Peripheral Circulation and Regulation

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Chapter 21

• Peripheral Circulation and Regulation

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Peripheral Circulatory System

• Systemic vessels
• Transport blood through most all body parts from
  left ventricle and back to right atrium
• Pulmonary vessels
• Transport blood from right ventricle through
  lungs and back to left atrium
• Blood vessels and heart regulated to ensure blood
  pressure is high enough for blood flow to meet
  metabolic needs of tissues

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Blood Vessel Structure

• Arteries
• Elastic, muscular, arterioles
• Capillaries
• Blood flows from arterioles to capillaries
• Most of exchange between blood and interstitial
  spaces occurs across the walls
• Blood flows from capillaries to venous system
• Veins
• Venules, small veins, medium or large veins

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Capillaries

• Capillary wall consists mostly of endothelial
  cells
• Types classified by diameter/permeability
• Continuous
• Do not have fenestrae
• Fenestrated
• Have pores
• Sinusoidal
• Large diameter with large fenestrae

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Capillary Network

• Blood flows from arterioles through
  metarterioles, then through capillary network
• Venules drain network
• Smooth muscle in arterioles, metarterioles,
  precapillary sphincters regulates blood flow

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Structure of Arteries and Veins

• Three layers except for capillaries and venules
• Tunica intima
• Endothelium
• Tunica media
• Vasoconstriction
• Vasodilation
• Tunica adventitia
• Merges with connective tissue surrounding blood
  vessels

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Structure of Arteries

• Elastic or conducting arteries
• Largest diameters, pressure high and fluctuates
• Muscular or medium arteries
• Smooth muscle allows vessels to regulate blood
  supply by constricting or dilating
• Arterioles
• Transport blood from small arteries to capillaries

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Structure of Veins

• Venules and small veins
• Tubes of endothelium on delicate basement
  membrane
• Medium and large veins
• Valves
• Allow blood to flow toward heart but not in
  opposite direction
• Atriovenous anastomoses
• Allow blood to flow from arterioles to small
  veins without passing through capillaries

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Blood Vessel Comparison
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Aging of the Arteries

• Arteriosclerosis
• General term for degeneration changes in arteries
  making them less elastic
• Atherosclerosis
• Deposition of plaque on walls

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Pulmonary Circulation

• Moves blood to and from the lungs
• Pulmonary trunk
• Arises from right ventricle
• Pulmonary arteries
• Branches of pulmonary trunk which project to
  lungs
• Pulmonary veins
• Exit each lung and enter left atrium

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Systemic Circulation Arteries

• Aorta
• From which all arteries are derived either
  directly or indirectly
• Parts
• Ascending, descending, thoracic, abdominal
• Coronary arteries
• Supply the heart

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Branches of the Aorta
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Major Arteries
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Head and Neck Arteries
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Arteries of the Brain
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Head and Thorax Major Arteries
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Arteries of Upper Limb and Shoulder
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Arteries of Abdomen and Pelvis
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Arteries of Pelvis and Lower Limb
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Arteries of Lower Limb
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Systemic Circulation Veins

• Return blood from body to right atrium
• Major veins
• Coronary sinus (heart)
• Superior vena cava (head, neck, thorax, upper
  limbs)
• Inferior vena cava (abdomen, pelvis, lower limbs)
• Types of veins
• Superficial, deep, sinuses

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Major Veins
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Veins of Head and Neck
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Head and Thorax Veins
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Veins of Shoulder and Upper Limb
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Veins of Thorax
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Hepatic Portal System
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Veins of Abdomen and Pelvis
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Veins of Pelvis and Lower Limb
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Veins of Lower Limb
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Dynamics of Blood Circulation

• Interrelationships between
• Pressure
• Flow
• Resistance
• Control mechanisms that regulate blood pressure
• Blood flow through vessels

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Laminar and Turbulent Flow

• Laminar flow
• Streamlined
• Outermost layer moving slowest and center moving
  fastest
• Turbulent flow
• Interrupted
• Rate of flow exceeds critical velocity
• Fluid passes a constriction, sharp turn, rough
  surface

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Blood Pressure

• Measure of force exerted by blood against the
  wall
• Blood moves through vessels because of blood
  pressure
• Measured by listening for Korotkoff sounds
  produced by turbulent flow in arteries as
  pressure released from blood pressure cuff

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Blood Pressure Measurement
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Blood Flow, Poiseuilles Lawand Viscosity

• Poiseuilles Law
• Flow decreases when resistance increases
• Flow resistance decreases when vessel diameter
  increases
• Viscosity
• Measure of resistance of liquid to flow
• As viscosity increases, pressure required to flow
  increases

• Blood flow
• Amount of blood moving through a vessel in a
  given time period
• Directly proportional to pressure differences,
  inversely proportional to resistance

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Critical Closing Pressure, Laplaces Law and
Compliance

• Vascular compliance
• Tendency for blood vessel volume to increase as
  blood pressure increases
• More easily the vessel wall stretches, the
  greater its compliance
• Venous system has a large compliance and acts as
  a blood reservoir

• Critical closing pressure
• Pressure at which a blood vessel collapses and
  blood flow stops
• Laplaces Law
• Force acting on blood vessel wall is proportional
  to diameter of the vessel times blood pressure

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Physiology of Systemic Circulation

• Determined by
• Anatomy of circulatory system
• Dynamics of blood flow
• Regulatory mechanisms that control heart and
  blood vessels
• Blood volume
• Most in the veins
• Smaller volumes in arteries and capillaries

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Cross-Sectional Area

• As diameter of vessels decreases, the total
  cross-sectional area increases and velocity of
  blood flow decreases
• Much like a stream that flows rapidly through a
  narrow gorge but flows slowly through a broad
  plane

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Pressure and Resistance

• Blood pressure averages 100 mm Hg in aorta and
  drops to 0 mm Hg in the right atrium
• Greatest drop in pressure occurs in arterioles
  which regulate blood flow through tissues
• No large fluctuations in capillaries and veins

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Pulse Pressure

• Difference between systolic and diastolic
  pressures
• Increases when stroke volume increases or
  vascular compliance decreases
• Pulse pressure can be used to take a pulse to
  determine heart rate and rhythmicity

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Capillary Exchange andInterstitial Fluid Volume
Regulation

• Blood pressure, capillary permeability, and
  osmosis affect movement of fluid from capillaries
• A net movement of fluid occurs from blood into
  tissues. Fluid gained by tissues is removed by
  lymphatic system.

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Fluid Exchange Across Capillary Walls
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Vein Characteristics andEffect of Gravity on
Blood Pressure

• Vein Characteristics
• Venous return to heart increases due to increase
  in blood volume, venous tone, and arteriole
  dilation

• Effect of Gravity
• In a standing position, hydrostatic pressure
  caused by gravity increases blood pressure below
  the heart and decreases pressure above the heart

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Control of Blood Flow by Tissues

• Local control
• In most tissues, blood flow is proportional to
  metabolic needs of tissues
• Nervous System
• Responsible for routing blood flow and
  maintaining blood pressure
• Hormonal Control
• Sympathetic action potentials stimulate
  epinephrine and norepinephrine

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Local Control of Blood Flow by Tissues

• Blood flow can increase 7-8 times as a result of
  vasodilation of metarterioles and precapillary
  sphincters in response to increased rate of
  metabolism
• Vasodilator substances produced as metabolism
  increases
• Vasomotion is periodic contraction and relaxation
  of precapillary sphincters

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Nervous Regulation of Blood Vessels
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Short-Term Regulation ofBlood Pressure

• Baroreceptor reflexes
• Change peripheral resistance, heart rate, and
  stroke volume in response to changes in blood
  pressure
• Chemoreceptor reflexes
• Sensory receptors sensitive to oxygen, carbon
  dioxide, and pH levels of blood
• Central nervous system ischemic response
• Results from high carbon dioxide or low pH levels
  in medulla and increases peripheral resistance

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Baroreceptor Reflex Control
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Baroreceptor Effects
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Chemoreceptor Reflex Control
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Effects of pH and Gases
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Long-Term Regulation of Blood Pressure

• Renin-angiotensin-aldosterone mechanism
• Vasopressin (ADH) mechanism
• Atrial natriuretic mechanism
• Fluid shift mechanism
• Stress-relaxation response

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Renin-Angiotensin-AldosteroneMechanism
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Vasopressin (ADH) Mechanism
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Long Term Mechanisms

• Fluid shift
• Movement of fluid from interstitial spaces into
  capillaries in response to decrease in blood
  pressure to maintain blood volume
• Stress-relaxation
• Adjustment of blood vessel smooth muscle to
  respond to change in blood volume

• Atrial natriuretic
• Hormone released from cardiac muscle cells when
  atrial blood pressure increases, simulating an
  increase in urinary production, causing a
  decrease in blood volume and blood pressure

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Shock

• Inadequate blood flow throughout body
• Three stages
• Compensated Blood pressure decreases only a
  moderate amount and mechanisms able to
  reestablish normal blood pressure and flow
• Progressive Compensatory mechanisms inadequate
  and positive feedback cycle develops cycle
  proceeds to next stage or medical treatment
  reestablishes adequate blood flow to tissues
• Irreversible Leads to death, regardless of
  medical treatment