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Flashcards in Fluid Physiology Deck (24)
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1

What is diffusion

Movement of solute from high conc to low conc through solute permeable membrane

2

What is osmosis

Movement of water from high conc to low conc until solute concentrations are equalized on both sides of solute impermeable membrane

3

What is osmolarity

Measure of solute concentration per unit VOLUME of solvent (1L)

4

What is osmolality

Measure of solute concentration per unit MASS of solvent (1kg)
Only solvents that contribute to osmotic pressure / can't cross membrane - Na, glucose, urea, alcohol

5

What is osmolality in ICF and ECF

285-290

6

Why is osmolality used instead of osmolarity in labs

Mass does not vary with pressure but volume does

7

What does osmolarity determine

The osmotic pressure and how the solvent will diffuse across membrane

8

What is tonicity

The measure of the osmotic pressure gradient between two solutions separated by semi-permeable membrane determining the extent of diffusion
Only takes into account solutes that CANNOT cross

9

What is TBW in average 70kg man

42l

10

What is volume of water in intracellular space

28l (2/3)

11

What is volume of water in extracellular space

14l (1/3)

12

What proportion of water in the extracellular space is intravascular

3l (20%)

13

What is BP determined by

Volume in intravascular space

14

In the extracellular compartment what moves to maintain gradient

Small ions and water
Large CANNOT cross
Water moves to equilibrate the osmolarity increasing or shrinking the volume of set spaces

15

Why do people with low protein leak water

Low protein = high water and water will move from high to low concentration leading to oedema

16

Can you still have a depleted intravascular compartment with oedema

YES as water moves out to follow protein causing oedema

17

Can K and Na move freely across membrane

No so maintain electrical potential of cells
Active Na/K channels transport across using ATP
3 Na for 2 K

18

Why is it difficult to prescribe fluid

Everyone is different
Age
Gender
Muscle mass

19

What is the aim of fluid therapy

Replete the right space with the right amount of solute to regain osmole equilibrium

20

How much water do we need in our body

25-30ml/kg/day

21

How much Na

1mmol / kg / day

22

How much K

1mmol / kg / day

23

How much glucose

50-100g / day

24

How much salt is recommended

<2g dietary a day so if prescribe 0.9% NaCL will go over