Not all organs are the same age! ( Courtesy: Sri S S Venkatramanani)
R V Rao
Rajaram Krishnamurthy
Really, the age of organs are not uniform. Do you think so? No, not all organs of the body are of the same age. While every organ shares the same chronological age (the number of years you have been alive), their biological ages vary significantly based on their unique cellular turnover rates, genetics, and lifestyle factors.
Each organ has a unique aging process: some tissues, like the lining of the gut, regenerate very rapidly, while others, like certain parts of the brain and heart, barely renew at all.
Variations in Organ Ages
- Fastest Turnover: Cells lining the stomach and intestines replace themselves every few days. The epidermis (outer layer of skin) renews roughly every two to four weeks, and red blood cells last about 120 days.
- Slower Turnover: The liver has a high regenerative capacity and its cells turn over on average about every 6-12 months. The entire skeleton is remodeled over approximately 10 years.
- Slowest Turnover: Neurons in most parts of the brain and the heart muscle cells have very low turnover rates and are largely the same age as the person's chronological age. The cells in the center of the eye lens last an entire lifetime.
Biological vs. Chronological Age
Recent research using blood protein analysis and machine learning has confirmed that individual organs can age at different rates from the body as a whole, a concept known as "organ age clocks".
- A person with a chronological age of 40 might have a heart that functions like a 50-year-olds, while their brain functions like a 30-year-old's.
- Accelerated aging in a specific organ is linked to a higher risk of developing diseases related to that organ and an increased mortality risk.
This difference in aging rates means the body does not decline in unison, and lifestyle choices (diet, exercise, smoking, alcohol consumption) can influence how quickly individual organs age.
Organs have a reserve ability to function beyond the usual needs. For example, the heart of a 20-year-old is capable of pumping about 10 times the amount of blood that is actually needed to keep the body alive. After age 30, an average of 1% of this reserve is lost each year.
The biggest changes in organ reserve occur in the heart, lungs, and kidneys. The amount of reserve lost varies between people and between different organs in a single person.
These changes appear slowly and over a long period. When an organ is worked harder than usual, it may not be able to increase function. Sudden heart failure or other problems can develop when the body is worked harder than usual. Things that produce an extra workload (body stressors) include the following:
Illness
Medicines
Overactive thyroid gland
Significant life changes
Sudden increased physical demands on the body, such as a change in activity or exposure to a higher altitude
Loss of reserve also makes it harder to restore balance (equilibrium) in the body. Medicines are removed from the body by the kidneys and liver at a slower rate. Lower doses of medicines may be needed, and side effects become more common. Recovery from some illnesses may be less than 100%, leading to more and more disability.
Side effects of medicine can mimic the symptoms of many diseases, so it is easy to mistake a medicine reaction for an illness. Some medicines have entirely different side effects in the elderly than in younger people.
AGING THEORY
No one knows how and why people change as they get older. Some theories claim that aging is caused by injuries from ultraviolet light over time, wear and tear on the body, or byproducts of metabolism. Other theories view aging as a predetermined process controlled by genes.
No single known process can explain all the changes of aging. Aging 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
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 sex organs (such as the breasts and ovaries). Bones become thinner and more likely to break with minor trauma.
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 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.
Hyperplasia:
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). Ongoing research suggests that tissues previously thought to have limited or no ability to regenerate - nerves, skeletal muscle, heart muscle, and the lens of the eye - may have some regenerative ability. But in most cases we have not yet learned how to harness this ability for medical treatment.
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 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 your:
Hormone production
Immunity
Skin
Sleep
Bones, muscles, and joints
Breasts
Face
Reproductive system - female
Reproductive system - male
Heart and blood vessels
Kidneys
Lungs
Nervous system
Baynes JW. Aging. In: Baynes JW, Dominiczak MH, eds. Medical Biochemistry. 6th ed. Philadelphia,
KR IRS 181225
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