Composition of Body Fluids Flashcards
Total body water varies and depends on what factors?
Total body water as a percentage of body weight varies with age and depends on gender and percentage of body fat.
What proportion of fluid in the body is intracellular vs extracellular?
The intracellular fluid compartment accounts for 2/3 of the body’s fluid, and the extracellular compartment comprises the remaining 1/3.
What are the two subdivisions of the extracellular fluid compartment?
Plasma and interstitial fluid.
Differentiate osmolarity from osmolality.
Osmolarity is a measure of the number of particles per volume of solute (the concentration of an osmotic solution) and is usually written in Osm/L or mEq/L. Osmolality is a measure of the number of particles per weight of solution and is usually written in Osm/kg.
What is the normal serum osmolality?
285 +/- 10 mOsm/kg
What is the calculation for serum osmolality?
Osmcalc = 2[Na+] + (glucose/18) + (BUN/2.8) with glucose and BUN measured in mg/dL.
What is the primary regulator of renal water excretion?
ADH/vasopressin
How does ADH act on the kidney?
It acts on the late distal tubule and cortical collecting duct to increase water permeability and mediate the urine concentration.
What are the two important regulators of ADH secretion from the posterior pituitary?
Osmoreceptors in the hypothalamus and volume (stretch) receptors in the left atrium and blood vessels.
What is the strongest stimulant for ADH release?
Significant volume loss resulting in hypotension.
List six physical findings which suggest the presence of hypovolemia.
Tachycardia, narrowed pulse pressure, orthostatic hypotension, prolonged capillary refill, resting tachycardia with hypotension, and low central venous pressure.
How do you calculate maintenance fluids and electrolytes for a 24 hour period?
Maintenance fluids: use the 4/2/1 rule. Electrolytes: Sodium and Chloride 2-3 mEq/100 mL of water per 24 hours; Potassium 1-2 mEq/100 mL of water per 24 hours.
