1. Normal osmolality of serum
A. 260
B. 270
C. 280
D. 290
E. 300
Body maintains the serum osmolality within a 2 mOsm of 280. It is virtually constant day to day, irrespective of solute and fluid intake.
2. What is the intracellular osmolality when the plasma osmolality is 280?
A. 270
B. 280
C. 290
Water is freely permeable across cell membrane and interstitium. The osmolality of vascular, interstitial and intracellular space have as a result the same osmolality.
3. Cells defend their
A. Size
B. Osmolality
When there is a decrease in serum osmolality and water moves into cell to equilibrate. Starling forces regulate fluid transfer between ICF and ECF. This will increase the size of the cell. The cells normalize their size by leaking potassium. Sodium leaks into cells. Thus cells alter solute content to keep the size optimal.
4.Serum osmolality is contributed by. Select all that are correct.
A. Sodium
B. Potassium
C. Glucose
D. BUN
E. Creatinine
Serum osmolality is calculated by the following formula
(2xSerum Sodium) + (Serum glucose/18) + (BUN/2.8) mOsm/kg
5. In hyperglycemic state glucose can freely enter cells to balance osmolality.
A. True
B. False
You need insulin to drive the glucose into cells. Obviously there is not enough Insulin in hyperglycemic states. Hence it will increase serum osmolality and will draw water out of cells.
6. BUN cam freely enter cells, thus does not contribute to osmolar imbalance between ICF and ECF.
A. True
B. False
7. Which of the following is defended as a priority by the body?
A. Volume
B. Osmolality
Body defends the volume first. Even if the osmolality is low, if there is contraction of vascular volume, it will defend it by water retention.
8. What is the % volume loss that will trigger defensive actions by the body?
A. 0-2 %
B. 4-6%
C. 8-10%
9. What is the osmolality change that will trigger defensive actions by the body?
A. 2%
B. 4%
C. 6%
D. 8%
Remember body maintains the osmolality very closely around normal.
10. Sensors for volume loss are
A. baroreceptors in atrium
B. Juxtaglomerular apparatus
C. Both
D. Neither
10. Sensors for osmolality change
A. Osmoreeptors in thalamus
B. Thirst center in thalamus
C. Both
D. Neither
11. Hyperosmolality induced by urea will stimulate thirst center and osmolality receptors in thalamus
A. True
B. False
Remember urea equilibrates between ICF and ECF.
12. Stimulation of osmoreceptors results in
A. Secretion of angiotensin II
B. Secretion of ADH from posterior pituitary
C. Both
D. Neither
13 Angiotensin II is a potent stimulus for
A. Thirst
B. ADH release from posterior pituitary
C. Both
D. Neither
14. Stimulation of baroreceptors initiate. Select all that apply
A. Angiotensin II release
B. ADH release
C. Aldosterone release
D. All of the above
15. ADH primarily acts upon. Select all that apply
A. Glomerulus
B. Proximal tubule
C. Loop of Henle
D. Distal tubule
E. Collecting ducts
It acts on medullary thick portion of ascending limb of loop of Henle and concentrates medullary interstitium. Water absorption from collecting tubule is increased by medullary interstitial concentration and by increasing water permeability.
16. How much fluids (approximately) reach distal tubules in normal individuals
A. 3 liters
B. 6 liters
C. 9 liters
D. 18 liters
17. In normals the osmolality of urine at the distal tubule is
A. 50
B. 100
C. 200
D. 300
18. Sodium absorption from medullary thick ascending limb of loop of Henle in normals
A. 5%
B. 15%
C. 25%
D. 35%
Medullary thick ascending limb of loop of Henle plays a significant role in hypertonicity of the medullary interstitium to facilitate water absorption from collecting tubules.
19.In the total absence of ADH the urine volume will be
A. 3 liters
B.6 liters
C. 9 liters
D. 18 liters
In normals remember that the distal tubule receives approximately 18 liters of urine with an osmolality of 50. If there is no ADH, this amount of urine will be excreted.
19. Defenses for volume expansion are
A. Release of atriopeptin from cardiac atria
B. Oropharyngeal reflex to suppress thirst
C. Intrarenal Prostaglandin E2
D. All of the above
E. None of the above
Atriopeptin and Oropharyngeal reflex suppresses ADH release and thirst. Intra renal Prostaglandin E2 suppresses the effect of ADH on nephron segments. Prostaglandin E2 is produced by renal interstitial cells in response to increase in medullary hypertonicity.
20. In hypotonic disorders
A. Ratio of solutes to water is reduced
B. Serum osmolality is reduced
C. Serum sodium is reduced
D. All of the above
E. None of the above
21. When serum sodium is low , it means
A. Total body sodium is low
B. Total body sodium is normal
C. Total body sodium is increased
D. Any of the above
22. Example of low serum sodium with low total body sodium is
A. Nasogastric suction
B. Inappropriate ADH secretion
C. Congestive heart failure
23. Example of low serum sodium with normal total body sodium is
A. Nasogastric suction
B. Inappropriate ADH secretion
C. Congestive heart failure
24. Example of low serum sodium with increased total body sodium is
A. Nasogastric suction
B. Inappropriate ADH secretion
C. Congestive heart failure
25. Serum sodium is 130 with serum osmolality of 300 mOsm/kg. Most likely it is
A. Inappropriate ADH secretion
B. Diabetic ketoacidosis
C. Uremia
D. Ethanol intoxication
Measured serum sodium can be reduced when there is hyperglycemia or excessive mannitol. These solutes are restricted to the ECF, draw water from the cellular compartment, reducing the serum sodium even though the serum osmolality is high.
26. Serum sodium is 138 with serum osmolality of 300 mOsm/kg. Most likely it is
A. Inappropriate ADH secretion
B. Diabetic ketoacidosis
C. Uremia
Ethanol and BUN are distributed in total body water, hence the serum sodium remains normal even though the serum osmolality increases.
27. Spurious hyponatremia can be seen in
A. Uremia
B. Excessive mannitol administration
C. Hyperlipemia
Spurious hyponatremia can be seen in hyperlipemia and hyperproteinemia. It is a laboratory phenomenon. There is no sodium in the lipid layer.
28. Serum sodium of 125 with serum osmolality of 270 mOsm/kg
A. Primary increase in water ingestion
B. Ability of kidney to maximally dilute is limited
C. Both
D. Neither
29. Decreased sodium delivery to distal nephron segments occurs in all of the following except
A. Congestive heart failure
B. Cirrhosis
C. Sepsis
D. Nephrotic syndrome
Decreased sodium delivery to distal nephron segments generally occurs in a setting of decreased effective arterial blood volume. In sepsis there is decrease in systemic vascular resistance accounting for reduced arterial blood volume. Most of the sodium is reabsorbed in proximal tubule.
30. Decreased sodium delivery to distal nephron segments results in inability to create an osmotic gradient with interstitium.
A. True
B. False
Ascending thick limb of loop of Henle is water impermeable. 25% of sodium is absorbed from this site. This contributes to generation of renal medullary interstitial hypertonicity, which is essential for absorption of free water from collecting tubules.
31. With a normal diet, a normal individual can consume how much fluid without becoming hyponatremic
A. 5 liters
B. 10 liters
C. 15 liters
D. 20 liters
Maximally dilute urine is 50 mOsm/kg, each 50 mOsm of solute can capture 1 liter of free water. Normal individual on normal diet produces roughly 1000 mOsm of solute. That means he can consume 20 liters of fluid without becoming hyponatremic. Check out Beer potomania.
32. In inappropriate ADH secretion, select the best option
A. Hyponatremia
B. Volume expansion
C. Natriuresis
D. Hypouricemia
E. Normal or reduced BUN and creatinine
F. All of the above
33. In inappropriate ADH secretion, there is serum hyponatremia and is associated with
A. normal urinary sodium excretion
B. decreased urinary sodium excretion
C. increased urinary sodium excretion
Volume expansion result in release of atriopeptin, which enhances urinary sodium wasting by both increased glomerular filtration and by suppressing sodium tubular absorption. Volume expansion also reduces rate of proximal tubular absorption. Of course in normals, the volume expansion would have suppressed ADH secretion, except in this group of patients it is not under such regulatory control.
34. In patients with inappropriate ADH secretion, there is volume expansion but it is not associated with edema.
A. True
B. False
Interstitial edema is influenced by Starling forces, hydrostatic and oncotic pressures. In patients with inappropriate ADH secretion these forces are not altered and hence there is no edema formation.
35. In patients with congestive heart failure, the hyponatremia is due to
A. Non-osmotic, volume mediated ADH release
B. Reductions in the rate of sodium delivery to the diluting segment
C. Both
D. Neither
36. Acute hyponatremia is a medical emergency.
A. True
B. False
Untreated acute hyponatremia is uniformly fatal., Brain cells swells, proceeding to seizures, coma and death. In chronic hyponatremai CNS manifestations are far less common. In chronic hyponatremia the brain cells lose solutes, principally potassium chloride, minimizing brain cell swelling for a given reduction in body water osmolality.
37. In patients with acute hyponatremia associated with volume contracted states, the treatment of choice is
A. 3-5% saline over 4-6 hours
B. Normal saline over 4-6 hours
C. Restrict water to 800 ml/day
We should attempt to raise the serum sodium gradually. Too rapid hyponatremia correction may be associated with osmotic demyelination syndrome. Also remember acute hyponatremia needs to be treated as medical emergency. Serum sodium levels below 120 mEq/L are associated with serious brain swelling. Rate of change of sodium is more important than the exact levels.
38. The best way to treat chronic hyponatremia is by restriction of electrolyte free water to less than 1 L/day along with high dietary salt intake
A. True
B. False
39.. What are the alternative method of treating chronic hyponatremia, if you are unable to restrict fluids?
A Normal saline in combination with a loop diuretic
B. Lithium carbonate
C. Neither
D. Both
Normal saline in combination with a loop diuretic is the best option. Loop diuretic will induce urinary salt loss and therefore reduce the risk for volume expansion. Lithium carbonate or demeclocycline, block the effect of ADH at the level of collecting ducts.