Homeostatic Regulation of Body Fluids Flashcards
Molarity definition
The amount of a substance dissolved in a solution relative to its molecular weight
Equivalence definition
The amount of a substance dissolved in a solution relative to its molecular weight and stoichiometry
Osmolality
Number of solute particles per kg of H2O
Concentration multiplied by number of dissociable particles
Determinant of the direction of water flow between the body compartments
Osmolality vs osmolarity
Osmolarity: number of solute particles per LITER of H2O
Osmolality: Number of solute particles per KG of H2O
What 3 ions are normally the most active solute particles?
Na
Cl
HCO3
Osmosis
Movement of water across membranes down its concentration gradient
Determined by the number of solute particles
Driven by osmotic pressure
Oncotic pressure
Osmotic pressure generated by large molecules and proteins
Tonicity
The effect of a solution on the volume of the adjacent cell
Body water
60% of body weight (for a 70 kg male)
Water content less in adipose tissue
Distributed across the 3 body compartments
What ‘third space’ is created in pathological conditions?
When there is extra fluid begin stored in the bowels
How is plasma osmolality measured?
2(plasma [Na]) + [glucose] + [urea]
3 body compartments
Plasma
Interstitial
Intracellular
No difference between plasma and interstitial
Capillary fluid exchange
Water moves freely between compartments
Determined by hydrostatic pressure and oncotic pressure
Sum of starling’s forces
3 factors that determine hydrostatic pressure
Arterial/venous pressure
Length of capillary
Pre and post capillary sphincters
3 characteristics of the membrane that influence the movement of fluid
Surface area
Permeability to water
Permeability to proteins