Lecture 11 Vascular System

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Lecture 11Vascular System
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• What functions does circulatory system serve?
• Closed circulatory system
• Tissue fluid plasma ? tissues ? returns to
• capillaries ? venous return
• lymphatic vessels as lymph in lymphatic vessels

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Blood Vessels Conduct Blood in Continuous Loops

• Artery- a vessel that transports blood away from
  the heart.
• Arteriole- a small blood vessel located between
  an artery and a capillary.
• Vein- a vessel that transports blood toward the
  heart.
• Venule- a small blood vessel that receives blood
  from the capillaries, located between a capillary
  and a vein.

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• Histology of Blood Vessels
• Tunica interna (intima)
• simple squamous epithelium known as endothelium
• basement membrane
• internal elastic lamina
• Tunica media
• circular smooth muscle elastic fibers
• Vasoconstriction/vasodilation response to
  sympathetic nervous stimulation
• external elastic lamina (membrane)
• Tunica externa
• elastic collagen fibers

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• Anatomy of Blood Vessels
• Closed system of tubes that carries blood
• Arteries carry blood from heart to tissues
• elastic arteries pressure reservoir
• muscular arteries vasoconstriction/dialation
• Arterioles few layers of muscle in tunica media
• Capillaries are thin enough to allow exchange
• Venules merge to form veins that bring blood back
  to the heart
• Vasa vasorum vessels in walls of large vessel

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Arteries vs. Veins

• Each has 3 layers.
• The middle layer of an artery shows more smooth
  muscle.
• The lumen is smaller in arteries.
• Some veins contain valves.
• Veins are blood reservoirs (hold 65 of blood).

Valve
Smooth Muscle
Artery
Vein
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• Types of Arteries
• Elastic Arteries
• High density of elastic fibers- absorb variations
  in blood pressure/pulse
• Aorta, common carotids, etc.
• Muscular Arteries
• Smooth muscle subject to sympathetic control
• Brachial, external carotids, etc.
• Arterioles
• Incomplete smooth muscle in tunica media
• Control of blood flow to tissues

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http//anatomy.iupui.edu/courses/histo_D502/D502f0
4/Labs.f04/connective20lab/Lab3f04.html
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Pulse- a pressure wave created by the ejection of
blood from the left ventricle into the aorta.
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• Veins
• Proportionally thinner walls than same diameter
  artery
• tunica media less muscle
• lack external internalelastic lamina
• Still adaptable to variationsin volume
  pressure
• Valves are thin folds of tunica interna designed
  to prevent backflow
• Venous sinus has no muscle at all
• coronary sinus or dural venous sinuses
• Act as reservoir for considerable proportion of
  blood volume

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• 60 of blood volume at rest is in systemic veins
  and venules
• function as blood reservoir
• veins of skin abdominalorgans
• blood is diverted from it intimes of need
• increased muscular activityproduces
  venoconstriction
• hemorrhage causes venoconstriction to help
  maintain blood pressure
• 15 of blood volume in arteries arterioles

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• Veins
• Sizes
• Venules
• Medium size
• Large veins

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• What is the difference between an artery and a
  vein?

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• Phlebitis
• Swelling, tenderness,irritation of superficial or
  deep veins
• Generally not serious
• Causes?
• Lack of exercise, genetic
• Varicose veins
• Thickened, twisted
• Usually in legs
• Causes?
• Valves - defective, not enough

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• Movement of Blood
• Arteries
• hydrostatic pressure
• pumping action of heart
• Blood pressure/velocity
• Decreases in capillaries.
• Greater surface area
• Veins
• No hydrostatic pressure
• Squeezing action from adjacent musculature
• Valves ensure direction

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• Capillaries sites of exchange
• Microscopic/narrow
• Basement membrane endothelial cells

• Permeability varies depending on structure
• 3 types based on presence/absence of pores in
  endothelial cells
• Continuous capillaries most regions
• Fenestrated incomplete endothelial lining
• Sinusoids pores through endothelium increase
  permeability

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• Blood Supply and Capillary Beds
• Capillary bed interconnected network of
  capillaries
• Precapillary sphincter smooth muscle band
  controls flow of blood through bed
• Capillary Bed bypass Metaarteriole ?
  thoroughfare channel
• Metaarteriole arteriole end, smooth muscle in
  walls
• Thoroughfare Channel direct capillary passage to
  venuole

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• Anastomosis Union of 2 or more arteries
  supplying the same body region
• blockage of only one pathway has no effect
• circle of willis underneath brain
• coronary circulation of heart
• collateral circulation Alternate route of blood
  flow through an anastomosis
• Alternate routes to a region can also be supplied
  by nonanastomosing vessels

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• Flow through Capillary Bed
• Regulated by tissue CO2 level (how)
• Autonomic nervous system
• smooth muscle constriction/relaxation modulates
  flow
• Vasoconstriction
• Vasodilation
• Precapillary sphincter regulates flow
• Vasomotion intermittent contraction relaxation
  of sphincters
• Pulses of blood flow - 5-10 times/minute
• Ateriovenous anastomoses
• Dilation ? reduced flow through parallel bed

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• Circulation Patterns
• Pulmonary
• Systemic
• Cardiac
• Blood Supply to brain
• Portal systems hepatic portal
• Fetal

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Circulatory Routes

• Systemic circulation is left side heart to body
  back to heart
• Hepatic Portal circulation is capillaries of GI
  tract to capillaries in liver
• Pulmonary circulation is right-side heart to
  lungs back to heart
• Fetal circulation is from fetal heart through
  umbilical cord to placenta back

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• Naming of Vessels
• Often take names from
• tissue/organ
• Renal, gastric, splenic
• Sometimes location
• Subclavian, femoral, axillary etc.
• Trunk
• Short, relatively large diameter
• Soon branch
• Pulmonary, celiac, thyrocervical, brachicephalic
  (always include trunk after name)

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Pulmonary Circulation

• Deoxygenated blood right ventricle ? air sacs ?
  left atria
• Pulmonary trunk, L/R pulmonary arteries and veins
• Differences from systemic circulation
• pulmonary aa. are larger, thinner with less
  elastic tissue
• resistance is low pulmonary blood pressure is
  reduced

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• Systemic Circulation
• Aorta is largest artery of the body
• ascending aorta
• 2 coronary arteries supply myocardium
• arch of aorta -- branches to the arms head
• thoracic aorta

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• Blood Supply to Brain
• Internal carotids Vertebral arteries
• Join to form cerebral arterial circle (circle of
  Willis)
• Return via. Vertebral veins, internal jugular

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Fig. 13.32
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• Hepatic Portal System
• What is a portal system?
• Begins with capillaries surrounding intestine
• Splenic/inferior mesenteric
• superior mesenteric
• ends with capillaries arising from Hepatic Portal
  Vein
• Products of digestion stored/modified in liver

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Arterial Supply and Venous Drainage of Liver
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Fetal Circulation

• Oxygen from placenta reaches heart via fetal
  veins in umbilical cord.
• bypasses liver
• Heart pumps oxygenated blood to capillaries in
  all fetal tissues including lungs.
• Umbilical aa. Branch off iliac aa. to return
  blood to placenta.

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Lung Bypasses in Fetal Circulation
Ductus arteriosus is shortcut from pulmonary
trunk to aorta bypassing the lungs.
Foramen ovale is shortcut from right atria to
left atria bypassing the lungs.
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• The End
• Go forth and Circulate