2010 BGD Practical 3 - Week 2 Summary

From Embryology

Practical 3: Oogenesis and Ovulation | Gametogenesis | Fertilization | Early Cell Division | Week 1 | Implantation | Week 2 | Extraembryonic Spaces | Gastrulation | Notochord | Week 3 | Quiz


Week 2 is about implantation and the endocrine signaling to block the normal menstrual cycle. We will also consider abnormal events that may occur in development during the second week. This involves abnormalities of implantation and conceptus development.

Note - Normal placentation will be covered in detail in a separate practical class.

Practical Audio

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BGD Cycle A 2010 Audio - Dr Mark Hill Monday 12th May 2010 12-2pm G2G4.

Note - this is a live unedited recording from the practical and may contain errors in either descriptions or content.

listen Part 6 | download (725 Kb MP3 5:49)

Implantation Sites - Normal and Abnormal

Abnormal implantation sites.jpg

Sites of normal and abnormal blastocyst implantation.

Site of most common (normal) implantation is the posterior wall of uterus (shown by X). Abnormal implantation: tubal pregnancies (shown by A-F), ovarian (H), and abdominal (G). Implantation at the internal os generates the clinical condition placenta previa, (resulting in bleeding or placental separation during pregnancy). Note that spontaneous abortion of blastocysts is quite common and studies of blastocysts that do not implant indicate chromosomal abnormalities in many of these embryos.

Implantation Images Day 8 and 9

Gray0032.gif Overview of blastocyst implantation in uterine wall during the second week of development.

Identify the embryoblast and trophoblast layers of the conceptus.

Carnegie Stage 4 (stages 1-23 describing key steps in embryonic development) represents the beginning of implantation.

The blastocyst initially attached to the uterine endometrium (adplantation), syncitiotrophoblasts then secrete enzymes that digest extracellular matrix, allowing the blastocyst to sink into the uterine wall, eventually being completely enclosed within the uterine wall. Note the majority of growth occurs in the trophoblastic shell. The amniotic forms between the inner cell mass and the cytotrophoblast shell; this cavity is lined by epiblast cells.

The inner cell mass divides initially into 2 layers; epiblast and hypoblast (bilaminar embryo). Hypoblast cells migrate around the original blastoceol cavity forming the primary yolk sac. These hypoblast cells are replaced by the endoderm during gastrulation. This endoderm lined cavity is the yolk sac.

Placental Abnormalities

Placental abnormalities

Placenta Accreta - Abnormal adherence, with absence of decidua basalis. The incidence of placenta accreta also significantly increases in women with previous cesarean section compared to those without a prior surgical delivery.

Placenta Increta - occurs when the placenta attaches deep into the uterine wall and penetrates into the uterine muscle, but does not penetrate the uterine serosa. Placenta increta accounts for approximately 15-17% of all cases.

Placenta Percreta - placental villi penetrate myometrium and through to uterine serosa.

Placenta Previa

Placenta Previa
In this placenatal abnormality, the placenta overlies internal os at the cervix of the uterus, essentially covering the birth canal. This condition occurs in approximately 1 in 200 to 250 pregnancies.

In the third trimester and at term, abnormal bleeding can require cesarian delivery and can also lead to abruptio placenta.

Ultrasound screening programs during 1st and early 2nd trimester pregnancies now include placental localization. Diagnosis can also be made by transvaginal ultrasound.

Hydatidiform Mole

Hydatidiform Mole
A placental tumor with no embryo development.

Several forms of hydatidiform mole: partial mole, complete mole and persistent gestational trophoblastic tumor.

Many of these tumours arise from a haploid sperm fertilizing an egg without a female pronucleus (the alternative form, an embryo without sperm contribution, is called parthenogenesis).

The tumour has a "grape-like" placental appearance without enclosed embryo formation. Following a first molar pregnancy, there is approximately a 1% risk of a second molar pregnancy.


Practical 3: Oogenesis and Ovulation | Gametogenesis | Fertilization | Early Cell Division | Week 1 | Implantation | Week 2 | Extraembryonic Spaces | Gastrulation | Notochord | Week 3 | Quiz


Glossary Links

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2010 BGD: Lecture 1 | Lecture 2 | Practical 3 | Practical 6 | Practical 12

Cite this page: Hill, M.A. (2024, May 19) Embryology 2010 BGD Practical 3 - Week 2 Summary. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/2010_BGD_Practical_3_-_Week_2_Summary

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