Cardiovascular System
Chapter 13
Heart Anatomy
• Approximately the size of your fist
• Location:
– Superior surface of the diaphragm
– Left of the midline
– Anterior to the vertebral column, posterior to the
sternum
Coverings of the Heart: Anatomy
• Pericardium – a double-walled sac around the
heart composed of:
– Superficial fibrous pericardium
– Deep two-layer serous pericardium
• Parietal layer lines the internal surface of the fibrous
pericardium
• Visceral layer or epicardium lines the surface of the
heart
• They are separated by the fluid-filled pericardial cavity
Coverings of the Heart: Physiology
• The pericardium:
– Protects & anchors the heart
– Prevents overfilling of the heart with blood
– Allows for the heart to work in a relatively frictionfree environment
Heart Wall
• Epicardium – visceral layer of the serous
pericardium
• Myocardium – cardiac muscle layer forming
the bulk of the heart
• Endocardium – endothelial layer of the inner
myocardial surface
External Heart: Major Vessels of the
Heart
• Vessels returning blood to the heart:
– Superior & inferior venae cavae
– Right & left pulmonary veins
• Vessels conveying blood away from the heart:
– Pulmonary trunk, splits into right & left pulmonary
arteries
– Ascending aorta (three branches) –
brachiocephalic, left common carotid, &
subclavian arteries
External Heart: Vessels that
Supply/Drain the Heart
• Arteries:
– Right & left coronary (in the atrioventricular
groove), marginal, circumflex, and anterior
interventricular
• Veins:
– Small cardiac, anterior cardiac, and great cardiac
Atria of the Heart
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Atria are the receiving chambers of the heart
Each atrium has a protruding auricle
Pectinate muscles mark atrial walls
Blood enters right atrium from superior and
inferior venae cavae and coronary sinus
• Blood enters left atrium from pulmonary veins
Ventricles of the Heart
• Ventricles are the discharging chambers of the
heart
• Papillary muscles and trabeculae carneae
muscles mark ventricular walls
• Right ventricle pumps blood into the
pulmonary trunk
• Left ventricle pumps blood into the aorta
Pathway of Blood Through the Heart &
Lungs
• Right atrium  tricuspid valve  right ventricle
• Right ventricle  pulmonary semilunar valve 
pulmonary arteries  lungs
• Lungs  pulmonary veins  left atrium
• Left atrium  bicuspid valve  left ventricle
• Left ventricle  aortic semilunar valve  aorta
• Aorta  systemic circulation
Coronary Circulation
• Coronary circulation is the functional blood
supply to the heart muscle itself
• Collateral routes ensure blood delivery to
heart even if major vessels are occluded
Heart Valves
• Heart valves ensure unidirectional blood flow
through the heart
• Atrioventricular (AV) valves lie between the atria
and the ventricles
• AV valves prevent backflow into the atria when
ventricles contract
• Chordae tendineae anchor AV valves to papillary
muscles
• Right side  tricuspid
• Left side  bicuspid
Heart Valves
• Aortic semilunar valve lies between the left
ventricle and the aorta
• Pulmonary semilunar valve lies between the
right ventricle and pulmonary trunk
• Semilunar valves prevent backflow of blood
into the ventricles
Microscopic Anatomy of Heart Muscle
• Cardiac muscle is striated, short, fat,
branched, and interconnected
• Intercalated discs anchor cardiac cells
together & allow free passage of ions
– Sends impulses from cells
• Heart muscle behaves as a functional
syncytium
– All muscle cells are connected & act as 1 unit
Blood Vessels
• Blood is carried in a closed system of vessels
that begins and ends at the heart
• Three major types of vessels:
– Arteries – carry blood away from the heart
– Veins – carry blood toward the heart
– Capillaries – contact tissue cells & directly serve
cellular needs
Generalized Structure of Blood Vessels
• Arteries and veins are composed of three
tunics – tunica interna, tunica media, tunica
externa
• Lumen – central blood-containing space
surrounded by tunics
• Capillaries are composed of endothelium w/
sparse basal lamina
• *arteries have more pressure flowing through
them
Elastic Arteries
• Thick-walled arteries near the heart; the aorta
& its major branches
– Allow low-resistance conduction of blood
– Withstand & smooth out large blood pressure
fluctuations
– Serve as pressure reservoirs
– Help pump blood by stretching & constricting,
moves the blood
Muscular Arteries & Arterioles
• Muscular arteries – distal to elastic arteries;
deliver blood to body organs
– Have thick tunica media w/ more smooth muscle
– Active in vasoconstriction
• Arterioles – smallest arteries; lead to capillary
beds
– Control flow into capillary beds via vasodilation
and constriction
Capillaries
• Capillaries are the smallest blood vessels
– Walls consisting of a thin tunica interna, one cell
thick
– Allow only a single RBC to pass at a time
– Pericytes on the outer surface stabilize their walls
• There are three structural types of capillaries:
– Continuous
– Fenestrated
– Sinusoids
Continuous Capillaries
• Abundant in the skin, muscles, & brain
– Endothelial cells provide an uninterrupted lining
 because of tight junctions between cells
• Continuous capillaries of the brain:
– Have tight junctions completely around the
endothelium
– Constitute the blood-brain barrier
Fenestrated Capillaries
• Found wherever active capillary absorption or
filtrate formation occurs (e.g., small intestines,
endocrine glands, kidneys)
• Characterized by:
– An endothelium riddled with pores (fenestrations)
– Greater permeability than other capillaries
Sinusoids
• Highly modified, leaky, fenestrated capillaries
w/ large lumens
• Found in the liver, bone marrow, lymphoid
tissue, & in some endocrine organs
• Allow large molecules (proteins & blood cells)
to pass between the blood and surrounding
tissues
• Blood flows sluggishly, allowing for
modification in various ways
Capillary Beds
• A microcirculation of interwoven networks of
capillaries, consisting of:
– Vascular shunts – metarteriole-thoroughfare channel
connecting an arteriole directly with a postcapillary
venule
• Closes blood flow if the tissues don’t need the blood & helps
blood keep its oxygen
– True capillaries – 10 to 100 per capillary bed,
capillaries branch off the metarteriole and return to
the thoroughfare channel at the distal end of the bed
– Metarteriole – passageway between terminal arteriole
& the postcapillary venuole
Capillary Beds
Venous System: Venules
• Venules are formed when capillary beds unite
– Allow fluids and WBCs to pass from the
bloodstream to tissues
• Postcapillary venules – smallest venules,
composed of endothelium and a few pericytes
• Large venules have one or two layers of
smooth muscle (tunica media)
Venous System: Veins
• Veins are:
– Formed when venules converge
– Composed of three tunics:
• Thin tunica media
• Thick tunica externa  consists of collagen fibers and
elastic networks
– Capacitance vessels (blood reservoirs) that contain
65% of the blood supply
Venous System: Veins
• Veins have much lower blood pressure &
thinner walls than arteries
• To return blood to the heart, veins have
special adaptations
– Large-diameter lumens – offer little resistance to
flow
– Valves (resembling semilunar heart valves), which
prevent backflow of blood
• Venous sinuses – specialized, flattened veins
w/ extremely thin walls
Blood Pressure (BP)
• Force per unit area exerted on the wall of a
blood vessel by its contained blood
• The differences in BP within the vascular
system provide the driving force that keeps
blood moving from high to low pressure areas