Aging is the negative physiological change. As people age, their bodies go through changes that cause senescence, which is the loss of bodily processes and the inability to deal with metabolic stress. In people, changes in the body are usually followed by changes in the mind and behavior. Other changes, involving social and economic factors, also happen.
Aging starts as soon as a person turns 18 years old and is an important part of life, just like being born, growing up, and becoming an adult. Gerontology, the study of age, is mostly interested in the changes that happen to a person between the time they reach adulthood and the time they die. Finding the things that cause these changes is the point of study in gerontology. By using what you’ve learned, you can lessen the effects of some illnesses that come with getting older.
The basic biological factors that cause aging and the general health state are both biological and physiological features of aging. People get more likely to get sick as they get older, so it’s clear that changes in the person must happen that make them more sensitive to getting sick. For instance, a young adult may get better quickly from asthma, but an older person may not make it.
Physiologists have found that while people are alive, many systems, like the heart, kidneys, brain, and lungs, slowly lose their ability to do their jobs. Part of this drop is because cells are dying off in these organs, which means the person has less spare capacity. Also, the cells that are still alive in an older person might not work as well as cells that are still alive in a younger person. Sometimes, enzymes inside cells may not work as well, so chemical processes may take longer to complete. The cell may die in the end.
Effect of aging of the body systems
Heart and blood vessels
Heart diseases are the main reason people die after age 65. So, as people get older, their hearts are more likely to get cardiovascular disease. Even if there is no sickness that can be seen, the heart changes in ways that are bad as we age. Changes in structure include the loss of muscle fibers over time and the growth of fat and connective tissue. In heart muscle fibers, lipofuscin, or “age pigment,” a solid substance that doesn’t dissolve, builds up over time. These granules, which are made up of proteins and lipids, show up for the first time around age 20 and keep getting bigger until they may take up as much as 5–10% of the space of a muscle fiber by age 80.
The heart also slowly loses its ability to work as people get older. When you are 20 to 90 years old, your heart pumps about half as much blood as it used to. The effects of getting older are very different for each person. For instance, some people who are 80 years old may have heart performance that is the same as a person who is 40 years old.
The heart rate doesn’t change much with age when the person is at rest. The heart muscle fibers do not tighten as quickly in the old as they do in the young during each beat. As people get older, some molecular enzymes that make the energy needed for muscles to contract become less active. This leads to a decrease in power, or rate of work.
Even though these things happen, the heart can still do what it needs to do when it’s not sick. Your heart can speed up to double or triple the amount of blood it pumps every minute when you work out, but as you get older, its highest output drops and its spare capacity grows.
Arteriosclerosis, or narrowing of the arteries, becomes much more common with age and is often seen as a normal part of getting older. This isn’t always the case. Arteriosclerosis can happen to anyone, even teens. It is a problem that gets worse over time, and by middle age, almost everyone has some form of it. So, it is not possible to tell the difference between how blood vessels in people change with age and how they change when they are sick. Heart and blood valve changes that come with getting older can be seen in some animal species, like rats, that don’t get arteriosclerosis.
In general, as people age, their blood veins become less flexible. More fibrous tissue is being added, which makes the walls of bigger blood vessels thicker over time. As people age, the connective tissue itself gets stronger. Cross-links are made both inside the molecules of collagen, which is a main part of connective tissue, and between collagen fibers that are next to each other. These changes happen in blood vessels even when there aren’t the plaques on the artery wall that cause atherosclerosis and make it hard for blood to flow through the arteries. The slowly losing flexibility makes it harder for blood to move, which can cause blood pressure to rise. In turn, this makes the heart work harder to keep the blood flowing.
It is true that both systolic and diastolic blood pressures rise with age, but the rate of rise for systolic pressure is faster than that for diastolic pressure, which makes the pulse pressure wider. The rise in blood pressure stops in the eighth decade of life, and it may even go down a little in very old age.
In general, people who are overweight or fat have higher blood pressure than people who are a healthy weight. Since the number of obese people rises with age, at least until age 55–60, this may be one reason why blood pressure rises with age.
The digestive system
It’s more likely that people lose their teeth because they haven’t taken care of them in a long time than because they are getting older. As people get older, they lose more teeth and get more mouth diseases. However, if programs to fluoridate water are increased and child tooth decay rates are lowered, older people in the future will definitely have better teeth than older people today.
There is some evidence that the stomach produces less hydrochloric acid and other digestive enzymes as people get older. However, digestion is still pretty normal for older people. The stomach and intestines get sugar, proteins, vitamins, and minerals from food just like they do for young people. A small decrease in fat intake has been found in some studies, but it probably doesn’t have much of an effect in real life.
These results have important implications for how older people eat. There is no proof that older people need to take in more of any food, like vitamins and minerals, because their bodies can’t absorb them as well. You can avoid nutritional deficits as long as you eat a variety of foods to make sure you get enough of all the nutrients. It’s most possible that deficiencies happen because of bad eating habits, like eating too many carbs and not enough protein. People over 65 are most likely to be lacking in protein, calcium, iron, vitamin A, and thiamine (also known as vitamin B1).
The nervous system
Normal changes that happen to the brain as people age are not very noticeable. There is a small loss of neurons (nerve cells) in the brain as people get older. There are, however, a very large number of neurons, so any deaths probably don’t have a big effect on behavior. We still don’t fully understand how memory works in the brain, so we can’t say for sure that an aging brain’s neurons are to blame for memory loss in older people.
Neurons are very sensitive to not getting enough oxygen. Because of this, it is likely that cell loss and other problems seen in aging brains are not caused by getting older, but by diseases like arteriosclerosis that cut off blood flow to parts of the brain, limiting the oxygen that can reach those areas. Memory loss and cognitive decline in older people may also be caused by genetic and external factors, such as being exposed to certain poisons, smoking, or not getting enough exercise. For example, having a bigger waist and being overweight later in life are linked to cognitive loss and a thinner cerebral cortex. The cerebral cortex is mostly made up of neural cell bodies that break down over time, which is linked to memory and cognitive problems.
It’s likely that changes in the way the brain works cause responses to slow down and memory problems that are common in older people. Even small changes in the way brain cells connect to each other could cause big changes in behavior, but until we know more about how the brain works, we can’t connect behavioral changes to changes in the brain’s structure or function. It is known that because age happens slowly, the nervous system can keep working well even in people who are very old.
The way people act depends a lot on how well their senses (like the eyes and ears) and nerve endings in their skin, muscles, joints, and internal organs receive and process information. There isn’t a straight link between how sensitive sensors are and how well behavior works, though, because the normal level of stimulation is much higher than the lowest level needed to stimulate the sense glands. Some people also learn to deal with slow loss of function in one sense organ by using knowledge from other sense organs. Modern technology has also made it possible to adjust for loss of vision or hearing with glasses or hearing aids.
As people get older, they are more likely to have gross sense problems. Many of these are caused by diseases. In the United States, 25.9 percent of people aged 65 to 74 were found to be blind, but only 1.3 percent of people aged 20 to 44 were found to be blind. Out of every 1,000 people aged 65 to 74, 54.7 were functionally deaf, compared to just 5.0 out of every 1,000 people aged 25 to 34.
Vision with aging
Young children have bad visual acuity, which means they can’t tell the difference between small details. This gets better as they get older. From about the middle of your 20s to your 50s, your vision starts to get a little worse, and it gets a little worse faster after that. The use of glasses or contacts makes up for this loss easily. The pupil gets smaller as you age as well. Because of this, increasing the amount of light can make it much easier for older people to see.
As people get older, their eyes become less able to change the focus of their vision to see things close up and far away. This is called presbyopia, and it means that things far away are usually easier to see than things close up. This change in vision is caused by the lens of the eye becoming more hard over time. This mostly happens between the ages of 10 and 55. There aren’t many changes after age 55. A lot of people in their 50s get bifocal glasses to make up for this change in their bodies.
The eyes of older people are less sensitive to low light than the eyes of younger people. This means that older people have worse “night vision.” Also, older people are more sensitive to glare than younger people.
Eye diseases like glaucoma and cataracts (which cause higher intraocular pressure and cloudy lenses) become more common as people get older. However, improvements in surgery and contact lenses have made it possible for many people to have their cataracts removed and their vision restored.
Hearing
When it comes to tones of frequencies that people normally hear, hearing doesn’t change much with age. More than 50 years old, though, people gradually lose the ability to hear tones at higher levels. Tone frequencies of 10,000 cycles per second are hard for most people over the age of 65 to hear. This loss of hearing for high frequencies makes it harder to tell people apart by their sounds and understand what people are saying in a group, but it doesn’t usually get in the way of a person’s daily life. There is often a difference between readings of pure tone thresholds and the ability to understand speech. This is because listening habits and intelligence level play a big role in determining the ability to understand speech.
Other problems with senses
It’s possible for other senses to become less sensitive after age 70. Atrophy and loss of taste buds from the tongue in older people are linked to less sensitive taste. It’s hard to give an exact answer on how getting older affects the sense of smell because it’s so subjective. Smoking, being around strong smells at work, and breathing in harmful chemicals all affect how sensitive you are to smells.
Quantitatively measuring how sensitive someone is to pain is hard to do in a lab setting. There is some proof that it gets a little weaker after age 70.
Older people tend to react more slowly than younger people. It takes a little longer for reflexes to work and for nerve signals to travel through the body. People over 65 need more time to react when a light comes on than people under 65. When you need to make a choice, the slowing down that comes with getting older is worse. In some experiments, it takes longer to start a response when the instructions say, “Press the button with your left hand when the red light comes on and with your right hand when the green light comes on.” This is in contrast to experiments where the instructions say, “Push the button if either light comes on.” These and other experiments have shown that the brain, not the end organ (eye), is where responses slow down.
Skin
The main way skin changes with age is that it loses its flexibility over time. This basic change does play a part, but other things, like weather exposure and genetics, also make lines and the changes in skin color that come with getting older worse. There are fibers of the proteins elastin and collagen that make it possible for the skin to take up extra space and stay close to the structures below. A slow loss of elasticity has been seen in studies of the skin’s tiny structures. In addition, there are more cross-links between the collagen fibers, which makes the collagen network much less flexible.
System of hormones with aging
Health problems in the endocrine system have long been thought to play a big role in determining age. This is because hormones control many body systems.
Thyroxine is a hormone that the thyroid gland makes. It controls how active all of the body’s cells are. When the production of thyroxine drops, all metabolic processes slow down, and the rate of baseline metabolism drops. Metabolic metabolism is the rate at which heat is given off by cells when they are resting and not eating. Since basal metabolism slows down with age, it made sense to think that aging was caused by thyroid function going away, but this turned out to be false. Experimental studies have shown that getting older doesn’t change the thyroid gland’s ability to make thyroxine, but it does change how different parts of the body use thyroxine. We need to do more research on cellular metabolism to figure out why this is the case.
Because getting older makes it harder to deal with stress, and because the adrenal cortex (the outside part of the adrenal gland) is involved in many of these changes, many studies have been done to look at how the adrenal cortex changes as people age. There are fewer hormones released by the adrenal cortex in the blood after age 50, but the gland can still make hormones when given adrenocorticotrophic hormone (ACTH), which is a hormone released by the pituitary gland that controls the adrenal cortex’s activity. This ability has been shown to be the same in old and young.
The pituitary gland is known as the “master gland” of the body because it makes chemicals that make other endocrine glands work better, like the adrenal glands, thyroid, and ovary. So, it was once thought that the reason these glands don’t work as well as they used to is because the pituitary gland isn’t stimulating them enough. Researchers have come up with ways to measure the very small amounts of these hormones that control things in the blood, but as of now, no formal studies have been published that look at how blood levels of these hormones change with age.
Insulin is a hormone that controls how the body uses sugar and other nutrients. The pancreas is responsible for producing it. Type 2 diabetes mellitus happens when the pancreas doesn’t make enough insulin. As part of a test for diabetes, the glucose tolerance test measures how quickly sugar is taken out of the blood. As people get older, their bodies become less efficient at getting rid of extra sugar from their blood. At this point, we don’t know if this is the start of diabetes or just a normal part of getting older. People over 65 who don’t have any of the other signs of diabetes can get it. In addition, it has been shown that older people can make more insulin with extra activation, compared to diabetics. When blood sugar levels rise even a little in healthy young people, the pancreas releases more insulin. People over 65 have less sensitive pancreas, which means that a higher blood sugar level is needed to get it to work. A person over 65 can make as much insulin as a person younger if they are stimulated the most.
Men and women both lose some of their sex hormones as they age. This has been known for a long time. At menopause, a woman’s body gets rid of a lot less estrogens, which are female sex hormones. Androgens, which are male sex hormones and their breakdown products, are gradually eliminated from a man’s body between the ages of 50 and 90. This makes the idea of a male “climacteric” very unlikely.
Research based on interviews shows that sexual behavior gradually decreases in both men and women between the ages of 20 and 60. For men, the average number of sexual encounters drops from four per week when they are 20 to one per week when they are 60. Almost all men ages 20 to 45 said they were sexually active in some way. Only about 5% of men between the ages of 45 and 60 said they had lost their sexual desire.
Few large-scale studies have been done on the sexual behavior of people over 60, but stories from clinics show that at least some men are still sexually active at 90.
There are big differences between men and women when it comes to how sexually active they are. In people, the amount of sex hormones in the blood has less of an effect on sexual behavior than do psychological and social factors. Still, men have used male sex hormones for a long time and had some rough times using them to feel better. People tried to make old men younger by injecting them with animal sperm and other androgenic substances, but if they worked, they only worked for a short time. In the early 1900s, sex glands from other animals were put into people. The results were not clear, and the side effects were often very bad. Around the same time, a procedure was created to block the spermatic tubes. People thought that stopping the loss of sperm would make the sex glands make more androgenic hormones, which would make the person feel younger. All of these ideas turned out to be wrong, so that treatment was quickly given up as a way to get younger.
As people age, they lose some of their tissues. Giving anabolic steroids, which are hormones that help tissues grow, may be a big step forward in the future. The substances that are offered have a lot of bad effects, so they can’t be used all the time. Scientists in the fields of chemistry and pharmacology are still working on making new steroids that have anabolic benefits without the bad side effects.
Skeletal System in Aging
As we age, our bones lose calcium over time. Because of this, they become weaker and more likely to break, even from small falls. Fractures also take longer to heal in older people than in younger people. In recent years, hip surgery has made a lot of progress. For example, broken bones can now be fixed with metal pegs or new structures, and older people can benefit greatly from these changes.
As people get older, they are also more likely to get osteoporosis, a disease in which bones lose calcium and minerals. It happens more often in women than in men after menopause, and it’s most noticeable in the spine. One of the main signs of the disease is back pain. It can be handled by giving the person more calcium and steroid hormones at the same time.
As people get older, their joints become less mobile, and the number of people who get arthritis rises.
Physiology of breathing with Aging
Both vital capacity and the total volume of air that the lungs can hold decrease with age. Vital capacity is the total amount of air that can be released from the lungs after a maximum inhale. On the other hand, the amount of air that the lungs can’t get rid of rises. More specifically, these changes in how we breathe are caused by the chest bones becoming stiffer and the muscles that move the chest during breathing becoming weaker.
The lungs also have elastin and collagen in them, which make them stretchy. According to what was said before, the lungs become less flexible as they age because cross-links form between elastin and collagen.
How much oxygen and carbon dioxide move from the air in the lungs to the blood depends on how much blood flows through the lungs and how much air comes in and out. What makes the membranes that split air and blood in the lungs work the way they do is also important for making sure the body gets enough oxygen. As people get older, their lungs can move a little less oxygen from the air to the blood. However, this difference is only noticeable when they need a lot of oxygen, like when they are working out hard. One main reason why older people’s lungs don’t move oxygen as well as they should is that the blood flow to the air sacs in the lungs isn’t adjusted properly.
Emphysema is a lung disease in which the lungs get swollen and squishy with air. It most often happens to people between the ages of 45 and 65. In the US, the death rate from emphysema rose sharply in the middle of the 20th century and stayed high. Because smoking causes bronchitis (inflammation of the lungs), that was the main reason for the rise. Chronic obstructive pulmonary disease (COPD) is a worsening lung disease that has the signs and symptoms of both emphysema and bronchitis.
People who smoke cigarettes have much worse lung function tests than people of the same age who don’t smoke. Values for people who smoke cigarettes are about the same as values for people who don’t smoke who are 10–15 years older. It has been shown, though, that within one to two years of quitting smoking, a person’s lung performance nearly approaches that of a nonsmoker. This is true even for heavy smokers aged 50 to 60.
Nephrons with aging
The kidneys get rid of waste from the body by separating it from the blood and turning it into pee. During this process, a lot of chemicals build up in the pee, where they are more concentrated than in the blood. As people age, their kidneys lose their ability to concentrate. This means that they need more water to get rid of the same amount of waste. This decrease in the ability to focus is likely partly balanced by a decrease in the excretory load. This is because older people are less active, eat differently, and lose muscle mass. These changes in kidney function might not show up in pee volume, since amounts change a lot with age and are mostly based on how much fluid a person drinks.
Kidney function is getting worse in part because blood flow to the kidneys is slowly going down. The kidneys get a lot of extra blood—about 25% of the blood that the heart pumps every minute—so the loss of kidney function with age doesn’t usually cause trash to build up in the blood. This kind of buildup is caused by a disease that hurts the kidneys. Loss of some nephrons, which are useful parts of the kidney, and less activity of cellular enzymes cause the kidney to be less able to concentrate.
Mechanisms for regulation
Some parts of the body, like the systems that control how acidic or sugary the blood is, are enough to keep levels normal when the person is at rest, even if they are very old. But older people need more time than younger people to get back to normal levels when things go off track.
Physiologists make changes to the body and watch how fast it recovers in order to test how well the body’s control systems work. When the acidity of the blood is raised to the same level in young and old people, it returns to normal in 6–8 hours for the young, but it takes 18–24 hours for the old. In the same way, older people take longer than younger people to get back to their fasting levels after being given sugar intravenously orally. People over 65 also have a weaker reaction to insulin, which speeds up the removal of sugar from the blood.
The body’s systems for adapting to changes in temperature are not as good in older people as they are in younger people. Because of this, older people might like temperatures that are more even and a little higher than younger people. The old are more likely to pass out from heat prostration in hot weather, and the risk of this condition rises with age.
One of the stresses on the body that comes with daily life is exercise. When taken in the right amounts, it is a good way to keep your body strong. Several studies have shown that adults who are physically active are less likely to get cardiovascular disease than adults who are not physically active.
As people get older, their ability to do physical work gets worse over time. As people get older, their muscles lose strength, but muscles that are used more throughout life lose less power than muscles that are not used. In this way, a loss of muscle strength may be caused by not using the muscles enough.
Older people can’t do as much work as they used to because their bodies can’t get enough air to their working muscles. For young people, getting more oxygen is mostly done by speeding up the heart rate. Young adults can get their heart rate up to over 200 beats per minute when they are working hard, but older people can only get it up to about 150 beats per minute. Additionally, older people have a harder time getting oxygen from their lungs to their blood when they work out hard.
When older people do less than their maximum amount of exercise, their blood pressure, heart rate, and breathing rate rise more than when younger people do the same amount of exercise. This means that the same amount of work causes older people to be more physiologically stressed than younger people. Also, it takes longer for older people to get their blood pressure, heart rate, and breathing back to normal levels.
Aging too quickly
Progeria is a very uncommon disease that starts in early childhood and looks a lot like normal aging. It causes hair loss, thin skin, blood vessels to show up more on the head, and vascular disease. It is common for children with progeria to look old, and they rarely live past the ages of 15 to 18. Heart sickness is generally what kills people.
The disease doesn’t happen very often. Even though these patients seem to be getting older faster than they should, they don’t seem to be changing any other ways, except for getting heart disease earlier. A lot of tests that check their mental and physical health give results that are normal for their age. It is not likely that the child with progeria is just getting older faster. It is more accurate to think of progeria as a rare disease that looks a bit like aging.
The mental effects of getting older
Short-term memory and brain problems are the most noticeable psychological effects of getting older. These problems make thinking and responding more slowly. Some of these changes may happen naturally as people age, but study shows that long-term lifestyle factors, like food, exercise, and sleep habits, and disease play a big role. For instance, aerobic exercise, which increases blood flow and oxygen supply to the brain and body, has been linked to better brain function in older people. On the other hand, long-term illnesses, depression, and sleep issues all have bad effects on memory. Depression, for instance, is linked to fewer synapses (connections between neurons) in the brain, which makes it harder for older people to remember things and think clearly. Also, both not getting enough sleep and getting too much sleep can affect memory. For example, older people who sleep more than nine hours a night have a higher risk of dementia.
Older people do worse on standard tests of “intelligence” because their thinking skills get worse over time. However, when they have all the time in the world to do tests that don’t depend too much on school skills, they do just a little worse than young adults. When it comes to tests that are based on language, general knowledge, and well-practiced tasks, age differences don’t matter much. Learning experiments have shown that older people can learn new things and remember them just as well as younger people, even though they do it more slowly. The difference in how people learn based on their age gets bigger as the subject gets harder.
As people get older, they tend to be more careful and rigid in how they act, and they pull away from social contacts. It’s possible that these patterns of behavior aren’t really caused by getting older, but by social norms and expectations. Many people who “age successfully” make conscious efforts to keep their minds sharp by continuing to learn new things and making new friends in younger age groups.
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