Body fluids

What is interstitial fluid?

Fluid between the cells of tissues, including lymph, about 10.2 litres.

What is plasma?

Fluid in the vascular space, about 3 litres

What is extracellular fluid?

All fluids found outside the cells. This is about 14 litres in a 70kg person

What is intracellular fluid?

The fluid within cells. known also as cytoplasm. It is about 28 litres in a 70kg person.

What is a transcellular fluid?

Fluid in the CSF joints, ocular fluid G-I tract, about 0.8 litres

What are the processes which affect the total volume of each body fluid compartment?

• filtration

• reabsorption

• diffusion

• osmosis

What is osmolarity?

• the total number of dissolved particles (ions, molecules or mix of both) per litres of solution

• Molarity x number of particles per molecule once the particle dissolves

• measured in osmoles/ litre of solution (osmol/L or OsM)

What is osmolality?

The total number of dissolved particles per Kg of water

What are the osmotically active ions?

Na+ and Cl-

Is Na+ osmotically active in the capillary wall?

No, Na+ is freely permeable

As a consequence water flows from the capillary into the extracellular fluid which leads to local oedema.

What is a hypotonic solution?

Causes cellular swelling

What is hypertonic solution?

Causes cellular shrinkage.