The processes of gamete production, fertilization, and
development follow an orderly sequence of events. Zygotes contain all the
information necessary for growth, development, and eventual reproduction of the
which is a fertilized egg consisting of one cell, will begin
rapidly by mitosis forming the early developing human
embryo. Fertilization and the initial stages of this mitotic cell division occur in the
oviduct. The early embryo
is migrates down the fallopian tube and completes most of its
development in the wall of the uterus.
Fertilization and Initial Development of the Embryo
is a combination of maternal and fetal tissue which allows for
exchange of materials with the fetus and mother.
Needed materials such as
food and oxygen diffuse through the placenta to the fetus, while
wastes from the
fetus diffuse to the mother. The umbilical cord
is a fetal structure containing
blood vessels which allows materials to be carried between the
fetus and placenta in both directions. The amniotic fluid
surrounds the fetus and helps to provide a
shock absorber to protect the fetus against mechanical injury in
the event the
mother is shaken or injured in some manner.
Fetal Development in the Uterus
The embryo will
eventually develop into a three cell layered
structure. This structure
is called a gastrula and will eventually differentiate
to form the specialized cells. Differentiation means that the cells will develop specific
jobs and develop into
specific tissues in the maturing organism. An
example of this is that the outer
cell layer of the developing gastrula will develop into the
skin and nervous system
of a mature human organisms. Most multicellular animals
undergo a similar pattern
of development and differentiation.
Development is a highly regulated process After
this small cluster of cells called
the gastrula forms in humans, tissues begin to form.
humans, the embryonic development of essential organs occurs
in early stages of pregnancy.
During the first three months of human development, organs begin to form.
The human embryo is usually referred to as a fetus when human like
features become visible in its structure. All organs and body features are developed by the end of the
sixth month. During the last three months of pregnancy, organs and features develop
well enough to function
| Human Development at 6 weeks
||Human Development at 4 months
The embryo (or fetus) may encounter risks from faults in
its genes and from its mother's
exposure to environmental factors such as inadequate diet, use
of alcohol, tobacco, drugs, other toxins, or infections.
While the patterns of development discussed previously hold
true for humans, these developmental patterns vary between different plants and different animals.
Aging is a complex series of developmental changes
which occur with the passage of time. This
process is influenced by both heredity and the environment.
This process eventually leads to the
death of the organism.
Reproduction and development are subject to environmental
impact. Human development, birth,
and aging should be viewed as a predictable pattern of events.
Reproductive technology has medical, agricultural, and ecological applications.
In many instances, these technologies have progressed at a
faster rate than the ethical considerations resulting from
these technologies. Some of these techniques include
birth control methods used to block the process of
fertilization. Many technologies now exist to
enhance the process of fertilization and development in humans
and other organisms. Hormone
therapy can cause increased egg production. Surgery can
open blocked fallopian tubes in females and the vas deferens
in males. In vitro fertilization (test-tube babies) is a
widely used technique to aid infertile couples, allowing them
to have children where this otherwise would not be possible.
The in vitro