Complications of Aging
Learning Objectives
After studying this chapter, the student is expected to:
1. Describe the metabolic and structural changes in tissues.
2. Discuss the effects of hormonal changes as women and men age.
3. Describe the common changes in the heart and the arteries.
4. Explain the causes and effects of osteoporosis and osteoarthritis in older individuals.
5. Discuss the common changes in nervous system function.
6. Describe common changes in the digestive system and the urinary system.
7. Explain the increased incidence of infections and cancer.
8. Explain how multiple system disorders can interact and cause complications.
Key Terms
arteriosclerosis
articular cartilage
atherosclerosis
cataracts
cholesterol
dyspareunia
fractures
frequency
glaucoma
incontinence
intervertebral discs
kyphosis
neurofibrils
neurotransmitter
nocturia
osteoarthritis
osteoblastic
periodontal disease
plaques
presbyopia
retina
sedentary
senescence
xerostomia
The Aging Process
Aging begins after birth but becomes more evident at about 30 years of age. The process is irreversible, but the rate and effects of aging vary greatly among individuals and do not necessarily match chronologic age. The typical changes in various organs do not occur at the same time or in any particular order. The extent of the changes also depends on the individual’s genetic makeup, lifestyle, and health status. Many diverse research projects are taking place into the physiologic changes related to aging with the goal of delaying changes or reversing them. Much of this research is in developmental biology and includes the study and expression of various genes that have been identified in normal development.
Senescence refers to the period of life from old age to death. Overall, women live longer than men. The average life span is increasing, creating a higher proportion of older individuals in the population. This trend occurs largely because of improved social and living standards, better nutrition, and advancements in health care. Physical exercise that occurs on a routine basis and increases cardiac output and ventilation may slow tissue changes associated with senescence by providing improved nutrition and oxygenation to the tissues. Cognitive activities requiring problem solving such as card games, puzzles and reading seem to reduce senescence in the central nervous system. Social interaction during exercise or games is also significant in maintaining function.
With aging, a general reduction in function occurs throughout the body at the cellular and organ level, and the body is characterized by a decreased capacity to adapt to change. Aging is a natural process, but it is affected by many pathologic processes. Degenerative changes associated with aging may predispose an individual to certain pathologies, and pathologic changes can hasten aging. Of particular concern are the organs and tissues that cannot regenerate, such as the brain and myocardium. This chapter covers only some of the more significant effects of aging that are linked to pathologic problems. For additional information, a gerontology reference should be consulted.
There are different theories about the causes of aging. One theory suggests that aging is programmed genetically through the cells and that this control directly limits the cells’ reproductive capacity (see Chapter 1). Predetermined cell death is termed apoptosis. Other possible factors include wear-and-tear, cellular damage resulting from accumulated wastes and altered protein (amyloid) or lipid (lipofuscin) components, or increased degenerative changes in collagen and elastin fibers. In addition, random errors occur during cell mitosis. Some theories suggest that aging is related to resident latent viruses or increased autoimmune reactions in which the body rejects its own tissues, or to environmental agents that affect cells. One concern relates to free radicals such as peroxides, reactive chemicals produced during cell metabolism. Free radicals are known to damage nucleic acids and cells, leading to cancer and other diseases. It is likely that many factors contribute to the aging process, and that these factors may vary in individuals.
Changes in the tissues are obvious. Cells assume less regular arrangements in tissues later in life. Elastic fibers are lost, and the number of collagen cross-linkages or other abnormal structures in tissues and organs increases. Mitosis, or cellular reproduction, gradually slows down, partly in response to the slower metabolic rate, resulting in decreased tissue repair. Some cells such as neurons and muscle cells cannot replicate, and when they die function is reduced in these tissues. Certain cells appear to have limits on the number of times they can replicate, and therefore they are not replaced in older individuals. Other cells accumulate wastes or are altered by environmental factors and become less functional or die, ultimately leading to organ failure. It has become evident that prolonged exposure to numerous environmental factors such as radiation, viral infections, and chemicals over the years leads to an increased risk of cancer and other diseases in older people. Many of these changes also occur in younger individuals, so they are not unique to the aging process.
Physiological Changes with Aging
Hormonal Changes
Generally hormone secretions remain relatively constant with advancing age, but the number of tissue receptors may decrease, thus diminishing the body’s response to hormones. This effect is apparent in disorders such as type 2 diabetes mellitus, which is common in older persons. In this condition, sufficient insulin is produced, but because the number of cell receptors is reduced, glucose does not enter the cells (see Chapter 16). In the absence of any specific pathology, the pituitary, thyroid, parathyroids, adrenals, and pancreas appear to maintain relatively normal function, producing hormones in adequate quantities.
The major natural hormonal change occurs in women at about age 50, when the ovaries cease to produce estrogen and progesterone; subsequently, serum levels of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) rise in response to natural feedback mechanisms (see Chapter 19). The effects of the decreased estrogen and progesterone are described in the following sections. Although there is a gradual decrease in testosterone levels in the male, the testes do not totally cease to function.
Testosterone levels in males peak during teen and early adulthood. After the age of 30 testosterone levels decrease about 1% a year. The decline is usually not obvious until later in life.
Reproductive System Changes
Menopause is the term given to the change that occurs in women at around age 50, when the ovaries cease to respond to FSH and LH, resulting in lack of ovulation, cessation of the menstrual cycle, and declining estrogen and progesterone levels. The decreased levels of sex hormones lead to changes such as thinning of the mucosa, loss of elasticity, and decreased glandular secretions in the vagina and cervix. These changes may cause inflammation and dyspareunia, or painful sexual intercourse. The effects can be minimized by topical (local) administration of estrogen creams. There are risks associated with oral hormone replacement therapy; therefore individual case assessment is necessary. The pH of the vaginal secretions becomes more alkaline, thus predisposing older women to recurrent vaginal infections. Breast tissue also decreases in volume. These changes in hormone levels in the early stage of menopause frequently lead to systemic signs such as “hot flashes,” which involve periodic sweating or vascular disturbances. Also headaches, irritability, and insomnia are common manifestations. The effects of menopause may be felt for short or long periods of time (several years) and are more marked in some women than others. Approximately 25% of women experience significant effects. If surgical removal of the ovaries is necessary before menopause occurs naturally, similar effects will be evident.
In males, testosterone levels decline gradually, the testes decrease in size, sperm production is somewhat reduced, and the glandular secretions of the prostate are decreased, but the older male is capable of fathering a child. The common problem in older males is benign prostatic hypertrophy (BPH) (see Chapter 19), in which the central part of the gland around the urethra hypertrophies, resulting in some degree of obstruction of the urethra. If urinary flow is significantly impaired, surgery may be necessary.
Cancer of the reproductive organs is more common in both males (prostatic cancer) and females (uterine and breast cancer) in later years and may be related to altered hormonal levels. Frequent examinations by a physician in addition to routine self-examination and testing (e.g., mammograms) are essential to lessen the risk of advanced malignancy.
Changes in the Skin and Mucosa
Some changes in the skin are related to genetic factors; many are based on exposure to sun and weather. With aging, both the skin and mucous membranes become thin and fragile. The dermis is thinner and subcutaneous tissue is diminished. Fewer capillaries are present and cell proliferation is decreased, resulting in slower wound healing and atrophy of the glands. The numbers of sensory receptors in the skin and mucosa decline. These factors increase susceptibility to injury, bruising occurs frequently, and the mucosal membranes become inflamed or ulcerated.
The skin is often dry and appears wrinkled as elastic fibers are reduced and collagen fibers become less flexible. Obvious lesions include skin tags (small projections of skin) on the neck and axillary areas, keratoses (rough raised masses, often dark in color) over the body, and lentigines or liver spots (dark flat macules), often on the hands and face. The hair becomes gray as melanocytes are reduced in number, and thinning occurs as the number of hair follicles decreases.
Cardiovascular System Changes
Age-related changes occur in the cardiac muscle fibers and the connective tissues in the heart. Fatty tissue and collagen fibers accumulate in the heart muscle with aging and may eventually interfere with impulse conduction and cardiac muscle contraction. The size and number of cardiac muscle cells declines, reducing the strength of cardiac contractions. In the absence of any pathologic changes, the left ventricle appears smaller, because demand is also reduced. Cardiac muscle fibers do not undergo mitosis and cannot be replaced. Heart valves often thicken and therefore become less flexible and efficient. In some individuals, vascular degeneration causes a decrease in the oxygen supply to the heart muscle and reduces the ability of the heart muscle to use oxygen. Thus, cardiac output and cardiac reserve are diminished, decreasing the maximum cardiac output possible with stress. Adequate fluid intake is important to maintain cardiovascular function, as the percentage of fluid in the body declines in older individuals. Again, a regular fitness program is most helpful in maintaining cardiac function.
The common pathologies of the cardiovascular system are associated with degenerative changes in the arteries, both in the heart and throughout the body (see Chapter 12). Loss of elasticity and accumulation of collagen in the arterial walls result in thickening of the arterial walls, thus limiting expansion of the large arteries and obstructing the lumina of smaller arteries. This leads to arteriosclerosis and elevated blood pressure. Also, degenerative changes promote the accumulation of cholesterol and lipid in the walls of large arteries, the condition known as atherosclerosis, particularly when the individual has elevated blood lipid levels. These lipid plaques obstruct blood flow and predispose to thrombus formation. Atherosclerosis is a common cause of angina, myocardial infarctions (heart attacks), peripheral vascular disease in the legs, and strokes. Dietary changes, including reduced cholesterol intake, and regular exercise programs assist in lowering blood lipid and cholesterol levels and lessen the risk of vascular degeneration and high blood pressure.
