Aging Effects
Changes in fluid balance or pH are often the result of disease or damage to a particular organ. For instance, a weak heart (congestive heart failure) that cannot pump efficiently allows blood to back up in the circulation. In turn, this may cause edema, usually found in the lower legs and feet. Such edema results if the right ventricle is weak. If edema is pulmonary, it will usually be as a result of the weakening of the left ventricle of the heart.
After puberty, the thymus gland involutes (shrivels up) and is replaced by connective tissue. This means there is a decrease in the amount of thymosin produced, resulting in a decline in the defence mechanisms of the body. As the immune system becomes less effective in combating disease, the elderly become more prone to infections. This diminished capacity can be as much as 50% of that of a younger person.
T-cells are less responsive to antigens; therefore, fewer cytotoxic T-cells respond to an infection. This is partly because of the gradual decrease in size of the thymus gland and its reduced production of the hormone, thymosin. Because the helper T-cell production is reduced, B-cells become less responsive, and antibody levels do not rise as quickly after antigen exposure. Depressed lymphocyte function is also accompanied by a decrease in macrophage activity. The result is an increased susceptibility to viral and bacterial illnesses.
Increased cancer incidences also indicate a decline in immune system surveillance, causing tumor cells to proliferate instead of being destroyed. In addition, the elderly frequently take drugs or have therapies that depress the immune system. For instance, the use of steroids in the treatment of arthritis and the use of drugs and radiation in the treatment of cancers all cause immunosuppression, leaving them open to secondary infections and diseases.
A decreased secretion of growth hormone leads to a decrease in muscle mass while at the same time, increasing fat storage.
Levels of circulating autoantibodies (antibodies directed against self) increase in the elderly and explains why they are more prone to the development of autoimmune diseases.
As the thyroid slows its secretion of thyroxine, the result is a lower basal metabolic rate.
This page was updated in November 2005.
