Arteriolar Physiology

  • Arterioles play both local and systemic roles in the regulation of blood flow. The key physiological feature of arterioles is their large but modifiable resistance to blood flow which is achieved by vasoconstriction and vasodilation. Arteriolar resistance is under the control of the autonomic nervous system. SNS fibers innervate the vascular smooth muscle cells of arterioles and can induce smooth muscle cell contraction by releasing norepinephrine on smooth muscle cell beta1 receptors. The resultant reduction in arteriolar diameter (vasoconstriction) can dramatically increase the arteriolar resistance to blood flow. Alternatively, reduced activation of SNS fibers results in increased arteriolar diameter (vasodilation) and thus reduced resistance to blood flow.
Local Roles
  • Local changes in arteriolar resistance by the SNS is one of the key ways in which blood can be directed to various tissues to meet physiological demands. For example, local regulation of cutaneous arterioles is a key component of temperature regulation in which blood is directed to or away from the skin to radiate or conserve heat. Another example involves regulation of the arterioles which supply the bowel, allowing blood to be directed to the GI System to support processes of absorption and digestion when food has been ingested.
Systemic Roles
  • As mentioned previously, arterioles are the largest source of resistance within the circulatory system. Consequently, systemic changes in arteriolar resistance is a key process involved in Short-term Systemic Arterial Pressure Regulation).