affected:

Answer 15

Sensed: Plasma osm
Sensor: Hypothalamic osmoreceptors
Effector: AVP
Affected: Urine osm and thirst

Question 16

ADH response to plasma osm changes (3)

Answer 16

1. Change in Na cause change in plasma osm.
2. Body alters water intake and renal water absorption to maintain isotonic ECF.
3. Osm is maintained at expense of ECF vol.
   - -> increase in total body Na content.
   - -> eventual ECF expansion.

Question 17

Renal sympathetic nerves (renal SNA)

Answer 17

Dec. GFR
Inc. renin secretion
Inc. Na+ reabsorption

Question 18

RAAS

Answer 18

Inc. angiotensin II (Na+ reabsorption)
Inc. aldosterone (Na+ reabsorption in DCT, CD, and TAL)
Inc. angiotensin II stimulates avp

Question 19

Natriuretic peptides (ANP, BNP, etc)

Answer 19

Inc. GFR
Dec. renin secretion
Dec. aldosterone secretion
Dec. NaCl and water reabsorpiton by CD
Dec. AVP secretion
AVP

Question 20

AVP

Answer 20

Inc. water reabsorption by DCT and CD.