Factors Maintaining BP:
Number of factors co-ordinate to maintain the normal blood pressure The heart blood vessels blood and the autonomic verves control the BP in man under various changing conditions of the body:
1. The Heart : The force and frequency affect the pumping action of the heart This is an important factor in
maintaining BP
2. Cardiac output : This depends on the venous return and pumping capacity of the heart which is also an important factor
3. Peripheral resistance:This is governed by the elasticity of vessel and the lumen of the blood vessels as well as the velocity and viscosity of the blood these govern the peripheral resistance which is a vital factor in maintenance of diastolic pressure of the blood
4. Blood volume:Total circulating blood also affects blood pressure Increase in volume would raise and a decrease in volume pari passu decrease the BP
5. Vasomotor centre : It is situated in the medulla oblongata it receives the information about pressure in the lumen of arteries through baroreceptors and chemoreceptors baroreceptors are found in the arch of the aorta and at the base of bifurcation of each of common carotid arteries (carotid sinus) chemoreceptors are found in the aortic body and carotid body Aortic body is a small nodule situated at the lower part of the arch of aorta carotid body is a small nodule situated on occipital artery (a branch of external carotid artery)
Baroreceptors are sensitive to decrease in BP whereas chemoreceptors are sensitive to increase in CO2 or decrease in O2 in blood the impulses from carotid sinus and carotid body are relayed to vasomotor centres through the IX cranial nerve (Glossopharyngeal) vagus the X cranial nerve carries the impulse from aortic arch and aortic body to the vasomotor centres this mechanism is of vital importance in maintaining the equilibrium of cardiovascular system
Vasomotor centres in medullar obtongata contain two centres pressor center and depressor center pressor center causes vasoconstriction by stimulating sympathetic nerves depressor centers cause an inhibition of pressor centers and decrease in activity of the sympathetic nerves thus when there is fall in BP baroreceptors and chemoreceptors are stimulated and this increases activity of pressor centers if BP is high depressor centers inhibit pressor centers to inhibit sympathetic nerves and produce vasodilatation
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