| Action potential An
alteration in electrical charge along a heart muscle cell membrane;
the first of several steps leading to the cell's contraction.
Afterload The mechanical
load encountered by the heart following the onset of contraction;
the forces that resist the flow of blood from the heart. The afterload
may increase with age due to increasingly stiff arteries.
Arteries Blood vessels
that carry blood away from the heart to all parts of the body. Some
enlarge with age and become thicker and stiffer.
Arterioles The very
small arteries that take blood from arteries to capillaries.
Atherosclerosis A
condition of the arteries in which the interior of the artery wall
is made thick and irregular by deposits of fatty substances and
invasive cells from the blood and arterial wall and matrix substances
synthesized by the cells.
Atrioventricular node
A group of special muscular fibers at the base of the wall between
the right atrium and ventricle. They relay the electrical impulses
to the ventricle to initiate contraction. These electrical impulses
originate in the heart's pacemaker, the sinoatrial node in the right
atrium.
Atrium One of the
two upper chambers of the heart. The right atrium receives blood
depleted of oxygen from the veins; the left atrium receives blood
with fresh oxygen from the lungs. The left atrium cavity enlarges
with age.
Autonomic nervous system
That part of the nervous system that controls involuntary muscles,
such as the heart. It uses chemicals, such as catecholamines, to
send messages from the brain to the heart. With age, the body's
response to catecholamines declines.
Aorta The largest
artery in the body. It conducts blood away from the heart, then
branches into many smaller arteries that take the blood to the rest
of the body. The diameter of the aorta enlarges with age and its
walls become stiffer.
Baroceptor response
The body's response to pressure sensitive nerves in the aorta that
help regulate heart rate; the response grows weaker with age.
Blood pressure The
force the flowing blood exerts against artery walls. Systolic blood
pressure occurs when the heart contracts and pumps blood into the
aorta. Diastolic blood pressure occurs when the aortic valve closes
and the heart relaxes and refills with blood.
Calcium pump proteins
Proteins on the sarcoplasmic reticulum that remove calcium from
the cell cytosol after a contraction. Their number declines with
age.
Calcium transient
The transient increase in calcium in the cytosol following excitation
which causes a contraction. It grows longer with age.
Capillaries The smallest
blood vessels that take blood from arterioles to cells of the body.
Cardiac output The
amount of blood a heart pumps each minute. It is calculated by multiplying
heart rate by stroke volume.
Contractile proteins
Proteins in myocytes that change their configuration in order to
bring about a shortening, or contraction, of the cell. They may
change with age.
Coronary heart disease
Also called coronary artery disease and ischemic heart disease.
A narrowing of the coronary arteries due mostly to atherosclerosis
(see above) resulting in a decreased flow of blood to the heart
muscle and thus lower levels of oxygen reaching the heart.
Coronary flow The
flow of blood through the coronary arteries that nourish the heart
muscle.
Contractile state
The ability of the heart muscle cells to contract. Also referred
to as contractility.
Cytosol The fluid
inside heart and blood vessel cells.
Diastole The period
during a heart beat when the chambers are filling with blood and
the heart muscle is relaxed.
DNA (deoxyribonucleic
acid) A large chain of molecules in the nucleus of each cell that
carries the genetic information necessary for all cellular functions,
including the building of proteins.
Echocardiography A
method of graphically recording the structure and movement of the
heart by the echo obtained from beams of ultrasonic waves.
End diastolic volume
The volume of blood in the left ventricle at the end of diastole,
just before the next beat.
End systolic volume
The volume of blood left in the heart at the end of systole.
Ejection fraction
The fraction of end diastolic volume pumped out with each beat.
Frank-Starling law of
the heart Also called the Starling law of the heart. A phenomenon
in which the more the heart muscle is stretched the more vigorously
it contracts.
Gene A portion of
DNA that codes for a specific protein or other molecule. Each gene
contains a specific sequence of chemicals. The sequence is referred
to as a "code" because it specifies the order of amino acids in
the end product.
Gene expression The
process by which genes are activated to produce messenger proteins
which in turn serve as templates for synthesis of proteins that
regulate cell function. Age-related changes in gene expression may
account for some changes in heart function.
Heart attack The death
of a portion of heart muscle, resulting when an obstruction in one
of the coronary arteries prevents an adequate oxygen supply to that
muscle. Heart attacks may be referred to in terms of the obstruction
("coronary thrombosis") or in terms of the damage done ("myocardial
infarction").
Heart rate The number
of beats per minute. See also maximum heart rate.
Heart failure A condition
in which the heart is unable to pump the amount of blood needed
by the body. Heart failure can develop from many heart and circulatory
disorders, such as high blood pressure and heart attack. It often
leads to congestion in the body tissues, with fluid accumulating
in the abdomen and legs and/or in the lungs. This condition, which
may develop over a period of years, is often called congestive heart
failure.
High blood pressure
An unstable or persistent elevation of blood pressure above the
normal range. Blood pressure often increases within the normal range
with age. High blood pressure increases the risk of heart disease
and stroke.
Hypertrophy Enlarge
or enlargement. The walls of the heart and the myocytes that make
up the walls hypertrophy with age.
Ischemia Decreased
blood supply to the heart muscle.
Lifestyle An individual's
typical way of life, including diet, amount of physical activity,
smoking, drinking, and sleeping habits, and personality. Lifestyle
interacts with the effects of age and disease to influence heart
function and the condition of the arteries.
Maximum heart rate
The number of beats per minute during rigorous exercise. It declines
by about 25 to 30 percent between ages 20 and 80, regardless of
physical fitness status.
Maximum oxygen consumption
The amount of oxygen used by the body at peak exercise capacity.
Also known as VO2 max, it is considered the best measure of physical
fitness.
Mitral valve The valve
between the left atrium and ventricle. It closes more slowly with
age because the rate of blood flow into the left ventricle that
pushes it closed decreases with age.
Myocardial infarction
See heart attack.
Myocardium The heart
muscle.
Myocyte A heart muscle
cell. Myocytes decline in number but grow larger with age.
Organelle A structure
inside a cell, such as the sarcoplasmic reticulum.
Oxygen consumption
The amount of oxygen the entire body uses in a certain time period.
It is calculated by taking the amount of oxygen in the arteries
and subtracting the amount left in the veins after the body's cells
have taken out oxygen. The result is then multiplied by cardiac
output. See also maximum oxygen consumption.
Pacemaker See sinoatrial
node.
Preload The amount
of blood in the left ventricle before contraction.
Protein A molecule
made up of amino acids arranged in a specific order determined by
the specific message for its synthesis from a gene. Proteins are
essential for all life processes. Certain ones, such as the calcium
pump protein and the contractile protein myosin, appear to change
with age, which may account for some changes in the function of
the aging heart.
Sarcoplasmic reticulum
A structure or organelle inside a myocyte. Its function is to store
and release calcium for use during a contraction and to remove calcium
after a calcium transient causes a contraction. It removes calcium
more slowly with age. See calcium pump proteins.
Sinoatrial node The
heart's pace-maker. A group of specialized cells in the right atrium
wall that give rise to the electrical impulses that initiate contractions.
Stroke volume The
amount of blood pumped with each beat.
Systole The period
during a heart beat when the heart muscle contracts and blood is
pumped out.
Veins The blood vessels
that return blood to the heart after the body's cells have extracted
oxygen.
Ventricle A chamber
of the heart that pumps blood out. The right ventricle pumps it
to the lungs where it picks up oxygen; the left ventricle pumps
it into the aorta and then on to the rest of the body.
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