Regulation Of ECF Volume And NaCl Balance

Question 1

What occurs if ADH is always high?

Answer 1

If it is always high, then sodium is no longer controlled by ADH and is then controlled by free water that is taken in

This means that there is a diluted plasma osmolality and hyponatremia

Question 2

What is effective circulating volume?

Answer 2

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

0.7 L of vascular volume forms the ECV

Question 3

Why is there edema with CHF?

Answer 3

There is an increase in TBW but a decrease in ECV, so without adding that water to the circulating volume, it is held in the interstitium, leading to edema

Question 4

What are the four ways to counteract decreases in ECV?

Answer 4

1. Activation of RAAS
2. Stimulation of the sympathetic nervous system via the baroreceptor reflex
3. Increased ADH secretion
4. Increased renal fluid retention via altered Starling’s forces in the peritubular capillaries

Question 5

What are the two main functions of the osmoreceptors?

Answer 5

1. To regulate the release of antidiuretic hormone

2. To regulate thirst

Question 6

Which system is more sensitive: osmoreceptor or baroreceptor?

Answer 6

Osmoreceptors

Question 7

What do problems with sodium balance typically manifest as?

Answer 7

Altered ECF volume

Which is sensed in the ECV by the arterial and cardiac baroreceptors, which leads to RAAS/SNS activation and urine Na excretion

Question 8

What do problems with water balance typically manifest as?

Answer 8

Altered plasma osmolality

This is sensed in the plasma osmolality by the hypothalamic osmoreceptors, leading to ADH secretion to increase urine osmolality (H20 output) and thirst

Question 9

If ECFV is expanded, what happens to renal NaCl and water?

Answer 9

Excretion is increased for both

Question 10

If ECFV is contracted, what happens to renal NaCl and water?

Answer 10

Excretion is reduced

Question 11

What occurs with activation of the renal sympathetic nerves?

Answer 11

Increased activity = decreased NaCl excretion

Decreased GFR

Increased Renin secretion

Increased Na+ reabsorption along the nephron

Question 12

What occurs with activation of RAAS?

Answer 12

Decreased NaCl excretion

Increased Angiotensin II which stimulates Na+ reabsorption along the nephron

Increased Aldosterone stimulates Na+ reabsorption in the DT and CD

Increased Angiotensin II stimulates ADH secretion

Question 13

What occurs with increased secretion of ANP, BNP, and Urodilatin?

Answer 13

There’s increased NaCl excretion

Increased GFR, decreased Renin secretion, decreased aldosterone secretion, decreased NaCl and water reabsorption by the collecting duct, and decreased ADH secretion

Question 14

What occurs with increased ADH secretion?

Answer 14

Decreased water excretion

So there is increased water reabsorption by the distal tubule and collecting duct

Question 15

What are the major mechanisms for the regulation of renin release?

Answer 15

Perfusion pressure (low perfusion in afferent arterioles stimulates renin secretion and vice versa)

Activation of sympathetic nerve activity

NaCl deliver to macula densa (when NaCl is decreased, then renin is stimulated, which is called the tubuloglomerular feedback)

Question 16

Where is ANP produced?

Answer 16

It is produced in the atrial cardiac muscle cells

Question 17

What does ANP do?

Answer 17

It promotes natriuresis and accompanying diuresis, decreasing the plasma volume, and lowering BP

Directly inhibits Na+ reabsorption in the distal parts of the nephron and inhibits RAAS (renin, aldosterone, and ADH)

Question 18

If there is an increase in ECV, what are the results?

Answer 18

Decreased renin, angiotensin ii, aldosterone, ADH secretion, and sympathetic activity

Increased release of ANP and BNP by the heart and urodilatin by the kidneys

Question 19

If there is a decrease in ECV, what are the results?

Answer 19

Increased renal sympathetic nerve activity, renin secretion, angiotensin ii levels, secretion of aldosterone, and ADH secretion

Question 20

What is hyponatremia defined as?

Answer 20

A serum sodium of <135 mEq/L and a serum osmolality of <280 mOsm/kg