Implantation and the Placenta Flashcards
Describe the divisions of the endometrium of the uterus, and how it changes with the moon.
Endometrium - inner lining of the uterus, supports the embryo
Stratum functionale - the region that undergoes cyclic changes including build up/proliferation and thickening, during this time it becomes more vascular (Spiral Arteries) and more glandular (Uterine Glands)
Let’s catch up from before Implantation.
Briefly describe the steps between ovulation and the blastocyst stage.
- Secondary oocyte is released from the ovary, and travels through the oviduct
- Sperm penetrates the secondary oocyte
- Sperm and egg nuclei fuse, resulting in fertilization or a zygote
- Rapid mitotic cell divisions while traveling through our winding tubes
- A morula forms - tight little zona pellucida bound clump of like 16 cells
- Zona pellucida pops so growth can keep on keepin on
Describe the structure of a blastocyst.
What are the outer layer cells? How are they connected? What is on them?
What are the inner cells?
Outer cells - trophoblast (will form part of placenta)
Trophoblasts linked by tight junctions and support microvilli and Integrin adhesive glycoproteins on the cell surface
Accumulated cells - inner cell mass (will form embryo)
How does the endometrium change under the influence of progesterone?
How does this facilitate adplantation of the blastocyst?
Endothelium of endometrium develops integrin adhesive glycoproteins and specialized projections of plasma membrane called pinopodes. No one knows what pinopodes do, but yeah lets memorize that stupid word.
During adplantation the blastocyst approaches mass down to adhere to the endometrium.
Adplantation triggers differentiation in the trophoblast.
Describe the new trophoblast. What are the outer cells called? What are the inner cells called?
Describe how this little parasite starts leeching into the endometrium.
Differentiation: the outer cells are called cytotrophoblasts, and the inner cell mass has differentiated into the epiblast (closer to uterus) and the hypoblast (further from uterus)
The cytotrophoblast starts undergoing mitotic proliferation with daughter cells running to where the trophoblast is contacting the uterine wall. Then they fuse with the endometrium and they are called Syncytiotrophoblasts. These are proliferating too fast to form membranes between daughters, we’ve seen this before.
Syncytiotrophoblasts secrete lytic enzymes that let the it dig deeper into the endometrium
What is the decidual reaction?
Decidual reaction is endometrial response to implantation.
Connective tissue and stroma cells of the endometrium just off themselves to release proteins, lipids, and sugars to feed the little syncytiotrophoblast leeches.
This also eases penetration of trophoblast into uterine wall
What happens after the embryo has dug out a full embryo sized hole in the endometrium?
The point of adplantation is sealed with a fibrin plug.
Syncytiotrophoblasts are still explanding, and forming lil’ lacunae within it.
What two events allow for the syncytiotrophoblast to reach the maternal sinusoids, and siphon out blood into its own lacunae?
What is this the earliest form of?
- Decidual reaction
- Lytic invasion of syncytiotrophoblasts
earliest form of uteroplacental circulation
Describe the formation of the connecting stalk.
Syncytiotrophoblast continues to expand
Extraembryonic mesoderm (between trophoblast and inner cell mass) also expands. Then splits to form somatic and splanchnic layers, and the Chorion in between.
The two layers of extraembryonic mesoderm join to form the connecting stalk.
Describe the formation of the primary villi.
Cytotrophoblast extends into syncytiotrophoblast between lacunae to form the primary villi.
Describe the formation of the secondary villi.
The somatic extraembryonic Mesoderm pushes into primary villi, right in the middle.
Describe the formation of tertiary villi.
The mesoderm of the secondary villi differentiates into connective tissue and vasculature.
The vasculature will link to embryonic circulatory system
What is the placental barrier?
What structur marks the formation of the placental barrier?
Placental barrier is the term for the 4 layers that make up the exchange between maternal and embryonic systems
1) Capillary endothelium of the villus
2) Loose connective tissue around the capillary of the villus
3) Cytotrophoblast
4) Syncytiotrophoblast
The formation of tertiary villi marks the formation of this barrier.
Describe the formation of free villi.
Cytotrophoblast retracts from tertiary villi, removing a layer from placental barrier and leading to greater exchange between host and embryo
Where do the cytotrophoblast cells go when they withdraw from the villi?
They go fuck up the mom!
They invade endometrium and even myometrium, just causing chaos and disrupting and replacing the lining endothelial cells and the vascular smooth muscle cells as they B-line toward the arteries on their hunt for BLOOD
This alters the maternal vascular system ELIMINATING neural and hormonal control of the spiral arteries, so the embryo can have an all you can eat buffet
