1 conception implantation placentation

Question 1

Conception. Where does it occur and what are the

phases of conception

Answer 1

Usually occurs in the ampulla of the fallopian tubes shortly after ovulation, and usually within 12 hours of copulation.
Ovum reaches the uterine lumen in 3-4 days after ovulation.

phases:
1) Capacitation - semen must be in the uterus, interacting with uterine epithelium to degrade/modify their glycoprotein coat, allowing them to undergo the acrosome reaction.

2) The Acrosome reaction
1 - sperm contacts the corona radiata of the ovum. If it is capacitated, then it can penetrate corona radiata.
2 - sperm penetrates the zona pelucida
3 - the cell membranes fuse

3) The ovum the rapidly completes meiosis 2, and the two pronuclei fuse, restoring haploid. (primary oocytes are frozen in prophase of meosis 1, secondary oocytes which are ovulated are froze in metaphase of meoisis 2)

Question 2

Implantation timeline

Answer 2

After conception, cleavage divisions cause the cell to divide without growing, up to the morula stage.

At day 4 the 16 cell morula exists. With the inner cell mass and outer cell mass.

It then sheds the zona pellucida and forms a blastocyst, with its inner cell mass, outter cell mass, and a blastocyst cavity.

AT day 6 implantation occurs, usually in the superior/posterior wall of the uterus.

Question 3

Placentation timeline

Answer 3

At day 9/10 lacunae form in the syncytiotrophoblasts

Day 11/12 the maternal capillaries are eroded and bleed into the lacunae.

Day 12/13 primary villi grow into the lacunae, solid cores of syncytiotrophoblasts around cytotrophoblasts.

The cytotroph core cells apoptose, and a mesodermal core is left, forming a secondary villus

Tertiary villi form with mesoderm cells in the core form the capillary system.

By day 17 the vessels are complete and the placental circulation with the fetus begins.

Question 4

Membranes formed after implantation

Answer 4

The decidua basalis is endometrium under the blastocytes

Decidua capsularis over it

Decidua vera aka Decidua parietalis is the rest.

Syncytiotrophoblasts and cytotrophoblasts form the placenta

The hypoblast cells form the extraembryonic mesodermal cells which thicken, and then vaculolate for form the separate yolk sac and the chorion cavities, as well as the stalk attaching the embryo to the developing placenta.

The amniotic cavity is formed on the opposite side of the yolk sac in the cavity surrounded by the epiblast cells.