Body Fluid Compartments Flashcards
What is osmolarity?
Concentration of osmotically active particles present in a solution
What are the units used for osmolarity?
mosmol/l
What is needed to be able to calculate the osmolarity of a solution?
Molar concentration of the solution
Number of osmotically active particles
What is the units used for osmolality?
osmol/kg = term can be used interchangeably with osmolarity in body fluids
What is the osmolarity of most body fluids?
About 300 mosmol/l
What is tonicity?
The effect a solution has on cell volume
What effect does a hypertonicity have?
Less water so concentrated salt solution = causes cell shrinkage due to decrease in cell volume
What occurs if a solution is isotonic?
No movement as there are equal concentrations of salt and water
What does hypotonicity cause?
Cell lysis = contains more water and increases cell volume
What does tonicity take into account?
Takes the ability of solute to cross the cell membrane into consideration
How much does total body water (TBW) contribute to body weight?
60% of body weight in males
50% of body weight in females
Difference due to difference in body fat
What are the components of total body water?
Intracellular fluid (ICF) = 67% of TBW Extracellular fluid (ECF) = 33% of total body water
What are the components of the extracellular fluid?
Plasma (20%), interstitial fluid (80%), lymph and transcellular fluid (both negligible)
How are body fluid compartments measured?
Using tracers = must obtain distribution volume
What are some examples of useful tracers?
3H2O for total body water
Inulin for extracellular fluid
Labelled albumin for plasma
How is the concentration of a tracer in water calculated?
V (litres) = Dose (D)/Sample concentration (C)
How is the distribution volume of a tracer calculated?
Distrubution volume (litres) = Quantity (mol)/Concentration (mol/l)
What must be ensured to ensure that water homeostasis is maintained?
Input must equal output
Why is water balance maintained by increased water ingestion?
Decreased excretion of water by kidneys alone is insufficient
What is the ion composition of the intracellular fluid?
10mM of Na+, 140mM of K+, 7mM of Cl-, 10mM of HCO3-
What is the ion composition of the extracellular fluid?
140mM of Na+, 4.5mM of K+, 115mM of Cl-, 28mM of HCO3-
What do cell membrane and membrane transport mechanisms enable cells to do?
Maintain internal environments that differ in compositions compared to their surroundings
What are the main ions of the fluid compartments?
ECF = Na+, Cl-, HCO3- ICF = K+, Mg2+, negatively charged proteins
What is significant about the osmotic concentrations of the extracellular and intracellular fluids?
They are identical = about 300 mosmol/l
Why is the regulation of fluid balance and electrolyte balance tightly intertwined?
Changes in solute concentration lead to changes in water concentration
What is fluid shift?
Movement of water between the ICF and ECF in response to an osmotic gradient
What does gain or loss of water do?
Causes changes in fluid osmolarity = ICF and ECF will be changed in the same way
What does gain or loss of NaCl do?
Causes change in fluid osmolarity = leads to Na+ excluded from ICF and osmotic water movements
What do changes to NaCl do to the ECF and ICF?
Produces opposite changes in volumes (i.e one will increase while the other decreases)
What does an increase in NaCl in the extracellular fluid cause?
Extracellular fluid volume will increase and the intracellular fluid volume will decrease
What does a decrease in the NaCl content of the extracellular fluid cause?
Extracellular fluid volume will decrease and the intracellular fluid volume will increase
What occurs when there is gain or loss of isotonic fluid?
Doesn’t change the fluid osmolarity = only changes the ECF volume
What organ changes the composition and volume of the ECF?
The kidney
What is the regulation of the ECF vital for?
The long term regulation of blood pressure
How can the plasma osmolarity be estimated?
Double the plasma sodium ion concentration
When does electrolyte balance occur?
When the rate of gain equals the rate of loss
Why is electrolyte balance important?
Total electrolyte concentrations can directly affect water balance = via changes in osmolarity
What can the concentrations of individual electrolytes affect?
Cell function
Why are Na+ and K+ particularly important?
Major contributors to the ECF and ICF respectively, ad directly affect functioning of all cells
What accounts for 90% of the osmotic concentration of the ECF?
Presence of sodium salts
What does the total amount of sodium in the ECF represent?
Balance between input and output
Why is sodium a major determinant of the ECF volume?
Mainly present in the ECF
What does potassium balance play a key role in?
Establishing membrane potential = minor fluctuations have detrimental consequences
Where is the majority of potassium located?
Over 95% is intracellular
What can small leakages or increased cellular uptake of potassium cause?
Impacts plasma K+ concentration = causes muscle weakness which may lead to paralysis, or cardiac irregularities causing arrest
How does salt imbalance manifest?
Changes in extracellular fluid volume
