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“And now here is my secret, a very simple secret: It is only with the heart that one can see rightly; what is essential is invisible to the eye.”
Antoine de Saint-Exupéry, The Little Prince
“There are no lungs like the ones that breathe poetry.”
D. Antoinette Foy
"Your gut is always right.
Sharon Osbourne
Changes in the Cardiovascular System
There are many changes in the cardiovascular system as we age, but it is in many cases unclear whether these changes are the result of normal aging or the result of disease. Blood pressure, for example, tends to increase with age. It is thought that natural, age-related stiffening of the blood vessels may be the reason. However, an age-associated increase in blood pressure is not found in individuals who live in isolated and less technologically developed societies or in people who grow old in a special environment such as a mental institution, suggesting that there may be environmental components, as well.
In the heart itself, disease is increasingly common with age. The cells responsible for producing heartbeats become infiltrated with connective tissue and fat. Similar but less dramatic changes occur in other parts of the heart’s electrical conducting system. The elastic properties of the heart muscle are altered with age and the heart contracts less efficiently, including a prolonged contraction time, decreased response to medications intended to stimulate the heart and increased resistance to electrical stimulation.
The aging heart also responds less efficiently to stresses. The maximum heart rate decreases in a linear fashion and is typically estimated by subtracting a person’s age from 220. The resting heart rate and the amount of blood pumped by the heart (the cardiac output) do not change. When it is working hard, the cardiac output may increase even though there is a decrease in the maximum heart rate because the amount of blood pumped with each beat, the stroke volume, increases to compensate for the decreased heart rate. Following stress, it takes longer for an older person’s heart rate and blood pressure to return to resting levels.
Changes in the blood vessels also occur with age. Irregularities in size and shape develop in the cells that line blood vessels and the layers in the blood vessel wall become thickened with connective tissue. The large arteries increase in size and thickness. Blood flow to various organs is decreased, dropping by 50 percent in the kidney and by 15 to 20 percent in the brain.
Changes in the Respiratory System
Natural changes in the respiratory system decrease lung function and increase the risk of pulmonary disease over time. However, some of these changes can be mitigated by regular exercise.
The trachea, large airways, and small end units of the airway expand as we age. Counterintuitively, this decreases the surface area of the lung while increasing lung volume. These changes are exacerbated by reduced lung elasticity and the collapse of small airways. The general effect of all this is that we take in more air but also exhale less fully. The amount of residual air left in the lungs after each breath increases from about 20 percent of the total lung capacity at age 20 to 35 percent at age 60. In addition, the end of the ribs calcifies to the sternum, making the chest wall more rigid and increasing the workload of the respiratory muscles.
Importantly, the lungs also become less efficient at transferring oxygen to the bloodstream. This decrease in oxygenation is largely due to a mismatch between those parts of the lung that are aerated and the parts receiving blood flow. The parts of the lung with the greatest blood flow are also the parts that tend to collapse with age, causing the mismatch. Carbon monoxide diffusion capacity, a measure of gas exchange capability, also decreases with age, but the contribution of this change to the decreased arterial oxygenation is unknown. Maximum oxygen consumption (VO2 max), a measure of overall cardiopulmonary function, tends to decline with age but also is influenced substantially by exercise. Endurance training can increase the lung capacity and functioning even of sedentary older people.
Changes in the Gastrointestinal System
Overall, the gastrointestinal tract (essentially a continuous tube from the mouth to the anus) shows fewer age-associated changes than other body systems. In particular the lining of the gut, whose surface is the size of two tennis courts, maintains an extraordinary capacity for regenerating itself throughout the course of life.
Mouth and Teeth
Natural, age-related changes do not generally lead to the loss of teeth; poor dental hygiene is a much more important factor. Cavities or periodontal (gum) disease are the typical causes of tooth loss, and both can be mitigated by good dental care. There are age-related patterns in the location of cavities as we age, with an increased frequency of root cavities and cavities around sites of previous dental work.
Older people who have lost teeth often experience dietary changes that can increase the likelihood of malnutrition. False teeth reduce taste sensation and do not completely restore normal chewing ability. Older people without teeth also tend to show alterations in swallowing. Even with a full set of teeth, older people do not chew as efficiently as younger people and tend to swallow larger pieces of food. Swallowing can take an older person 50 to 100 percent longer than a younger person, probably because of subtle changes in the swallowing mechanism.
Esophagus and Stomach
Older people experience higher rates of problems with esophageal motility (the movement of food down the esophagus), but these problems appear to stem from diseases such as diabetes mellitus, central nervous system disorders, or neuropathies rather than aging. In the stomach, aging is associated with a thinning of the stomach lining and smooth muscle and increased white blood cells and aggregations of lymphoid tissue in the gastric wall, but these changes do not appear to affect the movement of food through the stomach. While the secretion of stomach acid decreases with age, a complete loss of stomach acid signifies disease rather than normal aging.
Intestine
Although changes occur with aging in both the small and large intestine, it is the changes in the large intestine that have the greatest impact on the quality of life.
The lining of the small intestine atrophies slightly with age. When eating, older people show reduced intestinal muscle contractions, although there seems to be no difference in the speed with which substances are transported through the small intestine when a person is not actively eating. The intestines’ ability to absorb foods and drugs generally does not change significantly. Older people tend to absorb highly fat-soluble compounds, such as vitamin A faster and may absorb and metabolize some sugars, calcium, and iron differently. The activity of some enzymes such as lactase, which helps us digest some sugars (particularly those found in dairy products) appears to decline with age, but the levels of other enzymes remain normal. The absorption of fat may change, but this may relate more to changes in the pancreas than to changes in the intestine.
There are more impactful changes in the large intestine. Here the lining atrophies, blood vessel abnormalities become more common and we experience changes in the muscle layer. These factors contribute to an increased likelihood of diverticuli, small outpouching in the lining of the large intestine. Approximately thirty percent of people over age 60 have diverticuli. The condition results from increased pressure inside the intestine that is caused by a disorder of intestinal muscle function. Weakness in the bowel wall near blood vessels is another contributing factor.
Constipation is also a common ailment of old age because the food transport in the large intestine slows down and subtle changes occur in the coordination of large intestinal muscle contractions. The number of certain narcotic (opiate) receptors increases as we age and this increase may lead to significant constipation when an older person takes narcotic medications. Mild dehydration compounds the problem.
The 100 trillion bacteria living in the gut, called the microbiome, are increasingly being studied for their importance in maintaining health and protecting against or producing illnesses such as cancer, inflammatory bowel disease, mental health concerns, and obesity. The microbiome interacts powerfully with the body’s immune system. Recent studies have noted shifts in the microbiome over a person’s life that may be detrimental: beneficial organisms seem to decline while pathological species increase.
Liver and Pancreas
The liver and pancreas have a variety of functions, including detoxification, hormone production, and digestion. Broadly speaking, these organs maintain adequate function throughout life. Total failure is due to disease rather than aging.
The liver plays an important role in metabolizing drugs and other compounds, and the efficiency of this process declines with age. The liver also decreases in size with age and its shape adjusts to the contours of adjacent organs. Aged liver cells contain increased lipofuscin pigment produced by the oxidation of fatty acids, which may be an indicator of cell membrane damage. Liver cells also increase in volume and show reductions in several important cellular functions, such as chemical processing and energy production. Overall, older livers show a reduced ability for regeneration and repair.
In the pancreas, secretion of the digestive enzyme trypsin moderately decreases with age, but other processes appear unchanged. The most common structural change in the pancreas is atrophy of the acinar cells that produce digestive juices. Some reports suggest that older people have more scar tissue in the lobes of the pancreas, but the impact of this is not known.
