No one knows how and why people change as they get older. Some theories claim that ageing is caused by injuries from ultraviolet light over time, wear and tear on the body, or byproducts of metabolism. Other theories view ageing as a predetermined process controlled by genes.
No single process can explain all the changes of ageing. Ageing is a complex process that varies as to how it affects different people and even different organs. Most gerontologists (people who study aging) feel that aging is due to the interaction of many lifelong influences. These influences include heredity, environment, culture, diet, exercise and leisure, past illnesses, and many other factors.
Unlike the changes of adolescence, which are predictable to within a few years, each person ages at a unique rate. Some systems begin aging as early as age 30. Other aging processes are not common until much later in life.
Although some changes always occur with aging, they occur at different rates and to
different extents. There is no way to predict exactly how you will age.
TERMS TO DESCRIBE TYPES OF CELL CHANGES
Cells shrink. If enough cells decrease in size, the entire organ atrophies. This is often a normal ageing change and can occur in any tissue. It is most common in skeletal muscle, the heart, the brain, and the sex organs (such as the breasts).
The cause of atrophy is unknown, but may include reduced use, decreased workload, decreased blood supply or nutrition to the cells, and reduced stimulation by nerves or hormones.
Cells enlarge. This is caused by an increase of proteins in the cell membrane and cell structures, not an increase in the cell’s fluid. When some cells atrophy, others may hypertrophy to make up for the loss of cell mass.
The number of cells increases. There is an increased rate of cell division. Hyperplasia usually occurs to compensate for a loss of cells. It allows some organs and tissues to regenerate, including the skin, lining of the intestines, liver, and bone marrow. The liver is especially good at regeneration.
It can replace up to 70% of its structure within 2 weeks after an injury.
Tissues that have limited ability to regenerate include bone, cartilage, and smooth muscle (such as the muscles around the intestines). Tissues that rarely or never regenerate include the nerves, skeletal muscle, heart muscle, and the lens of the eye. When injured, these tissues are replaced with scar tissue.
The size, shape, or organization of mature cells becomes abnormal. This is also called atypical hyperplasia.
Dysplasia is fairly common in the cells of the cervix and the lining of the respiratory tract.
The formation of tumors, either cancerous (malignant) or noncancerous (benign). Neoplastic cells often reproduce quickly. They may have unusual shapes and abnormal function.
As you grow older, you will have changes throughout your body, including changes in