4.2 Antenatal Development (lecture notes 4)
Think about the last time you bought a bookcase or an entertainment center from a
store that required that you assemble the purchased item yourself. You likely took the
box home, dumped out all of the pieces on the floor, and pulled out the instruction
manual. You may have first made sure that all of the necessary pieces were present
before you moved to Step 1 and started putting the piece of furniture together. Consider
what would happen if one of the necessary parts were missing: How might the
functionality of your furniture change if you skipped a step in the manual? Or what might
happen if you chose to assemble the piece in an altogether different order than that
prescribed by the instructions?
Somewhat surprisingly, the process of prenatal development is not unlike assembling a
piece of furniture. In both instances, one must have the right raw materials available,
and these raw materials must be assembled in the correct order. If materials are
missing in the process of human development (e.g., errors in cell division can result in
infants having only one of two sex chromosomes) or if extra materials are available (as
in the case of children with extra chromosomes, such as those with Down syndrome;
see Figure 4.3), human development may proceed down a different path. If the timeline
of prenatal development takes a different course (such as when infants are born
premature or preterm), postnatal development may also be impacted. The goal here is
to inform you about the timeline of prenatal development and the factors or
circumstances that might impact how development occurs in utero and after birth (for
more information, see Kline et al., 1989).
, Figure 4.3: Individuals
with Down syndrome, such as the boy shown here, have an extra chromosome. [3]
4.2.1 Three Major Stages of Prenatal Development
Pregnancy begins with an egg and a sperm. When ovulation occurs, an egg is released
from one of a woman’s two ovaries. As shown in Figure 4.4, the egg travels through the
fallopian tube to the uterus, which has built up a thick lining in preparation for the
implantation of the fertilized egg. If fertilization does not occur, the egg is expelled along
with the uterine lining during the woman’s next menstrual cycle. Fertilization can only
occur during a short window around the middle of a woman's menstrual cycle. For
fertilization to occur, unprotected sexual intercourse must occur around the time of
ovulation, as sperm can only survive in the female body for approximately five days.
Think about the last time you bought a bookcase or an entertainment center from a
store that required that you assemble the purchased item yourself. You likely took the
box home, dumped out all of the pieces on the floor, and pulled out the instruction
manual. You may have first made sure that all of the necessary pieces were present
before you moved to Step 1 and started putting the piece of furniture together. Consider
what would happen if one of the necessary parts were missing: How might the
functionality of your furniture change if you skipped a step in the manual? Or what might
happen if you chose to assemble the piece in an altogether different order than that
prescribed by the instructions?
Somewhat surprisingly, the process of prenatal development is not unlike assembling a
piece of furniture. In both instances, one must have the right raw materials available,
and these raw materials must be assembled in the correct order. If materials are
missing in the process of human development (e.g., errors in cell division can result in
infants having only one of two sex chromosomes) or if extra materials are available (as
in the case of children with extra chromosomes, such as those with Down syndrome;
see Figure 4.3), human development may proceed down a different path. If the timeline
of prenatal development takes a different course (such as when infants are born
premature or preterm), postnatal development may also be impacted. The goal here is
to inform you about the timeline of prenatal development and the factors or
circumstances that might impact how development occurs in utero and after birth (for
more information, see Kline et al., 1989).
, Figure 4.3: Individuals
with Down syndrome, such as the boy shown here, have an extra chromosome. [3]
4.2.1 Three Major Stages of Prenatal Development
Pregnancy begins with an egg and a sperm. When ovulation occurs, an egg is released
from one of a woman’s two ovaries. As shown in Figure 4.4, the egg travels through the
fallopian tube to the uterus, which has built up a thick lining in preparation for the
implantation of the fertilized egg. If fertilization does not occur, the egg is expelled along
with the uterine lining during the woman’s next menstrual cycle. Fertilization can only
occur during a short window around the middle of a woman's menstrual cycle. For
fertilization to occur, unprotected sexual intercourse must occur around the time of
ovulation, as sperm can only survive in the female body for approximately five days.
