cardiac cycle
one heartbeat
-includes atrial contraction, ventricular contraction, a short pause during which the entire heart is relaxed
systole
contraction of atria or ventricles
diastole
the time when the atria or ventricles are relaxed
what are the mechanical events of the heart?
systole and diastole
mechanical events of the heart are preceded and caused by _____.
electrical events
true or false: the hearts electrical events are NOT brought about by nerve impulses.
true
1 % of cardiac muscle cells are ______, while the remaining 99% are _____.
autorhythmic cell while the remaining 99% are contractile cells
autorhythmic cells
- do not contract
- initiate and conduct action potentials that spread throught the heart causing depolarization and repolarization of contractile cells
depolarization leads to the contraction of ______ cells.
contractile cells
repolarization leads to the ______ or contractile cells.
relaxation
atrial relaxation is a _____ event.
mechanical event
ventricular depolarization is an ______ event.
electrical event
true or false: the heartbeat requires input from nerves
FALSE
_____ cells initiate and conduct action potentials that cause the electrical events of the heart.
autorhythmic cells
what three criteria must be met for the heart to efficiently pump blood through the vessels of the cardiovascular system?
- excitation must be coordinated, so that the cells of each heart chamber contract as a unit
- coordination between the paired atria and the paired ventricles so that both members of a pair contract at the same time
- atrial excitation and resulting contraction must be completed before the onset of ventricular contraction
explain the disadvantage in regards to blood flow if the cells of a ventricle do not contract as a unit
blood would not be pumped from a ventricle
electrocardiogram ECG or EKG
recording of the electrical events of the heart
the blips of the ECG in order
p q r s t
p wave
caused by the spread of depolarization
QRS complex
caused by the spread of depolarization through the ventricles
t wave
caused by the spread of repolarization through ventricles
atrial repolarization does not show on a normal ECG because:
it occurs at the same time as ventricular depolarization
true or false: electrical events cause mechanical events
true
why are the durations of mechanical and electrical events NOT the same?
because muscle fibers continue to contract until the cells are repolarized
electrical and mechanical event of the p wave
electrical event: atrial depolarization
causes
mechanical event: atrial systole (contraction)
electrical and mechanical event of the QRS complex
electrical: ventricular depolarization
causes
mechanical: ventricular systole
electrical and mechanical event of the t wave
electrical : ventricular repolarization
causes
mechanical: ventricular diastole (relaxation)
heart block
- change in the hearts electrical events
- ventricles often miss a beat
PQ interval
time from the beginning of the p wave to the beginning of th QRS complex
-beginning of atrial depolarization to the beginning of ventricular depolarization
an increased pq interval indicates :
a delay in action potential traveling through the conduction system of the ventricles
QRS interval
measure of how long it takes the ventricles to depolarize
- usually less than .10 sec.
- an enlarged ventricle can cause an increase QRS interval
QT interval
contraction of the ventricle last almost from the beginning of the Q wave to the end of the T wave.
- .35 sec
- an enlarged ventricle can result in an increased QT interval
an increased QT interval is a change in the _______.
duration of the hearts electrical events
heart block is a change in the :
sequence of the hearts electrical events
because ventricles often miss a beat
lead
each combination of two electrodes
only two electrodes are working at one time
lead 1
records the difference in electrical potential between the electrodes on the right and left arms
lead 2
records the difference in electrical potential between the electrodes on the right arm and left leg
lead 3
records the difference in electrical potential between the electrodes on the left are and left leg
the electrode on the right leg is the ______
ground electrode
mean electrical axis QRS axis
the electrical line from the apex to the base
any change in the mean electrical axis indicates a change in the ;
direction of electrical events of the heart
the electrode on the right arm is always _____
negative
the electrode on the left leg is always _____
positive
one factor that influences the amplitude of an event is the _______ of an event
direction
a recorded electrical event is largest in the lead that _______ the direction of that event
most closely parallels
the mean electrical axis is almost parallel to lead ___?
lead 2
any change in the mean electrical axis indicates a change in the ______ of electrical events in the heart.
direction of electrical events in the heart
three examples of how mean electrical axis can change?
- pregnancy
- if one ventricle is enlarged relative to the other
- if areas of the heart muscle are damaged due to a heart attack
during ventricular relaxation pressure increases or decreases?
decreases
sound one occurs when
closure of the atrioventricular valves
sound two occurs when
closure of the semilunar valves
an abnormal heart sound is called a _____
heart murmur
auscultation means
listening to body sounds
systemic arteriol blood pressure
- most commonly measured
- provides most valuable info about condition of cardiovascular system and overall health
the pressure in your arteries is pulsatile. what does pulsatile mean?
it rises and falls with each contraction and relaxation of the ventricles
systolic pressure
highest arterial pressure attained during one cardiac cycle
diastolic pressure
lowest arterial pressure attained during one cardiac cycle
mean arteriol pressure
average pressure experience by arteries
-homeostatically regulated by your body
(1/3 x pulse pressure) + diastolic pressure
pulse pressure=
systole - diastole
pulse rate
of heart beats in one minute
kortoff sounds do not occur when :
blood does not flow through the artery or when the blood flow is smooth
-does not occur when there is no turbulece
kortoff sound would be heard when blood ___.
spurts through the artery
cardiac output =
heart rate X stroke volume
resting pulse is taken. upon standing cardiac output basically remains constant, but stroke volume ______ due to the pull of gravity and heart rate _______ to keep cardiac output the same.
decreases due to the pull of gravity and increases to keep cardiac output the same
define heart murmur
and abnormal heart sound
different electrical views of the heart can be obtained using the three standard _____
limb leads
give two durations or intervals that are prolonged due to an enlarged heart
QT interval, QRS
_______ precedes and causes the ventricles to contract
depolarization precedes and causes the ventricles to contract
