Functional extracellular fluid and transcellular fluid

The contents of functional extracellular fluid

Bone and connective tissue contain 15% of the total body fluid (that's 9% of the mass of the organism) but they are slow to mobilise and wont participate in infusion physiology to a relevant degree. The rest is the functional ECF.

Functional ECF is about 30% of the total body fluid, or about 20% of total body mass (18% to be precise)

Transcellular fluid compartment: small but useful

This is a small but important compartment; 2.5% of total body fluid is locked up in these secretions.

The compartment is characterized by being formed from the secretions of epithelial cells, and it exist in epithelial-lined cavities.

Examples include:

• Vitreous humour
• Pleural fluid
• CSF
• Peritoneal fluid
• Aqueous humour
• Urine in the bladder
• Bowel mucus