Cardiovascular System

Aging is associated with decrements in body structure and function in many different organs and systems. For example, heart rate, breathing rate, bone density, brain size, and kidney functioning all decrease, and blood cholesterol level increases. The organ that is perhaps most reflective of the

Superior Vena Cava 4*

Upper Body

Right t Pulmonary Veins

II Left T Pulmonary II Veins

Right t Pulmonary Veins

II Left T Pulmonary II Veins

Right

Left

Lung

Right Pulmonary Artery

Right Ventricle

Left Pulmonary Artery

Semilunar

Aorta 1

Left Atrium

[j Mitral i Valve

Left

Ventricle

Aortic

Right Ventricle

Semilunar

Left

Ventricle

Aortic

-——-- Valve

---valve

Inferior

Aorta i

Vena Cava

Lower Body

Figure 2-2 blood flow.

Schematic diagram of the cardiovascular system, showing direction of

Figure 2-2 blood flow.

Schematic diagram of the cardiovascular system, showing direction of overall vitality of a person and the failure of which is the number one cause of death is the heart.

As schematized in Figure 2-2,the human heart consists of four chambers (left atrium, right atrium, left ventricle, right ventricle), a series of valves, and a complex of arteries and veins. The carbon dioxide-filled blood returns to the heart from various parts of the body and flows into the right atrium by way of two large veins, the superior and inferior vena cava. The right atrium fills, contracts, and the blood is pushed through the interconnecting tricuspid valve into the right ventricle. When it is full the right ventricle contracts, the tricuspid valve closes, the semilunar valve between the right ventricle and the pulmonary arteries opens, and blood is pumped through the left and right pulmonary arteries into the corresponding lungs. After being oxygenated in the lungs, blood flows through the pulmonary veins into the left atrium; when full, the left atrium contracts and squeezes the blood through the mitral valve into the left ventricle. The filled left ventricle then contracts, forcing the blood through the aortic valve into the aorta. The many branches of the aorta carry blood to all parts of the body except the lungs.

The relaxation/filling (diastolic) phase of heart action takes place on both sides of the heart simultaneously, as does the contraction/emptying (systolic) phase. Arterial blood pressure is expressed as systolic over diastolic pressure in pounds per square inch. The regular, periodic beating or rhythm of the normal heart, which occurs roughly 3 billion times during a life span of 75 years, is produced by the alternative diastolic and systolic phases. The number of heartbeats per minute, which varies with the individual and the need for oxygen, is approximately 70 in the normal adult resting heart. Maximum heart rate, however, may increase to 200 beats per minute in a young adult. Resting heart rate does not show much age variation, but maximum heart rate ranges from 200 beats per minute in young adults to as low as 150-160 in older adults.

Among the structural changes in the cardiovascular system that occur with aging are atrophying of heart tissue, decreases in the size of cardiac muscle cells, and increases in connective tissue and in fat and calcium deposits in the heart. The result is that the heart muscle and valves thicken and stiffen. The coronary arteries, which supply nourishment and oxygen to heart muscles, become narrower, less flexible, and clogged. Due to cross-linkages in collagen molecules, the aorta and cardiac vessels also harden, shrink, and become less elastic. The blood cholesterol level increases and hemoglobin and red blood cell count decrease after age 65. Because the muscles of the heart become less efficient with advancing age, the maximum heart rate and stroke volume decrease, heartbeats are fewer and more irregular, blood volume output is less, blood pressure increases, and the volume of blood supplied to the body and to the heart itself is reduced. Consequently, both the rate at which oxygen and nutrients are transported to the cells and the rate at which waste products are carried away decline. The effects on behavior are seen in the fact that older people tire more quickly and take longer to return to a resting state after exerting themselves.

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