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Anatomy Lecture Objectives
Chapter 19
Chapter 19 - Vascular System
A. categories and general functions:
1. arteries - carry blood away from heart
2. capillaries - allow exchange of materials between blood and tissue fluid
3. veins - return blood to heart
B. wall structure - most blood vessel walls have 3 layers
lumen = space inside vessel
1. tunica intima / tunica interna
endothelium - simple squamous e.
subendothelial layer - loose c.t. (collagen)
2. tunica media
a. smooth muscle - cells circularly arranged
controlled by ANS and chemical factors
constriction (smooth muscle contracts) decreases blood flow and
increases systemic blood pressure
dilation (smooth muscle relaxes) increases blood flow and decreases
systemic blood pressure
b. elastic c.t.
3. tunica adventitia / tunica externa
c.t. attaches vessel to surrounding structures
vasa vasorum nourish outer part of vessel wall
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Anatomy Lecture Objectives
Chapter 19
C. arteries
1. elastic (conducting) - large arteries near heart (aorta and major branches)
conduct blood to muscular arteries
low resistance
tunica media = circular elastin sheets with few smooth m. cells
recoil maintains blood pressure during diastole
2. muscular - middle-sized arteries, distal to elastic arteries
distal to elastic arteries
tunica media very thick; much smooth m. and some elastin
regulate blood flow to organs
have an internal and an external elastic lamina
3. arterioles - smallest arteries
tunica media contains smooth m. only
diameter controlled by ANS and chemical messengers
diameter determines blood flow and blood pressure
D. capillaries
wall consists of endothelium and basal lamina (no tunica media or externa)
8 to 10 mm in diameter
join and branch to form capillary beds
cells are joined at spots around perimeter by tight junctions and desmosomes
intercellular clefts are spaces between cells
1. types
a. fenestrated capillaries (high permeability)
have fenestra (openings) in endothelial cells
some fenestra are covered by a membrane, others are not
also have intercellular clefts
found in small intestine, synovial joints, kidney
b. continuous capillaries
intercellular clefts but no fenestra
most common type
c. sinusoids
wide, leaky capillaries, usually fenestrated
fewer cell junctions
allow passage of large particles
found in bone marrow, spleen, liver
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Anatomy Lecture Objectives
Chapter 19
d. low-permeability capillaries
2. capillary beds
metaarteriole
thoroughfare channel
venule
capillaries
precapillary sphincter - smooth m. cell wrapped around origin of capillary
controls blood flow through capillaries
when sphincter is closed, blood is diverted to thoroughfare channel
sphincter controlled by autoregulation (local control, not nervous system)
E. veins
have thinner walls than arteries for the same diameter (larger lumen)
act as capacitance vessels - store extra blood (65%)
low pressure
tunica adventitia thicker than tunica media
venous valves prevent backflow
F. a vascular anastomosis occurs when vessels join midstream
anastomoses provide alternate pathways (collateral channels)
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Anatomy Lecture Objectives
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G. circulatory routes
1. pulmonary circuit: right ventricle to lungs to left atrium
pressure supplied by right ventricle
low pressure system
takes low oxygen blood (75% saturated) to lungs and brings high oxygen
(98% saturated) blood back to heart
right ventricle
pulmonary semilunar valve
pulmonary trunk
left and right pulmonary arteries
lobar arteries (3 R, 2 L) take blood to lung lobes
pulmonary capillaries
pulmonary veins (superior and inferior, L and R)
left atrium
2. systemic circuit: left ventricle to body to right atrium
pressure supplied by left ventricle
high pressure system
takes O2 to tissues and removes CO2
distributes nutrients from digestive tract to body
collects wastes and takes them to kidney for excretion
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Anatomy Lecture Objectives
Chapter 19
a. circulatory pathways of the brain (cerebral arterial circle, circle of Willis)
anterior communicating a.
anterior cerebral a.
internal carotid a.
posterior communicating a.
posterior cerebral a.
basilar a.
vertebral a.
cross section of neck:
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Anatomy Lecture Objectives
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b. hepatic portal circulation
portal system = two capillary beds in series, joined by veins or arteries
capillaries of small intestine,
part of large intestine and stomach
superior mesenteric vein
capillaries of spleen, stomach
and pancreas
splenic vein
capillaries of distal large intestine
and rectum
inferior mesenteric vein
hepatic portal vein
liver
liver sinusoids
hepatic veins
inferior vena cava
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Anatomy Lecture Objectives
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c. fetal circulation
placenta = organ formed from extra-embryonic membranes and endometrium to
exchange materials between fetal and maternal blood
umbilical vein from placenta
fetal liver
hepatic portal vein
ductus venosus
inferior vena cava
right atrium
foramen ovale
right ventricle
pulmonary trunk
left atrium
left ventricle
ductus arteriosus
aorta
lungs
internal iliac a.
umbilical a. to placenta
adaptations:
1) to bypass the fetal liver
ductus venosus - allows some umbilical vein blood to go through the fetal liver
but diverts most of it directly into the inferior vena cava
2) to bypass the non-functional fetal lungs
a. foramen ovale – opening in interatrial septum that allows blood to go from the
right atrium directly into the left atrium
b. ductus arteriosus – vessel that connects pulmonary trunk and aorta
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