Chapter 5

The Cardiovascular

System

The Cardiovascular system

• Heart—pumps blood to lungs and systemic circulation

• Blood vessels—are the pipelines for carrying blood to and from the tissues

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The heart serves as two pumps

• The right heart pumps blood to the lungs, where the blood is oxygenated.

• The left heart pumps the oxygenated blood to the systemic circulation.

Types of blood vessels

• Arteries • Veins • Pulmonary veins • Arterioles• Capillaries • Venules

Anatomy of the heart• Four chambers

• Right and left atria—receive blood from the veins

• Right and left ventricles--pump blood into the arteries

• Striated muscle

• Stimulated by nervous system, which triggers contractions

• Functions as syncytiumVisit the American Heart Association at www.americanheart.org

Basic anatomy of the heart

Conducting system of the heart

1. Wave of excitation begins at the sinoatrial (SA) node

2. Travels by way of ephaptic conduction in the atria to the atrioventricular (AV) node

3. Then through the atrioventricular bundle, bundle branches, and Purkinje fibers, which conduct the impulses throughout the ventricular myocardium

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The conducting system of the heart

The cardiac cycle

• The pattern of contraction and relaxation of the heart

• Diastole• Systole

• Valves between atria and ventricles • Allow unidirectional blood flow• prevent backflow

• Atrial contraction• Ventricular contraction

The cardiac cycle (cont.)

• End diastolic volume (EDV) – Amount of blood in each ventricle at the

end of diastole

• End systolic volume (ESV)– Amount of blood in each ventricle at the

end of systole

• Stroke volume (SV)– The difference between EDV and ESV (the

amount of blood ejected out of each ventricle with each cardiac contraction)

The cardiac cycle

Cardiac output

• The amount of blood ejected by the heart each minute

• At rest, approximately 5 liters per minute

• In well-trained athlete, can increase to over 40 liters per minute

• Important limiting factor in athletic performance

Formula for determining cardiac output

CO=HR x SV

where HR is heart rate and SV is stroke volume.

Methods for measuring cardiac output

• Direct method

• Fick method

• Indicator dilution method

Control of heart rate and stroke volume

• heart rate is determined by the influence of the vagal and sympathetic nerves on the SA node

• stroke volume is determined largely by end diastolic volume which is related to ventricular contraction force as described by the Frank-Starling law of the heart

• during exercise both heart rate and cardiac contractility increase

Nine factors that affect heart rate

1. Age2. Gender 3. Size4. Posture5. Ingestion of food

6. Smoking7. Emotion8. Body temperature9. Heat and humidity

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Factors that affect stroke volume

• Gravity

• Muscular activity

• Size of the heart

• Nervous influences

The one-way valves of the veins

Heart murmurs

• Faulty valves cause regurgitation of blood or restricted blood flow– Heart compensates for increase in retained

blood by increasing its contraction force– As contraction force increases, more

oxygen is consumed– Murmurs may be minor or may severely

limit exercise

Heart rate is more important than stroke volume in aerobic exercise because

1. Stroke volume levels out at approximately eight times the resting level

2. Heart rate is proportional to the work load imposed

3. Heart rate is proportional to the oxygen consumed

The stages of typical heart rate response to exercise

1. At the beginning of exercise, the heart rate rises rapidly.

2. At the end of exercise, the heart rate rapidly declines within the first two or three minutes.

3. After the initial rapid decline, the rate decreases more slowly.

Heart rate changes in a moderately conditioned, middle-aged subject at work loads of 100 and 150 watts on a bicycle ergometer

Changes in cardiovascular function following endurance training

Differences in exercise that affect heart rate

1. Static vs. dynamic exercise

2. Intensity of the exercise

3. Duration of the exercise

How training affects the heart

• Decreases resting heart rate and heart rate during exercise

• Increases stroke volume

• Increases cardiac reserve capacity

Anatomy of blood vessels

• Aorta and large arteries

• Arterioles

• Resistance vessels

• Venules and veins

Hemodynamics: principles governing blood flow• Pressure

– Blood flows through the vessels because of a pressure gradient

• Flow– Larger and more metabolically active tissues

require greater blood flow

• Resistance– viscocity– length of the vessel– vessel diameter

Visit Anatomy and Physiology of the Cardiovascular System at www.mercksharpdohme.com/disease/heart/coronary_health/anatomy/home.html

Microcirculation

• Network in which arterioles give rise to metarterioles

• Metarterioles act as major thoroughfares through tissues

• Metarterioles join a collecting venule

• True capillaries arise from metarterioles

• AV shunts provide another route for blood flow

Microcirculation

Distribution of blood to systemic tissues at rest and during heavy exercise

Blood distribution

• Changes in diameter of small arteries and arterioles are controlled by:– Nervous regulation– Chemical regulation

Blood pressure

• Driving force for moving blood through the circulatory system

• High blood pressure plays major role in such health issues as heart attacks, stroke, and kidney disease

• Blood pressure is affected by age, gender, emotional state, time of day, and body position

• Defined as systolic pressure over diastolic pressure

Range of systemic arterial blood pressure as a function of age

Effect of exercise on blood pressure

Aerobic exercise--elevates systolicpressure but has little effect on diastolicpressure.

Isometric exercise--intrathoracic pressuredramatically increases, decreasingvenous return to the right atrium andputting a greater load on the heart.

The typical time course of the arterial blood pressure response to rest-exercise-recovery in a healthy young male.