Blood Vessels

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Blood Vessels
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Types of vessels

• Arteries and arterioles
• Carry blood away from heart
• Capillaries
• Connect arterial system to venous system
• Site of exchange of substances
• Veins and venules
• Return blood from periphery to heart

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Arteries

• High pressure vessels
• Walls are composed of three layers
• Tunica intima (Inner layer) endothelium
• Tunica Media (middle layer)
• Tunica externa (outer layer)

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Tunica intima

• Layer of squamous epithelium which provides a
  smooth surface for efficient blood flow.
• Also has substances to prevent clotting

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Tunica media

• Thick layer of smooth muscle and elastic fibers
• Very important for regulation of blood flow
• Muscles are responsible for vasoconstriction
  (narrowing) and vasodilation (enlarging) the
  diameter of the vessel as needed.
• Elastic fibers allow for flexibility to
  accommodate rapid changes in system.

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Tunica externa

• Thin layer of connective tissue
• Provides some protection, also connects to
  surrounding tissue.

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Veins/venules

• Low pressure vessels
• Have same three layers as arterial walls
• Less smooth muscle, so tunica media is smaller
• Lumen is larger
• Major difference is presence of valves

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• Artery and vein

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Capillaries

• Smallest blood vessels in body
• Site of gas/fluid exchange between bloodstream
  and tissues
• Walls composed of a single layer of endothelial
  cells
• Walls are semipermeable

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Capillary
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Capillary network

• Thousands of capillaries connect arterioles and
  venules

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Types of exchange

• Diffusion movement of substances from area of
  greater concentration to area of lesser
  concentration
• Filtration movement across a membrane due to
  pressure
• Osmosis movement of water due to higher
  concentration of impermeable substances on one
  side of a membrane (proteins)

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Blood pressure

• Force applied by bloodstream on the walls of the
  vessels containing it.
• Pressure in a capillary influences movement of
  particles into and out of bloodstream