Definition of Aging

DEFINITION OF

AGING

FARHAD ZARGARI, MD, PHD

DEFINITION OF AGEING

DEFINITION

Entropy always wins. Each multicellular organism, using

energy from the sun, is able to develop and maintain its

identity for only so long. Then deterioration prevails over

synthesis, and the organism ages. Aging can be defined

as the time-related deterioration of the physiological

functions necessary for survival and fertility. The

characteristics of aging—as distinguished from diseases

of aging (such as cancer and heart disease)—affect all

the individuals of a species

DEFINITION

DEFINITION

Aging is the process of becoming older. It represents the

accumulation of changes in a person over time. Ageing

in humans refers to a multidimensional process of

physical, psychological, and social change. Most

developed world countries have accepted the

chronological age of 65 years as a definition of 'elderly'

or older person.

DEFINITION

1. The process of growing old, especially by failure of

replacement of cells in sufficient number to maintain full

functional capacity; particularly affects cells (neurons)

incapable of mitotic division.

2. The gradual deterioration of a mature organism

resulting from time-dependent, irreversible changes in

structure that are intrinsic to the particular species, and

eventually lead to decreased ability to cope with the

stresses of the environment, thereby increasing the

probability of death.

3. In the cardiovascular system, the progressive

replacement of functional cell types by fibrous

connective tissue.

4. A demographic term, meaning an increase over time

in the proportion of older people in the population.

DEFINITION

Aging has been defined as the collection of changes

that render human beings progressively more likely to die

(Medawar, 1952). Indeed, one hallmark of aging in

humans and in many other species is an age-related

increase in mortality rates shortly after maturity.

Mortality rates, expressed in deaths per 100,000 people, as a function of age for the 2010

US population.

DEFINITION

Aging can also be defined as a progressive functional

decline, or a gradual deterioration of physiological

functions with age, including a decrease in fecundity

(Partridge and Mangel, 1999; Lopez-Otin et al., 2013), or

the intrinsic, inevitable, and irreversible age-related

process of loss of viability and increase in vulnerability

(Comfort, 1964). Clearly, human aging is associated with

a wide range of physiological changes that not only

make us more susceptible to death but limit our normal

functions and render us more susceptible to a number of

diseases.

DEFINITION

The cells of the elderly (regardless of when they last

underwent mitosis) look the same as young cells.

However, old cells do not withstand a variety of

challenges quite so well as younger cells.

Various theories of aging attempt to explain the process -

bottom line, there is disruption of homeostasis.

DEFINITION

STAGES OF LIFE

Chronologic

al age

typically used

to note life’s

transitions:

DEFINITION

Chronological Age

Biological Age

Psychological Age

Functional Age

Population Age

Age

CHRONOLOGICAL AGE

Chronological age is defined as the number of years a

person has lived. Years, of course, being Earth revolutions

around the sun. This is the one we're all very familiar with.

When looking at chronological age, is 45 different than

20? Yes, but that number on its own fails to inform us of

anything else. All it says is that they were born 25 years, or

Earth-Sun revolutions, apart. In other words “Chronologic

age is not an accurate predictor of physical condition or

behavior”.

BIOLOGICAL AGE

Biological age (an organism's physical state as it ages) is

defined as a description of an individual's development

based on biomarkers. A biomarker is a recordable

molecular or cellular event. Here we're looking at the

individuals as they are, not necessarily when they were

born. Humans, in most cases, follow the same biological

path. For example, the easiest one that comes to mind is

the beginning of puberty and the increase of sex

hormones. More complicated ones exist, such as

increases and decreases in human growth hormone,

myelination events in the brain, and the degradation of

certain tissues as one gets older. So, it's like a continuum.

What if we aren't interested in the body?

PSYCHOLOGICAL AGE

Psychological age is defined as a subjective description

of one's experience using non-physical features. Now

we're trying to say how old a person is without markers.

We used the Earth's revolutions and biomarkers before,

now we have to rely on something that's a little more

ephemeral: experience, logic, and emotions.

Psychological age has been attempted by many

psychologists in the form of stage theories, which are

developmental steps that every person goes through.

Some of the more famous one's include Freud, Erikson,

and Piaget. What they attempt to do is define a person

by how they think, act, and reason without worrying as

much about your chronological age.

FUNCTIONAL AGE

Functional age is defined as a combination of

chronological, biological, and psychological ages. What

is happening is instead of focusing on one aspect at a

time, we are summarizing them to create a more holistic

picture of a person. Functional age would give you the

clearest understanding of a person. It is their listed age,

how far along their body systems have developed, and

a glimpse of their emotional and logical maturity.

However, if you haven't guessed it, this type of age is not

often used. The requirements to describe someone this

thoroughly means that you will need a lot of expert input

- test after test after test to give you the clearest

understanding of how old the person is.

POPULATION AGE

Population ageing is the increase in the number and

proportion of older people in society. Population ageing

has three possible causes: migration, longer life

expectancy (decreased death rate) and decreased

birth rate.

OLD AGE STAGES

Young-Old - (ages 65 - 74)

Middle-Old - (ages 75 - 84)

Old-Old - (age 85 and older)

IMPORTANT REMARKS

Adulthood is attainment of physiologically optimal

integrated function.

Function in adulthood is the standard measure.

Unsound and incorrect to state that changes with aging

are necessarily “abnormal”.

Three observations of the elderly:

Greater heterogeneity in responses

Changes in function do not occur simultaneously

Changes in function do not occur to the same degree

Old age should not be viewed as a “disease” nor should

a time clock be put on aging.

IMPORTANT REMARKS

Significant increase in longevity over past decades.

Due to decline in deaths resulting from infectious disease

along with improved public health.

Heart disease, cancer and stroke now most common

cause of death in the old age.

Death rates have actually declined in the elderly.

Is there a limit to human life span and should we prolong

life at the expense of overall health?

We should be talking in the context of “health span” not

life span.

SUCCESSFUL AGING

homeostasis less efficient, but still present

Homeostasis Less Efficient, but Still Present