✅ THIRD WEEK | EMBRYOLOGY 📚 EMBRYO DEVELOPMENT | GASTRULATION | NOTOCORD | PREGNANCY

Gastrulation

The process by which the three germ layers (ectoderm, mesoderm, endoderm) are established in the embryo during the third week of gestation.

Ectoderm

The outermost germ layer that forms the skin and nervous system.

Mesoderm

The middle germ layer that gives rise to muscles, bones, and the circulatory system.

Endoderm

The innermost germ layer that develops into the gastrointestinal tract and associated organs.

Trilaminar embryonic disc

The structure formed by the three germ layers during embryonic development.

Primitive streak

A structure that forms on the surface of the epiblast and marks the beginning of gastrulation.

Invagination

The process by which epiblast cells migrate towards the primitive line, detach, and slide below it to form the endoderm and mesoderm.

Notochord

A solid cord of cells that forms from prenotochordal cells and plays a crucial role in the development of the neural tube and spinal column.

Neurulation

The process of forming the neural tube, which will develop into the central nervous system.

Neuroenteric duct

A temporary duct that connects the amniotic cavity and the yolk sac during early embryonic development.

Oropharyngeal membrane

A membrane that will eventually form the oral cavity, located at the cranial end of the embryo.

Cloacal membrane

A membrane located at the caudal end of the embryo that will develop into the anal and urogenital openings.

Allantois

An embryonic structure that forms a diverticulum extending into the fixation pedicle, involved in waste storage and gas exchange.

Chorionic villi

Projections from the chorion that facilitate nutrient and gas exchange between the mother and embryo.

Primary villi

Initial projections formed by the cytotrophoblast and syncytiotrophoblast during the development of the placenta.

Secondary villi

Villi that develop when mesodermal cells invade the primary villi.

Tertiary villi

Definitive placental villi that contain blood vessels and are involved in nutrient and oxygen exchange.

Fixation pedicle

The structure that connects the embryo to the trophoblastic capsule, which later becomes the umbilical cord.

Stem villi

Villi that extend from the chorionic plate to the decidua basalis, anchoring the placenta.