1. 2 main sources of arteriolar tone
    • natural properties of arteriole wall: elasticity of smooth muscle surrounding arterioles
    • baseline sympathetic activity: resting activity
  2. intrinsic control of vasoconstriction/dilation
    chemical changes: histamine, local metabolic changes
  3. sensors for vasodilation
    within the endothelium, sense local changes in tissue and release nitric oxide which acts on smooth muscle to cause relaxation
  4. sensors for vasoconstriction
    also in the endothelium, releases endothelin which reduces blood flow by constricting smooth muscle around the arterioles
  5. meta-arterioles
    • larger vessels in the capillary beds that allow for more rapid transport
    • only use when tissue doesn't need high level of perfusion
    • use pre-capillary sphincters to open/close routes
  6. precapillary sphincters
    • bands of smooth muscle that sit at gates between meta-arterioles and capillary beds
    • can constrict and keep blood only in the meta-arterioles
    • local controls only- levels of O2, CO2, free adenosine, acidity, temperature
  7. cardiac suction
    ventricles contract, atrial volume increases and causes negative pressure that promotes movement of blood from veins into atria
  8. short term BP regulation
    • use baroreceptors in aortic arch and carotid sinus- they sense stretch in vessels from increase in BP
    • sense change and can make changes but if it lasts more than 4 minutes, they will adapt
    • adjust baseline para and symp nerve stimulation to adjust MAP and BP
  9. extrinsic control of arteriolar diameter
    • neuronal or hormonal control
    • sympathetic stimulation ( no para) to smooth muscle
    • release of norepinephrine that binds to alpha-1 or beta-2 receptors
  10. effects of epinephrine on arteriolar diameter
    • binds to beta-2 receptor and causes vasodilation
    • decreased sympathetic stimulation
    • decreases TPR and BP
  11. effects of norepinephrine on arteriolar diameter
    • binds to alpha-1 receptor and causes vasoconstriction
    • increased sympathetic stimulation
    • increases TPR and BP
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