ANAT2341 Lab 4 - Implantation and Villi Development

Implantation

Human Embryo Day 8 to 9


Implantation	Chorionic Cavity	Week 3	Amniotic Cavity
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Week 3 embryo

Villi Development

Chorionic Villi

Primary villi

Week 2 - first stage of chorionic villi development, trophoblastic shell cells (syncitiotrophoblasts and cytotrophoblasts) form finger-like extensions into maternal decidua.

Secondary villi

Week 3 - second stage of chorionic villi development, extraembryonic mesoderm grows into villi, covers entire surface of chorionic sac.

Basal region will form chorionic plate.

Tertiary villi

Week 4 - third stage of chorionic villi development, mesenchyme differentiates into blood vessels and cells, forms arteriocapillary network, fuse with placental vessels, developing in connecting stalk.

stem villi - or anchoring villi, cytotrophoblast cells attached to maternal tissue.

branched villi - grow from sides of stem villi, region of main exchange, surrounded by maternal blood in intervillous spaces.

terminal villi - not active outgrowths caused by proliferation of the trophoblast. Passive protrusions induced by capillary coiling due to growth of the fetal capillaries within the mature intermediate villi (third trimester).

chorionic plate - region of membrane at the base of the villi through which placental arteries and vein passes.

Anchoring Villi

Floating Villi

Placenta anchoring villi
Villi first trimester
Villi at term
Villi at term

Chorionoic Villi Location

Originally villi cover entire chorionic surface and then become restricted to decidua basalis region forming 2 regions:

Frondosum - "leafy" where villi are mainly located.
Capsularis - smooth chorion, where villi are absent or not abundant.


Week 4 (Stage 11)	Week 7 (Stage 18)

Additional Information

Human Villi Timeline

The placental vill development data below is based upon a recent immunochemistry confocal laser scanning microscope (CLSM) study.^[1]

Note that the paper uses clinical gestational age (GA) from last menstrual period (LMP) and has been corrected for post-conception (fertilization) age, approximately 14 days later.

Fertilization Age (weeks)	Gestational Age (weeks)	Vessel Lumen Diameter (range in microns, µm)	Features
3 to 4	5 and 6	10 - 15	a complex network of cords and vessels with redundant connections network comprises mainly cords, already connected together vessels and cords are connected to each other without any interruptions chorionic villus dominated by this network of vascular elements vessels and cords are located centrally as well as peripherally and as a consequence contact the overlying trophoblastic layer
5 to 6	7 and 8	10 - 26	villi dominated by capillary network of vessels and cords capillary network contains more vessels than cords
7 to 8	9 and 10	60 - 75 two central vessels 26 - 34 capillary network	villi have two large centrally located vessels surrounded by and connected to a peripheral capillary network capillary network contains vessels with a lumen in tight contact with overlying trophoblastic layer villous projections also contain blind ending capillary sprouts
9 to 10	11 and 12	70 - 90 two central vessels 26 - 34 capillary network	immature intermediate villi characterized by two large vessels surrounded by a capillary network capillary network has few cords blind ending capillary sprouts off the capillary network

Reference

↑ <pubmed>17545656</pubmed>

Decidua and villi location
Chorionic villi

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Cite this page: Hill, M.A. (2024, June 15) Embryology ANAT2341 Lab 4 - Implantation and Villi Development. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/ANAT2341_Lab_4_-_Implantation_and_Villi_Development

What Links Here?

[1] <pubmed>17545656</pubmed>

[1]