Transcript Blood Vessels

Chapter 21
The circulatory system III
Blood vessels
Arteries
Capillaries
Veins
Blood vessels
Defined: hollow tubes of smooth muscle, elastic and dense
connective tissue.
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Serve as conduits through which blood is circulated to every cell in
the body.
Tunica interna (intima) – -inner most layer of vessel wall. Lined with
endothelial cells overlying a sparse layer of loose CT.
Tunica media – -middle layer and thickest in arteries. Contains smooth
muscle, collagen and in larger vessels ( e.g.-aorta) elastin fibers.
Tunica externa (adventitia) -outer most layer covering vessels, consisting
of loose CT. It merges with neighboring blood vessels, nerves and/or
other organs. It contains the vasa vasorum which supply blood to
outer ½ of vessel wall in larger vessels.
Lumen: central canal or opening in the center of the vessel.
Neurovascular bundle
Conducting (elastic) arteries
Muscular arteries
Classes of Blood Vessels
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Arteries –-are the resistance vessels of the CV system.
Designed to withstand large fluctuations in blood
pressure.
Conducting (elastic or large) arteries: 1.0–2.5 cm diam.
 Biggest arteries; Aorta, carotids, pulmonary trunk,
common iliacs and subclavians are all examples.
 Contain a thin elastic layer between intima → media
and the media → externa.
 Have up to 70 layers of elastic tissue.
Distributing (muscular) arteries: 0.3 mm to1 cm diam.
smaller branches that distribute blood to specific
organs - have up to 40 layers of elastic tissue
Resistance (small arteries) and arterioles
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Small arteries are too variable in number and location
to be given specific individual names. 10 -300 μ diam.
Contain up to 25 layers of smooth muscle and little
elastic tissue.
Arterioles are the smallest of arteries and have only 3
layers of smooth muscle and little tunica externa.
Metarterioles – terminal aretrioles before capillary bed;
merge into through fare channels from which true
capillaries branch off.
Precapillary sphincters are at merge point and regulate
blood flow based on tissue needs
Tissue blood flow:
Terminal arterioles →
metarterioles which →
through fare channels.
Precap. SphinctersRegulate flow direction
into true capillaries or
through channels.
Capillaries
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For blood to serve any purpose, materials (eg. O2,
CO2, nutrients, wastes and hormones) must pass
through the walls of blood vessels.
There are only 2 sites in the vascular system for this to
occur: Capillaries and Venules.
Capillaries are composed of only an endothelium and
a thin basement membrane.
They average ~ 5 μ to 9μ in size.
Capillaries far out number venules in the
cardiovascular system.
Capillaries
Molecules pass into/out of capillary walls by 4 routes:
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1. Direct diffusion through the endothelial cell membrane
- down the concentration gradient O2 and CO2
2. Through intercellular clefts
- small molecules
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3. Pinocytotic vesicles and caveolae (in pocketing of vessel wall)
- large molecules and proteins
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4. Through fenestrations (pores) in the capillary wall
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CO2 and O2 easily diffuse through the endothelial cells
Capillaries
a) Continuous b) Fenestrated
c) Sinusoidal
Venules
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Venules and veins contain valves to maintain a one
way flow of blood back to the heart.
Venules are the smallest of veins (~15-20 μm).
Possess a tunica interna with a few fibroblasts
wrapped around them and tend to be more porous
than capillaries.
Most leukocytes migrate from blood stream through
postcapillary venules.
Venous valves
-muscles pump blood
by contracting and
compressing veins.
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Veins
Are sometimes called capacitance vessels
 At rest veins contain 54% of the blood volume
 Medium veins range up to 10 mm in diameter
(ex. ulnar, great saphenous, radial).
 Medium veins have a tunica interna, an
endothelium, a basement membrane and loose
CT with a thin interna elastic lamina
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Large veins
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Diameters greater than 10 mm.
Contain longitudinal bundles of smooth muscle and a
thick tunica externa.
Ex: vena cava, pulmonary veins, internal jugular and
renal veins
Pulmonary Circulation
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Blood flows through the lungs to get rid of CO2 and
pick up O2.
Begins in right ventricle → pulmonary trunk →
pulmonary arteries → lobar arteries → arterioles →
lung capillary beds → venules → pulmonary veins →
left atrium
Pulmonary Circulation
Pulmonary trunk → pulmonary arteries → lobar arteries
Systemic Circulation
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Blood flow to the entire body except for the
pulmonary circuit
Begins in left atrium → left ventricle → aorta → every
cell in the entire body → arteries → arterioles →
capillary beds → venules → veins → vena cava →
right atrium → pulmonary circulation
Major arteries off of aortic arch
Major arteries off of aorta
Specialized circulations
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Bronchial circulation goes to lung tissues proper to
provide nutritive blood to the lungs since the
pulmonary circuit does not provide blood to the lung
tissues
Circle of Willis provides blood flow to the brain. It
arrives there via two separate pathways.
Hepatic Portal circulation provides blood flow to the
liver via a portal pathway.
A portal circulation passes through two capillary beds
in series whereas most circulations pass through a
single capillary bed.
Blood flow to the head and brain
Circle of Willis
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Provides blood flow to the brain by either the internal
carotid artery or the basilar artery.
The internal carotid enters the cranial cavity through
the carotid foramen.
The basilar artery is formed by the convergence of the
two vertebral arteries that come up through the
transverse foramen of the cervical vertebra.
Circle of Willis
Hepatic Portal Circulation
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The hepatic portal circulation is unique in that blood
passes from the intestines into a primary capillary bed
outside of the liver and then into the hepatic portal
vein into a second capillary bed in the liver before it
passes out of the liver via the hepatic vein into the
inferior vena cava.
Hepatic Portal Circulation
Hepatic portal veins
Fetal Circulation
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The fetal circulation provides blood to the fetus from the
mother via the umbilical vessels.
Keep in mind that the fetal lungs are nonfunctional until after
the child is born.
Fetal circulation is provided by an interatrial shunt the
foramen ovale and a pulmonary → aorta shunt the ductus
arteriosis.
Blood from the placenta comes to the fetus via the umbilical
vein → right atrium → foramen ovale → LA → LV → body
or → RV → pulmonary trunk → ductus arteriosis → aorta.
Theses become the fossa ovale and ligamentum arterosis after
birth of the child.
Umbilical vein →RA →
LA →LV → aorta →
body →umbilical artery →
placenta.
Umbilical vein →RA →
RV →Pulmonary trunk →
ductus areteriosis →
aorta → body →
umbilical artery →
placenta.
Arteries to know
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Aorta: ascending, aortic arch, thoracic and abdominal
Coronary arteries: left ant. descending and circumflex
Brachiocephalic
Left and right Common Carotid
Internal and external Carotid arteries
Left and right Subclavian
Axillary, Brachial, Radial, Ulnar
Vertebral, Intercostal, Celiac trunk, Superior and
Inferior mesenteric, Common iliac, External iliac,
Suprarenal, Renal, Gonadal, Femoral, Popliteal, Ant.
and Post. Tibial, Fibular
Major arteries
Aorta
Brachiocephalic
Rt/Lt common
carotids
Int/ext carotids
Left subclavian
Arteries of the upper limb
Axillary
Brachial
Ulnar
Radial
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Abdominal blood flow - mesenteric arteries
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Arteries in the abdominal cavity
Suprarenal
Renal
Lumbar
Common iliacs
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Arteries to lower limb
Femoral
Popliteal
Ant/post
tibial
Veins to know
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Superior and inferior vena cava
Brachiocephalic, Subclavian, Cephalic
Internal and external jugular
Axillary, Brachial, Basilic, Median cubital
Hepatic, Suprarenal, Renal, Gonadal, Lumbar,
Common iliac, External iliac, Internal iliac, Femoral
Great saphenous, Popliteal, Ant and Post Tibial,
Peroneal
Superior sagittal and Transverse sinuses, Cavernous
sinus
Major veins
Superior vena cava
Inferior vena cava
Ext jugular vein
Int jugular vein
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Venous return from the head
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Venous return from the upper limb
Axillary
Med. cubital
Brachial
Basilic
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Venous return from abdomen
Hepatic
Suprerenal
Renal
Int/Ext iliac
Gonadal
Lumbar
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Hepatic portal circulation
Venous return from the lower limb
Femoral vein
Gt saphenous
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Popliteal
Ant/post
tibial