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
Epithelial-related factors
Vasodilation
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
(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