Pathophysiology of Sodium Handling

Question 1

LO 1. Discuss the concept of effective arterial blood volume and the hormonal mechanisms involved in its maintenance. Must also under understand how these systems interact when one (or several) components are diseased.

Answer 1

Effective arterial blood volume (EABV):
This is the volume of blood that is detected by volume sensors, located in the arterial side of the circulation. It is the amount of arterial blood volume required to adequately “fill” the capacity of arterial circulation.

Low volume sensors on the venous side. High volume are in the arterial side (carotid + aortic arch). Intrarenal occurs in macula densa - Kidney responds to low arterial pressure, causes release of renin, which activates RAAS.

Antinaturesis: ATII, Aldosterone, catecholamines, vasopressin (ADP) - preserves salt and water

Natriuresis: Natriuretic peptides, prostaglandins, bradykinin, dopamine - gets rid of as much salt/water as can

Question 2

LO 2. Discuss the forces involved in edema formation and maintenance.

Answer 2

1. Alteration in Starling forces
2. Arterial underfilling resulting in decreased effective arterial circulating volume
3. Excessive renal sodium and water retention

Question 3

LO 3. Identify the nephron site of action as well as potential side effects of diuretics.

Answer 3

Diuretics acting at the proximal tubule: Acetazacross the apical membrane into distal tubular cells. Therefore, they limit the diluting ability of the distal nephron, but have no effect on the concentrating gradient generated by the loop of Henle. They have the same side effects as the loop diuretics, except that they increase calcium reabsorption and decrease urinary calcium excretion.

Diuretics acting at the collecting ducts:
Triamterene and amiloride are sodium channel blockers, and spironolactone is a competitive inhibitor of aldosterone. These diuretics cause mild natriuresis and potassium retention. Spironolactone can be used in states of secondary hyperaldosteronism such as cirrhosis with ascites. These potassium-sparing diuretics can be used together with other classes of diuretics to prevent hypokalemia

Question 4

LO 4. Describe the “fate” of intravenous fluids containing different amounts of colloids, sodium, and glucose.

Answer 4

colloids: increase in plasma volume only
saline: increase in ECF and plasma volume
D5w: slight increase in all volume areas