Human embryonic development

Human embryonic development is the process by which a human embryo forms and develops from fertilization through the end of the eighth week of development.

Fertilization: The fusion of a sperm and an oocyte that produces a zygote. It begins development by combining parental genomes and activating the zygote.
Zygote: The single cell formed when sperm and oocyte unite. It is the first cell of the developing human organism.
In vitro fertilization: A fertility treatment in which eggs are fertilized with sperm outside the body and an embryo is transferred to the uterus. It allows fertilization and early embryo culture to occur under laboratory observation.
Implantation: The attachment and embedding of a blastocyst in the uterine lining. It establishes the embryo's connection with maternal tissues after fertilization and cleavage.
Gametogenesis: The production and maturation of sperm or eggs from germ cells. It creates the gametes that precede, but are not part of, embryonic development.
Cleavage (embryology): Rapid mitotic divisions of an early embryo that increase cell number without substantial overall growth. These divisions transform the zygote into a compact multicellular embryo.
Inner cell mass: The cluster of cells inside a blastocyst that gives rise to the embryo proper and some supporting tissues. Its cells establish the embryonic lineage within the blastocyst.
Preimplantation genetic testing: Testing embryos created through in vitro fertilization for selected genetic or chromosomal findings before transfer. It examines embryos before implantation, during the developmental stages covered here.
Primitive streak: A transient structure in the epiblast that marks the start of gastrulation and establishes body axes. Its appearance initiates cell movements that organize the early body plan.
Fetal development: Human development from the beginning of the ninth week after fertilization until birth. It follows the embryonic period, when organ systems grow and mature.

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Human biologyBroader topic: It shows how a human body's structures arise before birth.