Normal fluid physiology Flashcards
What percentage of total lean body weight is made up of water?
About 60%
This percentage reflects the total body water distribution across different compartments.
What are the two major body fluid compartments?
- Intracellular
- Extracellular
What percentage of total body weight is intracellular fluid?
40%
What percentage of total body water is accounted for by extracellular fluid?
33%
What are the two sub-compartments of extracellular fluid?
- Interstitial (outside blood vessels)
- Intravascular (inside blood vessels)
What is the percentage of interstitial fluid within the extracellular fluid?
75%
What is the percentage of intravascular fluid within the extracellular fluid?
25%
What regulates the movement of water between compartments?
Permeability of barriers and solute concentration differences
What type of membrane separates intracellular and extracellular compartments?
Semi-permeable cell membrane
What can freely cross the cell membrane?
Water
What are the main colloid particles within plasma?
- Albumin
- Globulins
- Fibrinogen
What does osmotic pressure (‘tonicity’) mean?
The ability of particles in a compartment to cause water movement
What is total fluid osmolality?
A measure of all particles dissolved within a fluid compartment
How is osmolality calculated?
2(Na+ + K+) + glucose + BUN
What is the normal serum osmolality for dogs?
Around 300 mOsm/kg
What is colloid osmotic pressure (COP)?
The contribution of colloid particles to plasma osmotic pressure
What is the normal COP in dogs?
21-25 mmHg
What is the classical theory of fluid flux across capillaries based on?
Oncotic and hydrostatic pressure gradients
What does Starling’s equation describe?
Net fluid filtration across capillaries
What is the revised Starling principle?
Fluid flux is determined by oncotic pressure difference between plasma and subglycocalyx space
What is the glycocalyx?
A gel-like matrix on the luminal surface of endothelial cells
What role does the glycocalyx play in vascular physiology?
- Vascular permeability
- Mechanotransduction
- Blood cell interactions
- Control of microenvironment
What has shedding of the glycocalyx been associated with?
Poorer outcomes in various disease processes
What is the primary electrolyte difference between extracellular and intracellular fluid?
High extracellular sodium and high intracellular potassium
What pump maintains the sodium and potassium concentration differences across cell membranes?
Na/K ATPase pump
What ion concentration is measured in standard biochemical tests?
Solutes within the extracellular fluid (ECF) only
What is the concentration of sodium in intravascular fluid?
145 mEq/L
What is the concentration of potassium in intracellular fluid?
120 mEq/L
Fill in the blank: The only difference between intravascular and interstitial fluid is the concentration of _______.
Proteins
True or False: The concentration of chloride in intracellular fluid is higher than in intravascular fluid.
False
