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Human biology lecture notes about prenatal development.
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Lecture 23Prenatal Development
B Nursing II HUB228 2022
Dept. Medical Biosciences
University of the Western Cape
, Introduction
Pregnancy = events occurring from fertilization to birth
Gestation period = length of pregnancy & time during which
development occurs
= 280 days → from last menstrual period until birth
Prenatal development can be divided into three periods:
1) Preembryonic period (weeks 1 - 2)
- the conceptus (pregnant woman’s developing offspring) is known as a
preembryo
2) Embryonic period (weeks 3 – 8)
- the conceptus is known as an embryo
3) Fetal period (weeks 9 – 38)
- the conceptus is known as a fetus
, Preembryonic period
The major events of this 2-week period include:
1) fertilization
2) cleavage (mitotic divisions) and blastocyst
formation
3) implantation
4) start of placentation
• this is a very sensitive period of development
as the foundations of the preembryo’s body
are being laid down
- a woman must be very aware & careful of what she
is taking into her body
- teratogens (factors that may cause severe
congenital abnormalities or even fetal death) such
as alcohol, nicotine & many drugs should be
avoided
www.flyfishingdevon.co.uk
, 1. Fertilization
• fertilization = fusion of the a
haploid sperm (containing 23
chromosomes) with a haploid
secondary oocyte (containing 23
chromosomes) to form a diploid
zygote (containing 46
chromosomes)
why is the volume of the
secondary oocyte much
greater than the sperm (2000
to 1)?
- the sperm only delivers the paternal
chromosomes at the site of www.jour.sc.edu
fertilization while the secondary
oocyte must provide all of the
nourishment & genetic
programming to support the
development of the preembryo for
the first week after conception
(before implantation & placentation
has occurred)
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