Chapters 13
The Cardiovascular System
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II. 13.1 Introduction
A. The functions of the cardiovascular system are:
• to bring oxygen & nutrients to all cells
• to remove wastes from cells, and
• to carry the cellular wastes to sites of excretion.
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III. 13.2 Structure of the heart
A. The precise location of the heart is as follows:
• in the mediastinum of the thoracic cavity
• medial to the lungs (between them)
• posterior to the sternum
• anterior to the spine
• base of the heart (upper portion) is beneath the 2nd rib
• the heart extends inferiorly & to the left ending in a bluntly
pointed apex at the level of the 5th intercostal space
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III. 13.2 13.2 Structure of the heart
B. Coverings of the Heart
1. The heart is enclosed by a double-layered pericardium.
2. The function of the serous fluid in the pericardial space is to
reduce the friction between the pericardial membranes as the
heart moves. http://www.youtube.com/watch?v=uR4t__B-Zwg
3. Pericarditis is an inflammation of the pericardium due to a viral
or bacterial infection.
• The inflammation produces adhesions in the layers of the
pericardial sac that binds the 2 layers together; this restricts the
movement of the heart AND causes significant pain.
• Also, restriction of cardiac movement reduces the effectiveness of
the heart’s pumping action.
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III. 13.2 Structure of the Heart
C. Wall of the Heart
• Epicardium (the visceral pericardium) - reduces friction as the heart
contracts & relaxes
• Myocardium – the muscles of the heart that pump blood out of the
heart chambers
• Endocardium – the inner layer; contains blood vessels and
specialized Purkinje fibers (carry impulses that cause the walls of
the ventricles to contract.
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III. 13.2 Structure of the Heart D. 2
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III. 13.2 Structure of the Heart
D. Heart Chambers & Valves
1. The chambers of the heart are the left & right atria
(singular: atrium) and the left & right ventricles.
2. drawing to label
3. The right atrium receives oxygen-poor blood (from the
body)from the inferior & superior vena cava and (from the
heart) from the coronary sinus.
4. The left atrium receives oxygen-rich blood (from the lungs)
via the 4 pulmonary veins – 2 veins from each lung/
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III. 13.2 Structure of the Heart
E. The path of blood through the heart:
• from coronary sinus and inf. & sup. vena cava into the right atrium
• thru the tricuspid valve into the right ventricle
• thru the pulmonary valve into the pulmonary arteries and thru the
lungs then into the pulmonary veins
• thru the pulmonary veins into the left atrium
• thru the mitral (bicuspid) valve into the left ventricle
• thru the aortic valve into the aorta then to the body
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III. 13.2 Structure of the Heart
F. Mitral valve prolapse
occurs when leaflets of the
valve bulge into the left
atrium during ventricular
contraction. This can allow
blood to regurgitate back
into the atrium.
• Patients with this condition must take
antibiotics before any invasive
procedure to prevent further damage to
the valves due to bacterial infection.
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III. 13.2 Structure of the Heart
G. The cells of the heart are supplied with blood by way of the
right & left coronary arteries
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III. 13.2 Structure of the Heart
H. The muscles of the heart can suffer damage when deprived of
oxygen. A first indication there is an interruption of oxygen to
the muscle cells is pain. A prolonged interruption of oxygen
supply will result in death of myocardial cells – a myocardial
infarction (aka heart attack).
I. Myocardial infarction results in irreversible, permanent
damage to the heart muscle. Angina pectoris is the result of a
temporary interruption of oxygen to cells and does not result
in tissue scarring or permanent damage.
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IV. 13.3 Heart Actions
A. The cardiac cycle
1. consist of:
• atrial systole (contraction) simultaneous with ventricular diastole
(relaxation) ; then
• ventricular systole (contraction) simultaneous with atrial diastole
(relaxation).
Note: the tricuspid & bicuspid (mitral) valves open & close
simultaneously; the pulmonic & aortic valves open & close
simultaneously.
• Systole = when the TV & MV are closed and the PV & AV are open
• Diastole = when the TV & MV are open and the PV & AV are closed
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IV. 13.3 Heart Actions
A. 2. The first heart sound (lubb) is the ventricular systole when
the A-V valves are closing; the second heart sound (dubb)
is the ventricular diastole when the pulmonary & aortic
valves are closing
B. Cardiac muscle fibers are similar to skeletal muscle except
the fibers connect in branching networks, they self-exciting,
and display rhythmicity. Stimulation to any part of the
network sends impulses throughout the network.
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IV. 13.3
Heart
Actions,
part C.1.
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Start here on Monday!
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IV. 13.3 Heart Actions
C. Cardiac pulse conduction starts in the sinoatrial (S-A) node
located in the right atrium. S-A node activity is rhythmic &
initiates 70 to 80 impulses a minute. Because its generated
the heart’s rhythmic contractions, it is called the heart’s
pacemaker.
D. 1. A recording of the electrical changes in the myocardium is
an electrocardiogram (ECK or EKG).
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IV. 13.3 Heart Actions
E. 2. Calcium ions(Ca2+) & potassium ions (K+) affect heart rate
in the following ways:
• hyperkalemia (increased levels of K+) decreases heart rate
• hypokalemia (low levels of K+) can lead to abnormal heart rhythm
• hypercalcemia (high levels of Ca2+) can lead to an abnormally long
contraction of the heart
• hypocalcemia (lowlevels of Ca2+) can depress heart action
NOTE about abnormal heart rhythms:
tachycardia means the heart rate is faster than normal
bradycardia means the heart rate is slower than normal
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V. 13.4 Blood Vessels
A. Arteries
1. The closed circuit (means that blood stays with vessels) includes
arteries, arterioles, capillaries, venules, & veins.
Paperman sez there are ~62000 miles of blood vessels in the
human body; enuf to stretch 2.5 times around the world!
2. Arteries are tri-layered, strong, elastic vessels that are adapted to
carry blood away from the heart under high pressure; they are
capable of constricting & dilating when stimulated by the
autonomic nervous system.
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Page 330 Blue Box:
Heart Transplant
The recipient’s failing heart is
removed except for the posterior
walls of the atria and their
connections to the vena cavae &
pulmonary veins.
The donor heart is prepared
similarly and is attached to the
atrial cuffs remaining in the
recipient’s thoracic cavity.
The recipient’s aorta & pulmonary
arteries are connected to those of
the donor heart.
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V. 13.4 Blood Vessels
A. Arteries
3. Arterioles are smaller vessels than arteries, have tri-layered walls
similar to arteries, & are capable of vasodilation & vasoconstriction
like arteries.
• As arterioles approach capillaries, they become smaller & their
walls thin; the walls of a very small artery consist only of an
endothelial lining & some smooth muscle fibers surrounded by a
small amount of connective tissue.
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V. 13.4 Blood Vessels
A. Arteries
4. Atherosclerosis is a disease of the arteries in which fatty plaques are
formed in the vessel walls. This causes narrowing & roughening of
the inner wall of the artery which, in turn, can lead to thrombus
formation.
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V. 13.4 Blood Vessels
B. Capillaries
1. Capillaries are the smallest of blood vessels; they connect the
smallest of the arterioles with the smallest of the venules.
Capillaries are extensions of the inner linings of arterioles & form a
semi-permeable layer through which exchanges of substances with
cells take place.
2. The number of capillaries in a tissue (or the density of the capillary
bed) is determined by the tissue’s rate of metabolism:
• muscle & nervous tissues (which require an abundant supply of
oxygen & nutrients) have a high density of capillaries
• tissues with slow metabolic rates (cartilage, the epidermis, the
cornea of the eye) have a low density of, or lack, capillaries.
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V. 13.4 Blood Vessels
B. Capillaries
3. The distribution of blood in the capillary pathways varies as the
metabolic demands of the surrounding tissue varies. The
distribution is controlled by pre-capillary sphincters which can
open or close a pathway based on the demands of surrounding
cells.
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V. 13.4 Blood Vessels
B. Capillaries
4. The endothelial cells in the capillaries of the brain are very tightly
connected & allow very few substances to enter the brain. This
serves as a protective barrier for the brain. The flip side – it makes
it difficult to treat infections such as encephalitis & meningitis, and
brain malignancies (neither antibiotics nor chemotherapeutic agents
cross the blood brain barrier).
5. Transport mechanisms:
• diffusion allows substances to cross membranes due to a
concentration gradient – nutrients & oxygen move out of
capillaries, carbon dioxide & other wastes move into capillaries.
• filtration & osmosis are the other 2 transport mechanisms.
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V. 13.4 Blood Vessels
C. Veins
1. (& 2.) The walls of veins also have 3 layers but the walls of veins
are thinner, less elastic, and have less smooth muscle than arteries.
The inner walls of veins have valves that prevent the back flow of
blood and keep it moving toward the heart.
3. When a drop in blood volume (due to hemorrhage) causes a drop in
blood pressure, the walls of veins are stimulated to constrict (by the
sympathetic nervous system); this maintains blood pressure by
returning more blood to the heart and ensures a nearly normal
blood flow even when as much as 25% of blood volume is lost.
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VI. 13.5 Blood Pressure
A. Blood pressure
1. Blood pressure is the force that blood exerts against the
inner walls of blood vessels. This force occurs throughout
the vascular system but the term blood pressure most
commonly refers to pressure in the arteries supplied by
branches of the aorta.
Paper man sez the human heart creates enuf pressure to squirt
blood 30 FEET!
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VI. 13.5 Blood Pressure
2. The maximum pressure during ventricular contraction is the
systolic pressure. When the ventricles relax, the arterial
pressure drops, and the lowest pressure that remains in the
arteries before the next ventricular contraction is the
diastolic pressure. In a blood pressure reading of 120 / 80,
120 is the systolic pressure and 80 is the diastolic pressure.
3. The surge of blood entering the arterial system during a
ventricular contraction causes the elastic arterial walls to
expand. This expansion can be felt in arteries near the
surface of the body as a pulse.
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VI. 13.5 Blood Pressure
B. Influencing Factors
• Heart action: the volume of blood discharge from the left
ventricle with each contraction is called the stroke volume.
If either stroke volume or heart rate increases so does
cardiac output and blood pressure will rise initially.
• Blood volume equals the sum of the formed elements &
blood plasma in the vascular system; blood pressure is
normally directly proportional to blood volume in the
cardiovascular system.
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VI. 13.5 Blood Pressure
B. Influencing Factors
• Peripheral resistance, the force produced by friction
between the blood and the walls of a blood vessel, hinders
blood flow; blood pressure must overcome peripheral
resistance if blood is to continue to flow. Therefore, factors
that alter PR will change blood pressure. If PR lessens, BP
lessens and visa versa.
• Viscosity is the ease with which a fluid’s molecules flow
past each other. The greater the viscosity, the greater the
resistance to flowing. Increased viscosity increases BP;
decreased viscosity decreases BP.
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VI. 13.5 Blood Pressure
Hypertension (high blood pressure) is a condition in which the arterial
pressure is persistently elevated.
• Primary hypertension (aka essential or idiopathic hypertension) is
when there is no identifiable cause.
• Secondary hypertension is high pressure that is due to an underlying
cause such as:
Kidney problems, adrenal gland tumors, thyroid problems
Certain defects in blood vessels you're born with (congenital)
Certain medications, such as birth control pills, cold remedies,
decongestants, over-the-counter pain relievers and some prescription
drugs
Illegal drugs, such as cocaine and amphetamines
Alcohol abuse or chronic alcohol use
Obstructive sleep apnea
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VI. 13.5 Blood Pressure
Some of the consequences of prolonged hypertension:
• the left ventricle is required to work harder, which can result in thicker
myocardium – enlarging the heart. If the coronary arteries cannot
supply sufficient blood to support the overgrowth, parts of the heart
muscle may die & be replaced with fibrous tissue
• the development of atherosclerosis which may cause coronary
thrombosis or coronary embolism
• Stroke (aka CVA – cerebral vascular accident)
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