QS Study

Vasomotor Tone

In physiological condition, vasoconstrictor area at vasomotor center transmits signals to the blood vessels that maintain a partial state of contraction in the blood vessel. This is called vasomotor tone. It maintains the diameter of the blood vessels, and therefore it plays a vital role in maintaining the blood pressure. Vascular resistance is the result of a calculation including vasomotor tone, blood flow, and blood viscosity.

Situation: On the floor of the 4th ventricle.

Mechanism: →↑ Discharge from Vasomotor center →↑ sympathetic activity →↑ Tone of vascular smooth muscle →↑ vasomotor tone

→↑ Arterial pressure →↑ BP

→↑ Veuous pressure →↑ CO →↑ BP

Factors regulating vasomotor tone – Vasomotor center is under the superior control of cerebral cortex and hypothalamus.

All vascular organs and arteries contain smooth muscle cells which can contract and relax to alter the blood pressure as per the body’s requirement. This contraction and relaxation of the smooth muscles are controlled by the various chemicals that are released by the endothelial tissue of the blood vessels.

Another mode in which the vasomotor tone is controlled is associated with the change in electrical potential along the cells of the vessels.

The sympathetic nerves that constrict arterioles and veins and decrease heart rate and stroke volume, discharge in a tonic fashion and BP are adjusted by variation in the rate of this tonic discharge.

Spinal reflex activity affects BP, but the main control BP is exerted by groups of neurons in the medulla oblongata that are collectively called the vasomotor area or Vasomotor Centre (VMC).