Body Fluid Compartments

Question 1

What is osmolarity?

Answer 1

Concentration of osmotically active particles present in a solution

Question 2

What are the units used for osmolarity?

Answer 2

mosmol/l

Question 3

What is needed to be able to calculate the osmolarity of a solution?

Answer 3

Molar concentration of the solution

Number of osmotically active particles

Question 4

What is the units used for osmolality?

Answer 4

osmol/kg = term can be used interchangeably with osmolarity in body fluids

Question 5

What is the osmolarity of most body fluids?

Answer 5

About 300 mosmol/l

Question 6

What is tonicity?

Answer 6

The effect a solution has on cell volume

Question 7

What effect does a hypertonicity have?

Answer 7

Less water so concentrated salt solution = causes cell shrinkage due to decrease in cell volume

Question 8

What occurs if a solution is isotonic?

Answer 8

No movement as there are equal concentrations of salt and water

Question 9

What does hypotonicity cause?

Answer 9

Cell lysis = contains more water and increases cell volume

Question 10

What does tonicity take into account?

Answer 10

Takes the ability of solute to cross the cell membrane into consideration

Question 11

How much does total body water (TBW) contribute to body weight?

Answer 11

60% of body weight in males
50% of body weight in females
Difference due to difference in body fat

Question 12

What are the components of total body water?

Answer 12

Intracellular fluid (ICF) = 67% of TBW
Extracellular fluid (ECF) = 33% of total body water

Question 13

What are the components of the extracellular fluid?

Answer 13

Plasma (20%), interstitial fluid (80%), lymph and transcellular fluid (both negligible)

Question 14

How are body fluid compartments measured?

Answer 14

Using tracers = must obtain distribution volume

Question 15

What are some examples of useful tracers?

Answer 15

3H2O for total body water
Inulin for extracellular fluid
Labelled albumin for plasma

Question 16

How is the concentration of a tracer in water calculated?

Answer 16

V (litres) = Dose (D)/Sample concentration (C)

Question 17

How is the distribution volume of a tracer calculated?

Answer 17

Distrubution volume (litres) = 
Quantity (mol)/Concentration (mol/l)

Question 18

What must be ensured to ensure that water homeostasis is maintained?

Answer 18

Input must equal output

Question 19

Why is water balance maintained by increased water ingestion?

Answer 19

Decreased excretion of water by kidneys alone is insufficient

Question 20

What is the ion composition of the intracellular fluid?

Answer 20

10mM of Na+, 140mM of K+, 7mM of Cl-, 10mM of HCO3-

Question 21

What is the ion composition of the extracellular fluid?

Answer 21

140mM of Na+, 4.5mM of K+, 115mM of Cl-, 28mM of HCO3-

Question 22

What do cell membrane and membrane transport mechanisms enable cells to do?

Answer 22

Maintain internal environments that differ in compositions compared to their surroundings

Question 23

What are the main ions of the fluid compartments?

Answer 23

ECF = Na+, Cl-, HCO3-
ICF = K+, Mg2+, negatively charged proteins

Question 24

What is significant about the osmotic concentrations of the extracellular and intracellular fluids?

Answer 24

They are identical = about 300 mosmol/l

Question 25

Why is the regulation of fluid balance and electrolyte balance tightly intertwined?

Answer 25

Changes in solute concentration lead to changes in water concentration

Question 26

What is fluid shift?

Answer 26

Movement of water between the ICF and ECF in response to an osmotic gradient

Question 27

What does gain or loss of water do?

Answer 27

Causes changes in fluid osmolarity = ICF and ECF will be changed in the same way

Question 28

What does gain or loss of NaCl do?

Answer 28

Causes change in fluid osmolarity = leads to Na+ excluded from ICF and osmotic water movements

Question 29

What do changes to NaCl do to the ECF and ICF?

Answer 29

Produces opposite changes in volumes (i.e one will increase while the other decreases)

Question 30

What does an increase in NaCl in the extracellular fluid cause?

Answer 30

Extracellular fluid volume will increase and the intracellular fluid volume will decrease

Question 31

What does a decrease in the NaCl content of the extracellular fluid cause?

Answer 31

Extracellular fluid volume will decrease and the intracellular fluid volume will increase

Question 32

What occurs when there is gain or loss of isotonic fluid?

Answer 32

Doesn't change the fluid osmolarity = only changes the ECF volume

Question 33

What organ changes the composition and volume of the ECF?

Answer 33

The kidney

Question 34

What is the regulation of the ECF vital for?

Answer 34

The long term regulation of blood pressure

Question 35

How can the plasma osmolarity be estimated?

Answer 35

Double the plasma sodium ion concentration

Question 36

When does electrolyte balance occur?

Answer 36

When the rate of gain equals the rate of loss

Question 37

Why is electrolyte balance important?

Answer 37

Total electrolyte concentrations can directly affect water balance = via changes in osmolarity

Question 38

What can the concentrations of individual electrolytes affect?

Answer 38

Cell function

Question 39

Why are Na+ and K+ particularly important?

Answer 39

Major contributors to the ECF and ICF respectively, ad directly affect functioning of all cells

Question 40

What accounts for 90% of the osmotic concentration of the ECF?

Answer 40

Presence of sodium salts

Question 41

What does the total amount of sodium in the ECF represent?

Answer 41

Balance between input and output

Question 42

Why is sodium a major determinant of the ECF volume?

Answer 42

Mainly present in the ECF

Question 43

What does potassium balance play a key role in?

Answer 43

Establishing membrane potential = minor fluctuations have detrimental consequences

Question 44

Where is the majority of potassium located?

Answer 44

Over 95% is intracellular

Question 45

What can small leakages or increased cellular uptake of potassium cause?

Answer 45

Impacts plasma K+ concentration = causes muscle weakness which may lead to paralysis, or cardiac irregularities causing arrest

Question 46

How does salt imbalance manifest?

Answer 46

Changes in extracellular fluid volume