Body fluid Compartments Flashcards
(32 cards)
What are the three compartments of water in the body
Intracellular-28L
Interstitial -10.5L
Plasma 3.5L
What is the total body water (approx) in the body
42L
Blood Volume =
Blood cells + Plasma Space
Extracellular =
Plasma Space + Interstitial space
Transcellular fluids include-
CSF Aqeous and vitreous humours of the eye Synovial Fluid Amniotic Fluid GI tract secretions Lymph
How would one measure the fluid compartments
- Add known amount of substance (g) to unknown volume (l)
- Measure the concentration (g/l)
- c= s/v
Substances that can be used are not toxic, not metabolised quickly and distribute in space of interest
To determine the plasma volume:
Something that doesn’t cross the capillaries ( large- Evans blue, albumin)
To determine the ECS:
something that doesn’t enter the cells easily 24Na, sucrose
To determine the TBW:
Something that distributes with all the water 3H2O
To determine the Interstitial Space:
ECS - plasma volume
To determine Intracellular space:
TBW- ECS
What are the main constituents of body fluids ?
Ions in the solution
Proteins
Dissolved gases, nutrients, metabolites
Cells in the blood
What is meant by the ionic composition of extra/intra cellular fluids and why is it important?
Na+, K+, Cl- are all major ions ( determine osmolarity, controls cell functions like cell signalling, muscle function, heart function, membrane potentials)
Concentrations of these differ considerably between ECF and ICF
It is important because the osmolarity in intracellular and extracellular must be equal. It prevents the movement of water due to any difference in osmolarity.
Osmole-
6.022 x 10^23 entities = 1 MOLE
Osmolarity-
1 Osmole per litre
of plasma controls the plasma volume (290 mosmol/litre)
of intracellular fluid controls the cell volume
Osmalility
1 Osmole per kg
Eg - 140mmol/litre of NaCl=
280 mosm/litre
How is pressure related to osmolarity
1 osmole in 22.4 litres exerts 760 mmHg
1 osmole/litre exerts 17,000 mmHg
Crystalloid osmotic pressure-
due to the small diffusible ions- capillary walls are permeable to ions so there will be no crystalloid osmotic pressure difference
Oncotic pressure-
due to the proteins- which cannot pass through capillary walls
Tonicity
Describes the volume change of a cell placed in a solution
describes the state of a solution in respect to osmotic pressure.
Hypertonic
greater solute in the solution
lower water potential in this solution compared to the solution on the other side
Plasma
[Na+] = 140 mmol/l
[K+] = 4 mmol/l
[Ca2+] = 2mmol/l
[Cl-] = 110mmol/l
[Bicarbonate] = 24mmol/l
Na + is the major ion. therefore controls the blood volume
Intracellular
[Na+] = 10 mmol/l
[K+] = 120 mmol/l
[Ca2+] = 100 mmol/l
K + is the major ion. therefore controls the cell volume
