L7: ECF 2 Flashcards
What is volume contraction vs volume expansion?
Volume contraction is when there is a decrease in ECF volume and volume expansion is when there is an increase in ECF volume
What kind of volume change does DI cause?
Hyperosmotic volume contraction
What causes DI?
ADH is very low or ADH is ineffective
What is the clinical presentation of DI?
- Plasma osmolarity is high
- Urine osmolarity is low
- polyuria (large volume of dilute urine)
- polydipsia
What are the two causes of DI?
Neurogenic and nephrogenic
What is neurogenic DI?
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)
What is nephrogenic DI?
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
What are the causes of Nephrogenic DI?
- defect in V2 receptor
- lithium toxicity
- hypercalcemia
What kind of volume change does increased sodium load cause?
Hyperosmotic volume expansion.
Increased sodium=increased plasma osmolarity= increased fluid intake=increased plasma volume
What happens after plasma volume is increased after increased sodium intake?
- 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
What kind of volume change does acute water load lead to?
Hyposmotic volume expansion
What kind of volume change does SIADH cause?
Hyposmotic volume expansion
What is SIADH and cause causes it?
- Syndrome of Inappropriate ADH Secretion: Essential uncontrolled release of ADH
- Caused by lung tumors and head injuries
What is the result of SIADH?
- Chronic ECH dilution
- hyponatremia
- ECF many transiently expand, but euvolemia is common
- excess renal sodium loss (decreased aldosterone, increased ANP
What is the major cation of the ECF?
Sodium
Changes in Na concentration of the ECF are generally caused by what?
Changes in body water content rather than Na content
What are the common causes of hyponatremia?
- blood volume depletion (high ADH and thirst after blood loss make this worse)
- excessive water conservation (SIADH)
- excessive water intake
What are the causes of hypernatremia?
- loss of water
- Gain of sodium
Why is persistent hypernatremia rare?
Excess sodium causes hyperosmolarity and thirst. Drinking water will quickly dilute the plasma sodium to normal
The terms isosmotic, hyperosmotic, and hyposmotic refer to what fluid?
The ECF THE ECF THE ECF ECF ECF ECF ECF
What is maximal bladder volume?
500-800 mL
When is the urge to urinate felt?
A bladder volume of 150mL
