Human Embryonic Development

These flashcards cover the vocabulary and key stages of human embryonic development, including fertilization, cleavage, implantation, and hormonal regulation.

Newborn

A single fertilized egg that develops over the span of $9$ months into an infant consisting of trillions of cells and capable of surviving outside the womb.

Sperm Migration

The journey of sperms up the vagina, through the uterus, to the uterine tube, occuring in a time span of about $1$ week.

Corona radiata

The surrounding layer of cells that hundreds of capacitated sperms must break through to reach the oocyte.

Zona pellucida

The layer surrounding the oocyte that becomes hardened after a sperm fuses with the oocyte to prevent polyspermy.

Polyspermy

The fertilization of an oocyte by more than one sperm.

Morula

A stage of pre-embryonic cleavage consisting of $16$ cells.

Blastocyst

A stage of pre-embryonic cleavage consisting of $70-100$ cells that includes the trophoblast and inner cell mass, typically implanting at day $7$.

Implantation

The process where trophoblast cells of the blastocyst adhere to the endometrium and digest endometrial cells until attached securely.

Inner cell mass (embryoblast)

The part of the blastocyst that will develop into an embryo.

Trophoblast

The part of the blastocyst that secretes human chorionic gonadotropin (HCG) and develops into the placenta.

Human chorionic gonadotropin (HCG)

A hormone that stimulates the growth of the corpus luteum to prevent its atrophy; levels rise significantly during the first trimester.

Corpus luteum

A structure that secretes progesterone and estrogen, which prevent menstruation and the loss of pregnancy.

Estrogen and Progesterone

Hormones secreted by the placenta during pregnancy that suppress FSH and LH to prevent other follicles from developing.

Chorionic villi

The surface in the placenta through which maternal and fetal blood components are conducted without the bloodstreams mixing directly.

Amnion

A protective layer that closely covers the embryo and is filled with amniotic fluid.

In vitro fertilization

A procedure involving egg collection from the ovaries, fertilization in a petri dish, and the transfer of embryos into the uterus.