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BLOOD VESSELS & HEMODYNAMICS
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T4. BLOOD VESSELS and HEMODYNAMICS
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toT4.3 BLOOD VESSELS & HEMODYNAMICSthe
Textbook: pg.707-733
Blood vessels- are dynamic structures that pulsate, constrict,
relax and even proliferate (multiply)
types of blood vessels:
1. Arteries
2. Capillaries
3. Veins
• Heart contracts ->moves blood (from ventricles)-> to large arteries-> blood moves
into smaller & smaller arteries->reaches the smallest branches (arterioles) –> leads
to the capillary beds of body organs & tissues -> blood drains into venules (smallest
veins) -> to larger & larger veins -> empty into the heart.
• Blood vessels (in adults) stretch for abt 100,000 Km (60,000 miles) thru the internal
body landscape!
• Arteries carry blood away from the heart, so they r said to “branch”, “diverge”, or
“fork” as they form smaller & smaller divisions.
• Veins carry blood toward the heart & so r said to “join”, “merge”, and “converge” into
the successively larger vessels approaching the heart.
• Arteries always carry oxygenated blood
• Veins always carry oxygenated-poor blood.
BUT (EXCEPTIONS)
o In the pulmonary circulation: the arteries, still defined
as vessels leading away from the heart, carry
oxygen-poor blood to the lungs, & the veins carry
oxygen-rich blood from the lungs to the heart.
o In the special umbilical vessels of the
fetus: the roles of veins & arteries also
differ with respect of oxygenation.
Arteries: red
Veins: blue
, Layer of blood vessels’ walls (from inside out order):
1. Tunica intima
2. Tunica media
3. Tunica externa
Tunica- a covering or tissue coat, membrane later.
1. Tunica intima- the most inner layer, it has an intimate contact with the
blood in the lumen (blood inside the vessels)
o It contains the endothelium- a simple squamous epithelium that lines the
lumen of all vessels (a thin membrane that lines the inside of the heart &
blood vessels~ a type of epithelium)
o The epithelium- tissues line the outer surfaces of organs & blood vessels
throughout the body & inner surface of cavities in many internal organs.
o The endothelium is continuous w/ the endocardial lining of the heart, & its flat
cells fit closely tgthr, forming a slick surface that minimizes friction as blood
mover thru the lumen.
o In vessels larger than 1mm in diameter, a subendothelial layer, consisting of
basement membrane & looses connective tissue, supports the endothelium.
, 2. Tunica media- is mostly consists of circularly arranged smooth muscle cells &
sheets of elastin. The activity of the smooth muscle cells r regulated by
vasomotor nerve fibers of the autonomic nervous system & a whole battery of
chemicals.
o This regulation causes: (depending on body needs)
a. Vasoconstriction: lumen diameter increases as the smooth muscle
contracts.
b. Vasodilation: lumen diameter decreases as the smooth muscle relaxes.
o the activities of the tunica media r critical in regulating circulatory dynamics
bc small changes in vessel diameter greatly influence blood flow & blood
pressure.
o Since the tunica media is the bulkiest layer in arteries, it is the most
responsible for maintaining blood pressure & circulation.
3. Tunica externa (TUNICA ADVENTITIA)- the outermost layer, also known as
TUNICA ADVENTITIA “coming from the outside”. It is composed largely of woven
collagen fivers that protect & reinforce the vessel & anchor it is surrounding
structures.
o The tunica externa is infiltrated w/
a. nerve fibers
b. lymphatic vessels
and in larger veins, a network of elastic fivers.
o In larger vessels, the tunica externa contains a system of tiny blood vessels,
the vasa vasorum- the vessels of the vessels that nourish the more external
tissues of the blood wall,
o The innermost (luminal) portion of the vessel obtains nutrients directly from
blood in the lumen
o The 3 vessel types vary in length, diameter, wall thickness and tissue makeup.
3 types of arterial vessels:
1. Elastic arteries
2. Muscular arteries
3. arterioles
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