Vasomotor mechanism and reflexes
Vasomotor mechanism and reflexes deals with the maintenance of the diameter of the blood vessels (arteries and arterioles) to maintain BP, thus regulates the blood flow to various organs or tissues according to their demand.
Functions of Vasomotor mechanism
Regulates blood flow to different organs according to their demand. i.e. shifting of blood from one organ to another on demand and Regulates peripheral resistance, thus the BP.
Vasomotor reflexes
There are two types of vasomotor reflexes:
Pressor reflex
When the BP falls below normal, the impulse frequency passing through the buffer nerves decreases causes the stimulation of cardio accelerator and vasoconstrictor centers of the medulla resulting in vasoconstriction to maintain BP to normal level.
Depressor reflex
A rise in BP above normal causes increased sensory impulse frequency through buffer nerves to the medullary vasomotor centers causes inhibition of vasoconstrictor and sympathetic centre, but stimulates vagal centre. It results in vasodilatation and decreased heart rate to establish normal BP.
Other reflexes
Hypothalamic reflex
Thermal stimuli – causes vasoconstriction during cold and vasodilatation by heat.
Cerebral cortex reflex
Stress, emotion, pain and exercise acts through dilator centre, vasodilatation in skeletal muscles.
Chemoreceptor reflex
Hypoxia, high CO2 and H+ ion causes vasodilatation.
Stretch reflex
Mesenteric stretch causes distension of intestine which in turn causes vasodilatation.