Post on 28-Jul-2015
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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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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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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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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 Flow, Poiseuille’s Lawand Viscosity
• Blood flow– Amount of blood
moving through a vessel in a given time period
– Directly proportional to pressure differences, inversely proportional to resistance
• Poiseuille’s 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
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Critical Closing Pressure, Laplace’s Law and Compliance
Critical closing pressure– Pressure at which a blood
vessel collapses and blood flow stops
Laplace’s Law– Force acting on blood
vessel wall is proportional to diameter of the vessel times blood pressure
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
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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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Vein Characteristics andEffect of Gravity on Blood
PressureVein 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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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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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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Long Term Mechanisms
• 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
• 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
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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