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