Cardiovascular system - Blood Vessels Chapter 13

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Cardiovascular system -Blood VesselsChapter 13
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Basic Anatomy of Circulatory routes
Carry blood away from the heart
Carry blood towards the heart
Connect capillaries to veins
Control blood flow into capillaries help
regulate BP
Allow for exchange of O2/CO2, nutrients/wastes
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Structure of Blood Vessels
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Arteries Veins
Both are comprised of 3 layers of tissue - tunica
interna, tunica media tunica externa -
surrounding lumen through which blood will flow
All structural difference between arteries
veins primarily due to differences in pressure of
blood flowing within
Lumen larger diameter in veins compared to
corresponding artery
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Arteries Veins

• Tunica Interna innermost endothelium of simple
  squamous epithelium basement membrane
• Arteries have an internal elastic lamina of
  elastic CT to allow for expansion under pressure
• Veins may have valves (folds of endothelium
  CT) to prevent backflow of blood due to low
  pressure

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Arteries Veins

• Tunica Media middle layer containing smooth
  muscle (for contractility/vasoconstriction)
  elastic CT (for elasticity)
• Arteries have relatively thick tunica media
  allowing for significant vasoconstriction
  elasticity
• Veins relatively thin tunica media therefore
  no significant constriction/elasticity

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Arteries Veins

• Tunica Externa (a.k.a. adventitia) made of
  collagenous CT
• Arteries thin layer
• Veins thickest layer of vein, trying to
  support against gravity low pressure

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As blood moves through CV system from arteries ?
veins, pressure within the vessels decreases
significantly Blood also has to move against
gravity in many veins

• Venous return is aided by
• Valves
• Muscular compression milking of veins through
  skeletal muscle contraction
• Respiratory pump breathing ? changes in
  pressure in abdominal/thoracic cavities

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Arterioles Venules

• Very small, almost microscopic vessels with only
  2 layers of tissue surrounding lumen
• Arterioles endothelium (tunica interna) very
  thin layer of smooth muscle cells (tunica media)
  regulate blood flow to tissues affect arterial
  blood pressure
• Venules endothelium (tunica interna) thin
  layer of CT (tunica externa)

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Capillaries

• Microscopic, very thin-walled vessels comprised
  of endothelium with basement membrane
• Found in all tissues of the body except for
  those that are avascular
• Usually form branching networks (capillary
  beds) within tissues for increased surface area

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Capillaries

• Structure of capillaries allows for
• filtration - at arterial end due to high
  capillary hydrostatic pressure (CHP)
• reabsorption - at venous end due to high blood
  osmotic pressure (BOP)

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Physiology of Circulation
Primary function of CV system is to maintain
adequate blood flow to capillaries of
tissues Under normal circumstances, capillary
blood flow is directly related to cardiac output
(increased C.O. ? increased blood flow, and
vice-versa) Capillary blood flow is also affected
by pressure resistance
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Physiology of Circulation
Pressure Blood pressure - the force exerted
on the wall of a vessel from the blood within
related to the beating of the heart Systolic
pressure pressure within artery when ventricle
contracts Diastolic pressure pressure
remaining within artery when ventricle
relaxes Circulatory pressure the difference
in pressures throughout the circulatory system
(high pressure in arteries (avg.100mm Hg at
aorta) ? low pressure in veins (avg. 2mm Hg at
IVC)) Blood flow is directly related to
circulatory pressure blood will move from high
to low pressure. If arterial blood pressure
increases, capillary blood flow will increase,
vice-versa
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Physiology of Circulation
Resistance
Resistance any force that opposes
movement Peripheral resistance refers to
resistance of blood flow in arterial side of
system mainly occurs at arterioles Peripheral
resistance primarily due to friction between
blood BV walls As peripheral resistance
increases (ie. with vasoconstriction of
arterioles), capillary blood flow decreases
(inverse relationship)
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Circulatory Routes - overview
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Circulatory Routes Pulmonary Circuit
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Circulatory Routes Systemic circuit

• Arterial blood from left ventricle into
  ascending aorta
• Venous return to right atrium through SVC, IVC
  coronary sinus