Placentation and role of trophoblast Flashcards
What are the stages of implantation and placentation
1.Attachment
2.Syncytia
3.Lacunae
4.Extraembryonic mesoderm
5.Primary villi
6.Secondary Villi
7.Tertiary villi
Name the 2 componenets of the endometrium
decidua functionalis
decidua basalis
Attachment
Decidualisation is the process when the stratum functionalis and stratum basalis get filled with glycoproteins and lipids.
The blastocyst has microvilli attached to its surface that allow for its loose binding to the decidua functionalis. The blastocyst also has integrins which strongly attach the blastocyst to the decidua by the selectins that are present on their surface.
This binding causes the release of chemokines from the trophoblast layer which stabilises this attachment and allows the blastocyst to burrow into the stroma of the decidua functionalis.
- Syncytia
trophoblast will differentitae into the synctiotrophoblast and the cytotrphoblast
The blastocyst contains trophoblast layer which differentiates into the cytotrophoblast. These will rapidly proliferate.
Their cell membrane will breakdown
Their cytoplasm and nuclei will fuse with other cells
Makes a pool of protoplasm
They have no defined cell membrane which forms this ‘’syncytia” layer- known as the Syncytotrophoblast
Functions:
- Releases HCG- stimulates the CL to keep making progesterone to allow for uterine blood vessels to continue supplying blood to uterus and prevent them from spasming, the surrounding tissue becoming ischemic and overall the lining being sloughed of.
- Releases Hydrolytic enzymes that allow for it to break down stromal tissue and further invade the endometrium.
Lacunae
The embryoblast will differentiate into the bilaminar disc which is composed of the epiblast and hypoblast.
The synctiotrophoblast will form finger like projections and these intervillous spaces known as lacunae. It will release hydrolytic enzymes that will break down stromal tissue and cause blood to pool within these lacunae
Extra embryonic mesoderm
The hypoblast cells form connective tissue known as extra embryonic mesoderm between the cytotrophoblast layer and the yolk sac and the amniotic cavity.
the extra embryonic mesoderm forms septates to form the somatopleuric extra embryonic mesoderm (near the cytotrophoblast) and the sphlancopleuric layer (near the yolk sac and the amniotic cavity.
it also forms the extra embryonic coleum
Primary villi
The cytotrophoblast cells proliferate rapidly and send their projections out the synctiotrophoblast and around the lacunae.
the primary villi is composed of
- the embryonic coleum
- the somatopleuric extra embryonic mesoderm
-the sphlancopleuric layer
Secondary Villi
the somatopleuric extra embryonic mesoderm invades the primary villi.
so you have a primary villus with this structure(inside to out)
- Somatopleuric extra embryonic mesoderm
- cytotrophoblast
-synctiatrophoblast
Tertiary villli
The extra embryonic mesoderm in the primary villi differentiates to form blood vessels- cappilaries
thus you form the maternal and embryo exchange system
The placenta
- the chrornic frondiosum (Tertiary villi) (embryonic component)
-Decidua basalis(maternal component)
What is the function of the placenta
-acts as the lungs, the gut and the kidneys of fetus
-Mother fetal interface
- Releases hormones such as HCG and progesterone
- has genetic material from both the mother and father
- the fetal and maternal circulations do not mix
What animal models are used to study human placental development
- Mice & Chimpanzees
- In mice the trophoblasts invade the decidua and come into direct contact with the maternal blood
- But there in no deep interstital invasion of the decidua
- they do not exhibit the same obstetric complications as humans
In chimpanzees:
the trophoblasts invade the decidua and come into direct contact with the maternal blood
there is deep intersital invasion of the decidua
- they exhibit similar obstretic complications as humans
- unethically unacceptable to experiment on them
