Fluids and electrolytes

Question 1

Plasma constituents

Answer 1

-90% water
-Gases
-Electrolytes
-Low molecular weight non-electrolytes, eg glucose, fatty acids, amino acids, vit, hormones, urea
-High molecular weight molecules - blood proteins

Question 2

Plasma Proteins

Answer 2

80% albumin
Globulins
Fibrinogen

Question 3

Function of plasma proteins

Answer 3

Oncotic funcctin
Coagulation
Buffering
Immune
Signalling
Transport
Non physiological - Drug binding, Bio marker

Question 4

ECF Osmolality

Answer 4

287mOsm/kg

Question 5

Osmolality

Answer 5

Number of osmoles of solute per kg of solvent.
(Total concentration of all solutes in solvent)

Question 6

Osmolarity

Answer 6

Number of osmoles of solute per L of solution

Question 7

Tonicity

Answer 7

Osmolality due to effective osmoles. Reflect cells volume
Hypotonicity => cell swelling
Hypertonicity -> cell dehydration

Question 8

Gibbs-Donnan effect

Answer 8

Describes behaviour of charged particles near semi permeable membrane that sometimes fails to distribute evenly across the two sides. Giib Donnan effect states situation at equilibrium

• E.g Charged non-diffusible anions set up Gibbs Donnan effect. Excess of particles inside cell => more water into cell. (Unstable situation would lead to cell rupture but does not occur due to counterbalancing mechanism)
• E.g Na+ main extracellular cation - excluded from cell because of low membrane permeability and active extrusion. Na effectively non-diffusible sets up Gibbs Donnan equilibrium which causes extracellular excess of anions cf intracellular => water moves out of cell - Double Donnan effect - second Gibbs Donnan equilibrium (due to extracellular sodium) opposes first. Balance between two opposing effects allows maintenance of stable cell volume

Donnan excess pressure - increase in oncotic pressure due to net negative charge on proteins (albumin), leads to retention of increase number of Na+ in plasma

Question 9

Total body water

Answer 9

= 60% of total body weight
In 70kg male = 42L

2/3 intracellular (28L)
1/3 extracellular (14L)
- 80% ISF (11L)
- 20% plasma (3L)

Question 10

Thirst

Answer 10

Physiological urge to drink. Conscious sensation stimulated by
- Hypertonicity
- Hypovolaemia
- Hypotension
- AT-II

Question 11

Molality

Answer 11

Number of moles of solute per kg of solution

Question 12

Strong ions

Answer 12

Strong ions dissociate completely.

Strong cations = Na, K, Ca, Mg
Strong anions = Cl, SO42-, lactate

SID is the difference between the concentrations of strong cations and anions

SID = [strong cations] - [strong anions]

In normal human plasma SID = 42mEq/L

Question 13

Colligative properties

Answer 13

Properties of a solution that depend only on the particle concentration (i.e osmolality).
- Only the the number of particles per unit volume is important, not the type of particles.

Colligative properties:
- Vapour pressure depression
- Freezing point depression
- Boiling point elevation
- Osmotic pressure