Body fluids and osmolarity Flashcards
where are body fluids found?
blood plasma
intracellular
interstitial
how much of body weight is water?
60%
how is water content in lean tissue measured
L/Kg
how much of total body water content is found in intracellular space?
40%
– including blood cells
how much of total body water content is found as interstitial fluid?
15%
how much of total body water content is found in plasma space?
5%
what makes up the extracellular space?
Plasma space and interstitial fluid
how much do blood cells and plasma space make up of the blood volume?
8%
what are other fluid compartments found in the body - transcellular fluid?
cerebrospinal fluid aqueous& vitreous humour synovial fluid amniotic fluid GI tract secretions Lymph fluid - these spaces are part of the extracellular space
how to measure fluid compartments (volumes) - dilution method?
- Add known amount of substance (in moles) to an unknown volume
- Measure the concentration (Grams per Litre)
- Volume = (Amount of Substance (Moles))/(Concentration of substance)
what substances can we use to measure fluid compartments?
non Toxic substances
substances that are not metabolised quickly
in the plasma volume somethings that is larges and insoluble as it does not diffuse across capillaries easily
in the extracellular space something that does not enter cells easily
what are the constituents of body fluid?
cations and anions - electrolytes
proteins
dissolved gases, nutrients and metabolites
cells in blood
what is osmolarity?
concentration of a solution expressed as the total number of solute particles per litre - milliosmoles/L
what is osmolality?
concentration of particles per Kg of solution
- milliosmoles/Kg
what are the most abundant ions in body fluids?
sodium, chloride and potassium
what should the relative osmolarity of ICF AND ECF be?
EQUAL
similarities of osmolarity and osmolality?
both units of measurements
both measure and calculate osmotic activity
how can derive other spaces?
interstitial space = extracellular space - plasma volumes
intracellular space = total body of water - extracellular space
how many particles in one osmole?
1 Osmole = 1 Mole = 6.02 x 1023
what is tonicity?
Relative concentration of solutes dissolved in solution which determine the direction and extent of diffusion
-Tonicity only applies when solutions are separated by a semi-permeable membrane
what is crystalloid pressure?
osmotic pressure is due to small diffusible ions
why must extra and intracellular osmolarity be equal?
as cell membranes are largely impermeable to ions
-ions that are able to cross capillary walls easily show no crystalloid pressue difference
what causes some oncotic pressure?
A small amount of protein in interstitial fluid
- pressure of around 35mmHg
why is oncotic pressure important?
for fluid transport across capillaries
