HEART ACTIONS
• A cardiac cycle is a complete heartbeat
• During a cardiac cycle, the pressure in the heart
chambers rises and falls
• These pressure changes open and close the valves
• The first part of a heart sound (lub) occurs when the
AV valves are closing
• The second part of a heart sound (dub) occurs when
the semilunar valves are closing
CARDIAC CONDUCTION SYSTEM
•
The heart is autorhythmic, able to contract itself without nervous or hormonal
stimulation
•
Components include: SA node, AV node, and specialized cardiac muscle tissue
and cells
•
These components coordinate the events of the cardiac cycle (heartbeat)
•
SA node – located in the right atrium near the opening of the superior vena cava;
initiates one impulse after another (pacemaker)
•
The impulse spreads to other areas of the myocardium due to cardiac muscle
cells and gap junctions
•
AV node – located in the inferior part of the right atrium
•
The impulse passes from the AV node to the AV bundle (group of fibers) and the
Purkinje fibers carry the impulse to distant regions of the myocardium
ELECTROCARDIOGRAM
•
Recording of the electrical changes in the myocardium during a cardiac cycle
•
Electrodes are placed on the skin and connected to wires that respond to weak
electrical changes
•
When the SA node triggers a cardiac impulse, the atrial fibers depolarize,
producing an electrical change = P wave
•
When the cardiac impulse reaches the ventricular fibers, they rapidly depolarize
producing an electrical change = QRS complex
•
The electrical changes that accompany ventricular muscle fiber repolarization
slowly produce a T wave, ending the ECG pattern
•
Physicians use ECG patterns to assess the hearts ability to conduct impulses
BLOOD PRESSURE
•
The force the blood exerts against the inner walls of the blood vessels
•
The maximum pressure achieved during ventricular contraction is called 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 called the diastolic pressure
•
A sphygmomanometer measures blood pressure
•
The cuff is wrapped around the arm so that is surrounds the brachial artery; air is pumped into
the cuff until the cuff pressure exceeds the pressure in that artery squeezing the vessel closed
and stopping its blood flow; as air is slowly released from the cuff, the air pressure inside it
decreases; when the cuff pressure is just slightly lower than the systolic blood pressure in the
brachial artery, the artery opens for a small volume of blood to spurt through, producing a
sharp sound heard through the stethoscope (systolic pressure); as the cuff pressure continues
to drop, louder sounds are heard; when the cuff pressure is just slightly lower than that within
the fully opened artery, the sounds disappear (diastolic pressure)
•
Normal blood pressure is 120/80
CARDIAC OUTPUT
• For the body to function properly, the heart needs to
pump blood at a sufficient rate to maintain an
adequate and continuous supply of oxygen and other
nutrients to the brain and other vital organs
• Cardiac output = describes the amount of blood your
heart pumps each minute
• A healthy heart pumps about 5-6 liters of blood every
minute when a person is resting
CARDIAC OUTPUT
Cardiac Output: It is determined by:
1. The amount of blood pumped by the left ventricle during
each beat (stroke volume)
2. The number of heart beats per minute
The amount of blood ejected by a ventricle during each contraction
(single beat) is called stroke volume
Cardiac output is an indication of the blood flow through
peripheral tissues; without adequate blood flow, homeostasis
cannot be maintained; helps keep blood pressure at the levels
needed to supply oxygen-rich blood to your organs
CARDIAC OUTPUT
For an adult at rest…
Stroke volume = 80 mL (average)
Heart rate = 75 beats per minute (average)
Therefore, Cardiac Output (CO) = Stroke Volume
x Beats per Minute
CO = 80 mL/beat x 75bpm
CO = 6000mL/min (6L/min)