Regulation of peripheral blood flow

• Dual control: local and systemic.

Intrinsic (local control)

Autoregulation

1. Myogenic mechanism

2. Metabolic mechanism

Local mediators

Vasodilation

• Increased CO2
• Increased K+
• Increased H+
• Increased Histamine
• Lactate
• Adenosine
• Increased local temperature

Vasoconstriction

• Decreased temperature

Epithelial-related factors

Vasodilation

• NO
• Prostacyclin

Vasoconstriction

• Thromboxane A2
• Serotonin relased by platelet
• Endothelin

Extrinsic (systemic control) by hormone

Vasodilator hormone

• Kinins
• VIP
• ANP
• Substance P
• Epinephrine (only in skeletal muscles and liver)

Vasoconstrictor hormone

• Norepinephrine
• Epinephrine (except in skeletal muscles and liver)
• Vasopression (ADH)
• Angiotensin II
• Neuropeptide Y

Extrinsic (systemic control) by neural factors

Vasodilation

• Decreased discharge of noradrenergic vasomotor fibres
• Activation of cholinergic dilator fibres to skeletal muscles

Vasoconstriction

• Increased discharge of noradrenergic vasomotor fibres

Factors affecting vasomotor centre

A. Directly stimulated by

• CO2
• Hypoxia

(Presumably directly on RVLM)

B. Excitatory inputs

• From cortex via hypothalamus
• From pain patheways
• From muscles
• From chemoreceptors

C. Inhibitory inputs

• From cortex via hypothalamus
• From lungs
• From carotid, aortic, and cardiopulmonary baroreceptors

D. Other factors

• Stimulation of chemoreceptors
• ICP