Ms. Komal Najam
Mechanisms of B.P Regulation
Nervous mechanism for B.P regulation
a. Baro-receceptor Mechanism
b. Chemoreceptor mechanism
Renal mechanism for B.P regulation
Reflexes and Responses
• Arterial blood pressure is defined as the lateral pressure exerted by the
column of blood on wall of arteries.
• LOCAL FACTORS DETERMINIG THE ARTERIAL BLOOD
There are four mechanisms for regulation of the blood pressure.
1. Nervous mechanism or shortterm regulatory mechanism
2. Renal mechanism or longterm regulatory mechanism
3. Hormonal mechanism
4. Local mechanism.
• Most rapid among all the mechanisms
• It operates through the vasomotor system.
Vasomotor system includes three components:
1. Vasomotor center (control heart rate)
2. Vasoconstrictor fibers (vasoconstriction)
3. Vasodilator fibers (vasodilation)
(Receives impulses from
Baroreceptors & Chemoreceptors.)
Rise in B.P activation of impulses to nucleus
baroreceptors of tractus solitarius
Reduces vasomotor inhibition of tractus solitarius acts
. tone vasoconstrictor area on vasomotor center
excites vasodilator area
Redution in peripheral resistance Blood-
& Vasodilatation occur pressure
(force of contraction &
Cardiac output decrease)
When blood pressure falls below
Carotid sinus and aortic arch
Cardiovascular center Rate of firing in afferent nerves
Sympathetic cardiac nerve activity
sympathetic vasoconstrictor nerve activity
parasympathetic nerve activity
arteriolar and venous
total peripheral resistance
Blood pressure increased
Decreased blood pressure
Decreased flow of blood
Decrease in O2 & Increase in CO2
Excitation in the chemoreceptors
Send impulses to vasoconstrictors
Blood pressure rises and
blood flow increases
• Long term regulation of Arterial B.P
• Renal Mechanism works even when
nerous mechanism adapts to the new
• Two ways of regulation of B.P
1. By regulation of ECF volume
2. Through reninangiotensin mechanism.
Increase in excretion of water excretion of salts (sodium)
B.P (pressure diuresis) (Pressure Natriuresis)
Blood pressure decrease in blood decrease in ECF
restored volume volume
Decrease in reabsorption Increase in ECF
B.P from & Blood
Blood pressure Increase in cardiac
Renin along with Angiotensin forms Renin-
Angiotensin system, which is a hormone system
that plays an important role in the maintenance of
Renin - J.G Cells of
Angiotensinogen - Liver Cells
ACE - Lungs
• Local mechanism regulates blood pressure by
Vasoconstriction & vasodilatation.
• Are also called EDCF (endothelium derived constricting
factors) as they are derived from vascular endothelium.
• Common EDCF are ET1, ET2 & ET3.
• Produced by stretching of blood vessels & cause
• Vasomotor center regulates the cardiac activity by
receiving impulses from different sources in the body.
After receiving the impulses from different sources, the
vasodilator area alters the vagal tone and modulates the
activities of the heart.
• Various sources from which the impulses reach the
1. IMPULSES FROM BARORECEPTORS – MAREY REFLEX
2. IMPULSES FROM RIGHT ATRIUM – BAINBRIDGE REFLEX
3. BEZOLD-JARISCH REFLEX
• Baroreceptors regulate the heart rate through Marey reflex.
Stimulus for this reflex is increase in blood pressure.
• Marey reflex is a cardioinhibitory reflex that decreases heart
rate when blood pressure increases.
• Whenever blood pressure increases, the aortic and carotid
baroreceptor are stimulated.
• stimulatory impulses are sent to nucleus of tractus solitarius
via Hering nerve and aortic nerve.
• then nucleus of tractus solitarius stimulates vasodilator area
and increase the vagal tone leading to decrease the heart rate
• Bainbridg reflex is a cardio accelerator reflex.
• Increases the heart rate when venous return is increased.
• This reflex rises from right atrium it right atrial reflex.
• Increase in venous return causes distention of right
atrium and stimulation of stretch receptors, situated in
the wall of right atrium.
• Stretch receptors, in turn, send nerve to vasodilator area
of vasomotor center. Vasodilator area is inhibited,
resulting in decrease in vagal tone and increase in heart
• This is also called coronary chemoreceptors.
• Bezold- Jarisch reflex is a pathological reflex and it does
not occur in physiological conditions.
• Conditions when Bezold-Jarisch Reflex Occurs.
1. Myocardial infarction
2 .Administration of thrombolytic agents
4. Aortic stenosis
• Hypertention; when sistolic pressure remain
elevated above 150 mm Hg and distolic pressure
remains 90 mm Hg is called hypetrtention.
• Hypotention;when the sistolic pressure
less then 90 mm Hg is called hypotention.