Aging is a Slow, chronic process that begins the moment we enter lifeand continues for as long as we live.
Many theories have emerged to explain the aging process. The theories fall into two main catagories programmed and damage or error theories. The programmed theories imply that aging follows a biological timetable, and the errors emphasize environmental assaults that can accumulate over time, leading to a decline in the functioning of cells, tissues, and organs, that ultimately results in aging (Flint & Tadi,2023)
In other words, our bodies reflect our genetic capacity to adapt and repair and the cumulative damage from disease processes. Aging highlights our strengths and our weaknesses.
With advancing age, all of the body systems eventually demonstrate reduced efficiency, slowed building & replacement and actual loss of tissue. While an individual' s aging experience is unique, generalizations can be observed for each of the body systems.
Virtually all organ systems are involved in physiologic changes associated with aging. Cumulatively, the loss of cell turnover, decreased function of mucous membranes, cachexia and skeletal muscle mass wasting, increased atherosclerotic decrease in vascular compliance, and cerebral atrophy eventually all contribute to the variety of changes we see in aging (Flint & Tadi,2023)
Skin
The skin's primary function is to protect the organism from the environment. It accomplishes this by providing a barrier that regulates temperature, retains fluid, and absorbs shock and ultraviolet radiation, among other things. As we age, the dermis decreases in thickness by about 20%. As it thins it loses vascularity, cellularity, and sensitivity. The skin's ability to dissipate or retain internal heat is diminished. The skin becomes thin, fragile and slow to heal. Evaporative heat loss is reduced due to the reduced efficacy of sweat glands and decreased peripheral circulation.
Subcutaneous fat deposition is altered in older adults. Muscle, blood vessels and bone become more visible beneath the skin due to thinning of subcutaneous fat on the extremities. Fat deposition occurs mainly on the abdomen and thighs.
Musculoskeletal
Muscle mass is a primary source of metabolic heat. When muscles contract, heat is generated. The heat generated by muscle contraction maintains body temperature in the range required for the normal function of its various chemical processes.
As early as the third decade of life there is a general reduction in the size, elasticity and strength of all muscle tissue. The loss of muscle mass continues throughout the elder years. Muscle fibers continue to become smaller in diameter due to a decrease in reserves of ATP, glycogen, myoglobin and the number of myofibrils. As a result, as the body ages, muscular activity becomes less efficient and requires more effort to accomplish a given task. The elderly are less efficient at creating the heat necessary to drive the important biochemical reactions necessary for life.
Respiratory function
Lung function diminishes with age. The major contributing factors are the progressive loss of elastic recoil within lung tissue,leading to increased work of breathing and residual volume and functional residual capacity. . These changes diminish gas exchange efficiency and make it more difficult to exercise.
Cardiovascular
Cardiac output of healthy exercising elders can usually be maintained, allowing moderate continued physical activity throughout their lives. Aging lowers the threshold for cardiovascular disease development. This is primarily due to losing cardioprotective and compensatory mechanisms that otherwise help prevent serious cardiac disease development. (Flint & Tadi,2023) Precautions are essential for older adults and people with high blood pressure, obesity or a history of heart disease and stroke. Temperatures exceeding 100°F or even temperatures in the 80s with high humidity can cause a dangerous heat index that can be hard on the heart. Hydration helps the heart pump blood through the blood vessels to the muscles more easily and helps the muscles work efficiently (AHA, 2022).
Endocrine and metabolism
Aging is accompanied by a generalized reduction in hormone production and activity. This reduction affects most metabolic functions of the body. Water,mineral, electrolyte, carbohydrate, protein, lipid and vitamin disorders are all more common in the elderly. Nutrition and the ability to use food for energy is seriously affected in the elder population.
Thyroid Hormone secretion decrease causing a decrease in metabolic function(Flint & Tadi,2023)
Alterations in glucose metabolism and insulin secretion develop with age, promoting the development of diabetes mellitus in the elderly Sex Hormone function is also impaired or altered with age. Women typically experience menopause in their late fifties and early sixties. Older adults also have lower calorie needs but similar or even increased nutrient needs compared to younger adults. This probably results from less physical activity, metabolism changes, or age-related bone and muscle mass loss. (Flint & Tadi,2023)
Neurosensory
Like other systems, the nervous system changes with age. There is loss of neurons in both the brain and spinal cord. There is loss of neuronal dendrites, which reduces the amount of synaptic transmission. The sense of smell, taste, sight, touch and hearing are all diminished over time (MedlinePlus 2020).
Decreased temperature sensitivity can increase the risk of injury from hyperthermia and hypothermia. Sensory neurons are decreased by 30% from the age of 10 years to 90 years old. Depression can be the result of impaired synaptic activity. Research indicates that as many as 25% of nursing home residents are clinically depressed. Depression is one of the most common reversible causes of weight loss.
Summary
Clearly the elderly are at a disadvantage when it comes to generating metabolic heat. They have less muscle mass and, therefore less generating apparatus. They have less alveolar surface, thus less oxidative reserve. Their skin provides less protection from heat loss. They have impaired neurotransmission, therefore less ability and/or desire to initiate activity. All of these factors put older adults at risk for hypothermia if their environmental circumstances expose them to heat loss greater than their resting heat generating capacity. Conversely, elders have a reduced capacity to dissipate heat through evaporation due to impaired sweat gland function and diminished cutaneous circulation.
References
American Heart Association [AHA] (2022). Keep Cool to be heart healthy in extreme heat accessed. https://newsroom.heart.org/news/keep-cool-to-be-heart-healthy-in-extreme-heat
Flint B, Tadi P. Physiology, Aging. [Updated 2023 Jan 4]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK556106/
MedlinePlus (2020). Aging changes in the senses.
https://medlineplus.gov/ency/article/004013.htm