Body Parts That Continue to Grow With Age

The body changes with aging because changes occur in individual cells and in whole organs. These changes result in changes in function and in appearance.

As cells age, they function less well. Eventually, old cells must die, which is a normal part of the body's functioning.

Old cells sometimes die because they are programmed to do so. The genes of cells program a process that, when triggered, results in death of the cell. This programmed death, called apoptosis, is a kind of cell suicide. The aging of a cell is one trigger. Old cells must die to make room for new cells. Other triggers include an excess number of cells and possibly damage to a cell.

Old cells also die because they can divide only a limited number of times. This limit is programmed by genes. When a cell can no longer divide, it grows larger, exists for a while, then dies. The mechanism that limits cell division involves a structure called a telomere. Telomeres are used to move the cell's genetic material in preparation for cell division. Every time a cell divides, the telomeres shorten a bit. Eventually, the telomeres become so short that the cell can no longer divide. When a cell stops dividing, it is called senescence.

Sometimes damage to a cell directly causes its death. Cells may be damaged by harmful substances, such as radiation, sunlight, and chemotherapy drugs. Cells may also be damaged by certain by-products of their own normal activities. These by-products, called free radicals, are given off when cells produce energy.

How well organs function depends on how well the cells within them function. Older cells function less well. Also, in some organs, cells die and are not replaced, so the number of cells decreases. The number of cells in the testes, ovaries, liver, and kidneys decreases markedly as the body ages. When the number of cells becomes too low, an organ cannot function normally. Thus, most organs function less well as people age. However, not all organs lose a large number of cells. The brain is one example. Healthy older people do not lose many brain cells. Substantial losses occur mainly in people who have had a stroke Overview of Stroke A stroke occurs when an artery to the brain becomes blocked or ruptures, resulting in death of an area of brain tissue due to loss of its blood supply (cerebral infarction) and symptoms that... read more or who have a disorder that causes the progressive loss of nerve cells (neurodegenerative disorders), such as Alzheimer disease Alzheimer Disease Alzheimer disease is a progressive loss of mental function, characterized by degeneration of brain tissue, including loss of nerve cells, the accumulation of an abnormal protein called beta-amyloid... read more or Parkinson disease Parkinson Disease (PD) Parkinson disease is a slowly progressive degenerative disorder of specific areas of the brain. It is characterized by tremor when muscles are at rest (resting tremor), increased muscle tone... read more .

Often, the first signs of aging involve the musculoskeletal system. The eyes, followed by the ears, begin to change early in mid-life. Most internal functions also decline with aging. Most bodily functions peak shortly before age 30 and then begin a gradual but continuous decline. However, even with this decline, most functions remain adequate because most organs start with considerably more functional capacity than the body needs (functional reserve). For example, if half the liver is destroyed, the remaining tissue is more than enough to maintain normal function. Thus, disorders, rather than normal aging, usually account for most of the loss of function in old age.

Even though most functions remain adequate, the decline in function means that older people are less able to handle various stresses, including strenuous physical activity, extreme temperature changes in the environment, and disorders. This decline also means that older people are more likely to experience side effects from drugs. Some organs are more likely to malfunction under stress than others. These organs include the heart and blood vessels, the urinary organs (such as the kidneys), and the brain.

Bones become less dense partly because they contain less calcium (which gives bones strength). The amount of calcium decreases because the body absorbs less calcium from foods. Also, levels of vitamin D, which helps the body use calcium, decrease slightly. Certain bones are weakened more than others. Those most affected include the end of the thighbone (femur) at the hip, the ends of the arm bones (radius and ulna) at the wrist, and the bones of the spine (vertebrae).

Changes in vertebrae at the top of the spine cause the head to tip forward, compressing the throat. As a result, swallowing is more difficult, and choking is more likely. The vertebrae become less dense and the cushions of tissue (disks) between them lose fluid and become thinner, making the spine shorter. Thus, older people become shorter.

Ligaments, which bind joints together, and tendons, which bind muscle to bone, tend to become less elastic, making joints feel tight or stiff. These tissues also weaken. Thus, most people become less flexible. Ligaments and tendons tend to tear more easily, and when they tear, they heal more slowly. These changes occur because the cells that maintain ligaments and tendons become less active.

The amount of muscle tissue (muscle mass) and muscle strength tend to decrease beginning around age 30 and continuing throughout life. Some of the decrease is caused by physical inactivity and decreasing levels of growth hormone and testosterone, which stimulate muscle development. Also, muscles cannot contract as quickly because more fast-contracting (fast-twitch) muscle fibers are lost than slow-contracting (slow-twitch) muscle fibers. However, aging's effects reduce muscle mass and strength by no more than about 10 to 15% during an adult's lifetime. In the absence of disease, most of the loss beyond that 10 to 15% is preventable with regular exercise. More severe muscle loss (called sarcopenia, which literally means loss of flesh) results from disease or extreme inactivity, not from aging alone.

Most older people retain enough muscle mass and strength for all necessary tasks. Many older people remain strong athletes. They compete in sports and enjoy vigorous physical activity. However, even the fittest notice some decline as they age.

Regular exercise Exercise in Older Adults At least 75% of people over age 65 do not exercise at recommended levels despite the known health benefits of exercise including Longer survival Improved quality of life (for example, endurance... read more to strengthen muscles (resistance training) can partially overcome or significantly delay loss of muscle mass and strength. In muscle-strengthening exercise, muscles contract against resistance provided by gravity (as in sit-ups or push-ups), weights, or rubber bands. If this type of exercise is done regularly, even people who have never exercised can increase muscle mass and strength. Conversely, physical inactivity, especially bed rest during an illness, can greatly accelerate the loss. During periods of inactivity, older people lose muscle mass and strength much more quickly than younger people do. For example, to make up for the muscle mass lost during each day of strict bed rest, people may need to exercise for up to 2 weeks.

By age 75, the percentage of body fat typically doubles compared with what it was during young adulthood. Too much body fat can increase the risk of health problems, such as diabetes Diabetes Mellitus (DM) and Disorders of Blood Sugar Metabolism . The distribution of fat also changes, changing the shape of the torso. A healthy diet and regular exercise can help older people minimize increases in body fat.

As people age, the following occur:

• The lens stiffens, making focusing on close objects harder.

• The lens becomes denser, making seeing in dim light harder.

• The pupil reacts more slowly to changes in light.

• The lens yellows, changing the way colors are perceived.

• The number of nerve cells decrease, impairing depth perception.

• The eyes produce less fluid, making them feel dry.

A change in vision is often the first undeniable sign of aging.

Changes in the lenses of the eye can cause or contribute to the following:

• Loss of near vision: During their 40s, most people notice that seeing objects closer than 2 feet becomes difficult. This change in vision, called presbyopia Causes , occurs because the lens in the eye stiffens. Normally, the lens changes its shape to help the eye focus. A stiffer lens makes focusing on close objects harder. Ultimately, almost everyone gets presbyopia and needs magnifying reading glasses. People who need glasses to see distant objects may need to wear bifocals or glasses with variable-focus lenses.

• Need for brighter light: As people continue to age, seeing in dim light becomes more difficult because the lens tends to become less transparent. A denser lens means that less light passes through to the retina at the back of the eye. Also, the retina, which contains the cells that sense light, becomes less sensitive. So for reading, brighter light is needed. On average, 60-year-olds need 3 times more light to read than 20-year-olds.

• Changes in color perception: Colors are perceived differently, partly because the lens tends to yellow with aging. Colors may look less bright and contrasts between different colors may be more difficult to see. Blues may look more gray, and blue print or background may look washed out. These changes are insignificant for most people. However, older people may have trouble reading black letters printed on a blue background or reading blue letters.

The pupil of the eye reacts more slowly to changes in light. The pupil widens and narrows to let more or less light in, depending on the brightness of the surroundings. A slow-reacting pupil means that older people may be unable to see when they first enter a dark room. Or they may be temporarily blinded when they enter a brightly lit area. Older people may also become more sensitive to glare Glare and Halos A number of other symptoms and problems can affect the eyes, including changes in the appearance of the eyes, color blindness, dry eyes, glare and halos, impaired depth perception, itchy eyes... read more . However, increased sensitivity to glare is often due to darkened areas in the lens or to cataracts Cataract A cataract is a clouding (opacity) of the lens of the eye that causes a progressive, painless loss of vision. Vision may be blurred, contrast may be lost, and halos may be visible around lights... read more .

Fine details, including differences in shades and tones, become more difficult to discern. The reason is probably a decrease in the number of nerve cells that transmit visual signals from the eyes to the brain. This change affects the way depth is perceived, and judging distances becomes more difficult.

The appearance of the eyes changes in several ways:

• The whites (sclera) of the eyes may turn slightly yellow or brown. This change results from many years of exposure to ultraviolet light, wind, and dust.

• Random splotches of color may appear in the whites of the eyes, particularly in people with a dark complexion.

• A gray-white ring (arcus senilis) may appear on the surface of the eye. The ring is made of calcium and cholesterol salts. It does not affect vision.

• The eye may appear to sink into the head because the amount of fat around the eye decreases.

It is important to see a doctor to determine whether hearing loss is due to cerumen (ear wax) impaction because this is easily treated.

As people age, hearing high-pitched sounds becomes more difficult. This change is considered age-associated hearing loss (presbycusis). For example, violin music may sound less bright.

The most frustrating consequence of presbycusis is that words become harder to understand. As a result, older people may think that other people are mumbling. Even when other people speak more loudly, older people still have difficulty understanding the words. The reason is that most consonants (such as k, t, s, p, and ch) are high-pitched, and consonants are the sounds that help people identify words. Because vowels are lower-pitched sounds, they are easier to hear. So older people may hear "Ell me exaly wha you wan oo ee," rather than "Tell me exactly what you want to keep." To help, other people need to articulate consonants more clearly, rather than simply speak louder. Understanding what women and children say may be more difficult than understanding what men say because most women and children have higher-pitched voices. Gradually, hearing lower pitches also becomes more difficult.

Many older people have more trouble hearing in loud places or in groups because of the background noise.

Thick hairs may grow out of the ears.

(See also Effects of Aging on the Mouth and Teeth Effects of Aging on the Mouth and Teeth With aging, taste sensation may diminish. Older people may find their food tastes bland so, for more taste, they may add abundant seasonings (particularly salt, which is harmful for some people)... read more and Effects of Aging on the Ears, Nose, and Throat Effects of Aging on the Ears, Nose, and Throat Aging affects the function of the ears, nose, and throat in varying degrees. The effects of aging result from many factors such as wear and tear caused by overuse of the voice, exposure to loud... read more .)

Generally, when people are in their 50s, the ability to taste and smell starts to gradually diminish. Both senses are needed to enjoy the full range of flavors in food. The tongue can identify only five basic tastes: sweet, sour, bitter, salt, and a taste called umami (commonly described as meaty or savory). The sense of smell is needed to distinguish more subtle and complex flavors (such as raspberry).

As people age, taste buds on the tongue decrease in sensitivity. This change affects tasting sweet and salt more than bitter and sour. The ability to smell diminishes because the lining of the nose becomes thinner and drier and the nerve endings in the nose deteriorate. However, the change is slight, usually affecting only subtle smells. Because of these changes, many foods tend to taste bitter, and foods with subtle smells may taste bland.

With aging, the nose tends to lengthen and enlarge, and the tip tends to droop.

Thick hairs may grow in the nose and on the upper lip and chin.

The skin tends to become thinner, less elastic, drier, and finely wrinkled. However, exposure to sunlight over the years greatly contributes to wrinkling and to making the skin rough and blotchy. People who have avoided exposure to sunlight often look much younger than their age.

The skin changes partly because collagen (a tough, fibrous tissue that makes skin strong) and elastin (which makes skin flexible) become chemically changed and less flexible; also, the aging body produces less collagen and elastin. As a result, the skin tears more easily.

The fat layer under the skin thins. This layer acts as a cushion for the skin, helping protect and support it. The fat layer also helps conserve body heat. When the layer thins, wrinkles are more likely to develop, and tolerance for cold decreases.

The number of nerve endings in the skin decreases. As a result, people become less sensitive to pain, temperature, and pressure, and injuries may be more likely.

The number of sweat glands and blood vessels decreases, and blood flow in the deep layers of the skin decreases. As a result, the body is less able to move heat from inside the body through blood vessels to the surface of the body. Less heat leaves the body, and the body cannot cool itself as well. Thus, the risk of heat-related disorders, such as heatstroke, is increased. Also, when blood flow is decreased, the skin tends to heal more slowly.

The number of pigment-producing cells (melanocytes) decreases. As a result, the skin has less protection against ultraviolet (UV) radiation, such as that from sunlight. Large, brown spots (age spots) develop on skin that has been exposed to sunlight, perhaps because the skin is less able to remove waste products.

The number of nerve cells in the brain typically decreases. However, the brain can partly compensate for this loss in several ways:

• As cells are lost, new connections are made between the remaining nerve cells.

• New nerve cells may form in some areas of the brain, even during old age.

• The brain has more cells than it needs to do most activities—a characteristic called redundancy.

Levels of the chemical substances involved in sending messages in the brain tend to decrease, but some increase. Nerve cells may lose some of their receptors for these chemical messages. Blood flow to the brain decreases. Because of these age-related changes, the brain may function slightly less well. Older people may react and do tasks somewhat more slowly, but given time, they do these things accurately. Some mental functions—such as vocabulary, short-term memory, the ability to learn new material, and the ability to recall words—may be subtly reduced after age 70.

After about age 60, the number of cells in the spinal cord begins to decrease. Usually, this change does not affect strength or sensation.

As people age, nerves may conduct signals more slowly. Usually, this change is so minimal that people do not notice it. Also, nerves may repair themselves more slowly and incompletely. Therefore, in older people with damaged nerves, sensation and strength may be decreased.

The heart and blood vessels become stiffer. The heart fills with blood more slowly. The stiffer arteries are less able to expand when more blood is pumped through them. Thus, blood pressure tends to increase.

Despite these changes, a normal older heart functions well. Differences between young and old hearts become apparent only when the heart has to work hard and pump more blood—for example, during exercise or an illness. An older heart cannot speed up as quickly or pump as fast or as much blood as a younger heart. Thus, older athletes are not able to perform as well as younger athletes. However, regular aerobic exercise can improve athletic performance in older people.

The muscles used in breathing, the diaphragm and muscles between the ribs, tend to weaken. The number of air sacs (alveoli) and capillaries in the lungs decreases. Thus, slightly less oxygen is absorbed from air that is breathed in. The lungs become less elastic. In people who do not smoke or have a lung disorder, these changes do not affect ordinary daily activities, but these changes may make exercising more difficult. Breathing at high altitudes (where there is less oxygen) may also be harder.

The lungs become less able to fight infection, partly because the cells that sweep debris containing microorganisms out of the airways are less able to do so. Cough, which also helps clear the lungs, tends to be weaker.

Overall, the digestive system is less affected by aging than most other parts of the body. The muscles of the esophagus contract less forcefully, but movement of food through the esophagus is not affected. Food is emptied from the stomach slightly more slowly, and the stomach cannot hold as much food because it is less elastic. But in most people, these changes are too slight to be noticed.

The liver tends to become smaller because the number of cells decreases. Less blood flows through it, and liver enzymes that help the body process drugs and other substances work less efficiently. As a result, the liver may be slightly less able to help remove drugs and other substances from the body. And the effects of drugs—intended and unintended—last longer.

The kidneys tend to become smaller because the number of cells decreases. Less blood flows through the kidneys, and at about age 30, they begin to filter blood less well. As years pass, they may remove waste products from the blood less well. They may excrete too much water and too little salt, making dehydration more likely. Nonetheless, they almost always function well enough to meet the body's needs.

Certain changes in the urinary tract may make controlling urination more difficult:

• The maximum volume of urine that the bladder can hold decreases. Thus, older people may need to urinate more often.

• The bladder muscles may contract unpredictably (become overactive), regardless of whether people need to urinate.

• The bladder muscles weaken. As a result, they cannot empty the bladder as well, and more urine is left in the bladder after urination.

• The muscle that controls the passage of urine out of the body (urinary sphincter) is less able to close tightly and prevent leakage. Thus, older people have more difficulty postponing urination.

In women, the urethra (the tube through which urine leaves the body) shortens, and its lining becomes thinner. The decrease in the estrogen level that occurs with menopause may contribute to this and other changes in the urinary tract.

The effects of aging on sex hormone levels are more obvious in women than in men. In women, most of these effects are related to menopause Menopause Menopause is the permanent end of menstrual periods and thus of fertility. For up to several years before and just after menopause, estrogen levels fluctuate widely, periods become irregular... read more , when the levels of female hormones (particularly estrogen) decrease dramatically, menstrual periods end permanently, and pregnancy is no longer possible. The decrease in female hormone levels causes the ovaries and uterus to shrink. The tissues of the vagina become thinner, drier, and less elastic (a condition called atrophic vaginitis). In severe cases, these changes can lead to itching, bleeding, pain during intercourse, and a need to urinate immediately (urinary urgency Urinary Urgency A compelling need to urinate (urgency), which may feel like almost constant painful straining (tenesmus), can be caused by bladder irritation. Uncontrolled loss of urine ( incontinence) may... read more ).

The breasts become less firm and more fibrous, and they tend to sag. These changes make finding lumps in the breasts more difficult.

Some of the changes that begin at menopause (such as lower hormone levels and vaginal dryness) may interfere with sexual activity. However, for most women, aging does not greatly detract from enjoyment of sexual activity. Not having to worry about becoming pregnant may enhance sexual activity and enjoyment.

The levels and activity of some hormones, produced by endocrine glands, decrease.

• Growth hormone levels decrease, leading to decreased muscle mass.

• Aldosterone levels decrease, making dehydration more likely. This hormone signals the body to retain salt and therefore water.

• Insulin, which helps control the sugar (glucose) level in blood, is less effective, and less insulin may be produced. Insulin enables sugar to move from the blood into cells, where it can be converted to energy. The changes in insulin mean that the sugar level increases more after a large meal and takes longer to return to normal.

• Cancer is more common among older people.

• Vaccines tend to be less protective in older people, but influenza, pneumonia, and shingles vaccines are essential and offer some protection.

• Some infections, such as pneumonia and influenza, are more common among older people and result in death more often.

• Allergy symptoms may become less severe.

As the immune system slows down, autoimmune disorders become less common.

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