Chapter 1

Organization of the Human Body- Life-Span Changes

What is Aging?

• Definition:– Process of becoming mature or old

• For biological purposes:– The bodily changes that occur with the passage of

time

How our Bodies Change through Time

• As a fetus:– Programmed cell death begins– However, we usually do not notice signs of

“aging” until the 30’s.

How Our Bodies Change Through Time

• 30’s:– Beginning of gray hair, faint facial lines, and minor

joint stiffness– Chances of conceiving a child with abnormal

chromosome numbers increases with the age of the egg, so females over 35 are considered to be of advanced maternal age

How Our Bodies Change Through Time

• 40’s/50’s:– First signs of adult-onset disorders (such as high

blood pressure of diabetes) may appear

How Our Bodies Change Through Time

• 60’s:– More gray or white hair, deeper skin wrinkles,

lowered immunity

Why Does Aging Occur• At the cellular level:– All cells have a set number of times that they can

divide.• Why?

– Portions of the tips of the chromosomes are lost with each cell division

– Older cells may not be able to build a spindle to separate duplicated chromosomes during cell division

• These cells may die or become enlarged– Impaired cell division leads to impaired wound healing– Uncontrolled cell division may lead to cancer

– Older cells loose efficiency in repairing DNA mutations and transporting substances across cell membranes

– Older cells have fewer mitochondria (where energy is extracted) and fewer lysosomes (break down damaged cell parts)

Why Does Aging Occur?

• At the tissue level:– Decreases in the production of collagen and elastin

(which are connective tissue proteins) through time leads to stiffening of the skin

– Lowered levels of subcutaneous fats with time leads to wrinkles

– Increases in the percent of fats compared to water in the tissue results in changes in metabolic rate• Percent of fat increases steadily in women and increases in

men until about age 60– Atrophy of tissues leads to shrinking organs

Why Does Aging Occur?

• At the biochemical level:– Lipofuscin and ceroid pigments (composed of

lipid-containing residues of lysosomal digestion) build up as the cell can no longer prevent the formation of damaging oxygen free radicals

– A protein called beta amyloid may build up in the brain (which may contribute to Alzheimer's)

– Metabolism slows down as thyroid gland function, glucose utilization, protein synthesis, and production of digestive enzymes all decrease • Noticed at the whole body level as weight gain, fatigue,

and lower tolerances for cold

Why Does Aging Occur?

• At the genetic level:– The gene p21 produces a protein that turns on

and off about 90 other genes whose specific actions promote the signs of aging.• The p21 gene intervenes when cells are damaged by

radiation or toxins, promoting their death (in order to prevent them from causing disease)• The p21 gene also stimulates the production of

proteins associated with certain aging disorders such as arthrytis, Alzheimer’s, and atherosclerosis