Intrinsic (local control)

Autoregulation

1. Myogenic mechanism

• Vascular smooth muscle
  * Contracts in response to an increase in transmural pressure stretch
  * Relaxes in response to a decrease in transmural pressure
• Independent of endothelium-related factors
• Mechanism unknown
  * Possible activation of calcium channel by stretch of vessel walls.

2. Metabolic mechanism

Any intervention that results in an oxygen supply that is inadequate for the requirement of the tissue gives rise to the formation of vasodilator metabolites

NB:

In placental circulation and hepatic portal circulation, there is no pressure autoregulation

Local regulation

Vasodilator metabolites

• Decreases in pO2 (according to WG21:p599, but not so, according to BL8: p182)
• Increases in pCO2
  * especially in skin and brain
• Increases in osmolality
• Increases in temperature
• H+
• K+
• Lactate
• Histamine
• Adenosine
  * In cardiac muscles,
  * Not in skeletal muscles [WG21:p599]
  * Also inhibits norepinephrine release

Localised vasoconstriction

• Injury
• Serotonin from platelets
• Drop in temperature

Endothelium-related vasoactive substances

See Endothelium-related vasoactive substances