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, occurring in a time span of about 7-10 days

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 $7$ and develops into embryo/baby

Implantation

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

occurs 7-10 days after fertilization

embryoblast (Inner cell mass)

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.\

only produced during pregnancy

Corpus luteum

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.

Ovulation

The release of a mature oocyte from an ovarian follicle, typically occurring around the midpoint of the menstrual cycle.

Fertilization

The process in which a sperm cell fuses with an oocyte to form a zygote, starting the development of a new organism.

occurs in the uterine tube

Pre embryonic development

including stages such as morula and blastocyst formation, occurs as the fertilized egg moves through the uterine tube to the uterus, The blastocyst implants into the uterine lining around day 7 post-fertilization.

Pre-embryonic cleavages

the series of rapid cell divisions that occur after fertilization, leading to the formation of a multicellular structure from the fertilized egg

Stages of pre-embryonic cleavage

Two cell → four cell → eight cell → morula 16 cell → blastocyst 70-100 cells (which will be implanted)

occurs in uterine tube

Two-cell, four-cell, and eight-cell

occurs in uterus

morula 16-cells, and blastocyst 70-100 cells

placenta

an organ that forms during pregnancy, facilitating the exchange of nutrients and waste products between the mother and the developing fetus.

function of placenta

allows maternal and fetal blood components to be conducted without mixing directly. It also secretes hormones like human chorionic gonadotropin (HCG) to support pregnancy.

Intervillous space

space within the placenta filled with maternal blood and surrounds the chorionic villi

Yolk sac

an extra-embryonic membrane that provides nutrients to the developing embryo in the early stages of development before the placenta is fully formed.

Amniotic fluid

A clear fluid that surrounds the embryo in the amniotic sac, providing cushioning and maintaining a stable temperature, while allowing for movement and development.

Uterus

The hollow muscular organ in a female mammal where a fertilized ovum implants and develops during pregnancy.

function of uterus

responsible for nurturing the embryo and fetus throughout gestation.

Chorion

The outermost membrane surrounding the embryo, contributes to the formation of the placenta.

function of chorion

plays a role in gas and nutrient exchange between the mother and developing fetus.

Amniocentesis

A medical procedure used to obtain a sample of amniotic fluid that surrounds a developing fetus, typically performed to test for genetic disorders or congenital conditions.

Fetal Blood Sample

A procedure where a sample of blood is drawn from the fetus, often done through the umbilical cord, to assess fetal health, genetic conditions, or blood type before birth.

Morula

16-cells

Blastocyst

70-100 cells