Download The Developing Embryo and Fetus

Fertilization and Implantation
Week One of Human Development
The Embryonic and Fetal Periods
During the 4th Week Primordial Germ Cells Migrate into
the Posterior Body Wall of the Embryo
Gametogenesis of Germ Cells in the Male and Female
reduces the number of chromosomes in the germ cells
from 46 to 23
Spermatogenesis and Differentiation
Sperm produced in the Seminiferous Tubules are
stored in the Epididymis
Gametogenesis of Germ Cells in the Male and Female
Maturing Follicle
Number of Primordial Follicles at 5 months: 7 million
at birth:
1 million
at puberty: 400,000 remain
Fewer than 500 follicles will be released during reproductive years
Changes in the condition of the uterus and corresponding
changes in the ovary during a regular menstrual cycle
Key Events
1.) maturation of a single oocyte and
follicle
2.) proliferation of the uterine
endometrium
3.) the process of ovulation
4.) developpment of the follicle into
corpus luteum
5.) if no implantation, the degeneration
of the corpus lteum and the sloughing
off of the uterine endometrium
Your Most Fertile Time
A woman’s most fertile period is typically several days before, and no
more than one day after, ovulation.
To increase chances of becoming pregnant, women should monitor
body temperature, cervical mucus production, and LH levels.
Fertility Fact
An average couple who do not practice contraception and have
intercourse twice a week have a better than 50% chance of
fertilizing any given oocyte. Because half of all embryos are
aborted, the chance that one month’s intercourse will produce a term
pregnancy is thus about 25%.
Summary of the Ovarian Cycle, Fertilization and
Human Development during the First Week
The Female Reproductive Organs
Miracle of Life: The Egg’s Journey
http://www.pbs.org/wgbh/nova
/miracle/program_adv.html
Fertilization is a Complex Interaction Between Sperm
and Oocyte
Miracle of Life: The Sperm’s Journey
http://www.pbs.org/wgbh/nova
/miracle/program_adv.html
Cleavage of the Zygote and Formation of the Blastocyst
Cleavage and Transport down the Oviduct
Miracle of Life: Cleavage
http://www.pbs.org/wgbh/nova
/miracle/program_adv.html
Embryonic Stem Cell Research
Abnormal Implantation Sites of the Blastocyst
How Dizygotic Twins Develop
How Monozygotic Twins Develop
Conjoined Twins (1 in 200,000 live births)
Parasitic Twins (1-2,000,000 births)
Implantation of the Blastocyst (Day 7)
By 8 Days, the Amniotic Cavity Appears
By 9 Days, the Embryo is Completely Implanted
in the Uterine Endometrium
Days 10-13 of Embryonic Development
Days 12-15 of Embryonic Development
In vitro Fertilization