Body Functions
Body functions are the physiological or psychological functions
of body systems. The body's functions are ultimately its cells'
functions. Survival is the body's most important business.
Survival depends on the body's maintaining or restoring homeostasis,
a state of relative constancy, of its internal environment.
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More than a century ago, French physiologist,
Claude Bernard (1813-1878), made a remarkable observation.
He noted that body cells survived in a healthy condition
only when the temperature, pressure, and chemical composition
of their environment remained relatively constant. Later,
an American physiologist, Walter B. Cannon (1871-1945),
suggested the name homeostasis for the relatively constant
states maintained by the body. Homeostasis is a key
word in modern physiology. It comes from two Greek words
- "homeo," meaning the same, and "stasis," meaning standing.
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Claude Bernard |
"Standing or staying the same" then is the literal meaning of
homeostasis. However, as Cannon emphasized, homeostasis does
not mean something set and immobile that stays exactly the same
all the time. In his words, homeostasis "means a condition that
may vary, but which is relatively constant."
Homeostasis depends on the body's ceaselessly carrying on
many activities. Its major activities or functions are responding
to changes in the body's environment, exchanging materials
between the environment and cells, metabolizing foods, and
integrating all of the body's diverse activities.
The body's ability to perform many of its functions changes
gradually over the years. In general, the body performs its
functions least well at both ends of life - in infancy and
in old age. During childhood, body functions gradually become
more and more efficient and effective. During late maturity
and old age the opposite is true. They gradually become less
and less efficient and effective. During young adulthood,
they normally operate with maximum efficiency and effectiveness.
Life Process
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All living organisms have certain characteristics
that distinguish them from non-living forms. The basic
processes of life include organization, metabolism,
responsiveness, movements, and reproduction. In humans,
who represent the most complex from of life, there are
additional requirements such as growth, differentiation,
respiration, digestion, and excretion. All of these
processes are interrelated. No part of the body, from
the smallest cell to a complete body system, works in
isolation. All function together, in fine-tuned balance,
for the well being of the individual and to maintain
life. Disease such as cancer and death represent a disruption
of the balance in these processes.
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The following is a brief description of the life process:
Organization
At all levels of the organizational scheme, there is a division
of labor. Each component has its own job to perform in cooperation
with others. Even a single cell, if it loses its integrity
or organization, will die.
Metabolism
Metabolism is a broad term that includes all the chemical
reactions that occur in the body. One phase of metabolism
is catabolism in which complex substances are broken down
into simpler building blocks and energy is released.
Responsiveness
Responsiveness or irritability is concerned with detecting
changes in the internal or external environments and reacting
to that change. It is the act of sensing a stimulus and responding
to it.
Movement
There are many types of movement within the body. On the cellular
level, molecules move from one place to another. Blood moves
from one part of the body to another. The diaphragm moves
with every breath. The ability of muscle fibers to shorten
and thus to produce movement is called contractility.
Reproduction
For most people, reproduction refers to the formation of a
new person, the birth of a baby. In this way, life is transmitted
from one generation to the next through reproduction of the
organism. In a broader sense, reproduction also refers to
the formation of new cells for the replacement and repair
of old cells as well as for growth. This is cellular reproduction.
Both are essential to the survival of the human race.
Growth
Growth refers to an increase in size either through an increase
in the number of cells or through an increase in the size
of each individual cell. In order for growth to occur, anabolic
processes must occur at a faster rate than catabolic processes.
Differentiation
Differentiation is a developmental process by which unspecialized
cells change into specialized cells with distinctive structural
and functional characteristics. Through differentiation, cells
develop into tissues and organs.
Respiration
Respiration refers to all the processes involved in the exchange
of oxygen and carbon dioxide between the cells and the external
environment. It includes ventilation, the diffusion of oxygen
and carbon dioxide, and the transport of the gases in the
blood. Cellular respiration deals with the cell's utilization
of oxygen and release of carbon dioxide in its metabolism.
Digestion
Digestion is the process of breaking down complex ingested
foods into simple molecules that can be absorbed into the
blood and utilized by the body.
Excretion
Excretion is the process that removes the waste products of
digestion and metabolism from the body. It gets rid of by-products
that the body is unable to use, many of which are toxic and
incompatible with life.
The ten life processes described above are not enough to
ensure the survival of the individual. In addition to these
processes, life depends on certain physical factors from the
environment. These include water, oxygen, nutrients, heat,
and pressure.
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