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Ψ Definitions:
• Senescence – The state of physical decline, in which the body gradually becomes less strong and efficient with age.
• Wear & tear theory – a theory of aging that states that the human body wears out by time and exposure to the environmental stressors.
• Oxygen free radicals – atoms that have an unpaired electron due to metabolic processes.
• Antioxidants – compounds that nullify the effects of oxygen free radicals by forming a bond with their unattached oxygen electron.
• B cells – cells manufactured in the bone marrow that create antibodies for isolating and destroying invading bacteria & viruses.
• T cells – cells created in the thymus that produce substances that attack infected cells of the body.
• Average Life Expectancy – the average number of years a newborn of a particular population group is likely to live.
• Genetic clock – a theory of aging that states that a there is a regulatory mechanism in the DNA cells that regulates the aging process.
• Hayflick limit – The Hayflick limit is the number of times a human cell will divide before it stops due to the telomere reaching a critical length.
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Causes
- Wear & tear theory: humans, like machines, wear out with extended use.
- The Wear & tear theory is refuted by research that finds activity promotes a longer and healthier life
- If this theory were true it would be voided by the fact that present technology allows us to replace or mend many of our damaged parts
Cellular Accidents
- Most cells in the human body are completely replaced every few years
- Some exceptions include select cells in the eyes, ears and brain which duplicate very slowly if at all
- Cell mutations are caused by environmental chemicals, toxins, radiation, and occur in the normal processing of DNA repair.
- When genetic instructions for creating new cells are imperfect, they don’t produce exact copies of the old cells
Free Radicals
- Free radicals are highly unstable because they have unpaired electrons and are capable of splitting or tearing apart molecules
- The most damaging free radicals in humans are the oxygen free radicals which scrambles DNA molecules - This produces errors in cell maintenance and repair that can eventually cause cancer, diabetes, & arteriosclerosis.
What can we do about it?
- Research suggests that by consuming foods high in antioxidants (containing vitamin A, C, E, and the mineral selenium) we can significantly slow down this natural process
- However, high doses of antioxidants in the pill form can actually cause opposite of the desired effect by increasing oxygen free radicals
- Oxygen free radical production is inevitable in humans and is usually the side effect of normal body growth and maintenance, in reaction to infections and inflammation of the intestinal tract, and as a result of ultraviolet radiation
- Point: the gradual accumulation of free-radical damage can be an attributing factor to the aging process
The Immune System
• B cells & T cells are the two main types of (white blood) cells that the immune system uses to attack invaders. Their function is to recognize foreign or abnormal substances in the circulatory system, isolate, then destroy them.
• B cells work by creating antibodies to destroy specific invading bacteria & viruses.
• T cells work by producing a substance that attacks any kind of infected cells.
• Natural killer cells (also known as NK
cells, K cells, & killer cells) (2% of white blood cells) play a major role in the host-rejection of both
tumors & virally infected cells.
Immune System + Time
• At about age 15 the thymus gland, (which produces the T cells), begins to shrink.
• By age 50, it’s only 15% as big as it was at puberty.
Ψ Do to B, T. & NK cell reduction , are diseases like cancer more common in the older adult?
Evidence…
• People with stronger immune systems outlive their contemporaries.
• Females tend to have stronger immune systems because they have a larger thymus gland
to start with.
• Downside to having a stronger immune system: more susceptible to autoimmune diseases such as rheumatoid arthritis & lupus in which an overactive immune system attacks the person’s own body.
The Genetics of Aging
- Females tend to have stronger immune systems because they have a larger thymus gland
- Downside to having a stronger immune system: more susceptible to autoimmune diseases such as rheumatoid arthritis and lupus in which an overactive immune system attacks the person’s own body
The Genetics of Aging
- Senescence accumulates in everyone at every point of the life span with variation as to the timing, duration, and type
- One theory is that this is normal and result of a natural genetic plan apparent in everyone
- Every living species has a genetically inherent maximum life span (~120 years in humans) that is not often exceeded
The Genetic Clock
The genetic clock theory states that humans have a “genetic clock” in their brain that gradually “switches-off” the genes that promote growth and “switches on” the genes that promote aging.
The genetic clock theory is strongly supported by laboratory research that showed that even cells grown in a controlled environment usually stop multiplying after about 50 divisions (the hayflick limit).
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