Artery and Vein Histology
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Walls have 3 layers:
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Tunica intima
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Tunica media
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Tunica externa
Tunica Intima
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Is the innermost layer near the lumen
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Includes:
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The endothelial lining
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Connective tissue layer
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Internal Elastic Membrane: In arteries, is a thick layer of elastic
fibers in the outer margin of the tunica intima
Tunica Media
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Is the middle layer
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Contains concentric sheets of smooth muscle in
loose connective tissue
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Binds to inner and outer layers
Tunica Externa (aka: Tunica Adventitia)
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Is outer layer
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Contains connective tissue sheath
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Anchors vessel to adjacent tissues
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In arteries:
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Contain collagen
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Elastic fibers
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In veins:
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Contain elastic fibers
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Smooth muscle cells
Arteries Vs. Veins
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Arteries and veins run side-by-side
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Arteries have thicker walls and higher blood
pressure
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Collapsed artery has small, round lumen
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Vein has a large, flat lumen
Arteries
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Carry blood away from the heart.
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Pulmonary arteries: The pulmonary trunk and its
branches; leave the right ventricle of
the heart and contain deoxygenated blood.
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Systemic arteries: The aorta and its
branches; leave the left ventricle of
the heart and contain oxygenated blood.
Elastic Arteries
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Also called conducting arteries, these are the
largest arteries
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Tunica media has many elastic fibers and few
muscle cells
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Elasticity evens out pulse force
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Examples:
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Pulmonary trunk
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Aorta
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Common carotid arteries
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Subclavian arteries
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Common iliac arteries
Muscular Arteries
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Also called distribution arteries, are
medium-sized (most arteries)
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Tunica media has many muscle cells
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Examples:
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External carotid arteries
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Brachial arteries
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Femoral arteries
Arterioles
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The smallest branches of arteries
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Feed into capillaries
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Have little or no tunica externa
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Have thin or incomplete tunica media
Capillaries
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The smallest vessels
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Structure: Simple squamous epithelium tube
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Lumen side has a thin basal lamina
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No tunica media, No tunica externa
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Location of exchange between blood and
interstitial fluid.
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Gasses and chemicals diffuse across their walls
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Types:
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Continuous
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Fenestrated
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Sinusoids
Continuous Capillaries
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Have complete endothelial lining (most common
type of capillary)
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Permit diffusion of:
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Water
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Small solutes
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Lipid-soluble materials
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Prevent diffusion of:
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Blood cells
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Plasma proteins
Fenestrated Capillaries
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Have pores in endothelial lining
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Permit rapid exchange of water and larger
solutes between plasma and interstitial fluid
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Are found in:
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Choroid plexus
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Endocrine organs
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Kidneys
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Intestinal tract
Sinusoids
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Modified, extremely leaky, fenestrated
capillaries
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Found in locales where large stuff needs to
exit/enter the bloodstream.
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Liver
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Spleen
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Bone marrow
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Endocrine organs
Veins
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Carry blood to the heart
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Are larger in diameter than arteries
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Have thinner walls
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Contain valves
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Folds of tunica intima that prevent blood from
flowing backward
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Venules: The smallest veins that carry blood
away from the capillaries
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Medium-sized veins:
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Thin tunica media and few smooth muscle cells
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Tunica externa with longitudinal bundles of
elastic fibers
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Large veins:
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Have all 3 tunica layers
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Thick tunica externa
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Thin tunica media
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Example: Inferior and Superior vena cava
