Body Fluids

Body fluid compartments.

Intracellular fluid, extracellular fluid, interstitial fluid, plasma, and transcellular fluid.

Describe the distribution of water of the body fluid compartments.

ICF 28 litres in a 70 kg person, ECF 14 litres, interstitial fluid 10.2 litres, plasma 3 litres and transcellular fluid 0.8 litres.

Describe the distribution of ionic composition of the body fluid compartments.

In interstitial fluid there is high potassium and low sodium, whereas in extracellular fluid there is low potassium and high sodium.

Concept of osmosis.

The movement of water molecules from a low solute concentration to a high solute concentration.

Osmotic pressure

Is the pressure that must be applied to oppose osmosis.

Osmolarity.

The total number of dissolved particles per litre of a solution.

Molarity x number of particles per molecule (once the particle dissolves).

Osmolality.

The total number of dissolved particles per Kg of water.

Oncotic pressure/ colloid osmotic

An alteration of osmotic forces due to changes of a large molecule distribution.

Explain the cause of movement of water particles across cell membrane and the capillary bed during osmosis.

Influenced by membrane properties and osmotically active solutes e.g. Na+ and Cl- . Cell membrane is nearly impermeable to Na+. If ECF [Na+] increases cell shrinks. In capillary bed water movement depends on hydrostatic pressure and osmotic pressure. Na+/ K+ pump helps maintain osmotic balance by actively transporting Na+ out.

Principles of tonicity.

Isotonic solution: have the same osmolality as plasma = 290 mosmoles/kg H2O

Hypertonic solutions: have a greater osmolality than plasma = >290 mosmoles/kg H2O

Hypotonic solutions: have a lower osmolality than plasma = <290 mosmoles/kg H2O

Intracellular fluid ICF

Fluid within cells also known as cytoplasm.

Extracellular fluid ECF

All fluids outside the cells.

Interstitial fluid

Fluid between cells of tissues, including lymph.

Plasma

Fluid in the vascular space.

Transcellular fluid

Fluid in the cerebrospinal fluid, joints, G-I tract.

What is the % of solids in female?

45%

What is the % of fluids in female?

55%

What is the % of solids in a male

40%

What is the % of fluids in a male?

60%

What is the ratio of intracellular and extracellular fluid in the total fluid in a male or female?

2/3 of the fluids is intracellular fluid. 1/3 extracellular fluid

Is K+ conc higher in the intracellular fluid or extracellular fluid?

It is higher in the intracellular fluid than extracellular fluid.

Isotonic solutions

=290 mosmoles/kgH2O

have the same osmalality as plasma

Hypertonic solutions

>290 mosmoles/kgH2O

Have a greater osmolality than the plasma

Water moves out of the cell.

Hypotonic solutions

<290 mosmoles/kg H2O

Have a lower osmolality than pplasma

water moves in

In the interstitial fluid is there a high conc or low conc of A- (fixed -ve charges on macromolecules) compared to the extracellular fluid?

There will be a higher conc in the interstitial fluid.

Is Cl- higher conc in intracellular fluid or extracellular fluid?

Cl- is higher in the extracellular fluid

Is K+ conc gradient out the cell more powerful than the electrochemical coming in?

yes

Is Na+ conc higher in intracellular fluid or extracellular

Na+ is higher in extracellular fluid

A rise in extracellular [K+] will make the membrane potential…

less negative than the resting membrane potential= membrane becoming depolarised.