Week 2 of Embryonic Development PDF
Document Details
Uploaded by Christy Forwood
Tags
Summary
This document provides information about week 2 of human embryonic development, including key processes like trophoblast differentiation, implantation, and the formation of the amnion and yolk sac. Important abnormalities like ectopic pregnancies and molar pregnancies are also mentioned.
Full Transcript
02/11/23 Week 2 of embryonic development: Week 2: Day 7-8 Trophoblasts that contact the endometrium continue to differentiate into cytotrophoblasts and syncytiotrophoblasts produces: hCG, lytic enzymes, factors. Decidual reaction: an increase in secretory function of the endometrium ( decidua is muc...
02/11/23 Week 2 of embryonic development: Week 2: Day 7-8 Trophoblasts that contact the endometrium continue to differentiate into cytotrophoblasts and syncytiotrophoblasts produces: hCG, lytic enzymes, factors. Decidual reaction: an increase in secretory function of the endometrium ( decidua is mucosal lining of the uterus or endometrium, modi ed by pregnancy ). Embryoblast or ICM differentiate into 2 layers: the epiblast ( 4 columnar epithelial cells ) and the hypoblast ( 3 cuboidal epithelial cells) to form a attened, almost circular bi-laminar embryonic disc. Day 9-10 Implantation complete ( brin plug ) Extracellular vacuoles appear in the syncytiotrophoblasts and join together to form lacunae. Amnioblasts separate from the epiblast and organise into amnion ( thin membrane that encloses the amniotic cavity ). The cells of the hypoblast extend to surround the yolk sac forming the primary yolk sac or the primary umbilical vesicle. Days 11 - 13 Formation of the extraembryonic mesoderm: supposed to epithelial of the amnion and the primary yolk sac. Formation of the chorionic or extraembryonic cavity. Transformation of the primary into the secondary yolk sac, which is also known as the secondary umbilical vesicle. Lacunae are lled with maternal blood, this is the beginning of uteroplacental circulation. Formation of primary chorionic villi. End of week 2: The formation of the bi-laminar disc sets the dorsal/ ventral axis ( epiblast is dorsal to the hypoblast). Week 2 abnormalities: abnormal implantation: ectopic pregnancy Implantation occurs in the uterine tube or outside the uterus. Molar pregnancy: Hydatidiform mole Occurs when only the trophoblast layers of the embryo proliferate and not the epiblast and as a result no embryo develops. Summary of the first two weeks:
