Blood Vessels

1
Mariebs Human Anatomy and Physiology Ninth
Edition Marieb w Hoehn

• Chapter 19
• Blood Vessels
• Lecture 4
• Part 2b Regulation of Blood Pressure

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

3
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

4
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

5
Neural Control of Blood Pressure
Controlling cardiac output and peripheral
resistance regulates blood pressure
Know this!
Figure from Holes Human AP, 12th edition, 2010
6
Neural Control of Blood Pressure
If blood pressure rises, baroreceptors initiate
the cardioinhibitory reflex, which lowers the
blood pressure
Know this!
Figure from Holes Human AP, 12th edition, 2010
7
Neural Control of Blood Pressure
Dilating arterioles helps regulate (lower) blood
pressure
Know this!
Figure from Holes Human AP, 12th edition, 2010
8
Factors Affecting Blood Pressure (MAP)
1/radius4 Vessel length Viscosity Turbulence
MAP (BP)
TPR
ANSParasympathetic Sympathetic
HR
Contractility
CO
HR x SV
ESV
Afterload
SV
EDV - ESV
EDV
CVP
Figure adapted from Aaronson Ward, The
Cardiovascular System at a Glance, Blackwell
Publishing, 2007
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
9
Factors Affecting Blood Pressure (MAP)
Figure from Martini, Anatomy Physiology,
Prentice Hall, 2001
MAP X TPR
1 / radius4
Vessel length
Viscosity
Turbulence
10
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

11
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