Blood pressure & its regulation

1. Blood Pressure & Its Regulation
Dr. Sara Sadiq

6. Factors determining BP:
Blood Pressure = Cardiac Output X Peripheral Resistance
(BP) (CO)
Flow
(PR)
Diameter of
arterioles
■ BP depends on:
1. Cardiac output  CO = SV X HR.
2. Peripheral resistance.
3. Blood volume.

8. Blood Pressure Measurements

10. Factors affecting BP
■ Sex:
M > F  due to hormones/ equal at menopause.
■ Age:
Elderly > children  due to atherosclerosis.
■ Emotions:
 due to secretion of adrenaline & noradrenaline.
■ Exercise:
 due to  venous return.

11. Factors affecting BP
■ Gravity:
 Lower limbs > upper limbs.
■ Hormones:
 (e.g. Adrenaline, noradrenaline, thyroid H).
■ Sleep:
 due to  venous return.
■ Pregnancy:
 due to  metabolism.

12. REGULATION OF ARTERIAL BLOOD PRESSURE
• SHORT-TERM CONTROL
(IN SEC – MIN)
• INTERMEDIATE-TERM CONTROL
(30 MIN – HOURS)
• LONG – TERM CONTROL

13. SHORT-TERM CONTROL OF BP
• Baroreceptor reflex
• Chemoreceptor reflex
• CNS ischemic response

14. Baroreceptors
•Baroreceptors sense stretch
and rate of stretch by
generating action potentials.
•Located in highly distensible
regions of the circulation to
maximise sensitivity

16. BARORECEPTOR MECHANISM
Increase in Blood
Pressure
Baroreceptors
Stimulation
Impulses via IX
Cranial Nerve
Normal Blood Pressure
Dilatation of
blood vessels
Bradycardia and reduction
in cardiac output
Decrease in
vasomotor tone
Increase in vagal
tone
Inhibition of
vasoconstrictor area
Stimulation of
vasodilator area
Nucleus of tractus solitarius

17. BARORECEPTOR REFLEXES TO RESTORE BLOOD PRESSURE TO NORMAL
When blood pressure becomes
elevated above normal
Carotid sinus and aortic arch
receptor potential
Rate of firing in afferent
nerves
Cardiovascular center
Sympathetic cardiac nerve activity
Sympathetic vasoconstrictor nerve activity
Parasympathetic nerve activity
Heart rate
stroke volume
arteriolar and venous
vasodilation
Cardiac output
total peripheral resistance
Blood pressure decreased
toward normal

18. BARORECEPTOR REFLEXES TO RESTORE BP TO NORMAL
When blood pressure falls
below normal
Carotid sinus and aortic
arch receptor potential
Rate of firing in afferent
nervesCardiovascular center
Sympathetic cardiac nerve
activity
sympathetic vasoconstrictor nerve
activity
parasympathetic nerve activity
Heart rate
stroke volume
arteriolar and venous
vasoconstriction
Cardiac output
total peripheral
resistance
Blood pressure increased
toward normal

19. Figure 15-22: The baroreceptor reflex: the response to increased blood
pressure

20. Chemoreceptors

23. Overview of short-term control mechanisms
From: Introduction to Cardiovascular physiology. J.R. Levick. Arnold 4th edition (2003)

25. INTERMEDIATE CONTROL OF BP
• Renin – Angiotensin vasoconstriction mechanism
• Stress relaxation mechanism

26. LONG – TERM CONTROL OF BP
• Renin/ angiotensin/ aldosterone system
• Vasopressin
• Atrial natriuretic peptide

27. Renin
Aldosterone
Adrenal cortex
Corticosterone
Angiotensinogen
(Lungs)
 renal blood flow &/or  Na+
++ Juxtaglomerular apparatus of kidneys
(considered volume receptors)
Angiotensin I
ACE
Angiotensin II
(powerful vasoconstrictor)
• Renin-Angiotensin System:

28. Arteries
Veins
Reduced renal
blood flow
Juxtaglomerular
apparatus
Renin
Angiotensinogen
Angiotensin I
Angiotensin II
Increased
pre-load
Increased
after-load
vasoconstriction
Increased aldosterone
secretion
Sodium retention
Fluid re-absorption
Increased
blood volume
Renin/angiotensin/
aldosterone system
LV filling pressure)
(LV pressure
beginning of systole)

30. Vasopressin (ADH)

32. REGULATION OF ARTERIAL BLOOD PRESSURE
Regulation of Blood Pressure
Nervous
Mechanism
Renal
Mechanism
Hormonal
Mechanism
Local
Mechanism
By
Vasomotor
Center and
Impulses
from
Periphery
By
Regulation
of ECF
Volume and
renin –
angiotensin
mechanism
By
Vasocons-
-trictor and
Vasodilator
Hormones
By Local
Vasocons-
-trictors and
Vasodilators

33. HORMONAL MECH. FOR CONTROL OF BP
• HORMONES RAISING BP:
• ADRENALINE
• NORADRENALINE
• THYROXINE
• ALDOSTERONE
• VASOPRESSIN
• ANGIOTENSIN
• SEROTONIN
• HORMONES DECREASING BP
• VIP
• BRADY KININ
• PROSTAGLANDIN
• HISTAMINE
• ACETYLCHOLINE
• ANP

34. LOCAL MECH. FOR CONTROL OF BP
A. Vasodilatos
1. EDRF
2. Bradykinin
3. Histamine
4. ANP
5. Substance P
6. Prostacyclin
7. Adenosine
8. K+
9. Acidosis
10. Hypoxia
B. Vasoconstrictors
1. Endothelin-1
2. Angiotensin II
3. Norepinephrine
4. ADH
5. Serotonin
6. Thromboxane A2

36. Thank You