Blood Vessels

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Blood Vessels
2
Types of Blood Vessels

• arteries
• arterioles
• capillaries
• venules
• veins

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Three Tissue Layers

• All blood vessels, except capillaries have
  three tissue layers
• tunica interna
• tunica media
• tunica externa

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Tunica Interna (intima)

• inner layer
• composed of simple squamous epithelium
• - cells are in direct contact with blood in the
  lumen
• rests on a connective tissue membrane
• - membrane is rich in elastic and collagenous
  fibers
• much less elastic tissue is present in veins

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Tunica Media

• middle layer
• usually thickest layer
• poorly developed in veins
• consists primarily of smooth muscle cells
• - cells arranged in concentric layers around
  tunica interna
• gap junctions facilitate impulse transmission
• elastin fibers are interspersed among smooth
  muscle cells

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Tunica Externa (adventitia)

• relatively thin outer layer
• consists primarily of longitudinally orientated
  collagen and elastin fibers
• attaches to surrounding tissues
• smooth muscles in the walls of arteries and
  arterioles are innervated by the sympathetic
  branches of the autonomic nervous system

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Arteries

• large, elastic vessels
• carry blood away from heart to tissues
• hollow center, through which blood flows, is
  called lumen

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Artery
endothelium
basement membrane
smooth muscle
internal elastic lamina
external elastic lamina
lumen
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Arterioles

• small vessels
• carry blood from arteries to capillaries
• play an important role in regulating blood flow
  from arteries to capillaries
• change in diameter of arterioles can
  significantly affect blood pressure

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Arteriole
smooth muscle fiber
endothelium
capillary
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Vasoconstriction

• contraction of smooth muscles
• reduces diameter of vessels
• Vasodilation
• relaxation of muscle fibers
• diameter of vessels increases

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Capillaries

• microscopic vessels
• smallest vessels
• form connections between smallest arterioles and
  smallest venules
• single layer of squamous epithelial cells and a
  basement membrane

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Capillaries (cont.)

• no tunica media or tunica externa
• form semipermeable membranes through which
  substances in blood are exchanged for substances
  in tissue fluid surrounding body cells
• exchange only occurs in capillaries because thick
  walls of arteries and veins provide too great a
  barrier for exchange

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Capillaries (cont.)

• density of capillaries within a tissue is related
  to rate of tissues metabolism
• muscle and nerve tissues are richly supplied
  with capillaries because of their high metabolic
  rate
• tissues with low metabolic rates such as
  cartilage, epidermis, and cornea lack capillaries

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Capillaries (cont.)

• capillary arrangement differs in various body
  parts
• some capillaries pass directly from arterioles to
  venules
• others lead to branched networks
• - allow blood to follow different pathways
  through a tissue

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Branched Networks

• allow cells with increased need for oxygen and
  nutrients sufficient supply during exercise, for
  example physical exertion or stressful situations
  
• allow capillary networks in other tissues to
  receive less blood when demand is less
  critical

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Precapillary Sphincters

• regulate distribution of blood in various
  capillary pathways by vasoconstriction controlled
  by the CV center in brain
• encircle capillary entrances
• respond to demands of cells supplied by
  individual capillaries

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Exchanges in the Capillaries

• substances are moved through capillary walls
  primarily by
• - diffusion (most important type of transfer)
• (high concentration to lower)
• - osmosis
• (involves the forcing of molecules
  through membrane by
  hydrostatic pressure)

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Exchanges in the Capillaries
pores
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Blood Brain Barrier

• Consists of
• - specialized brain capillaries
• - astrocytes
• prevents passage of materials from blood to
  cerebrospinal fluid and brain

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Blood Brain Barrier (cont.)

• endothelial cells of capillary walls - more
  tightly fused than in other parts of body
• some substances such as glucose may freely pass
  through endothelium but other may not

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Venules

• microscopic vessels that drain blood from
  capillaries into veins

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Veins

• carry blood from venules to heart
• some veins contain flap-like valves
• (in arms and legs)
• valves project inward from their linings
• valves close if blood backs ups in a vein
• valves stay open as long as blood flow is toward
  the heart
• also serve as blood reservoirs

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Veins
lumen
valve
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Blood Pressure

• force exerted by blood against inner walls of the
  blood vessels
• commonly refers to pressure in systemic arteries
• generated by contractions of ventricles
• rises to about 120 mm Hg during systole
• drops to 80 mm Hg during diastole

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Blood Pressure (cont.)

• Influenced by
• - heart action
• - blood volume
• - resistance to flow
• - viscosity of the blood
• - changes in diameter of arteries and veins
  greatly influences flow and pressure of blood

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Hemorrhage and/or Lower Arterial Blood Pressure

• muscular walls of veins are stimulated by
  sympathetic nerve impulses
• resulting venous constriction helps raise the
  blood pressure

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Hemodynamics

• Study of the forces involved in the circulation
  of blood throughout the body

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Heart Action

• produces blood pressure by forcing blood into
  arteries
• determines how much blood enters arterial system
  with each ventricular contraction
• rate of fluid output

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Stroke Volume

• volume of blood discharged from either ventricle
  with each contraction (systole) (about 70 ml)

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Cardiac Output

• volume of blood pumped from one ventricle per
  minute
• Factors influencing cardiac output
• - blood pressure
• - the force of friction as blood moves along
  blood vessels

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Cardiac Output (cont.)

• stroke volume x heart rate
• For example
• stroke volume 70 ml
• heart rate 75 beats per minute
• cardiac output 5250 ml per minute
• 5.25 liters/minute

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Blood Volume

• equal to sum of the blood cell and plasma volumes
• about 5 liters
• blood pressure is directly proportional to blood
  volume

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Resistance to Flow

• friction between blood and walls of vessels
  causes peripheral resistance which hinders blood
  flow
• Resistance depends on
• - blood viscosity
• - blood vessel length
• - blood vessel radius

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Viscosity

• thickness of the blood
• depends on the ratio of red blood cells to plasma
  volume
• resistance to blood flow is directly related to
  viscosity of the blood

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Blood Vessel Length

• the longer the vessel, the greater the resistance
• Blood Vessel Radius
• the smaller the radius of the blood vessel, the
  greater the resistance to blood flow

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Major Arteries
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Arteries (structure)

• elastic arteries (conduction arteries)
• - large arteries are elastic arteries
• muscular arteries (distributing)
• - medium sized arteries are muscular
• anastomoses
• - interconnections between arteries allow for
  alternate pathways
• end arteries
• - arteries that do not anastomose

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Coronary Arteries

• branch from ascending aorta
• supply the heart muscle

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Aorta

• largest artery in the body
• extends upward from left ventricle
• arches over heart to the left
• Three major arteries originate from aorta
• - brachiocephalic
• - common carotid artery
• - left subclavian artery

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Brachiocephalic Trunk

• arises from aortic arch
• carries blood to right side of upper body
• becomes right subclavian

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Brachiocephalic Trunk (cont.)

• left common carotid and left subclavian arise
  directly from the aortic arch
• right common carotid arises from junction between
  brachiocephalic trunk and the right subclavian
  artery

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Common Carotid

• main artery that supplies the brain
• Subclavian
• main artery supplying the upper extremities
• becomes axillary artery

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Axillary Artery

• supplies axilla and chest wall
• becomes
• brachial artery divides into ulnar and radial
  arteries

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Ulnar Artery

• supplies elbow joint and forearm
• Radial Artery
• supplies forearm, wrist, hand, and fingers

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Thoracic Aorta

• branches into intercostal arteries

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Intercostals

• 10 pairs
• Supply
• - intercostal muscles, vertebrae, spinal cord,
  back muscles
• Other branches supply
• - bronchi, lungs, esophagus, pericardium, and
  diaphragm

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Abdominal Aorta

• Branches into
• - phrenic artery
• - ciliac trunk
• - renal arteries
• - gonadal arteries
• - lumbar arteries
• - superior and inferior mesenteric arteries
• - iliac arteries

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Phrenic

• supplies diaphragm
• Celiac Trunk
• supplies stomach, spleen and liver
• (gastric, splenic, and hepatic arteries)
• Renal
• supply kidneys

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Gonadal (testicular or ovarian)

• supply testes in the male, ovaries in the female
• Lumbar (4 pairs)
• supply abdominal wall and the spinal cord

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Superior Mesenteric

• supplies small intestine,appendix, ascending and
  transverse colon
• Inferior Mesenteric
• supplies descending colon and rectum

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Iliac Arteries

• Branch into
• - common iliac
• - internal iliac
• - external iliac
• - femoral artery
• - popliteal
• - anterior and posterior tibial
• - peroneal

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Common Iliac

• aorta divides at level of pelvic brim into right
  and left common iliac
• Internal Iliac
• supplies pelvis and gluteal muscles, external
  genitalia, and visceral structures

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External Iliac

• supplies lower abdominal wall, and upper leg
• becomes femoral artery
• Femoral Artery
• supplies groin, lower abdominal wall and thigh
• becomes popliteal artery at knee

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Popliteal

• supplies knee joint, thigh, and calf
• divides into anterior and posterior tibial
  arteries
• Anterior Tibial
• supplies the lower leg
• becomes dorsalis pedis artery in the foot

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Posterior Tibial

• supplies lower leg
• becomes plantar arch in the foot
• Peroneal
• branch of posterior tibial artery
• supplies the lower leg

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Major Veins
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Veins (structure)

• tissue layer
• - thinner tunica interna and media compared to
  arteries
• - thicker tunica externa
• contain one-way valves which prevent back-flow of
  blood
• venous sinuses are enlarged channels that drain
  blood from brain and heart

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The Great Veins

• superior venal cava
• inferior vena cava

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Superior Vena Cava

• drains the head and upper extremities
• Inferior Vena Cava
• drains the torso and lower extremities

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Veins of the Head and Upper Extremities

• brachiocephalic
• internal and external jugular
• subclavian
• axillary

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Brachiocephalic

• drains subclavian and internal jugular veins
• Internal Jugular
• drains the brain, face, and neck
• External Jugular
• drains deep parts of face, exterior of the
  cranium and auricular veins

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Subclavian

• drains axillary and external jugular veins
• Axillary
• drains upper extremity (brachial, cephalic, and
  basilic veins)

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Torso and Lower Extremities

• inferior phrenic
• hepatic
• renal
• left and right gonadal
• lumbar
• iliacs
• femoral
• popliteal

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Inferior Phrenic

• drains diaphragm
• Hepatic
• drains liver
• Renal
• drains kidneys

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Left Gonadal

• drains left kidney and left gonad
• Right Gonadal
• drains right gonad
• Lumbars
• drain abdominal wall and spinal cord

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Common Iliac

• drains lower extremity and pelvic region
• Internal Iliac
• drains gluteal and thigh muscles, urinary
  bladder, rectum, and reproductive organs
• External Iliac
• drains femoral and great saphenous veins

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Femoral

• drains deep structures of thigh
• Popliteal
• drains anterior and posterior tibial veins and
  the small saphenous vein

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Azygos System

• unpaired veins
• drains blood from lungs, esophagus, pericardium,
  vertebrae, diaphragm, and thoracic spinal cord
• connects with superior and inferior vena cava

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Hepatic Portal System

• detours venous blood from pancreas, spleen,
  stomach, and gall bladder through liver for
  filtration
• also receives oxygenated blood from the systemic
  circulation via hepatic artery
• all blood leaves liver through hepatic veins
  which drain into inferior vena cava