From Wikipedia,
the free encyclopedia.
Human biology is an
academic field of
biology which focuses on
humans; it is closely related
to
medicine,
primate biology, and a number
of other fields.
A human being is a
multicellular
eukaryote made up of an
estimated 100,000 billion
cells. As a species, humans
are
primates and can be
distinguished from other primates
by their more highly evolved
brains. Even though humans are
multicellular animals, many of the
basic life processes of human
cells are basically the same as in
simple unicellular eukaryotes such
as
yeast and even
prokaryotes.
One of the major biological
differences between humans and
yeast is that yeast are
unicellular organisms — when a
yeast cell divides, it produces a
new and independent organism. A
human being is initially just one
cell, a
zygote, but when that cell
divides, it forms an
embryo. The early embryo is
made up of
totipotent
stem cells, which go on to
differentiate. Differentiation
is the process by which an
unspecialized cell becomes
specialized into one of the many
cells that make up the body, such
as a heart, liver, or muscle
cells. During differentiation,
certain
genes are turned on, or become
activated, while other genes are
switched off, or inactivated. This
process is intricately
regulated. As a result, a
differentiated cell will develop
specific structures and perform
certain functions. Differentiation
can involve changes in numerous
aspects of cell physiology; size,
shape, polarity,
metabolic activity,
responsiveness to signals, and
gene expression profiles can
all change during differentiation.
When developed, the human body
is made up of many different types
of cells — see
list of distinct cell types in the
adult human body. These cells
make up
tissues, groups of cells that
perform a similar function. For
example, muscle cells make up
muscle tissue. Similarly, groups
of tissues which perform some
function make up an organ, and
groups of related organs makes up
an organ system. The human body
depends on all its organ systems
in order to survive and reproduce.
Major organ systems of the
human body:
The study of development from
fertilized cell to fully developed
body is studied in
developmental biology, the
structure of the developed human
body is studied in
human anatomy and its function
in
human physiology. The human
body can develop problems, and
these are studied in
medicine.
