Pathophysiology of Water Handling

Question 1

What is the most common cause hyponatremia?

Answer 1

A relative excess of water.

Question 2

The tonicity of the ECF reflects the tonicity of ___.

Answer 2

Cells

Question 3

The tonicity of ___ reflects the tonicity of the cells.

Answer 3

ECF

Question 4

What happens to urine osmolality and specific gravity when serum osmolality increases?

Answer 4

Urine becomes more concentrated with the osmolality of serum increases.

Question 5

What is the major factor that controls water metabolism?

Answer 5

The renal excretion of water.

Question 6

What hormone is the major player in controlling the renal excretion of water?

Answer 6

ADH

Question 7

What does ADH stand for?

Answer 7

Anti-diuretic hormone

Question 8

What is another name for ADH?

Answer 8

Vasopressin

Question 9

Big picture: What does ADH do?

Answer 9

Makes you retain water and sodium so you retain water.

Question 10

What are the three essential features of a normal diluting system?

Answer 10

1. Normal function of the diluting segment.
2. Normal delivery of tubular fluid to the distal diluting segment of the nephron.
3. Absence of vasopressin

Question 11

What is more important to maintain, blood volume or tonicity?

Answer 11

Blood volume. This gets back to the osmolarity regulation with a low-volume override.

Question 12

What is the most common electrolyte disturbance in hospitalized patients?

Answer 12

Hyponatremia

Question 13

What are two common causes of hypertonic hyponatremia?

Answer 13

1. Hyperglycemia

2. Administration of mannitol or glycerol

Question 14

For each increase in serum glucose of 100mg/dL, how much does sodium fall?

Answer 14

1.6mEq/L

Question 15

When one asks, “what is the serum osmolality,” one must always ask, “what is the serum _____”

Answer 15

Glucose. Because hyperglycemia is the most common cause of hypertonic hyponatremia.