BGDA Practical 3 - Week 2 Summary
Practical 3: Oogenesis and Ovulation | Gametogenesis | Fertilization | Early Cell Division | Week 1 | Implantation | Week 2 | Extraembryonic Spaces | Gastrulation | Notochord | Week 3 |
Introduction
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.
Implantation Sites - Normal and Abnormal
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.
Abnormal implantation sites or Ectopic Pregnancy occurs if implantation is in uterine tube or outside the uterus.
- sites - external surface of uterus, ovary, bowel, gastrointestinal tract, mesentry, peritoneal wall
- If not spontaneous then, embryo has to be removed surgically
Tubal pregnancy - 94% of ectopic pregnancies
- if uterine epithelium is damaged (scarring, pelvic inflammatory disease)
- if zona pellucida is lost too early, allows premature tubal implantation
- embryo may develop through early stages, can erode through the uterine horn and reattach within the peritoneal cavity
- Links: Ectopic Implantation (Pregnancy) | Ectopic pregnancy ultrasound Flash | Quicktime
Implantation Images Day 8 and 9
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
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
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 |
Terms
BGDA: Lecture 1 | Lecture 2 | Practical 3 | Practical 6 | Practical 12 | Lecture Neural | Practical 14 | Histology Support - Female | Male | Tutorial
Glossary Links
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Cite this page: Hill, M.A. (2024, June 15) Embryology BGDA Practical 3 - Week 2 Summary. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/BGDA_Practical_3_-_Week_2_Summary
- © Dr Mark Hill 2024, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G