Aging and the Body Systems 

Article by Tammy Petersen

 

Cardiovascular System

The main function of this system is the internal transport of cells and dissolved materials, including nutrients, wastes, and gases.

The main function of this system is the internal transport of cells and dissolved materials, including nutrients, wastes, and gases.

Differences between cardiovascular functioning in older and younger persons have been extensively quantified. However, interactions between age, disease, and lifestyle are often overlooked. Whether the high prevalence of cardiovascular disorders such as hypertension, coronary artery disease, and heart failure is due to an aging process or whether these disorders merely occur more frequently in elderly persons because of a longer exposure to risk is not yet established. It is reasonable to ascertain, however, that the capabilities of the cardiovascular system gradually decline with age.

Not so fun fact:

The 25% reduction in maximum cardiac output that occurs with aging is completely due to the age-associated reduction in maximum heart rate.

Fun fact:

Older people in good physical condition can match or exceed the aerobic capacity of unconditioned younger people.

 Age-related changes in the blood include a decrease in the volume of packed red blood cells or constriction or blockage of peripheral veins by a blood clot. If the clot becomes detached, it might pass through the heart and become wedged in a small artery (most often in the lungs) causing a pulmonary embolism.

Age-related changes in blood vessels are often related to arteriosclerosis, a thickening and toughening of arterial walls in which the walls become less tolerant of sudden increases in pressure. This can lead to an aneurysm or rupture of the vessel causing a stroke, heart attack, or massive blood loss depending on the vessel involved. Additionally, calcium deposits can form on weakened vascular walls which increases the risk of a stroke or heart attack. Blood clots can form as plaque deposits. And, there might be pooling of blood in the veins in the legs because valves are not working effectively.

Age-related changes in the heart include a reduction in maximum cardiac output, changes in the activities of nodal and conductive fibers, a reduction in the elasticity of the heart’s fibrous tissues, progressive atherosclerosis (fatty buildup or plaques) that can restrict coronary circulation, and replacement of damaged cardiac muscle fibers by scar tissue. With age, the heart can atrophy, remain unchanged, or develop moderate or marked hypertrophy. Atrophy usually coincides with various wasting diseases and is not observed during aging in healthy persons. A modest increase in left ventricular wall thickness is normal with age; an exaggerated increase occurs in persons with hypertension. Other normal age associated changes include enlargement of the left atrium and slight enlargement of the left ventricular cavity.

Aging affects aerobic capacity and cardiovascular performance during exercise. Peak exercise capacity and peak oxygen (O2) consumption decrease with age, but there is great variation from one individual to another. Aerobic capacity decreases by 50% between ages 20 and 80, because maximum cardiac output decreases by 25% and peripheral O2 utilization decreases as muscle mass and strength decrease. Other possible disorders include inefficient redistribution of blood flow to working muscles and reduced O2 extraction and utilization per unit of muscle.

Cross-cultural studies suggest that diet, exercise habits, and smoking also affect the blood vessels and hearts of older persons. For instance, a difference in dietary sodium accounts for some of the differences in age-associated blood pressure changes. However, some changes occur because the sodium sensitivity of arterial pressure regulation increases with age. Physical conditioning appears to lessen the vascular stiffening associated with aging since stiffening is increased by only about half as much in endurance-trained seniors as compared to sedentary ones. Exercise can also improve the aerobic capacity of older persons by increasing cardiac output and O2 utilization.

Age-related changes in the blood include a decrease in the volume of packed red blood cells or constriction or blockage of peripheral veins by a blood clot. Also, there might be pooling of blood in the veins in the legs because valves are not working effectively.

Age-related changes in the heart include a reduction in maximum cardiac output, changes in the activities of nodal and conductive fibers, a reduction in the elasticity of the heart’s fibrous tissues, progressive atherosclerosis (fatty buildup or plaques) that can restrict coronary circulation, and replacement of damaged cardiac muscle fibers by scar tissue.

Age-related changes in blood vessels are often related to arteriosclerosis, a thickening and toughening of arterial walls in which the walls become less tolerant of sudden increases in pressure.

Aging affects aerobic capacity and cardiovascular performance during exercise. Peak exercise capacity and peak oxygen consumption decrease with age, but there is great variation from one individual to another. Aerobic capacity decreases by 50% between ages 20 and 80.

Physical conditioning appears to lessen the vascular stiffening associated with aging since stiffening is increased by only about half as much in endurance-trained elderly persons as compared to sedentary ones. Exercise can also improve the aerobic capacity of older persons by increasing cardiac output and oxygen utilization.

 Muscular System

The major functions of this system are locomotion, support, and heat production. When you hear the words “muscular system” we are referring to skeletal muscle only (not cardiac or smooth muscle).

As the body ages, there is generally a reduction in the size and power of all muscle tissues. In particular, skeletal muscle fibers become smaller in diameter. The overall effect of this is reduced muscular strength and endurance and a tendency to tire rapidly. Because the performance of the heart also decreases, blood flow to active muscles does not increase during exercise as rapidly as it does in younger people.

Not so fun fact:

In healthy young persons, 30% of body weight is muscle, 20% is adipose tissue, and 10% is bone. Muscle accounts for 50% of lean body mass and about 50% of the total amount of body nitrogen. By age 75, about 15% of body weight is muscle, 40% is adipose tissue, and 8% is bone. Thus, half the muscle mass has disappeared because of sarcopenia.

Skeletal muscles also become less elastic. Aging skeletal muscles develop increasing amounts of fibrous connective tissue, a process called fibrosis. Fibrosis makes muscle less flexible so that movement and circulation are restricted.

Tolerance for exertion decreases. A lower tolerance for exercise results partly from the tendency to fatigue rapidly and partly from the reduced ability to eliminate heat generated during muscular contraction. Plus, the ability to recover from muscular injury decreases.

Between the ages of 30 and 75, overall lean body mass decreases primarily due to reduced skeletal muscle mass. This loss is called sarcopenia and occurs as the number and size of muscle fibers progressively decrease.

Despite age-related reductions in muscle strength, muscle functional ability is similar in older and younger adults. Usually, healthy elderly persons can easily climb stairs, rise from a squatting position, walk along a straight line, hop on either foot, and perform typical activities of daily living.

 As the body ages, there is generally a reduction in the size and power of all muscle tissues. In particular, skeletal muscle fibers become smaller in diameter. The overall effect of this is reduced muscular strength and endurance and a tendency to tire rapidly. Because the performance of the heart also decreases, blood flow to active muscles does not increase during exercise as rapidly as it does in younger people.

 Skeletal muscles also become less elastic. Aging skeletal muscles develop increasing amounts of fibrous connective tissue, a process called fibrosis. Fibrosis makes muscle less flexible so that movement and circulation are restricted.

Tolerance for exertion decreases. A lower tolerance for exercise results partly from the tendency to fatigue rapidly and partly from the reduced ability to eliminate heat generated during muscular contraction.

Ability to recover from muscular injury decreases. The number of skeletal muscle cells/fibers is generally set before birth, and most of these fibers last a lifetime. This means that the average person does not experience an increase in the number of muscle fibers at all during a lifetime. The dramatic muscle growth that occurs after birth is achieved mainly by enlargement of existing fibers in a process called muscle hypertrophy. The body does, however, have a limited number of specialized cells called satellite cells. Satellite cells are muscle cells that retain the capacity to fuse with damaged muscle fibers and regenerate functional muscle fibers in an adult. As a result, the body has a limited ability to repair damaged tissue by replacing aged or worn out skeletal muscle fibers. Unfortunately, the number of satellite cells steadily decreases with age as the amount of fibrous tissue increases. As a result, when an injury occurs, repair capabilities are restricted, and scar tissue formation is the usual result.

Between the ages of 30 and 75, overall lean body mass decreases primarily due to reduced skeletal muscle mass. This loss is called sarcopenia and occurs as the number and size of muscle fibers progressively decrease. The pathogenesis of sarcopenia involves several age-related factors such as reduced levels of physical activity, changes in the central or peripheral nervous system that seem to affect total number of motor units, and reduced rate of skeletal muscle protein synthesis. In many elderly persons, loss of muscle mass might be accelerated as a result of greater dietary protein requirements coupled with reduced protein intake.

In healthy young persons, 30% of body weight is muscle, 20% is adipose tissue, and 10% is bone. Muscle accounts for 50% of lean body mass and about 50% of the total amount of body nitrogen. By age 75, about 15% of body weight is muscle, 40% is adipose tissue, and 8% is bone. Thus, half the muscle mass has disappeared because of sarcopenia.

The faster contracting type II muscle fibers decrease with age to a greater extent than do the slower contracting type I muscle fibers. Type II fibers participate in sudden powerful muscle contractions, whereas type I fibers function to maintain posture and to perform rhythmic, endurance-type exercises. The age-related loss of muscle fibers correlates with a loss of maximum isometric contraction force, which decreases 20% by age 60 and 50% by age 80.

The reasons for these changes in body composition and isometric contraction force are not completely understood, but contributing factors include a relative deficiency of anabolic hormones — growth hormone, insulin-like growth factor I (IGF-I), dehydroepiandrosterone (DHEA), and testosterone — and a decrease in the routine performance of vigorous muscular work. Current research indicates that exercise increases the levels of many hormones that decline with age, so it would appear that people who continue to exercise into old age would probably not experience such negative changes.

People whose mobility is restricted because of acute illness, in particular those who are bedridden, are at risk of deconditioning and an accelerated loss of muscle mass and strength. The rate of loss is anywhere from 1.5% to 3% per day. Deconditioning is greatest in the antigravity muscles which are essential for performing activities of daily living, such as sitting up, standing up, and pulling oneself up. Some geriatricians estimate that for one day of absolute bed rest, two weeks of reconditioning are necessary to return to baseline function.

Despite age-related reductions in muscle strength, muscle functional ability is similar in older and younger adults. Usually, senior persons can easily climb stairs, rise from a squatting position, walk along a straight line, hop on either foot, and perform typical activities of daily living.

Skeletal System

The major functions of this system are in structural support, protection of soft tissues, mineral storage, and blood production.

The bones of the skeletal system become thinner and relatively weaker as a normal part of the aging process. Everyone begins to lose bone mass between the ages of 30 and 40. Over this period of time, the number of osteoblasts (bone building cells) begins to decline, while the number of osteoclasts (cells that break down bone) remains the same. The balance between the activities of osteoblasts and osteoclasts is very important when it comes to the maintenance of bone health and strength; when osteoclasts remove calcium faster than osteoblasts can deposit it, bones become weaker.

Fun fact:

The skeleton undergoes continual remodeling which is defined as the replacement of old bone with new bone.
As a matter of fact, bone is completely regenerated every 10 years.

A decline in sex hormones, as well as aging itself, both contribute to the loss of bone density. In men, testosterone production declines gradually, so bone loss is linear and slow. In women, a rapid phase of bone loss occurs during the first 5 to 10 years after menopause due to the immediate and dramatic decrease in estrogen. In addition to this rapid bone loss during early menopause, women accumulate less skeletal mass than men during their growing years — particularly during puberty. This results in smaller, narrower, more fragile bones with thinner cortices. In old age, therefore, the consequences of bone loss are greater among women than among men, and the incidence of bone fractures is two-to-threefold higher.Once the number of osteoblasts declines, women lose roughly 8% of their skeletal mass each decade, while men lose about 3% each decade. All parts of the skeleton are not equally affected. The ends of long bones (like the humerus), vertebrae, and the jaws lose more than their fair share which results in fragile limbs, a reduction in height, and the loss of teeth. Thus, a significant percentage of women and a smaller proportion of men suffer from osteoporosis, a condition characterized by reduced bone mass sufficient enough to compromise normal functioning.

Digestive System

The major functions of this system are the processing of food and the absorption of nutrients, minerals, vitamins, and water.

Because of the large functional reserve capacity of most of the gastrointestinal (GI) tract, aging has relatively little effect on GI functioning. The digestive system is made up of the mouth, teeth, tongue, salivary glands, pharynx, esophagus, stomach, pancreas, liver, gallbladder, large intestine, and small intestine. Essentially, normal digestion and absorption occur in the elderly; however, there are many changes in the digestive system that parallel the age-related changes seen in the other systems. Like other systems, the rate of new cell growth declines and tissues become more susceptible to damage.

Not so fun fact:

Many drugs, including nonsteroidal anti-inflammatory drugs (NSAIDs), can cause esophageal injury. The elderly are at high risk of pill-induced esophagitis and its complications, particularly when esophageal transit is delayed. Drugs should be swallowed in an upright position and followed by a good drink.

Not so fun fact:

With age, calcium absorption diminishes, even in healthy persons who are not deficient in vitamin D. Vitamin D deficiency also often occurs in the elderly. Since vitamin D enhances calcium absorption, a deficiency can ultimately lead to malabsorption of calcium. Malabsorption of calcium is almost certainly a major factor in age-related bone loss in men and women. Accordingly, the dietary calcium requirement is higher in the elderly.

Due to a decrease in smooth muscle tone along a majority of the aging GI tract, food moves through the system more slowly as the contractions necessary for the movement and breakdown of food become weaker. Constipation becomes a problem along with hemorrhoids. Weakening of the cardiac sphincter, a muscle that regulates the flow of food from the esophagus into the stomach, can lead to esophageal reflux which causes “heart burn.”

With age, cancer rates increase, especially in the colon and stomach. Plus, changes in other systems have direct and indirect effects on the digestive system. For example, the reduction in bone mass and calcium content in the skeleton is associated with erosion of the tooth sockets and tooth loss.
When toxins, such as alcohol and chemicals, are absorbed by the digestive tract and transported to the liver for processing or storage, the liver cells are not immune to the effects of these compounds. Chronic exposure leads to damage and disease in the liver and many other organs.

Endocrine System

This system’s major function is to direct long-term changes in the activities of other organ systems through the production of hormones.

Overall, the endocrine system shows relatively few functional changes with age. The most dramatic exception, however, is the decline in the concentration of reproductive hormones. In addition, age-related changes in other tissues affect their abilities to respond to hormonal stimulation. As a result, most tissues become less responsive to circulating hormones, even though many hormone concentrations remain normal.

Fun fact:

Levels of pregnenolone, which is a hormone derived from cholesterol, decreases with age. In rodents, pregnenolone is the most potent memory enhancer known. In humans, it has been shown to improve sleep and to enhance productivity but not to affect mood, strength, cognition, or overall function. Currently, no evidence supports the use of pregnenolone in the elderly.

Because levels of some important hormones decrease with age, restoring low hormone levels might seem like a safe and logical way to help reverse some of the effects of aging. However, any resulting improvement in functional status might be gained at the expense of reduced longevity. For example, increased metabolism, which often results from hormone administration, can lead to tissue damage because of free radical generation. Therefore, hormonal supplementation is usually limited but might be a viable method of correcting documented low hormone levels or relieving symptoms caused by low levels.

Based on recent studies, exercise can have a positive effect on hormone levels. The effects exercise has, however, appears to depend on the type, frequency and duration of the exercises that are being done.

Lymphatic System

The major function of the immune system is defense against infection and disease.

With advancing age, the lymphatic system becomes less effective at combating disease and fighting off infections. T and B cells are the primary cells involved with immunity and attack specific invaders as they penetrate mechanical, chemical, and other cellular barriers.

Fun fact:

Allergies are caused by the production of antibodies to a substance not normally recognized as harmful in the average human body. For some reason, these typically harmless substances trigger an immune reaction in susceptible individuals thus eliciting a normal immune response after inhalation, ingestion, or penetration through the skin.

Not so fun fact:

In the US, infectious disease ranks 8th among most causes of death but rises to rank 4th in persons over 65. Similarly, cancer incidence increases exponentially after the age of 30. Many believe that immune senescence and the decline in “immune surveillance” contribute to these statistical increases.

Not so fun fact:

While vaccines do not work as well in the immune system of older adults, vaccinations for diseases such as influenza, pneumonia, hepatitis B, tuberculosis, diphtheria, and tetanus have been found to reduce mortality in the elderly and are still worthwhile

T cells, the cells responsible for cellular immunity and for coordination and regulation of immunity, become less responsive. As a result, fewer T cells respond to an infection or invasion by a pathogen.

B cells, the cells that produce antibodies, are also less responsive, so antibody levels do not rise as quickly after an infection develops in an elderly person. The net result is an increased susceptibility to viral and bacterial infections.

For this reason, vaccinations for viruses like the flu are strongly recommended for elderly people. In addition, the increased incidence of cancer in the elderly reflects the fact that surveillance by the lymphatic system declines, and tumor cells are not eliminated as effectively.

Two complementary forms of immunity rid humans of pathogens and cancer cells: nonspecific (or innate) defenses and specific (or adaptive) defenses. Nonspecific immunity provides a rapid but incomplete defense against a variety of threatening agents until the slower, specific immune response develops.

Nutrition plays a factor in a healthy immune system as well. In both healthy and nutritionally-deficient older adults, vitamin and other dietary supplements enhance the response of the immune system resulting in fewer days of infectious illnesses.

Older adults often experience loss and stress, and suppressed immunity has been associated with bereavement, depression, and poor social support. Maintaining an active social life and receiving treatment for depression could boost the older adult’s immune system.

Nervous System

The major function of this system is to direct immediate responses to stimuli by coordinating the activities of other systems.

The aging process affects all body systems, and the nervous system is no exception. Anatomical changes begin shortly after maturity (probably by age 30) and accumulate over time. Although an estimated 85% of elderly over the age of 65 lead relatively normal lives, there are noticeable changes in mental performance and central nervous system (CNS) functioning.

Not so fun fact:

Alzheimer’s disease is a complex disease resulting from a combination of genetic mutations, genetic susceptibility, and environmental factors. It is a progressive disorder characterized by the loss of higher cerebral function, and it is the most common cause of senile dementia, commonly termed “senility.” The first symptoms usually appear at 50-60 years of age. Alzheimer’s disease affects an estimated 2 million people over the age of 65 in the US and causes approximately 100,000 deaths each year.

Fun fact:

The olfactory system, which is involved in the sense of smell, is very sensitive. As few as four molecules of an odorous substance can activate an olfactory receptor.

Some common age-related anatomical changes in the nervous system include a reduction in brain size and weight due primarily to a decrease in the volume of the cerebral cortex. There is also a reduction in the number of neurons.

Blood flow to the brain is decreased as a result of fatty deposits that gradually accumulate in the walls of blood vessels and reduce the rate of arterial blood flow. This condition is called atherosclerosis and causes problems in more than just the brain. While reduced blood flow does not cause a cerebral crisis, it does increase the probability of suffering a stroke.

There are also changes in the synaptic organization of the brain which ultimately interferes with the body’s ability to adjust to internal and external stimuli. The number of dendrite branches and interconnections decrease, while the rate of neurotransmitter production declines. At the same time many neurons begin accumulating abnormal intracellular deposits or plaques. There is evidence that when these are present in excess, clinical abnormalities similar to Alzheimer’s disease occur.

These anatomical changes are linked to a number of functional alterations. In general, neural processing becomes less efficient. For example, memory consolidation often becomes more difficult, and sensory systems of the elderly, notably hearing, balance, vision, smell, and taste, become less acute. Light must be brighter, sounds louder, and smells stronger before they are perceived.

Reproductive System

The main function of this system is to produce sex cells and hormones.

The aging process affects the reproductive systems of both men and women. The most striking age-related changes in the female reproductive system occur at menopause, while changes in the male reproductive system occur more gradually and over a longer period of time.

Not so fun fact:

The male equivalent of menopause is called the male climacteric. During this gradual change, circulating testosterone levels begin to decline between the ages of 50-60. Sperm production, however, continues, so men can father children well into their eighties.

Menopause is usually defined as the time ovulation and menstruation cease. It typically occurs between the ages of 45-65. Estrogen and progesterone levels decline which results in a thinning of the urethral and vaginal walls. The reduced estrogen levels have also been linked to osteoporosis and a variety of cardiovascular and neural effects including “hot flashes,” anxiety, and depression.

There is currently much debate over the use of hormone replacement therapy in women since it appears that detrimental effects might outweigh any benefits of the therapy. Some clinicians are now tentatively suggesting the use of testosterone therapy for older men.

Respiratory System

The major function of this system is the delivery of air to sites in the lungs where gas exchange can occur between the air and circulating blood.

The effects of aging on the lungs are physiologically and anatomically similar to those that occur during the development of mild emphysema. Although aging affects ventilation, gas exchange, compliance, and other parameters of lung function as well as the defense mechanisms of the lungs, pure age-related changes do not lead to significant airway obstruction in the nonsmoker.

Not so fun fact:

Emphysema is a chronic, progressive condition characterized by shortness of breath and an inability to tolerate physical exertion. The underlying problem is destruction of respiratory exchange surfaces. As the condition progresses, the reduction in exchange surface limits the ability to provide adequate oxygen. The condition is widespread and is to some degree a normal consequence of aging. An estimated 66% of adult males and 25% of females have detectable areas of emphysema in their lungs. Unfortunately, the damage is irreversible.

Many factors interact to reduce the efficiency of the respiratory system in elderly individuals. Elastic tissue deteriorates throughout the body and reduces the lungs’ ability to inflate and deflate. The rib cage does not move as freely because of arthritic changes. This, in combination with the changes in elasticity, causes a reduction in chest movement which limits respiratory volume. These changes contribute to the reduction in exercise performance and capabilities seen with increasing age.

Finally, some degree of emphysema is normally found in people aged 50-70. On average, roughly 1 square foot of respiratory membrane is lost each year after age 30. However, the extent varies widely depending upon the lifetime exposure to cigarette smoke and other irritants.

The major functions of this system are in structural support, protection of soft tissues, mineral storage, and blood production.

The bones of the skeletal system become thinner and relatively weaker as a normal part of the aging process. Everyone begins to lose bone mass between the ages of 30 and 40. Over this period of time, the number of osteoblasts (bone building cells) begins to decline, while the number of osteoclasts (cells that break down bone) remains the same. The balance between the activities of osteoblasts and osteoclasts is very important when it comes to the maintenance of bone health and strength; when osteoclasts remove calcium faster than osteoblasts can deposit it, bones become weaker.

Integumentary (Skin) System

The major functions of this system are protection from environmental hazards and temperature control.

In general, aging skin thins as cell activity declines and as the network of elastic and collagen fibers supporting it decreases. This makes older people more prone to injury and recurring skin infections, causes the sagging and wrinkling notorious of aging, and slows skin repair.

Fun fact:

An organ is defined as a combination of tissues that performs a specific function or group of functions. So yes, the skin is an organ! As a matter of fact, it is the largest organ of the body in surface area and weight!

Fun fact:

The number of melanocytes is about the same in people of all races. Differences in skin color occur primarily as a result of the amount of melanin produced by individual melanocytes.

Not so fun fact:

Most of the age-related changes that appear in the skin occur in the dermis, the deeper layer of skin. Collagen fibers stiffen and elastic fibers lose their elasticity and clump together, and neither is replaced at an adequate pace. Consequently, crevices known as wrinkles form as damage continues.

Aging results in a decrease in the melanin pigment in skin, which means older people are more sensitive to the sun and tend to avoid it. Avoiding sunlight can cause the production of Vitamin D to decrease by as much as 75%. This can then result in muscle weakness and a reduction in bone strength because vitamin D is necessary for functioning of both the muscular and skeletal systems.

Glandular activity in the skin decreases and leads to dry, scaly skin. Sweat glands become less active, and at the same time blood supply to the skin is decreased. This combination makes the elderly less able to lose body heat, so overexertion or exposure to extreme temperatures can cause dangerously high body temperatures.

As you can see, aging leads to many changes in the skin.

Urinary System

The major function of this system is the elimination of excess water, salts, and waste products.

Although renal function declines substantially with age, it usually remains sufficient for removing bodily wastes. Nevertheless, reduced renal function decreases the elderly person’s ability to respond to various physiological and pathological stresses. In general, aging is associated with an increased incidence of kidney problems. There is a decline in the number of nephrons by about 30-40% between ages 25 and 85. Nephrons are the basic functional units of the kidneys and are made up of a renal corpuscle and renal tubules. There is also a reduction in filtration rate due to cumulative damage to the system and to reduction in blood flow to the kidneys.

Fun fact:

A typical adult kidney measures approximately 4 inches in length and 1.2 inches in thickness. This is about the size of a large bar of bath soap.

Not so fun fact:

Elderly people on salt-restricted diets have a decreased ability to conserve sodium. This can contribute to the increased tendency of elderly persons to develop dehydration. Still, the most important cause of dehydration is the loss of the sensation of thirst, a characteristic common in the elderly. Loss of thirst is especially important when elderly persons are confronted with an illness or an infection that increases demands for or limits the intake of salt and water.

Urine is formed by the kidneys through three processes: filtration, reabsorption and secretion. The ultimate source of urine is blood, and a large amount of blood is transported to the kidneys for filtration by way of the renal arteries. Renal blood flow progressively decreases from 1200 mL/minute at age 30 to 40 years to 600 mL/minute at age 80. A decrease in the glomerular filtration rate, or the rate at which blood is forced through and filtered by the renal corpuscle in the kidneys, is the most important functional defect caused by aging.

Since the kidneys receive up to 25% of the resting cardiac output through the renal arteries, a large portion of total blood volume is filtered through the renal corpuscle each day. At this rate, it wouldn’t take long to totally deplete the body’s entire blood volume. Since this is obviously not a common problem, the body must have some way to recover a majority of that filtered blood. The process that returns necessary items from the filtrate back into the blood is called reabsorption.

Reabsorption is responsible for returning 99% of filtrate back to the circulatory system. Reduced nephron sensitivity which occurs with age, however, results in less reabsorption of water, so urination becomes more frequent while daily fluid requirements increase. At the same time, there is usually a loss of thirst which compounds the problem. The muscles that help regulate the release of urine become weaker which leads to problems with incontinence and often involves slow leakage of urine. This is usually a more common problem in women. In males, urinary retention might develop due to chronic inflammation of the prostate gland. Swelling of the gland prevents the flow of urine as it puts pressure on the urethra.

Check out AAHF specialty CEC programs to learn more about exercise and nutrition for special populations!

References

Petersen, T. SrFit: The Personal Trainer’s Resource for Senior Fitness, Second Edition. The American Academy of Health and Fitness, 2008.

Petersen, T. SrFit: The Personal Trainer’s Resource for Senior Fitness, Third Edition. The American Academy of Health and Fitness, 2018.