BIOL 271 Lecture Notes - Theca Interna, Tunica Externa, Tunica Media

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9 Mar 2014
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Vessels and Circulation
Anatomy of Blood Vessels
closed system of tubes
arteries carry blood away from the heart (to tissues)
elastic arteries
muscular arteries
arterioles
capillaries are thin enough to allow exchange
venules merge to from veins
veins carry blood toward the heart
Arteries
3 different layers (tunics)
tunica interna (intima)
simple squamous epithelium (endothelium)
basement membrane
internal elastic lamina
tunica media
circular smooth muscle
elastic fibers (external elastic lamina)
tunica externa (adventitia)
elastic & collagen fibres
vasoconstriction
SNS innervates vascular smooth muscle (stimulation >>
vasoconstriction)
injury to artery or arteriole >> vasospasm decreases blood
loss
vasodilation
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decreased SNS stimulation >> vasodilation
NO, K+, H+, lactic acid and chemicals of inflammation also
>> vasodilation
elastic arteries
largest-diameter arteries (e.g.: aorta)
abundance of elastic fibers in tunica media
stretch during ventricular systole
recoil on ventricular diastole, propelling blood
aorta also propels blood into coronary aa
muscular arteries
medium sized aa
called distributing arteries because they distribute blood to
body (constrict and dilate to adjust flow)
more smooth muscle in tunica media than elastic aa
Arterioles
very small aa
deliver blood to capillaries
vasoconstrictor and vasodilator to regulate BP and blood flow to
capillaries
Capillaries
microscopic vessels
usually connect arterioles to venules
found near almost every cell in the body (none in epithelium,
cartilage, cornea, and lens)
most concentrated in tissues with high metabolic rates (muscle,
liver, kidneys, brain)
site of exchange of gases, nutrients, wastes between blood and
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interstitial fluid
materials cross capillary wall…
through endothelial cell embraces
within pinocytic vesicles
through intercellular clefts
channels between tightly packed endothelial cells
through fenestrations
holes that go all the way through endothelial cells
types:
continuous
continuous endothelium interrupted only by
intercellular clefts
found in skeletal and smooth muscle, connective
tissue and lungs
fenestrated
many small holes/pores (fenestrations) in endothelial
cell membranes
found in kidneys, choroid and ciliary plexuses, villi of
small intestine and in endocrine glands
gets rid of larger waste products and absorbs larger
nutrients
sinusoids
large lumen
very large fenestrations in endothelial cell membranes,
large intercellular clefts
basement membrane incomplete or absent
allow protein and blood cells to pass from tissue to
bloodstream
found in red bone marrow, liver, spleen, anterior
pituitary, thyroid and parathyroid gland
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