CVS Lect 6 Blood Pressure, Pathophysiology

8/14/2019 CVS Lect 6 Blood Pressure, Pathophysiology

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Blood Pressure andBlood Pressure and

Pathophysiology ofPathophysiology ofHypertensionHypertension

(Short and Long Term(Short and Long TermRegulation of BP)Regulation of BP)


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Short-Term Regulation of BloodPressure:

Baroreceptorsare sensory receptorssensitive to stretch. Baroreceptors

are located in the carotid sinuses andthe aortic arch. The baroreceptorreflex changes peripheral resistance,

heart rate, and stroke volume inresponse to changes in bloodpressure.


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ChemoreceptorsChemor

eceptorsare sensoryare sensory

receptors sensitive to oxygen,receptors sensitive to oxygen,carbon dioxide, and pH levels in thecarbon dioxide, and pH levels in the

blood.blood.

The CNS ischemic responseThe CNS ischemic re

sponseresults from high carbon dioxide orresults from high carbon dioxide or

low pH levels in the medulla andlow pH levels in the medulla and

increases peripheral resistance.increases peripheral resistance.

Thus it increases BP. This is clearlyThus it increases BP. This is clearly

observed in some patients sufferingobserved in some patients suffering

from ischemic attacks.from ischemic attacks.


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Adrenalin and noradrenalin are

released from the adrenal medulla as aresult of sympathetic stimulation. They

increase heart rate, stroke volume, and

vasoconstriction.

Renin is released by the kidneys in

response to low blood pressure. Renin

promotes the production of angiotensin

II, which causes vasoconstriction and anincrease in aldosterone secretion.


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ADHADHreleased from the posteriorreleased from the posteriorpituitary causes vasoconstriction, raisingpituitary causes vasoconstriction, raising

blood pressure.blood pressure. Atrial natriuretic hormoneAtrial natriuretic hormoneis releasedis released

from the heart when atrial blood pressurefrom the heart when atrial blood pressureincreases. It stimulates an increasedincreases. It stimulates an increased

urinary production, causing a decrease inurinary production, causing a decrease inblood volume and blood pressure.blood volume and blood pressure.

Fluid shiftFluid shift is a movement of fluid fromis a movement of fluid fromthe interstitial fluid to maintain bloodthe interstitial fluid to maintain bloodvolume.volume.

The stressrelaxationThe stressrelaxation responseres

ponse is anis anadjustment of the muscles of bloodadjustment of the muscles of bloodvessels in response to a change in thevessels in response to a change in thevolume.volume.


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LONG-TERM REGULATION OFLONG-TERM REGULATION OF BLOODBLOOD

PRESSUREPRESSURE

The kidneysThe kidneys regulate blood pressure byregulate blood pressure by

controlling blood volume. In response to ancontrolling blood volume. In response to an

increase in blood volume, the kidneysincrease in blood volume, the kidneys

produce more urine and decrease bloodproduce more urine and decrease bloodvolume. Renin angiotensin II, aldosterone,volume. Renin angiotensin II, aldosterone,

vasopressin, atrial natriuretic hormone, andvasopressin, atrial natriuretic hormone, and

sympathetic stimulation play a role insympathetic stimulation play a role incontrolling urinary volume.controlling urinary volume.


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LONG-TERM REGULATION OFLONG-TERM REGULATION OF BLOODBLOOD

PRESSUREPRESSURE

The kidneysThe kidneys regulate blood pressure byregulate blood pressure by

controlling blood volume. In response tocontrolling blood volume. In response to

an increase in blood volume, the kidneysan increase in blood volume, the kidneys

produce more urine and decrease bloodproduce more urine and decrease blood

volume. Renin angiotensin II, aldosterone,volume. Renin angiotensin II, aldosterone,

vasopressin, atrial natriuretic hormone,vasopressin, atrial natriuretic hormone,

and sympathetic stimulation play a role inand sympathetic stimulation play a role incontrolling urinary volume.controlling urinary volume.


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LONG-TERM REGULATION OF BLOOD

PRESSUREThe kidneys regulate blood pressure by

controlling blood volume. In response to

an increase in blood volume, the kidneys

produce more urine and decrease blood

volume. Renin angiotensin II, aldosterone,

vasopressin, atrial natriuretic hormone,

and sympathetic stimulation play a role incontrolling urinary volume.


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Fluid shift and stress-relaxationresponses help control pressure.

Blood Pressure and the Effect ofGravity

In a standing person hydrostaticpressure caused by gravity increases

blood pressure below the heart anddecreases pressure above the heart.


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Control of Blood Flow in Tissues:

Local Control of Blood Flow by the Tissues Blood flow through a tissue is usually proportional to the

metabolic needs of the tissue. Exceptions are tissuesthat perform functions that require additional blood.

Control of blood flow by the metarterioles andprecapillary sphincters can be regulated byvasodilator substances or by lack of nutrients.

Only large changes in blood pressure have an effect onblood flow through tissues.

If the metabolic activity of a tissue increases, the

number and the diameter of capillaries in the tissueincrease over time.


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Nervous and Hormonal Regulation of LocalCirculation:

1. The sympathetic nervous system (vasomotorcenter in the medulla) controls blood vesseldiameter. Other brain areas can excite or inhibitthe vasomotor center.

2. Vasomotor tone is a state of partial

contraction of blood vessels. 3. The nervous system is responsible for routing

the flow of blood and maintaining bloodpressure.

4. Sympathetic action potentials stimulateadrenalin and noradrenalin release from theadrenal medulla and these hormones causevasoconstriction in most blood vessels.


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REGULATION OF MEAN ARTERIAL PRESSUREREGULATION OF MEAN ARTERIAL PRESSURE

Mean Arterial pressure (MAP) isMean Arterial pressure (MAP) is

proportional to cardiac outputproportional to cardiac output

times the peripheral resistance.times the peripheral resistance.

MAP = CO X PRMAP = CO X PR

MAP = DBP + (Pulse pressure /3)MAP = DBP + (Pulse pressure /3)

Pulse Pressure = SBP - DBPPulse Pressure = SBP - DBP

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CVS Lect 6 Blood Pressure, Pathophysiology