Chapter 19Blood Vessels

Lecture 4

Part 2b: Regulation of Blood Pressure

Marieb’s HumanAnatomy and

PhysiologyNinth Edition

Marieb Hoehn

2

Regulation of Blood Flow/Pressure• Blood flow/pressure can be affected by

1) Autoregulation • Local factors within tissue capillary beds

• Cause localized reaction

2) Neural mechanisms• Responses to changes in arterial pressure or blood gas levels

(baroreceptors or chemoreceptors)

• Cause more widespread changes

• VERY rapid

3) Endocrine mechanisms (will be covered with endocrine/urinary systems)

• Enhance short-term adjustments

• Direct long-term changes

• Work mainly through changes in blood volume

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Autoregulation of Blood Flow/Pressure

• Local changes in response to metabolic needs of tissues

• Occurs at the level of the precapillary sphincters; not dependent on neural or hormonal mechanisms

• Changes in local blood flow may, or may not, necessitate activation of neural and/or hormonal mechanisms

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Autoregulation of Blood Flow/Pressure

• Local vasodilators increase blood flow– Decreased O2 (except pulmonary circulation) or

increased CO2

– Increase in lactic acid production

– Histamine; release of nitric oxide (NO)

– Increased K+ or H+

– Certain prostaglandins

– Elevated local temperature

• Local vasoconstrictors decrease blood flow– Certain prostaglandins, thromboxanes (released by

activated platelets and WBCs)

– Endothelins released by damaged endothelial cells

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Neural Control of Blood PressureControlling cardiac output and peripheral resistance regulates blood pressure

Know this!

Figure from: Hole’s Human A&P, 12th edition, 2010

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Neural Control of Blood Pressure

If blood pressure rises, baroreceptors initiate the cardioinhibitory reflex, which lowers the blood pressure

Know this!

Figure from: Hole’s Human A&P, 12th edition, 2010

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Neural Control of Blood PressureDilating arterioles helps regulate (lower) blood pressure

Know this!

Figure from: Hole’s Human A&P, 12th edition, 2010

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Factors Affecting Blood Pressure (MAP)

Contractility

Afterload

CVP

CO

HR

SV

ESV

EDV

ANSParasympathetic Sympathetic

MAP – Mean Arterial Pressure = Average effective pressure driving blood flow through the systemic organs

**The MAP is dependent upon CO and TPR, i.e., MAP = CO x TPR

TPR – Total Peripheral Resistance; depends upon *blood vessel radius, vessel length, blood viscosity, and turbulence

MAP (BP) TPR1/radius4; Vessel length; Viscosity; Turbulence

Figure adapted from: Aaronson & Ward, The Cardiovascular System at a Glance, Blackwell Publishing, 2007

= EDV - ESV

= HR x SV

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Factors Affecting Blood Pressure (MAP)

MAP = X TPR 1 / radius4

Vessel length

Viscosity Turbulence

Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001

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Review

• Factors influencing blood pressure– Cardiac output (CO)– Blood volume– Blood viscosity– Peripheral resistance (PR)

• Cardiovascular system function can be regulated by– Tissue autoregulation– Neural mechanisms– Endocrine mechanisms

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Review

• Veins are a large reservoir of blood and exert a large effect upon blood pressure

• Venous blood flow depends upon– Skeletal muscle contraction– Breathing movement– Vasoconstriction of veins (venoconstriction)

• Central venous pressure is the pressure near the right atrium– If CVP increases, blood may back up– Increased CVP can lead to edema