Lecture 9 (Second week of development) Flashcards
What are Epiblast cells?
Epiblast cells adjacent to the cytotrophoblast are called AMNIOBLASTS and together with the rest of the EPIBLAST line the amniotic cavity
Describe the endometrial stroma adjacent to the implantation site
- Oedematous
- Highly vascular
What is the function of the large tortuous glands?
Secrete glycogen and mucus
What happens on Day 8?
- Blastocyst is partially embedded in the ENDOMETRIAL STROMA
- Trophoblast has differentiated into two layers in the area over the embryoblast
- Cells in the CYTOTROPHOBLAST divide and migrate into the SYNCYTIOTROPHOBLAST where they fuse and lose their individual cell membrane
- Cells of the inner cell mass/embryoblast differentiate into two layers
What are the two layers that the cells of the inner cell mass/embryoblast differentiate into in Day 8?
- HYPOBLAST LAYER = a layer of small cuboidal cells adjacent to the blastocyst cavity
- EPIBLAST LAYER = a layer of high columnar cells adjacent to the amniotic cavity
What are the two layers the Trophoblast differentiates into in day 8?
- CYTOTROPHOBLAST = inner layer of mononucleated cells
- SYNCTIOTROPHOBLAST = outer multinucleated zone without distinct cell boundaries
What happens on Day 9?
- Blastocyst is more deeply embedded in ENDOMETRIUM and penetration defect is closed by a FIBRIN COAGULUM
- Vacuoles appear in SYNCYTIUM and fuse forming TROPHOBLASTIC LACUNAE (LACUNAR STAGE)
- EXOCOELOMIC (HEUSER) MEMBRANE with the HYPOBLAST forms the lining of the EXOCOELOMIC CAVITY called the PRIMITIVE YOLK SAC
What happens on Day 11 & 12?
- Blastocyst is completely embedded in the endometrial
- Trophoblastic lacunae are in open connection with MATERNAL SINUSOIDS in the endometrial stroma -> maternal blood enters the lacunar system
- EXTRAEMBRYONIC MESODERM proliferates and fills the space between the EXOCOELOMIC MEMBRANE and the inner aspect of the trophoblast
Describe how the Uteroplacental circulation is established
As the trophoblast continues to erode more and more sinusoids -> Maternal blood begins to flow through the trophoblastic system
What is the Extraembryonic cavity/Chorionic cavity?
Large cavities that develop in the extra embryonic mesoderm
Describe the Decidua reaction that occurs in Day 12
- Cells of the endometrium become POLYHEDRAL and loaded with glycogen and lipids
- Intercellular spaces are filled with extravasate
- Tissue is oedematous
What happens on Day 13?
- Surface defect in the endometrium has healed
- Bleeding occurs at the implantation site due to increased blood flow into the lacunar spaces
- Secondary yolk sac/Definitive yolk sac is formed
- Connecting stalk from extraembryonic mesoderm for the UMBILICAL CORD
In which day do Primary villi appear?
Day 13
What is the Syncytiotrophoblast responsible for?
Hormone production including HUMAN CHORIONIC GONADOTROPIN (hCG) which serves as the basis for pregnancy testing
How does the maternal body not reject the embryo despite it being “foreign” since 50% is the father’s genome?
There is a shift from cell-mediated immunity to humoral (antibody-mediated) immunity
[this makes the mother at increased risk for certain infections such as influenza]
Where in the uterus can abnormal implantation sometimes occur?
Normally the human blastocyst implants along the ANTERIOR or POSTERIOR wall of the uterus but sometimes it implants close to the cervix -> Obstructs cervix -> Later in development the placenta causes severe, even life-threatening bleeding in the second part of pregnancy and during delivery
What are Ectopic pregnancies?
Pregnancies when implantation takes place outside the uterus
Where is the most common site for Ectopic pregnancies?
95% if pregnancies occur in the uterine tube and 70% of those in the AMPULLA
What happens in ectopic pregnancies?
The embryo dies about the SECOND MONTH of gestation and may result in severe haemorrhaging in the mother
Where does the blastocyst attach itself to in the abdominal cavity in Ectopic pregnancies?
- Peritoneal lining of the Rectouterine cavity (POUCH OF DOUGLAS)
- Peritoneal covering of the intestinal tract or to the OMENTUM
What is a Hydatidiform mole?
The trophoblast develops and forms placental membranes although little or no embryonic tissue is present
[these moles secrete high levels of hCG and may produce benign or malignant tumours]
Describe how large doses of progestins and/or oestrogens inhibit implantation
Large doses of progestins and/or oestrogens do not prevent fertilisation but prevent implantation of the blastocyst -> Endometrium progresses to the LUTEAL PHASE of the menstrual cycle as the zygote forms, undergoes cleavage and enters the uterus -> Large amount of oestrogen disturbs the normal balance between oestrogen and progesterone necessary for implantation
How do Intrauterine devices (IUD) work?
- Interferes with implantation causing a LOCAL INFLAMMATORY RESPONSE
- Contain progesterone -> interferes with endometrium development prevention implantation
- Copper wire -> Toxic to sperms and causes uterine endothelial cells to produce substances toxic to sperms
