2. Blood pressure
Definition: Blood pressure is the lateral pressure which is exerted right angle
to the blood flow through blood vessel.
B.P is expressed as –
- Systolic pressure
- Diastolic pressure
- Mean pressure
- Pulse pressure
Function of blood pressure
• To maintain a sufficient pressure head to keep the blood
flowing.
• To provide for the motive force of filtration at capillary bed.
• helps in supplying nutrition to the tissue cells.
• formation of urine, lymph etc.
3. Regulation of Blood Pressure
• Several factors control blood pressure
• Cardiac output and peripheral resistance are
very much important.
• Arterial Blood pressure = Cardiac output * total
peripheral resistance.
NERVOUS MECHANISM
Arterial baroreceptor mechanism:
• Baroreceptors are nerve endings
• Located at the walls of the arteries –
• Abundant in
(i) internal carotid artery ii) Walls of the aortic arch
7. • Baroreceptors are not stimulated at
all by pressure between 0 and 60
mm Hg.
• Above 60 mm Hg they respond
progressively more and more.
• Max. at 180 mm Hg.
• Increase in no. of impulses for each
unit change of arterial pressure (ΔI
/ ΔP ) is greater at near normal
mean pressure
8. • Slight change in pressure causes strong
sympathetic reflex → art. pr. readjusted
• Changes in arterial pressure → rapid
response of baroreceptor.
• Systole → ↑ increase in no. of impulses .
• Diastole → ↓ decrease in no. of impulses.
9. Baroreceptor respond much more to changing Pressure
(rising/ falling) than to a stationary pressure
• Reflex initiated by baroreceptor due to rise in BP
• Baroreceptor reflex →inhibit vasoconstrictor center ( medulla)
@ Vasodilatation of peripheral circulation.
@ Decreased Cardiac Output
@ Decreased strength of contraction
Excite vagal center.
Low pressure has apposite effect.
10. • Decreased carotid sinus pressure → B.R. become
inactive → No. inhibitory effect
on Vasomotor Center (V.M.C)
V.M.C activated
B.P rises
11. • Buffer action of baroreceptor
Baroreceptor opposes increase & decrease
of B.P.
↓
it is called buffer system
After removal of baroreceptor nerve
extreme variability of B.P due to simple
events like lying, standing , excitement,
eating etc.
12. Fig: Two hours records
of arterial pressure
in a normal dog
(above) and in the
same dog (below
several weeks after
the baroreceptors
has been
denervated.
13. Role of atrial and pulmonary receptors
Atria & pulmonary arteries
Stretch receptor (are also called low pressure receptor)
• with low pressure receptor intact → BP changes less with
changes of blood volume.
An Experiment :
• 300 ml of blood is imposed to dog.
• With no receptor → BP rises to 120 mm Hg.
• With low pressure receptor absent but baroreceptor present →
BP rises to 50 mm Hg.
• With all receptors present → BP rises to 15 mm Hg
14. Role of atrial and pulmonary receptors…………
* Low pressure receptors cannot detect
systemic arterial pressure
** But can detect increase in pressure
due to increase in volume → reflexes
elicited parallel to B.R.
* Pulmonary receptor → operate identically
like B.R.
15. Atrial receptor acts in different way
Stretching of atria → reflex vasodilatation of
peripheral arterioles → in peripheral resistance
↓
↓BP towards normal
Control of H.R.
Atrial volume → stretch SA node → HR
by 20 – 70% → B.P.
16. Role of Vasomotor Center (VMC)
B.P. ↓
↓
Slowly flowing blood to brain
↓
Slow removal of CO2
↓
CO2 Conc.
↓
Ischemia
of brain
Lactic acid and
other acid
Increased VMC
activity
Sympathetic
vasoconstriction
↓
Increased B.P
↓
This is called CNS ischemic response
17. Role of Vasomotor Center (VMC………….
• Brain (CNS) ischemia → tremendous VMC
activity → Elevate BP to 270 mm Hg.
• CNS ischemia does not become very active
until the BP falls below 50 mm Hg.
18. Role of Chemo-receptor :
* Location : Bifurcation of carotid arteries →
Carotid body
• Arch of aorta → Aortic body.
* Size : 1- 2 mm
* Specialized Receptors → Sensitive to O2
lack, CO2 excess and H+ excess
* Nerve Pathway :
Carotid body → Hering’s nerve
Vasomotor Center
Aortic body → Vagus nerve
19.
20. O2 conc. in arterial blood blood flow to chemoreceptor
Excitation of
chemo-receptor
Impulse
VMC
Reflexly elevates B.P
The O2 lack reflex is not so powerful in normal arterial pressure range.
* It can exert reasonable feedback effect on arterial pressure when
BP ranges 40-80 mm Hg.
↓
↓
↓
Mechanism
23. Hormonal Control :
• Norepinephrine – epinephrine mechanism
Stimulation of sympathetic N.S →Nervous activation of blood vessel and heart
Release of epinephrine and nor-epinephrine in blood
Circulation in all parts of the body
Excite heart Constrict blood vessels
H. R. Increased B. P Peripheral resistance
E and NE circulates in blood for 1 to 3 min before being destroyed.
Prolonged excitation of circulation
The hormones can reach some parts of the circulation that have no sympathetic Nerve Supply.
24. Renin – angiotensin mechanism :
Arterial pressure Blood flow through kidney
Renin (Kidney)
(1 hour)
Renin Substrate Anginotensin –I
(plasmaprotein)
Converting enzyme (lung)
Angiotensinase Angiotensin II (3 min)
(inactivated)
Vasoconstriction
Arteriole Vein
Peripheral Resistance Circulatory filling pressure
Arterial Pressure Venous return
Helps the heart to pump against extra pressure
25. Other Effects of Angiotension :
Angiotensin Adrenal cortex
Kidney Aldosterone
Decreased excretion of salt and water
Blood volume
B.P.
26. Role of Vasopression :
Arterial pressure
(+)
Hypothalamus
(+)
Post. –pituitary gland
Vasopression
Vasoconstriction of blood vessels
Arterial pressure
• After removal of B.P. controlling mechanism, the vasopressing can increase B.P.
by 35mm Hg after Hemorrhage. But such effect is not seen in normal animal.
• * Vasopressing take part in long term regulation of B.P.
• * After 24 to 48 hrs. nervous reflexes put out but vasopressing mechanism does
not .
