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

Regulation of Blood Pressure

Dr.Mohammed Sharique Ahmed QuadriAssistant professor Al Maarefa College

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

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

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

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

Determinants of Mean Arterial Pressure

Major factors affecting arterial radius

What controls the blood pressure?

Regulatory mechanisms

Regulatory mechanisms

Cardiac out put

Peripheral resistance

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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

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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.

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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.

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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.

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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.

baroreceptors

Baroreceptor Reflexes to Restore Blood Pressure to Normal

Functions of the Baroreceptors• Maintains relatively constant pressure despite

changes in body posture.

DecreaseCardiac Output

Sensed ByBaroreceptors

Supine StandingDecreaseCentral

Blood Volume

VasomotorCenter

SympatheticNervous Activity

DecreaseArterial Pressure

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.

Other regulatory mechanisms

• Peripheral chemoreceptors• Central chemoreceptor • Cardiopulmonary baroreceptors

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

1. Increase secretion of ANP2. Decrease secretion of ADH3. Renal vasodilatation4. Increase heart rate

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.

Sympatheticactivity

Chemoreceptors VMCO2CO2pH

BP

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.

VasomotorCenter

CerebralIschemia

CO2 ArterialPressure

SympatheticActivity

Figure 18-3; Guyton and Hall

• CNS Ischemic response is not activated until pressure falls below 60mmHg;

• Prolonged CNS ischemia has a depressant effect on the vasomotor center.

CNS Ischemic Response

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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.

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Blood Pressure Abnormalities

• Hypertension– Blood pressure above 140/90 mm Hg

• Hypotension– Blood pressure below 100/60 mm Hg

Accurate Assessment of Blood Pressure

catagory Systolic B.P in mmHg

Diastolic B.P in mmHg

Normal <120 <80

Prehypertension 120-139 80-89

Stage 1 hypertension 140-159 90-99

Stage 2 hypertension 160 100

Data from JNC 7 report, JAMA 289:2560-2572,2003

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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

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

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

Hypertension

• Complication of hypertension– Congestive heart failure– Stroke– Heart attack– Spontaneous hemorrhage– Renal failure – Retinal damage

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