L7: ECF 2

Question 1

What is volume contraction vs volume expansion?

Answer 1

Volume contraction is when there is a decrease in ECF volume and volume expansion is when there is an increase in ECF volume

Question 2

What kind of volume change does DI cause?

Answer 2

Hyperosmotic volume contraction

Question 3

What causes DI?

Answer 3

ADH is very low or ADH is ineffective

Question 4

What is the clinical presentation of DI?

Answer 4

• Plasma osmolarity is high
• Urine osmolarity is low
• polyuria (large volume of dilute urine)
• polydipsia

Question 5

What are the two causes of DI?

Answer 5

Neurogenic and nephrogenic

Question 6

What is neurogenic DI?

Answer 6

When plasma ADH is low due to hypothalamic pituitary injury and the patient cannot secrete sufficient ADH.
*** Patient WILL respond to exogenous ADH agonists (desmopressin)

Question 7

What is nephrogenic DI?

Answer 7

DI that is renal in origin. The kidney is unable to respond to ADH or desmopressin.
***ADH is high since the pituitary is functioning normally

Question 8

What are the causes of Nephrogenic DI?

Answer 8

• defect in V2 receptor
• lithium toxicity
• hypercalcemia

Question 9

What kind of volume change does increased sodium load cause?

Answer 9

Hyperosmotic volume expansion.

Increased sodium=increased plasma osmolarity= increased fluid intake=increased plasma volume

Question 10

What happens after plasma volume is increased after increased sodium intake?

Answer 10

• ANP is released to impede Na reabsorption and increase GFR
• increase in MAP
• Decreased SNS stimulation leading to decreased renin release and decreased aldosterone secretion, overall leading to increased sodium loss

Question 11

What kind of volume change does acute water load lead to?

Answer 11

Hyposmotic volume expansion

Question 12

What kind of volume change does SIADH cause?

Answer 12

Hyposmotic volume expansion

Question 13

What is SIADH and cause causes it?

Answer 13

• Syndrome of Inappropriate ADH Secretion: Essential uncontrolled release of ADH
• Caused by lung tumors and head injuries

Question 14

What is the result of SIADH?

Answer 14

• Chronic ECH dilution
• hyponatremia
• ECF many transiently expand, but euvolemia is common
• excess renal sodium loss (decreased aldosterone, increased ANP

Question 15

What is the major cation of the ECF?

Answer 15

Sodium

Question 16

Changes in Na concentration of the ECF are generally caused by what?

Answer 16

Changes in body water content rather than Na content

Question 17

What are the common causes of hyponatremia?

Answer 17

• blood volume depletion (high ADH and thirst after blood loss make this worse)
• excessive water conservation (SIADH)
• excessive water intake

Question 18

What are the causes of hypernatremia?

Answer 18

• loss of water

- Gain of sodium

Question 19

Why is persistent hypernatremia rare?

Answer 19

Excess sodium causes hyperosmolarity and thirst. Drinking water will quickly dilute the plasma sodium to normal

Question 20

The terms isosmotic, hyperosmotic, and hyposmotic refer to what fluid?

Answer 20

The ECF
THE ECF
THE ECF
ECF
ECF
ECF
ECF

Question 21

What is maximal bladder volume?

Answer 21

500-800 mL

Question 22

When is the urge to urinate felt?

Answer 22

A bladder volume of 150mL