Medical Health Encyclopedia

Aging changes in organs - tissue - cells

AGING THEORY

No one really knows how and why people change as they get older. Some theories claim that aging is caused by accumulated injuries from ultraviolet light, wear and tear on the body, by-products of metabolism, and so on. Other theories view aging as a predetermined, genetically-controlled process.

However, no theory sufficiently explains all the changes of the aging process. Aging is a complex and varied process that varies in how it affects different people and even different organs. Most gerontologists (people who study aging) feel that aging is the cumulative effect of the interaction of many lifelong influences. These influences include heredity, environment, cultural influences, diet, exercise and leisure, past illnesses, and many other factors.

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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.

Although some changes typically occur with aging, they occur at different rates and to different extents. There is no reliable way to predict specifically how you will age.

TERMS

• ATROPHY
  • Cells shrink. If enough cells decrease in size, the entire organ atrophies. This is often a normal aging change and can occur in any tissue. It is most common in skeletal muscle, the heart, the brain, and the secondary 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.
• HYPERTROPHY
  • Cells enlarge. This size increase is caused by an increase in cellular proteins, such as the cell wall and internal cell structures, not an increase in the cell's fluid.
  • When some cells atrophy, others may hypertrophy in an attempt to compensate for loss of cell mass.
• HYPERPLASIA
  • The number of cells increases. There is an increased rate of cell division.
  • Hyperplasia usually occurs in an attempt to compensate for loss of cells. It allows some organs and tissues to regenerate, including the skin, the lining of the intestines, the liver and the 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 seldom or never regenerate include nerves, skeletal muscle, heart muscle, and the lens of the eye. When injured, these tissues are replaced with scar tissue.
• DYSPLASIA
  • 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.
• NEOPLASIA
  • The formation of cancerous, malignant tumors. This may be an extension of the processes causing hyperplasia and hypertrophy.
  • Neoplastic cells reproduce rapidly. They may have unusual shapes and abnormal function.