Trophoblast

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Human Blastocyst (day 5), trophoblast cells form the peripheral flattened epithelial layer of cells directly under the zona pellucida.[1]

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

  • Involvement of transcription factor NR2F2 in human trophoblast differentiation[2] "During the in vitro differentiation of human villous cytotrophoblast (CTB) cells to a syncytiotrophoblast (STB) phenotype, mRNA levels for the nuclear hormone receptor NR2F2 (ARP-1, COUP-TFII) increase rapidly, reaching a peak at day 1 of differentiation that is 8.8-fold greater than that in undifferentiated CTB cells."
  • Angiogenic growth factors[3] "Fourteen angiogenic growth factors were measured by multiplex growth factor analysis or ELISA in tissue culture supernatants from EVT and CTB from pregnancies at 8-10 and 12-14 weeks' gestation. Gestational age and cell type differences were observed. Extravillous trophoblast (EVT) and villous cytotrophoblast (CTB) are major producers of angiogenic growth factors that likely contribute to placental vascular development and spiral artery remodeling."

Trophoblast and Placental Villi

Early placental structure.jpg

Early placental development cartoon showing trophoblast contribution to placental villi.[4]

Legend

  • SYN - syncytiotrophoblasts
  • sCTB - subsyncytial cytotrophoblasts (this layer grows increasingly discontinuous in later trimesters)
  • EVT - extravillous cytotrophoblasts (anchor the villous tree in the decidua)

Cytotrophoblasts

Hyperglycosylated human Chorionic Gonadotropin (hCG) promotes the growth of cytotrophoblast cells and the endometrial invasion by these cells during implantation.[5]

Extravillous Cytotrophoblasts

  • maintain open maternal spiral arteries emptying into the maternal lacunae[6]


Syncytiotrophoblasts

File:Cytotrophoblast to syncytiotrophoblast cartoon
  • 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, lacunae, that fill with maternal blood
  • 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

hCG sources - produced by villous syncytiotrophoblast cells, hyperglycosylated hCG produced by cytotrophoblast cells, free beta-subunit made by multiple primary non-trophoblastic malignancies, and pituitary hCG made by the gonadotrope cells of the anterior pituitary.

  • 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


References

  1. ↑ <pubmed>19924284</pubmed>| PMC2773928 | PLoS One
  2. ↑ <pubmed>20195529</pubmed>| PLoS One
  3. ↑ <pubmed>20338637</pubmed>
  4. ↑ <pubmed>20107601</pubmed>| PLoS
  5. ↑ <pubmed>20735820</pubmed>
  6. ↑ <pubmed>20359743</pubmed>


Reviews

<pubmed>19876840</pubmed>

Articles

<pubmed>20081188</pubmed> <pubmed>20033790</pubmed> <pubmed>19582159</pubmed>

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Search October 2010

  • Syncytiotrophoblast - All (10230) Review (1104) Free Full Text (2508)
  • Cytotrophoblast - All (9828) Review (1062) Free Full Text (2401)


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Cite this page: Hill, M.A. (2024, May 6) Embryology Trophoblast. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Trophoblast

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© Dr Mark Hill 2024, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G
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