Body Water Balance Flashcards
Plasma Osmolarity =
= 2 x [Na] + [ Glucose/18 ] + [ BUN / 2.8 ]
What are the two Osmoreceptors in the hypothalamus ?
Supraoptic and Paraventricular
Where is vasopressin released from ?
The Hypothalamus
What is another name for vasopressin ?
Anti-Diuretic Hormone
What does Vasopressin do ?
It Increases the cAMP levels in the renal collecting duct epithelium causing Aquaporin-2 translocation to the lumen membrane.
What happens when your plasma osmolality hits 270 ?
Your thirst triggers will be stimulated. Vasopressin will be increasing H2O reabsorption in the distal tubule and collecting duct.
What do the osmoreceptors in the hypothalamus thirst center do ?
They drive the thirst behavior drive to increase water ingestion
What do the Osmoreceptors in the supraoptic nucleus of the hypothalamus do ?
Increase firing of nerve fibers with endings in the posterior pituitary releasing Vasopressin.
What triggers Osmoreceptors ?
Hyperosmotic plasma
How would you treat Hyponatremia due to GI fluid loss (Vomiting and Diarrhea), Why ?
Infusion of isotonic saline. The volume lost is isotonic so there will not be any flux between the ICV and
What are the adverse clinical effects of an increase in ECV ?
Increased cardiac filling, Jugular venous dissension, venous filling in the thorax,
Severe cases can cause pulmonary edema
When will GI fluid loss cause an abnormal increase in AVP ?
When the plasma volume is depleted. Infusion with isomolar or hypomolar saline will save the patient and lower AVP secretion. ds
How large of a depletion in ECFV must a patient sustain in order for AVP secretion to be activated ?
10-15 %
How do you calculate the concentration of the urine ?
Osmolar Clearance
Osmolar Clearance [ Cosm ] =
= Cosm =[ UF x Uosm ] / Posm
What is normal Cosm ?
2 +/- 0.5
What is the concept of free water clearance ?
The ability to concentrate urine depends on the difference between osmolar clearance and clearance of water. This is the free water clearance
Free Water Clearance = Ch20 =
= Ch2o= [ UF - Cosm ] = UF x [1 / [ Uosm / Posm ]]
A positive Ch20 means what ?
Dilute Urine and an increase in plasma osmolality
A negative Ch20 means what ?
Concentrated urine and a decrease in plasma osmolarity
What does ADH do to the concentration of the corticopapillary osmotic gradient ?
It increases the concentrations and favors a concentrated urine formation.
What is free water clearance used for ?
It is used to estimate the ability to concentrate or dilute the urine.
What the hell is free water ?
It is solute free water that is produced in the diluting segments of the kidney where NaCl is reabsorbed and free water is left behind.
What is the Free Water concentration in the presence of ADH ?
In the presence of ADO the solute free water is not excreted but is reabsorbed by the late distal tubule and collecting ducts. Ch2o is negative
