Body Fluids & Blood

Question 1

What are the X3 main fluid compartments in the body?

Answer 1

Intracellular space (ICS) (within cells)
Interstitial space (ISS) (surrounds cells)
Blood plasma (PV) (plasma volume)

Question 2

How many litres of water in total in the body (total body water)?

Answer 2

42L

Question 3

How is TBW distributed into the X3 body fluid compartments?

Answer 3

PV = 3.5L

ISS = 10.5L

ICS = 28L

Question 4

What volume of CSF is there in the body?

Answer 4

150ml

Question 5

What equation relates solute, volume and concentration?

Answer 5

C = S / V

Question 6

How would you calculate an unknown volume of fluid from a known amount of solute?

Answer 6

1) Add the known volume of solute to the unknown volume of fluid
2) Take a sample and measure the concentration
3) Use C = S / V

Question 7

What substances are used to measure plasma volume?

What properties must this have?

Answer 7

Evans blue
Labelled inulin
Albumin

These all must be large in molecular size so that they can not cross the capillary membranes.

Question 8

What substances are used to measure the extracellular space?

What properties must this have?

Answer 8

24Na
Sucrose

These can leave the plasma and stay in the plasma but NOT enter cells easily.

Question 9

What substances are used to measure total body water?

What properties must this have?

Answer 9

3H2O (tritiated water)

This will distribute to all spaces.

Question 10

How would you work out the ISS volume from the measurable space volumes?

Answer 10

ISS = ECS - PV

Question 11

How would you work out the ICS volume from the measurable space volumes?

Answer 11

ICS = TBW - ECS

Question 12

How can concentration of various ions between the ECF and ICF differ yet still be balanced?

Answer 12

Their overall osmolaritites balance, this being the concentration of the solutions as a whole as functional of the total sum of ions they contain.

Question 13

What is the osmolarity of plasma?

Answer 13

290mosm/L

Question 14

What causes crystalloid osmotic pressure?

Is there any pressure gradients due to crystalloid osmotic pressure between intracellular, interstitial and plasma spaces?

Answer 14

Crystalloid osmotic pressure = due to small, diffusible ions (K, Na, Cl)

They do not cross cell membranes therefore intracellular and extracellular osmolarity is equal (even if their concentrations are not).

The capillaries are permeable to these ions therefore there is no crystalloid osmotic pressure gradient driving fluid movement.

Question 15

What causes colloid osmotic pressure?

Where is this pressure highest, the capillaries or the interstitium?

Answer 15

Colloid osmotic pressure = due to large, non-diffusible proteins.

These are found in larger numbers in the plasma, driving reabsorption of fluid into the plasma at the venous end of the capillary beds.

Question 16

What does an isotonic solution do to a cell?

Answer 16

Nothing, their tonicity (osmolarity) is the same.

Question 17

What does a hypotonic solution do to a cell?

Answer 17

Causes it to swell a lyse.

Question 18

What does a hypertonic solution do to a cell?

Answer 18

Causes it to shrink.

Question 19

What are the plasma and intracellular concentrations of sodium?

Answer 19

Plasma = 140mol/L

Intracellularly = 10mmol/L

Question 20

What are the plasma and intracellular concentrations of potassium?

Answer 20

Plasma = 4mmol/L

Intracellularly = 120mmol/L

Question 21

What are the plasma and intracellular concentrations of calcium?

Answer 21

Plasma = 2mmol/L

Intracellularly = 100nmol/L

NB: nanomoles, NOT millimoles!

Question 22

Which is the main plasma protein that contributes to oncotic pressure?

Answer 22

Albumin

Question 23

What is the collective term for neutrophils, basophils and eosinophils?

Answer 23

Granulocytes?