Transcript ANPS 020 Black 01-17

Overview of the Cardiovascular System
Topics to be addressed:
Blood
Anatomy of Blood Vessels
Anatomy of the Heart
The Conduction System
The Cardiac Cycle
Cardiodynamics
Blood Flow and its Regulation
Adaptation and Disorders of the Cardiovascular System
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Blood Vessels : Anatomy
To understand the construction of a blood vessel, let’s first
review the important tissue types involved.
Endothelium
Recall that epithelial cells occur in sheets, with junctions (tight
junctions and desmosomes) tightly binding each cell to its
neighbors. A simple squamous epithelium contains a single layer
of flat cells; in blood vessels this simple squamous epithelium is
commonly called the endothelium.
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Blood Vessels : Anatomy
Connective tissue
Connective tissue is usually located between layers and on the
outside of organs; nerves travel in the connective tissue layers of
an organ.
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Blood Vessels : Anatomy
Nature Neuroscience
Smooth muscle
Smooth muscle is so named because it does not have visible striations in
its cytoplasm. It does contain actin and myosin, and contracts in the
presence of calcium. When the smooth muscle layer contracts, the vessel
diameter narrows (vasoconstriction). When the smooth muscle layer
relaxes, the vessel diameter increases (vasodilation).
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Blood Vessels : Anatomy
Most blood vessels have a 3-layered wall (3 tunics)
Tunica Intima : innermost
• lined by the endothelium
• supported by connective tissue (collagen)
Tunica Media : middle layer
• smooth muscle with various amounts of elastic fibers
Tunica Externa : outer layer
• connective tissue
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Nerves innervate blood vessels, but are seldom seen in images as
they are diffusely spread out within the muscle layer.
These nerves are important for controlling blood vessel diameter.
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Blood Vessels : Anatomy
Most blood vessels have a 3-layered wall
Arteries have
stronger, thicker
walls than the vein of
the same size;
arteries generally
contain more smooth
muscle and often
more elastic fibers.
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Vessels can be Categorized by Size
• Blood vessels closest to the heart have the largest diameter
• There is little smooth muscle in most veins
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Vessels can be Categorized by Function
Elastic Arteries:
The largest arteries
closest to the heart
contain a lot of elastic
fibers, and swell with
blood each time the heart
pumps
Capacitance Vessels:
Because veins have
little muscle and few
elastic fibers in their
wall, they have little
ability to resist stretch,
and often hold much
of the circulating blood
Muscular Arteries:
Smaller diameter arteries
distributing to organs
Exchange vessels
Capillaries are the only vessels where
materials move through the vessel wall
Resistance Vessels:
Arterioles are small
diameter with a few
layers of smooth muscle;
contraction or relaxation
of that muscle creates
great changes in
diameter, and thus great
changes in resistance to
blood flow.
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Distribution of Blood
• 30–35% of blood volume contained in heart, arteries and capillaries
• 60–65% of blood in the venous system
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Veins have valves to prevent blood from flowing backward
• Formed from foldings of tunica
intima
•Skeletal muscle activity around
deep veins compresses veins
and pushes blood toward heart :
the “muscular pump”
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Venous Valve Failure Allows Blood to Pool in Veins and
Creates Distension in the Vein Walls
Valve failure may be due to genetic factors
or to locally high venous pressure
Varicose Veins
Hemorrhoids are distensions of anal veins
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Blood Vessels : Anatomy of Capillaries
A capillary is little more than a tube of endothelial cells
supported by a basal lamina.
The thin wall allows exchange of materials
(nutrients, wastes, oxygen and carbon dioxide)
between the bloodstream and the tissues
Capillaries are thus called the exchange vessels
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How substances pass
through a capillary
wall
Through the epithelial cell
membrane
diffusion (passive)
pinocytosis (active)
Though pores (fenestrations)
in the epithelial cell
membranes (size filter)
Through spaces between
epithelial cells (bulk flow)
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There are 3 types of Capillaries based on
the degree of “leakiness”
1. Continuous Capillaries
• Have complete endothelial lining – cells
tightly bound to one another
• Are found in all tissues except epithelia
and cartilage
• Permit diffusion of water, small solutes,
and lipid-soluble materials
• Block RBC and plasma proteins
• Specialized continuous capillaries are
found in the CNS and create the
“blood-brain barrier”
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There are 3 types of Capillaries based on
the degree of “leakiness”
2. Fenestrated Capillaries
• Have small pores in endothelial lining
• Permit rapid exchange of water and
larger solutes between plasma
and interstitial fluid
• Found in areas requiring more exchange
Choroid plexus
Endocrine organs
Kidneys
Intestinal tract
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There are 3 types of Capillaries based on
the degree of “leakiness”
3. Sinusoidal Capillaries
• Have large gaps between
adjacent endothelial cells
• Permit free exchange of water
and large plasma proteins
between blood and interstitial fluid
• Found in:
Liver
Spleen
Bone marrow
Endocrine organs
• Phagocytic cells monitor blood at
sinusoids
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Pre-capillary Sphincters
Arterioles often have areas of extra muscle in their wall as
they branch into a capillary network; these sphincters
contract to decrease blood flow into a capillary bed
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Arteries and veins
generally parallel one
another and share the
same names.
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The Systemic Arteries
The single vessel leaving the
left side of the heart is the
Aorta
Parts of the aorta include:
The aortic arch
The thoracic aorta
(in the thoracic cavity)
The abdominal aorta
(below the diaphragm)
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The Systemic Veins
Blood returns to the right
side of the heart through
two large unpaired veins.
Above the diaphragm,
blood returns through the
superior vena cava
Below the diaphragm,
blood returns through the
inferior vena cava
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Pulmonary and Systemic
Circulation Patterns
General Functional Patterns
– Peripheral artery and vein
distribution is the same on right
and left (ie: is symmetrical),
except near the heart
– The same vessel may have
different names in different
locations
– Tissues and organs usually have
multiple arteries and veins;
vessels may be interconnected
with anastomoses
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