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Chapter 2 Related Activity
Janice Hoopiiaina
Option A3
Identifying the Three Phases of Prenatal Development
Human development begins even before birth. During this prenatal development, a
fertilized egg transforms into a living, breathing human being. This paper will discuss the three
phases of prenatal development: what happens to the fertilized egg, when body structures and
internal organs emerge, and when body systems begin to function (Kail 53).
A chemical change takes place when the first sperm manages to penetrate the cellular
wall of an egg; this chemical change blocks out all other sperm. The egg and the sperm then
fuse together and the two independent sets of 23 chromosomes are interchanged. This
fertilization process is the beginning of the new life formation, the zygote period. For the next
week, as the zygot travels down the fallopian tube to the uterus, the zygote grows rapidly
through cell division. Every twelve hours the cells divide. Sometimes the zygot separates into
two clusters that development into identical twins. When the zygot reaches the uterus,
implantation begins and takes about one week. The zygot burrows into the uterine wall and
connects itself to the woman’s blood vessels. Although the zygot is less than a millimeter in
diameter, its cells have already begun to differentiate. The cells near the center, called the
germ disc, will develop into the baby; and the outer cells become the placenta (Kail 54).
When the zygot is completely embedded in the uterine wall, it is call an embryo. During
the next five weeks many changes occur. The body structures and internal organs develop.
Three layers, ectoderm (outer), mesoderm (middle) and endoderm (inner), begin to form. The
ectoderm becomes hair, the outer layer of skin and the nervous system. The mesoderm forms
the muscles, bones, and nervous system. The endoderm forms the digestive system and the
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lungs. Specialization of the cells proceeds rapidly; and by the eighth week you can see eyes,
jaw, arms, and legs (Kail 56).
The final and longest phase of prenatal development is the period of the fetus. During
this period, the cartilage begins to turn to bone, the baby becomes much larger, and the bodily
systems begin to work. This is the time when the mother begins to feel the fetus moving inside
her. During the next five months, the fetus gains 7 or 8 pounds before birth. All regions of the
brain grow, particularly the cerebral cortex which is the wrinkled surface that regulates many
important behaviors. During the fifth and sixth months the skin thickens and is covered with a
thick greasy substance called vernix. This substance is to protect the baby while in the amniotic
fluid. By twenty-eight weeks, the fetus reaches the age of viability because most systems
function well enough to survive. The lungs are not developed and body temperature cannot be
regulated because the insulating layer of fat is lacking that develops during the eight month of
pregnancy. But with the help of intensive care, the fetus can survive.
After the zygot develops into the embryo, and the embryo develops into a fetus, and the
fetus reaches the stage of viability, the senses also begin to work. This is a sign of behavioral
maturity. Studies have been done that show, before birth, babies can even hear and taste
while still in the womb. (Kail 56-58).
Reflective Component: Although I have had four babies myself, I did not know what
each of the three stages enveloped: zygot, embryo, and fetus. It was interesting to me to learn
little details such as how a chemical change takes place when one sperm enters the wall of the
egg to block out other sperm. Also, I remember seeing a film like substance, particularly on one
of my babies that must have been the vernix; I never knew that it was to protect the baby from
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the amniotic fluid. Additionally, although I had heard that unborn babies can hear the mother’s
voice, but learning the study about The Cat in the Hat study really interests me. My daughter is
having a baby; she is due on April 1. This is, in fact, why I chose to write about this option. I am
excited to talk to her and have her try reading this book to her baby. I know we won’t have a
controlling pacifier, but I think it will still be interesting to see if the baby reacts positively to the
story after he is born.
Course objective: As my daughter’s baby has been developing, she and I have discussed
things like how big the baby was, what parts are developed, etc. So I have chosen to apply this
writing assignment to objective #9: Make practical application of material from class and text to
personal life. How the human body develops has always been of interest to me, but especially
now as it is so ‘close to home.”
References:
Kail, Robert, and John Cavanaugh. Human Development A Life-Span View, Fifth Edition.
California: Wadsworth Publishing, 2008. Print.