blood pressure.ppt

7/29/2019 Blood Pressure.ppt

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Cardiovascular PhysiologyArterial Blood Pressure


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Arterial Blood Pressure (BP)= The lateral pressure force generated by the pumping

action of the heart on the wall of aorta & arterial

blood vessels per unit area.

OR = Pressure inside big arteries (aorta & big vessels).

Measured in (mmHg), & sometimes in (cmH2O),where 1 mmHg = 1.36 cmH2O.

Of 2 components: systolic (= max press reached) = 110-130 mmHg.

diastolic (= min press reached) = 70-90 mmHg.

In normal adult 120/80 mmHg.


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Arterial Blood Pressure(continued)

Diastolic pressure is more important, becausediastolic period is longer than the systolic period inthe cardiac

cycle.

Pulse pressure= Systolic BP Diastolic BP.

Mean arterial pressure= Diastolic BP + 1/3 Pulsepress.

In normal adult 120/80 mmHg.


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Factors affecting ABP: 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.

Hormones(e.g. Adrenaline, noradrenaline, thyroidH).

Gravity Lower limbs > upper limbs.

Race Orientals > Westerns ? dietry factors, or

weather.


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Factors determining ABP:Blood Pressure = Cardiac Output X Peripheral

Resistance

(BP)(CO)Flow

(PR)Diameter ofarterioles

BP depends on:

1. Cardiac output CO = SV X HR.

2. Peripheral resistance.

3. Blood volume.


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Regulation of Arterial Blood

Pressure


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Regulation of ABP: Maintaining B.P. is important to ensure a steady

blood

flow (perfusion) to tissues. B.P. is regulated neurally through centers in

medulla oblongata:

1. Vasomotor Center (V.M.C.), or (pressor area):

Sympathetic fibers.

2. Cardiac Inhibitory Center (C.I.C.), or (depressorarea):

Parasympathetic fibers

(vagus).


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cardiac control centers in medullaoblongata

Regulation of ABP(continued)

1. Cardiacacceleratorcenter(V.M.C)

2. Cardiacinhibitorycenter(C.I.C)

Sympathetic n. fibers Parasympathetic n. fibers

Regulatory mechanisms depend on:

a. Fast acting reflexes:Concerned by controlling CO (SV, HR), & PR.

b. Long-term mechanism:

Concerned mainly by regulating the blood volume.


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PressureA. Regulation of Cardiac Output


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Regulation of CO:A fast acting mechanism.

CO regulation depends on the regulation of:

a. Stroke volume, &

b. Heart rate


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Mean arterial pressure

Cardiac output = Stroke volume X Heart rate

End Contraction

diastolic strength

volume

(EDV)Stretch

Sympathetic nParasympathetic n

Frank - Starling

Regulation of the CO:


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PressureB. Regulation of Peripheral Resistance


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Regulation of Peripheral Resistance

(PR):

A fast acting mechanism.

Controlled by 3 mechanisms:

1. Intrinsic.2. Extrinsic.

3. Paracrine.

Extrinsic mechanism is controlled throughseveral

reflex mechanisms, most important:

1. Baroreceptors reflex.

2. Chemoreceptors reflex.


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1. Baroreceptors reflex:

Baroreceptors are receptors found in carotid

sinus &

aortic arch.

Are stimulated by changes in BP. BP

+ Baroreceptors

= V.M.C ++ C.I.C

= Sympathetic

Vasodilatation & TPR

+ Parasympathetic

Slowing of SA node ( HR)

& CO


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2. Chemoreceptors reflex: Chemoreceptors are receptors found in carotid &

aortic bodies.

Are stimulated by chemical changes in blood mainly

hypoxia ( O2), hypercapnia ( CO2), & pH changes.

BP

+ Chemoreceptors++ V.M.C = C.I.C

+ Sympathetic

Vasoconstriction& TPR

= Parasympathetic

HR

Haemorrhage

Hypoxia

+ Adrenalmedulla


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3. Other Vasomotor Reflexes:

1. Atrial stretch receptor reflex:

Venous Return ++ atrial stretch receptors

reflex vasodilatation & BP.2. Thermoreceptors: (in skin/or hypothalamus)

Exposure to heat vasodilatation.

Exposure to cold vasoconstriction.

3. Pulmonary receptors:

Lung inflation vasoconstriction.


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4. Hormonal Agents:

NA vasoconstriction.

A vasoconstriction

Angiotensin II vasoconstriction. Vasopressin vasoconstriction.


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PressureC. Regulation of Blood Volume


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Regulation of Blood Volume:

A long-term regulatory mechanism.

Mainly renal:

1. Renin-Angiotensin System.

2. Anti-diuretic hormone (ADH), or

vasopressin.

3. Low-pressure volume receptors.


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1. Renin-Angiotensin System:

Most important mechanism for Na+ retention in

order to maintain the blood volume.

Any drop of renal blood flow &/or Na+, will

stimulate volume receptors found in

juxtaglomerular apparatus of the kidneys to

secrete Renin which will act on theAngiotensin System leading to production of

aldosterone.


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Renin

Aldosterone

Adrenal

cortex

Corticosterone

Angiotensinogen

(Lungs)

renal blood flow &/or Na+

++ Juxtaglomerular apparatus of kidneys(considered volume receptors)

Angiotensin I

Converting

enzymes

Angiotensin II(powerful vasoconstrictor)Angiotensin III(powerful vasoconstrictor)

Renin-Angiotensin System:

N.B. Aldosterone is the main regulator of Na+ retention.


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2. Anti-diuretic hormone (ADH), or

vasopressin:

Hypovolemia & dehydration will stimulate the

osmoreceptors in the hypothalamus, which will

lead to release of ADH from posterior pituitarygland.

ADH will cause water reabsorption at kidney

tubules.


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3. Low-pressure volume receptors:

Atrial natriuritic peptide (ANP) hormone, issecreted

from the wall of right atrium to regulate Na+excretion

in order to maintain blood volume.


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