Water, fluids, spaces and compartments Flashcards
What are the two primary fluid compartments in the body?
ICF
ECF
What three compartments make up the ECF?
Interstitial fluid
Intravascular fluid
Transcellular fluid
Define oedema.
Abnormal accumulation of fluid beneath the skin, or in one or more cavities of the body
How many litres of fluid are present in the ICF?
28L
How many litres of fluid are present in the interstitial fluid? (ECF)
10.5L
How many litres of fluid are present in the intravascular fluid? (ECF)
3.5L
What does mass =?
Concentration X volume
What is a plasma compartment tracer?
RISA
What is an extracellular compartment tracer?
Mannitol or inulin
What is a total body volume tracer?
THO
What makes up blood volume?
Red blood cells and plasma
What is Haematocrit?
Fraction of the blood that is RBCs
What is the equation for blood volume?
Plasma volume/ 1 - Hct
What is the initial body access point for ingested nutrients and exit point for body’s waste product?
Plasma water
How are all cells bar blood cells accessed?
Interstitial space
How do solutes enter/leave the body?
Via ECF
How do kidneys regulate water excretion
Diffuse across cell plasma membrane via aquaporins
What can alter type/number of aquaporins?
ADH
Where are numerous aquaporins expressed?
Late distal tubules
Collecting tubules
What does movement between body fluid compartments depend on?
Endothelial cell wall
What substances require specific integral membrane proteins to cross cell plasma membrane?
Small/large uncharged polar molecules
Ions
What are the main drivers of solute movement between intracellular and interstitial fluid compartments?
Osmotic pressure and electrochemical gradients
Define osmotic pressure.
Pressure that must be applied to a solution to prevent net flow of water into it
What are the main drivers of solute movement between interstitial and plasma compartments?
Hydrostatic pressure and oncotic pressure
How are charges separated across a plasma membrane?
Electrical force drives +ve ions into cell and -ve ions out
What is hydrostatic pressure?
Pressure exerted by a fluid at equilibrium due to force of gravity
What is oncotic pressure?
Type of osmotic pressure generated by impermeable proteins in solution
eg. large plasma proteins pull water into capillaries
What does water distribution in body compartments depend primarily on?
Conc. ion of electrolytes
What is normal osmolality?
290mOsm
What is tonicity?
Fluctuations in cell volume
What is an ineffective osmole?
Substance that, although osmotically active, can easily distribute across body compartments and so does not cause fluid shifts i.e. urea
How can fluid be lost?
Skin
Diarrhoea
diuretics
oedema
What happens in isosmotic dehydration?
ECF volume decreases
Osmolality of ECF does not change
ICF volume and osmolality does not change
eg. GIT fluids
What happens in hyperosmotic dehydration?
Loss of water in excess of solute
ECF volume decrease
ECF osmolality increases
ICF volume decrease (moves into ECF)
Osmolalities equalized
