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All cells change as they age, generally becoming larger. Their capacity to divide and reproduce tends to decrease. Normal cells have built-in mechanisms to repair minor damage, but the ability to repair declines in aging cells.
DNA is damaged through the aging process and changes occur:- in cellular membranes;
- with enzymes;
- in the transport of ions and nutrients;
- in the nucleus of chromosomes where such changes as clumping, shrinkage, and fragmentation occur.
Other changes occur in such organelles as the mitochondria and lysosomes where numbers are reduced, causing cells to function less efficiently. When the mitochondria decrease in function, metabolism is decreased to about 95% of capacity by age 50, and to 85% by age 70. This effect also ties in with a decrease in hormonal secretions. A decrease in metabolism has several effects:- toleration of cold is less;
- a tendency to gain weight increases;
- there is a decreased efficiency in the body’s use of glucose.
Cellular aging alters the tissues formed by these cells which, in turn, affect organ function. For instance, by the age of 85, lung capacity has decreased by 50%; muscle strength by 45%; and kidney function by 30%.
Collagen and elastin decrease in connective tissue formation, resulting in joint tissues becoming stiffer, less elastic, and less efficient in their function.
Lipid and fat content of tissues change. In men, there is a gradual increase in tissue lipids and fat until age 60; then there is a gradual decrease. In women, lipids and fats accumulate in the tissues continuously, but there is no decline as happens in men.
The total amount of water in the body gradually decreases. These changes in body fat and water reduction are the main reasons why the elderly respond differently to drugs than the younger population.