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Class notes CNA (CNA1O1)
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Anatomy of all body structures and how this tissues and structures work together.
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Introduction to the Human BodyHuman beings are arguably the most complex organisms on this planet. Imagine billions
of microscopic parts, each with its own identity, working together in an organized manner for the
benefit of the total being. The human body is a single structure but it is made up of billions of smaller
structures of four major kinds:
Cells
Cells have long been recognized as the simplest units of living matter that can maintain life and
reproduce themselves. The human body, which is made up of numerous cells, begins as a single, newly
fertilized cell.
Tissues
Tissues are somewhat more complex units than cells. By definition, a tissue is an organization of a great
many similar cells with varying amounts and kinds of nonliving, intercellular substance between them.
Organs
Organs are more complex units than tissues. An organ is an organization of several different kinds of
tissues so arranged that together they can perform a special function. For example, the stomach is an
organization of muscle, connective, epithelial, and nervous tissues. Muscle and connective tissues form
its wall, epithelial and connective tissues form its lining, and nervous tissue extends throughout both its
wall and its lining.
Systems
Systems are the most complex of the component units of the human body. A system is an organization
of varying numbers and kinds of organs so arranged that together they can perform complex functions
for the body. Ten major systems compose the human body:
Skeletal
Muscular
Nervous
Endocrine
Cardiovascular
Lymphatic
Respiratory
Digestive
Urinary
Reproductive
,Body Functions & Life Process
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.
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. "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
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 form 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.
The following are 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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