G4i: Microcirculation
Microcirculation = the smallest blood vessels of the body
- Small arteries & arterioles
- Venules & small veins
- Capillaries
Capillaries = thin walled vessels made up of tubes of endothelial cells lying on a BM
- Diameter 5 – 10µm
- Density varies: high in cardiac & skeletal m.
- Permeability varies: high in liver, low in brain (TIGHT JUNTIONS)
- Only ¼ are open at rest
- Contain 5% of total blood volume
Capillary Blood Flow
- Capillaries have no smooth m. ∴cannot actively VC
- Their ∆ diameter is passive process
- Depends on pre + post capillary sphincters
- Constriction of pre-capillary sphincter → closes capillary
- Blood flow through small arteries, metarterioles & arterioles supplying capillaries depends on the metabolic state of the tissue
Capillary function → 2 main
- Deliver & remove nutrient + metabolites to tissues by DIFFUSION
- Distribute fluid between intravascular + extravascular compartments by BULK FLOW