Regulation of ECF Volume and NaCl Balance

Question 1

What is effective circulating volume?

Answer 1

Portion of the ECF volume that is in the arterial system under particular pressure and is effectively perfusing the tissues.

Not measurable

0.7 L of vascular volume is ECV

Question 2

What is congestive heart failure?

Answer 2

Decreased cardiac output causing a decrease in effective circulating volume

Na+ and Fluid retention occurs, causing edema (which increases venous and capillary hydrostatic pressure)

Na+ and fluid retention continues without any improvement in ECV

Question 3

What are the four main responses seen when Effective Circulating Volume decreases?

Answer 3

• RAAS activation
• ADH secretion
• Sympathetic nervous system stimulation via barroreceptor reflex
• Increased renal fluid retention via altered Starling’s forces in peritubular capillaries

Question 4

What are the two functions of the osmoreceptors in the hypotalamus?

Answer 4

Regulate ADH secretion

Regulate thirst

Question 5

What controls ADH secretion?

Answer 5

Osmoreceptors (ADH secreted when osmolality increases)

Baroreceptors (ADH secreted when blood volume decreases)

Osmoreceptors are more sensitive than baroreceptors