1. Regulation of Blood Pressure
Dr.Mohammed Sharique Ahmed Quadri
Assistant professor
Al Maarefa College

2. Blood Pressure Force exerted by blood against a vessel wall
Depends on
Volume of blood contained within vessel
Compliance of vessel walls
Systolic pressure
Peak pressure exerted by ejected blood against vessel walls during cardiac systole
Averages 120 mm Hg
Diastolic pressure
Minimum pressure in arteries when blood is draining off into vessels downstream
Averages 80 mm Hg

3. Pulse Pressure
Pressure difference between systolic and diastolic pressure
Example
If blood pressure is 120/80, pulse pressure is 40 mm Hg (120mm Hg – 80mm Hg)
Pulse that can be felt in artery lying close to surface of skin is due to pulse pressure

4. Mean Arterial Pressure
Average pressure driving blood forward into tissues throughout cardiac cycle
Formula for approximating mean arterial pressure
Mean arterial pressure = diastolic pressure +
⅓ pulse pressure
At 120/80, mean arterial pressure = 80 mm Hg +
⅓ (40 mm Hg) = 93 mm Hg

5. Mean Arterial Pressure
Blood pressure that is monitored and regulated in the body
Primary determinants
Cardiac output
Total peripheral resistance
Mean arterial pressure = cardiac output x total peripheral resistance

6. Determinants of Mean Arterial Pressure

7. Major factors affecting arterial radius

8. What controls the blood pressure?
Regulatory mechanisms
Cardiac out put
Peripheral resistance

9. Mean Arterial Pressure
Constantly monitored by baroreceptors (pressure sensors) within circulatory system
Short-term control adjustments
Occur within seconds
Adjustments made by alterations in cardiac output and total peripheral resistance
Mediated by means of autonomic nervous system influences on heart, veins, and arterioles
Long-term control adjustments
Require minutes to days
Involve adjusting total blood volume by restoring normal salt and water balance through mechanisms that regulate urine output and thirst

10. BLOOD PRESSURE REGULATION
We will discuss Short Term Mechanisms:
BARORECEPTORS
Baroreceptors are stretch receptors present in the walls of blood vessels—CAROTID SINUS and AORTIC ARCH, for short term regulation of B.P.

12. BLOOD PRESSURE REGULATION
BARORECEPTORS
If blood pressure changes that is, increases or decreases Baroreceptors try to bring it back to normal value by adjusting cardiac output and peripheral resistance by working through ANS influences on heart, veins and arterioles.
They work in seconds.
Baroreceptors reflex is very important for regulation of Mean Arterial Pressure.

13. BLOOD PRESSURE REGULATION
BARORECEPTOR REFLEX
It has following components:
Receptors
Afferent Pathway
Center
Efferent Pathway
Effector Organ
RECEPTORS – located in Carotid Sinus and Aortic Arch, they are nerve endings and generate action potential in response to pressure present in the arteries.

14. BARORECEPTOR REFLEX
Afferent Pathway – Afferent nerve which carry impulse from carotid sinus is IX [Glassophyrangeal] and from aortic arch is X [Vagus]. Center – Cardiac Center is located in medulla [brain stem]. Efferent Pathway – From Cardiac center, we get Efferent ANS, Sympathetic and Parasympathetic fibers to heart and blood vessels. Effector Organ – Sympathetic causes increase heart rate and force of contraction of heart, vasoconstriction, therefore, increase CO and BP. Parasympathetic causes decrease heart rate, decrease force of contraction of heart, therefore, decreased cardiac output and decreased BP.

15. baroreceptors

16. Baroreceptor Reflexes to Restore Blood Pressure to Normal

17. Functions of the Baroreceptors
Maintains relatively constant pressure despite changes in body posture.
Decrease
Central
Blood Volume
Supine
Standing
Sympathetic
Nervous Activity
Decrease
Cardiac Output
Vasomotor
Center
Sensed By
Baroreceptors
Decrease
Arterial Pressure

18. Functions of the Baroreceptors
Opposes either increases or decreases in arterial pressure thereby reducing daily variations in arterial pressure.
They are unimportant in long term control of arterial pressure because the baroreceptors adapt.

19. Other regulatory mechanisms
Peripheral chemoreceptors
Central chemoreceptor
Cardiopulmonary baroreceptors

20. CARDIOPULMONARY (LOW PRESSURE) RECEPTORS:
Sense changes in blood volume or fullness of vascular system
Located in atria ,veins & pulmonary artery
IF THERE IS INCREASE IN BLOOD VOLUME THESE RECEPTORS BRING ABOUT FOLOWING CHANGES
Increase secretion of ANP
Decrease secretion of ADH
Renal vasodilatation
Increase heart rate

21. Carotid and Aortic Chemoreceptors
Chemoreceptors are chemosensitive cells sensitive to oxygen lack, CO2 excess, or H ion excess.
Chemoreceptors are located in carotid bodies near the carotid bifurcation and on the arch of the aorta.
Activation of chemosensitive receptors results in excitation of the vasomotor center.
Chemoreceptors are not stimulated until pressure falls below 80mmHg. O2
CO2 pH
Chemoreceptors
VMC
Sympathetic
activity BP

22. CNS Ischemic Response
CNS Ischemic response is activated in response to cerebral ischemia.
Reduced cerebral blood flow causes CO2 buildup which stimulates vasomotor center thereby increasing arterial pressure.
CNS Ischemic response is one of the most powerful activators of the sympathetic vasoconstrictor system.
Figure 18-3; Guyton and Hall
Vasomotor
Center
Sympathetic
Activity
Arterial
Pressure
CO2
Cerebral
Ischemia

23. CNS Ischemic Response
CNS Ischemic response is not activated until pressure falls below 60mmHg;
Prolonged CNS ischemia has a depressant effect on the vasomotor center.

24. RENIN-ANGIOTENSIN SYSTEM
It works in minutes and fully active in 20mins.
Renin is enzyme released by kidneys when arterial blood pressure becomes low.
Renin is synthesized by Juxta glomerular [JG cells] of the kidneys.
Renin enters the blood and acts on Angiotensinogin.

27. Blood Pressure Abnormalities
Hypertension
Blood pressure above 140/90 mm Hg
Hypotension
Blood pressure below 100/60 mm Hg

28. Accurate Assessment of Blood Pressure
catagory
Systolic B.P in mmHg
Diastolic B.P in mmHg
Normal
<120
<80
Prehypertension
80-89
Stage 1 hypertension
90-99
Stage 2 hypertension
160
100
Criteria by 7th joint national commiti
Data from JNC 7 report, JAMA 289: ,2003

29. Blood Pressure Abnormalities
Hypertension
Blood pressure above 140/90 mm Hg
2 broad classes
Primary hypertension
Secondary hypertension
Hypotension
Blood pressure below 100/60 mm Hg

30. Hypertension Most common of blood pressure abnormalities
Primary hypertension ( 90% OF CASES)
Catch all category for blood pressure elevated by variety of unknown causes rather than by a single disease entity
Potential causes being investigated
Defects in salt management by the kidneys
Excessive salt intake
Diets low in K+ and Ca2+
Plasma membrane abnormalities such as defective Na+-K+ pumps
Variation in gene that encodes for angiotensinogen
Endogenous digitalis-like substances
Abnormalities in NO, endothelin, or other locally acting vasoactive chemicals
Excess vasopressin

31. Hypertension Secondary hypertension
Accounts for about 10% of hypertension cases
Occurs secondary to another known primary problem
Examples of secondary hypertension
Renal hypertension
Endocrine hypertension
Neurogenic hypertension

32. Hypertension Complication of hypertension Congestive heart failure
Stroke
Heart attack
Spontaneous hemorrhage
Renal failure
Retinal damage

33. References Human physiology by Lauralee Sherwood, seventh edition
Text book physiology by Guyton &Hall,11th edition
Text book of physiology by Linda .s contanzo,third edition