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

  1. Deliver & remove nutrient + metabolites to tissues by DIFFUSION
  1. Distribute fluid between intravascular + extravascular compartments by BULK FLOW