Blood vessels

Layers

• Adventitia (outer layer of connective tissues
• Media (smooth muscles)
• Intima (endothelium plus underlying connective tissues)

Types of blood vessels

Aorta and large elastic arteries

Auxilary pump during diastole

Aortic lumen = 2.5cm

Artery lumen = 0.4cm

Arterioles

Resistance vessels

5 to 100 micrometers in diameter

Determines systemic vascular resistance and distribution of blood flow

Capillaries

Exchange of gas, nutrients and wastes

5 to 10 micrometers in diameter

True capillaries lack smooth muscles

Metarterioles

10 to 20 micrometer in diameter

Veins

Capacitance vessels

25 times more compliance than arterial system
* 4 times the capacity, and 6 times the specific compliance

For comparison

RBC: 3 micrometer in diameter

Hagen-Poiseuille's law does not apply to vessels under 300 micrometers because viscosity is affected by diameter (See Haemodynamics)