Crash Course : Reproductive System part 4

Zygote

The diploid cell formed by the fusion of sperm and egg nuclei; the first cell of a new organism.

Cleavage

The period of rapid mitotic cell divisions of the zygote, producing smaller cells called blastomeres.

Blastomere

One of the small cells resulting from the cleavage divisions of a zygote.

Morula

A solid ball of 16 or more blastomeres, formed during early cleavage.

Blastocyst

The pre-implantation stage of development; a hollow ball of cells with an inner cell mass and trophoblast layer.

Inner Cell Mass

The cluster of cells inside the blastocyst that will develop into the embryo.

Trophoblast

The outer cell layer of the blastocyst that facilitates implantation and contributes to the placenta.

Implantation

The process by which the blastocyst attaches to and embeds within the endometrium of the uterus.

Placenta

The temporary organ of pregnancy that allows for nutrient/waste exchange and hormone production between mother and fetus.

Embryonic Period

Weeks 3-8 of prenatal development; the time of major organ system formation (organogenesis).

Fetal Period

The period from week 9 of pregnancy until birth; characterized by growth and maturation of organs.

Human Chorionic Gonadotropin (hCG)

A hormone secreted by the trophoblast that maintains the corpus luteum; the basis for pregnancy tests.

Labor

The physiological process by which the fetus, placenta, and membranes are expelled from the uterus.

Dilation Stage

The first stage of labor, involving the thinning (effacement) and opening (dilation) of the cervix.

Expulsion Stage

The second stage of labor, during which the baby is delivered.

Placental Stage

The third stage of labor, involving the delivery of the placenta and fetal membranes (afterbirth).

Teratogen

An agent (e.g., drug, virus) that can cause birth defects during embryonic development.

Organogenesis

The process of organ formation, which occurs primarily during the embryonic period.