73. Basic concepts of gerontology

Gerontology is the study of physiological and pathophysiological changes of aging. It also includes studies diseases that commonly affect elderly, as well as how diseases that affect both young and older people affect them differently.

In the developed countries the society is aging in general. As healthcare improves more elderly people survive, and so the average age of the population increases. The number of people older than the age of 65 increases. This makes gerontology more and more important.

Changes in body composition:

As people age, their body composition changes. The fat-free mass (lean body mass) decreases, mostly due to atrophy of unused muscles. The fat mass increases, and the cell mass decreases.

Changes in physiological functions:

Several physiological functions decrease with age:

  • Neuromuscular system
    • Conduction velocity
  • Metabolic system
    • Basal metabolic rate
    • Cell water content
  • Kidneys
    • Glomerular filtration rate (GFR)
    • Renal plasma flow (RPF)
  • Respiratory system
    • Vital capacity of the lungs
    • Maximal breathing capacity
  • Cardiac system
    • Cardiac index

The cardiac index is the cardiac output divided by the body surface area. It relates the heart performance to the size of the individual.

The thirst sensation of elderly is reduced. This predisposes to hypovolaemia, which is a common finding in elderly. Due to muscle or bone pain they may have decreased ability to go to the supermarket to buy food, which can cause malnutrition. Immobilization is also common.

The reserve capacity of organs decreases in elderly, especially of the heart.

Diseases in elderly:

Many diseases are more commonly in the elderly, especially heart and kidney diseases and conditions like osteoporosis, Parkinson disease, diabetes, hypertension, dementia, cataracts, glaucoma and arthritis. The risk for cancer also increases with age.

Symptoms often present differently in elderly than in young people. In young people the pathological organ usually causes symptoms, while in elderly symptoms can arise in other organs than the pathological one. This is because organs work together, and it is always the weakest link that shows symptoms first. In elderly, this “weak link” is not necessarily the pathological organ.

For example, if an older person has considerably reduced heart function, a renal disease could present with symptoms of cardiac decompensation rather than renal symptoms.

Symptoms and diseases in elderly are less commonly acute and more commonly chronic. Symptoms tend to occur insidiously and become progressively worse rather than having a sudden onset. Some symptoms are often brushed off as being “due to aging”, which can cause conditions to go undiagnosed.

Multimorbidity is defined as the presence of more than one chronic condition in an individual and is more common in elderly. When a person is suffering from more than one condition symptoms may appear differently.

See disorders of thyroid function for some examples in how symptoms can be different in elderly.

Medications in elderly:

As elderly often suffer from multiple conditions, they’re often subject to polypharmacy, the use of multiple medications. Medications can interact with each other. The distribution and excretion of drugs change with age and can cause unexpected side-effects or interactions.

Mental health in elderly:

Elderly are more commonly affected by neurological disorders, which may alter their mental function. They are more prone to loneliness and depression.


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