The document summarizes prenatal development from conception through the first trimester. It describes the key stages and events, including conception and fertilization, the germinal period where the zygote implants and begins dividing, and the embryonic period where organs and structures begin to form from the three germ layers. During this time, the developing organism is most vulnerable to environmental teratogens that can disrupt development. By the end of the first trimester, the basic structures have begun to form and the fetus is growing rapidly.

1. Name
Semester: 1st
Department of Psychology
University of Kashmir.

2. INTRODUCTION:
• Pregnancy is broken down into weeks, and is
divided into three parts called trimesters.
Full term pregnancy is considered 40 weeks
and an infant delivered before the 37th week
is considered premature.
The first, second, and third months are the
first trimester of pregnancy.

4. CONCEPTION
• The first step of prenatal development begins to unfold
with conception.
• Conception or fertilization is the union of male and
female gamete (sperm & ovum).
• Gamete(or sex cells) is a mature haploid male or
female germ cell which is able to unite with another of
the opposite sex to form a zygote.
• The cell resulting from the uniting of the male and
female gamete is called ZYGOTE.

5. THE GERMINAL PERIOD (2 Week)
• Once fertilization has taken place, the zygote begins dividing and
moving down to the uterus , the muscular organ that will contain &
protect the developing infant. This process takes about a week,
followed by another week during which the mass of cells, now
forming a hollow ball (blastocyst) , firmly implants itself to the wall
of the uterus. This two-week period is called the germinal period of
pregnancy.
• The placenta also begins to form during this period. The placenta is
a specialized organ that provides nourishment and filters away
waste products from the developing baby. The umbilical cord also
begins to develop at this time, connecting the organism to the
placenta.
• Structures that feed and protect the developing organism begin to
form- Yolk sac, placenta, umbilical cord.
• Umbilical cord, is the long cord connecting the prenatal organism to
the placenta.

6. Normal Progression Of Development For
The First 10 Days Of Gestation

7. THE PERIOD OF THE ZYGOTE
• Once every 28
days, an ovum
matures, is
released from
one of the
woman’s ovaries
and is drawn to
the fallopian
tube.
• After
fertilization,
zygote will
undergo multiple
rounds of
cleavage, or cell
division, in order
to produced a
ball of cells,
called a blastula.

8. Cleavage, Blastula & Gastrula
• The zygote will undergo multiple
rounds of cleavage, or cell
division, in order to produced a
ball of cells, called a blastula, with
a fluid-filled cavity in its center,
called a blastocoel.
• The blastula eventually organizes
itself into two layers: the inner
cell mass (which will become the
embryo) and the outer layer or
trophoblast (which will become
the placenta); the structure is
now called a blastocyst.
• During gastrulation, the blastula
folds in on itself to form three
germ layers, the ectoderm, the
mesoderm, and the endoderm,
that will give rise to the internal
structures of the organism.

9. END OF GERMINAL PERIOD

10. TERMS
• Blastula: a 6-32-celled hollow structure that is formed after a zygote
undergoes cell division.
• Trophoblast: the membrane of cells that forms the wall of a blastocyst
during early pregnancy, providing nutrients to the embryo and later
developing into part of the placenta.
• Blastomere: any cell that results from division of a fertilized egg.
• Gastrulation: The cells in the blastula rearrange themselves spatially to
form three layers of cells in a process known as gastrulation. During
gastrulation, the blastula folds upon itself to form the three layers of cells.
Each of these layers is called a germ layer, which differentiate into
different organ systems ( Endoderm, Mesoderm, Ectoderm).
• Cleavage: The repeated division of a fertilized ovum, producing a cluster
of cells with the same size as the original zygote.
. The cells in the blastula rearrange themselves spatially to form three
layers of cells in a process known as gastrulation. During gastrulation, the
blastula folds upon itself to form the three layers of cells. Each of these
layers is called a germ layer, which differentiate into different organ
systems .

11. 4th Week Of Pregnancy

12. THE EMBRYONIC PERIOD(2-8 Weeks)
• Once firmly attached to the uterus, the developing
organism is called an embryo. The embryonic period will
last from two weeks after conception to eight weeks,
during this time the cells will continue to specialize and
become the various organs and structures of human infant.
By the end of eight weeks after conception, the embryo is
about 1 inch long and has primitive eyes, nose, lips, teeth,
little arms and legs, digestive tract and a beating heart.
• During these brief 6 weeks, the most rapid prenatal
changes take place, although no organ is fully developed or
completely functional at this time, nearly all are there.
• The sense of touch begins to develop, and the embryo can
move.

13. 6th Week Of Pregnancy

14. 7th Week Of Pregnancy

15. LAST HALF OF THE FIRST MONTH
• In the first week of the embryonic period, the blastula folds
in on itself to form three germ layers, the ectoderm, the
mesoderm, and the endoderm, that will give rise to the
internal structures of the organism.
• The Ectoderm, which will become the nervous system and
skin;
• The Mesoderm, which will develop the muscles, skeleton,
circulatory system, and other internal organs;
• The Endoderm, which will become the digestive system,
lungs, urinary tract, and glands.
• These 3 layers give rise to all parts of the body.

16. Differentiation Of Germ Layers

17. THE SECOND MONTH
• In the second month, growth continues rapidly.
The eyes, ears, nose, jaw and neck form. Tiny
buds become arms, legs, fingers and toes.
• Internal organs are more distinct: the intestines
grow, the heart develops separate chambers.
• Now 1 inch long and 1/7 of an ounce on weight,
the embryo can already sense its world.

18. Two Months

19. CRITICAL PERIOD
• As soon as the embryo begins to receive
nourishment from the mother through the
placenta, it becomes vulnerable to hazards such
as diseases of the mother, drugs and other toxins
that can pass from the mother through the
placenta to the developing infant.
• This time of pregnancy is called the critical
period, times during which some environmental
influence can have an impact-often devastating-
on the development of the infant.

20. CRITICAL PERIODS IN PRENATAL
PERIOD
Body System - Especially Sensitive Development
• Central nervous system/Brain - 4th to 8th weeks
• Heart - 5th to 9th weeks
• Upper limbs- 6th to 10th weeks
• Eyes- 6th to 10 weeks
• Lower limbs - 6th to 10th weeks
• External genitalia- 9th to 11th weeks

21. PRENATAL ENVIRONMENTAL
INFLUENCES
• Teratogens are environmental agents that cause
damage during the prenatal period. Their effects
usually conform to the critical period. The organism is
especially vulnerable during the embryonic period
when body structures are rapidly emerging.
• The effects of teratogens is not limited to immediate
physical damage. Serious psychological consequences
may appear later in development.
• Drugs, cigarette smoking, alcohol, hormones, radiation,
environmental pollution, and certain infectious
diseases are teratogens that can endanger the prenatal
organism.

22. EFFECTS OF TERATOGENS ON
DEVELOPMENT

23. THE FETAL PERIOD
• The fetal period is the time from about eight weeks after
conception until the birth of the child (now called a fetus) and is a
period of tremendous growth.
• However, in the first trimester we consider only 8-12th week.
• During this time, nervous system, organs and muscles become
organized and connected, and new behavioral capacities appear (
the brain signals & in response the fetus kicks, bends its arms,
opens its mouth, curls its toes etc).
• The heartbeat is now stronger. The head now appears very large
compared to the rest of the body because the brain is growing
rapidly.
• By the end of the third month, the developing baby is about four
inches long, weighs a little over an ounce, and signs of the baby's
sex are beginning to appear. Finger and toenails are developing. The
mouth opens and closes and the baby will begin to move its hands,
legs, and head. The mother will not yet be able to feel this
movement.

25. BIBLIOGRAPHY
• Berk E. Laura, Child Development, Fourth edition
• Meyer Glenn, Psychology
• Bee Helen, The Developing Child, Eighth Edition
• http://americanpregnancy.org/duringpregnancy/
fetaldevelopment1.htm
• http://www.webmd.com/baby/1to3-months
• http://www.biology-
online.org/dictionary/Cleavage