,5 types of blood vessels:arteries, arterioles, capillaries, venules, and veins.
• The further arteries branch the smaller they get becoming arterioles
Arteries → arterioles → blood enters the capillaries → venules → veins → heart
• pressures inside vessels vary with distance from the heart, and vessel
structure
Vessel Wall Structure in Arteries and Veins
3 layers
• deep to superficial—the tunica intima, tunica media, and tunica externa
• Function: provide strength for vessels
• Muscular and elastic and components allow control and diameter
***Artery and vein walls are too thick for diffusion so that is why they have
vasa vasorum (smaller blood vessels) to supply muscle cells and fibroblasts of
the tunica media and tunica externa.
Used to tell the difference between arteries and veins
tunica intima
• the inner layer of a blood vessel
• includes the endothelial lining and elastic fibers CT
• In arteries theres internal elastic membrane - thick layer of elastic fibers found
at the outer margin of the tunica intima
Tunica media
• middle layer
• contains smooth muscle tissue and CT
• The smooth muscle cells encircle the endothelium that lines the lumen (interior
space) of the blood vessel.
• collagen fibers bind the tunica media to the tunica intima and tunica externa.
• this contracts the vessel diameter
• thickest layer in small arteries
• External elastic membrane
,Tunica externa
• outer most layer
• CT tissue fibers of the tunica externa typically blend into those of adjacent
tissues,
• Function: stabilizing and anchoring the blood vessel.
CT sheath
• Arteries: contains collagen fibers with scattered bands of elastic fibers.
• Veins: thicker than the tunica media and contains networks of elastic fibers
and bundles of smooth muscle cells.
, Arteries
• High pressure system
• away from heart
• Walls thicker than veins which makes them elastic and contractile
Maintains • Elasticity allows the vessel diameter to change passively in response
shape to changes in blood pressure. this change takes place by actions of the
when cut sympathetic nervous system.
due to wall
thickness
• Arteries behave more like a truck tire, expanding only at high pressures, and
they have low capacitance.
• Vasoconstriction = artery constriction, important with clotting (hemostasis:
vascular phase)
• Vasodilation - smooth muscles relax, the diameter of the lumen increases
Both affect (1) the afterload on the heart, (2) peripheral blood pressure, and (3)
capillary blood flow.
Vessel walls
• tunica media contains more smooth muscle and elastic fibers than veins
This helps resist the arterial pressure created by the heart as it pumps
blood into the pulmonary trunk and aorta
• endothelial lining of an artery cannot contract, so its endothelium folds to
constrict
• This makes a pleated appearance
• Vessel Lumen. When not opposed by blood pressure, the elastic fibers in the
arterial walls recoil, which constricts the lumen.
lumen of an artery looks smaller than a vein.
• Heart to capillaries, blood passes through elastic arteries, muscular arteries,
and arterioles (Figure 21–2)
