THE HEART

The Heart

•right pulmonary arteries•semilunar valves•right atrium•superior vena cava•right pulmonary veins•Inferior vena cava•septum•aorta•left pulmonary arteries•pulmonary trunk•left ventricle

•left pulmonary veins•right ventricle•left atrium•atrioventricular valve

The Heart

The Heart

The Heart

Control of the Heartbeat

You cannot hold your pulse even for a single beat. Your heart continues beating regularly if you are

knocked unconscious, and may even continue beating for a while after you die.

The impulse that triggers the heartbeat actually originates from within the heart itself. There are nerves (autonomic NS) that connect to the

heart but they do not initiate or control the heartbeat A cardiac cycle is defined as a complete cardiac

movement, including systole, intervening pause, and diastole

Control of the Heartbeat

The contraction phase is systole, while the filling phase is diastole

A bundle of specialized muscle tissue, located in the wall of the right atrium, stimulates the muscle fibres to contract and relax rhythmically. The sinoatrial node (S-A node) = the pacemaker Atria contract while ventricles relax, and the ventricles

contract while atria relax. Heart sounds are created primarily from turbulence

in blood flow created by valves closing, not from contraction. Why do heart sounds come in pairs?

Control of Heartbeat

The Atrioventricular (AV) node is also located on the right side of the heart, just beneath the surface of the interventricular septum.

The Bundle of His, is a band of nerve fibers that originates at the AV node, then passes along the interventricular septum to the ventricles. The right and left bundle branches

proceed along the right and left sides of the interventricular septum to the tips of the two ventricles.

The Purkinje Fibers are the tree-like terminal branchings of the right and left bundles.

Control of Heartbeat

After the SA node fires: the electric signal spreads throughout the muscles

of both atria Atrium contract

The impulse then passes through the AV node to the Bundle of His

The signal is then divided between right and left bundle branches

When they reach the terminals of the Purkinje fibers they leap across to the cardiac muscle fibers Ventricles contract

All this happens in less than a second.

Electrocardiographs (ECGs)

Represents (and measures) the electric activity of the heart

A normal ECG graph appears as follows:

An upward deflection of the wave represents an electric impulse traveling towards a sensor

ECGs

Each of the letters designates a different phase of the cardiac cycle.

P wave: generation of the electrical impulse at the SA node and its subsequent spread through the atria.

PR interval: During this interval the impulse travels through the atria and the AV node.

ECGs

QRS complex. The time necessary for the impulse to spread through the bundle of His and its branches to complete ventricular contraction

ST segment. The ST segment represents the period between the completion reversal of charges in the ventricular muscle tissue.

T wave. The T wave represents the return to normal state of ventricular muscle tissue that occurs after ventricular contraction.

Chemical Regulators

When you are relaxed, your S-A node fires regularly around 70 times a minute.

This firing rate adjusts, however, to meet your body’s needs. Read the Chemical Regulators section on p. 305 There are two negative feedback loops

described Fill in the worksheet with the appropriate

information for each of these loops

Control of Heartbeat

Physical activity is not the only trigger for an increased heart rate.

The nervous system releases adrenaline when you are nervous, angry, or excited, or after a sudden shock or sharp pain. “fight or flight” response:

a physiological change that prepares the body for anticipated activity

attack, defence, or escape. As the heart rate increases, so does blood flow

to the muscles, resulting in more oxygen being delivered to the muscle cells.

Adrenaline

Cardiac Output

The amount of blood pumped by the heart is often referred to as the cardiac output = volume of blood pumped from each ventricle per unit of time. a measure of the level of oxygen delivery to the body Indicates the total level of work the muscles must perform

Two factors affect the cardiac output heart rate (HR) = number of times the heart beats in a unit of

time (minute) stroke volume (SV) = the amount of blood forced out of the

heart with each heartbeat

cardiac output = SV × HR Average person has a stroke volume of about 70 mL and a

resting heart rate of about 70 beats per minute, for a cardiac output of about 4900 mL/min.

Cardiac Output

• Out of Shape• Average• Extremely Fit

Cardiac Output

Individual A = Average Individual B = Out of Shape, Unhealthy

Low stroke volume results in a high resting heart rate

Individual C = Exceptionally fit very high stroke volume results in a low resting heart

rate can maintain the same level of oxygen delivery at a

much lower heart rate than the less fit individual B. Why is a low resting heart rate healthier?

When the heart is forced to work harder, it will break down sooner

ECGs

Activity: Research 1 of 3 other conditions on

www.ecglibrary.com left ventricular stenosis atrioventricular block Wolf-Parkinson White

Draw a normal ECG Draw the abnormal ECG for the condition Identify where the major differences are (which

sections of the ECG) between the two ECGs Explain the pattern and cause of the abnormal ECG

Blood Pressure

Blood Pressure