Anatomy And Physiology
Introduction to the Human Body
Human 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.
Introduction to the Human Body
Human 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.
