Trophoblast
Introduction
(Greek, trophe = "nutrition" and -blast, a primordial cell) During early development the trophoblast cells have an important contribution to extraembryonic tissues (fetal placenta and membranes) and processes of early development (adplantation, implantation and endocrine support of pregnancy).
In humans, week 1 blastocyst formation the outer layer of cells (adjacent to the zona pellucida) form a flat squamous epithelial layer of cells, the trophoblast layer. Week 2 following blastocyst hatching the trophoblast layer is involved with initial adhesion to the uterine wall and subsequent implantation within the wall. During this period the trophoblast layer differentiates into two distinct layers (syncitiotrophoblast and cytotrophoblast).
- Links: Blastocyst | Implantation | Week 2 | Week 3 | Placenta Development
Some Recent Findings
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Trophoblast and Placental Villi
Early placental development cartoon showing trophoblast contribution to placental villi.[3]
Legend
- SYN - syncytiotrophoblasts
- sCTB - subsyncytial cytotrophoblasts (this layer grows increasingly discontinuous in later trimesters)
- EVT - extravillous cytotrophoblasts (anchor the villous tree in the decidua)
Syncitiotrophoblasts
- form by fusion of rapidly dividing cytotrophoblast cells
- secrete proteolytic enzymes, enzymes break down extracellular matrix around cells
- Allow passage of blastocyst into endometrial wall, totally surround the blastocyst
- generate spaces that fill with maternal blood- lacunae
- secrete Human Chorionic Gonadotropin (hCG), hormone, maintains decidua and Corpus Luteum, basis of pregnancy diagnostic test, present in urine is diagnostic of pregnancy
- Later in development placenta will secrete hCG
Human Chorionic Gonadotropin
- levels peak at 8 to 10 weeks of pregnancy, then decline and are lower for rest of pregnancy
- 0-1 week: 0-50 mIU/ml
- 1-2 weeks: 40-300 mIU/ml
- 3-4 weeks: 500-6,000 mIU/ml
- 1-2 months: 5,000-200,000 mIU/ml
- 2-3 months: 10,000-100,000 mIU/ml
- 2nd trimester: 3,000-50,000 mIU/ml
- 3rd trimester: 1,000-50,000 mIU/ml
Non-pregnant females: <5.0 mIU/ml Postmenopausal females: <9.5 mIU/ml
Cytotrophoblasts
References
Reviews
Articles
<pubmed>19582159</pubmed>
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Cite this page: Hill, M.A. (2024, June 10) Embryology Trophoblast. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Trophoblast
- © Dr Mark Hill 2024, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G