Expansion
About 70 per cent in the venous system, 15 per cent arterial, 5 per cent capillary
Expansion
Of a total blood volume of about 5 litres in an adult:
- Systemic veins: about 65 to 70 per cent
- Systemic arteries: about 13 to 15 per cent
- Pulmonary circulation: about 9 to 12 per cent
- Heart chambers: about 7 per cent
- Capillaries: about 5 per cent
Total blood volume is roughly 70 ml per kilogram in an adult man, 65 ml per kilogram in a woman, and higher per kilogram in neonates at about 85 ml per kilogram.
The venous dominance is the key figure. It means the veins are capacitance vessels serving as a reservoir, and that sympathetic venoconstriction can autotransfuse a substantial volume centrally without any external fluid being given. It is also why only about 5 per cent of blood is engaged in exchange at any instant.