Body Fluid Compartments

Question 1

How much of our lean body mass is water?

Answer 1

2/3

Question 2

Why is water a universal solvent? What gives it those properties?

Answer 2

Water is polar
Polar because:
1. O is electronegative so it forms dipoles with H
2. O has lone pairs to form bonds

Question 3

What is the bond angle on an H2O molecule?

Answer 3

104.5

Question 4

Name the 3 types of chemical species in correspondence to their polarity & interactions with water.

Answer 4

Hydrophilic - Polar, dissolves in H2O
Hydrophobic - Non-polar, doesn’t dissolve
Amphiphillic - Partially polar&non-polar, partially dissolves

Question 5

What are the 4 factors affecting rate of diffusion?

Answer 5

Concentration gradient
Area of diffusion
Molecular mass of solute
Diffusion coefficient

Question 6

How is the diffusion coefficient affected by the molecular size of solute?

Answer 6

Larger molecules
= slower diffusion
= smaller diffusion coefficient

Question 7

What is osmotic pressure?

Answer 7

The hydrostatic pressure to prevent osmosis

Question 8

How is osmotic pressure generated?

Answer 8

After a substance is dissolved in water,
osmotic pressure proportional to their molar conc. is generated.

Question 9

What is the molarity of pure water?

Answer 9

55.6M

Question 10

What is the equation for osmotic pressure?

Answer 10

Osmotic pressure (π) = MRT
M = molality
R = 8.31 JK^-1 mol^-1 (ideal gas constant)
T = absolute temp. (K)

Question 11

What are the conditions for reverse osmosis (water purification)?

Answer 11

1. Impure water should be under pressure greater than the osmotic pressure
2. Semi-permeable membrane (permeable to only H2O)

Question 12

What does osmolarity & osmolality measure? What are their units?

Answer 12

Osmolarity = moles of solute particles / L
Osmolality = moles of solute particles / kg

Question 13

What is the osmolality of 150mM NaCl?

Answer 13

300mM,
because there is 150mM Na+ & 150mM Cl-

Question 14

Define isotonic and iso-osmotic & their relationship

Answer 14

Iso-osmotic = 2 solutions with the same osmolarity

Isotonic = 2 solutions with the same concentration
& volume of fluids stay the same

Isotonic always implies iso-osmotic, but not the reverse
(2 iso-osmotic solutions can still diffuse into cell)

Question 15

What cellular type of water is the most abundant in the body? How much?

Answer 15

Intracellular water - 2/3 of body water, 28L

Question 16

Where is interstitial water found?

Answer 16

Between cells, surrounding them

Question 17

What method is used to measure the volume of body fluids? & What do we use to perform this?

Answer 17

Dilution and the equation:
conc = mass/volume

e.g. put known mass sample into known conc. of fluid
-> sample is diluted
-> conc. used to work out volume

Deuterated (2^H2O) / Tritiated (3^H2O) water

Question 18

What practical item do we use to measure plasma volume? Why? &How do we practically measure it?*

Answer 18

Evans Blue dye
It has high affinity for serum albumin

Injecting 10ml of 1% Evan’s Blue into a subject’s vein
Take blood sample after waiting
Measure mass of dye per ml of blood

Question 19

What practical item do we use to measure extracellular volume? Why?

Answer 19

Inulin (not insulin)
- type of plant polysaccharide
It doesn’t move into cells

Question 20

Two main compartments of total body water

Answer 20

extracellular + intracellular water

Question 21

2 components of extracellular fluid

Answer 21

Plasma + interstitial water