第九章：与年龄有关的人类疾病

In Chapter 1, we discussed in some detail the distinctions between aging and disease. Recall that disease reflects a process that disrupts the physical and biochemical functions of the cell, whereas biological aging occurs within the bounds of normal cellular function. Defining the difference between aging and disease serves to clarify terms in discussing the biology of aging and helps establish the boundaries for experimental research. However, the strict lines drawn in this textbook between normal age-related functional loss and definable disease are not as clear-cut in the real world of aging humans.

The incidence of most diseases increases with age; this fact cannot be disputed. The real question with regard to aging and disease is, Why does normal age-related functional loss become disease? During the development and maturity phases of the life span, most physiological systems operate at a level where the difference between normal and abnormal function is easily detected. With aging, the difference between normal and abnormal becomes less well defined. For example, as you will learn in this chapter, all individuals over the age of 70 years have a certain amount of functional loss in the cardiovascular system. For most individuals, this decline does not result in significant alterations in overall physiological function or daily living. But for some, the decline in cardiovascular function will progress to a lethal disease called congestive heart failure.

In this chapter, we focus on clearly defined diseases that are limited, for the most part, to the post-reproductive period. To this end, we discuss five of the most common diseases of the elderly: Alzheimer‘s disease, Parkinson‘s disease, cardiovascular disease, type 2 diabetes, and osteoporosis. For each of these diseases, you‘ll learn how normal age-related changes in a particular organ or physiological system progress to an overt disease state. Cancer is not considered here, as this disease affects all age groups.

For some organ systems, such as the liver and respiratory tract, age-related disease occurs more as a consequence of environmental insult or lifestyle choices than as a result of aging per se. For example, smoking is the number one cause of age-related disease of the lung.