Body Fluids

Question 1

What is the typical volume of body fluid in a 70kg man?

Answer 1

42L

Question 2

Of the 42L body fluid, what volume is in the extracellular compartment?

Answer 2

14L

Question 3

What volume is in the intracellular compartment?

Answer 3

28L

Question 4

What are the 3 sub-compartments of the extracellular compartment?

Answer 4

Plasma, interstitial fluid, transcellular fluid

Question 5

What volume of fluid is in the plasma?

Answer 5

3L

Question 6

What volume of fluid is in the interstitial space?

Answer 6

10L

Question 7

What is the volume of transcellular fluids?

Answer 7

1L

Question 8

What are some examples of transcellular compartments?

Answer 8

Peritoneal space, CSF, Synovial fluid

Question 9

Definition of haematocrit

Answer 9

A measure of the proportion of blood occupied by cells (45%)

Question 10

What protein is about 50% of Ca2+ in circulation bound to?

Answer 10

Albumin

Question 11

What form of Ca2+ is biologically active?

Answer 11

Free Ca2+

Question 12

What form of Ca2+ does the body regulate?

Answer 12

Free Ca2+

Question 13

Definition of ‘volume of distribution’

Answer 13

The volume of fluid required to contain the total amount of drug in the body at the same concentration as that present in plasma

Question 14

What is the equation for volume of distribution?

Answer 14

Vd = Q (amount of drug) / Cp (plasma concentration of drug)

Question 15

What is the volume of distribution of Heparin for a 70kg person?

Answer 15

3.5L

Question 16

What is the volume of distribution for Gentamicin?

Answer 16

14-28L

Question 17

How can total body water be measured?

Answer 17

Using isotopes of water (deuterium oxide or tritiated water)

Question 18

How can plasma volume be measured?

Answer 18

Substance used that must remain confined within the vascular space (i.e. does not cross the capillary endothelium)

Question 19

What substance is used to measure Plasma volume?

Answer 19

Evan’s Blue - binds to plasma albumin

Question 20

Definition of Osmolality

Answer 20

Number of osmoles per unit mass of solvent (Osm/kg)

Question 21

Definition of Osmolarity

Answer 21

Number of osmoles per unit volume of the solution (Osm/L)

Question 22

What is the difference between Isotonic and Isosmotic?

Answer 22

Isosmotic solutions - same osmolarity

Isotonic solution - applying the solution to cells will not cause net fluid movement

Question 23

What is the example of a solution which is isosmotic with intracellular fluid but not isotonic?

Answer 23

Urea

Question 24

Why is urea not isotonic with intracellular fluid?

Answer 24

Urea crosses freely across plasma membranes, so will enter the cells, increasing intracellular osmotic pressure

Question 25

What causes plasma albumin levels to fall?

Answer 25

Liver failure, renal failure

Question 26

What are the effects of a fall in plasma albumin levels?

Answer 26

Pulmonary/peripheral oedema, ascites

Question 27

How are osmotic pressure changes corrected?

Answer 27

Using mannitol

Question 28

How does mannitol work?

Answer 28

Increases the plasma and extracellular space osmolality, so pulls water from the intracellular and transcellular spaces (CSF)

Question 29

What is mannitol used for?

Answer 29

Decrease intracranial pressure