Functioning of the Cardiovascular system

TOPICS COVERED IN THESE NOTES

(a) The Electrical Conduction System of the Heart

(b) Coronary Disease

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The electrical conduction system of the heart:

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The Heart’s Electrical Conduction System The cardiac muscle cells are excitable, meaning that with electrical stimulation they will all contract (this is known as a “syncytium”). Within the heart, there are areas of specialized tissue that are important in the regulation and coordination of this electrical activity. These specialized tissues are:

• the sinoatrial node (SA node)
• the atrioventricular node (AV node)

The contraction of the heart leads to the pumping of blood.

\n Important Facts:

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The sinoatrial node (SA node)

• This is a specialized region of tissue that is found in the right atrium where electrical signals that lead to contraction are initiated (also called the “pacemaker” of the heart).

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The ^^atrioventricular node (AV node)^^ • This is the specialized tissue that transmits the electrical signal from the atria into the ventricles and to a region that runs down the ventricular septum. The ventricular septum is the tissue that separates the two ventricles (the bundle of His, also known as the atrioventricular bundle).

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The heart’s electrical conduction system:

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An electrocardiogram:

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Bradycardia and Tachycardia:

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Regular aerobic exercise results in improvements in the efficiency of the cardiovascular system at rest and during exercise.

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• Bradycardia is one of the most easily observed adaptations that occurs with training. Bradycardia is characterized by a heart rate of 60 beats per minute or less at rest, while ^^tachycardia^^ is a heart rate of more than 100 beats per minute at rest.

• Generally, a lower heart rate is regarded as an indication of an athletic or strong heart.

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The Effects of Exercise During exercise, dramatic changes ocur in the cardiovascular system—changes known as ^^cardiovascular dynamics^^.

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The heart and the vessels constantly adapt to accommodate the ever-changing requirements of the body during exercise. Some of the factors that are considered when discussing cardiovascular dynamics are:

• cardiac output (Q),

• blood pressure (BP),

• distribution of blood flow

• oxygen consumption (VO2).

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Heart Disease:

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^^Coronary Circulation:^^ The system of vessels that supply essential materials via blood to the heart muscle itself is called coronary circulation.

\n Serious health repercussions and even death can occur if a narrowing or blockage of blood vessels restricts the flow of blood to the heart muscle. For example, a heart attack (a myocardial infarction) can result when blood flow to a section of the heart muscle becomes blocked due to plaque buildup or some other reason.

\n The coronary vessels (anterior)

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Coronary Artery Disease:

\n •^^Coronary artery disease^^ (also known as atherosclerosis) involves a gradual narrowing of the coronary arteries resulting from the accumulation of hard deposits of cholesterol (plaque), on the lining of the blood vessels.

\n The causes of coronary artery disease:

Besides a poor diet, other risk factors associated with coronary artery disease include:

• smoking,

• elevated blood lipids,

• hypertension,

• family history, and

• physical inactivity.

\n Each factor individually increases the risk of the development of coronary artery disease. When the factors are combined, the risk of coronary artery disease is magnified.

\n Summary:

• The electrical stimulation of the heart leads to the pumping of blood.

• Within the heart, areas of specialized tissue are important in the regulation and coordination of the heart’s electrical activity (SA and AV nodes).

• During exercise, dramatic changes occur throughout the cardiovascular system (referred to as “cardiovascular dynamics”).

• Serious health repercussions and even death can occur if a narrowing or blockage of blood vessels restricts the flow of blood to the heart.

• Poor diet, smoking, and physical inactivity are some factors that contribute to the development of coronary artery disease.