A conceptus (
Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power of the Roman Republic, it became ...
: ''conceptio'', meaning derivatives of
A zygote (, ) is a eukaryotic
Eukaryotes () are organism
In biology, an organism () is any organic, life, living system that functions as an individual entity. All organisms are composed of cells (cell theory). Organisms are ...
) is an
An embryo is the early stage of development of a multicellular organism
A multicellular organism is an organism
In biology, an organism () is any organic, life, living system that functions as an individual entity. All organisms ar ...
and its adnexa
(appendages or adjunct parts) or associated membranes (i.e., the products of conception).
The conceptus includes all structures that develop from the zygote, both embryonic and extraembryonic. It includes the embryo as well as the embryonic part of the placenta and its associated membranes:
:''For the alien race in 's , see .''
The amnion is a membrane that closely covers the when first formed. It fills with the which causes the amnion to expand and become the which serves to provide a protective environment for the developing em ...
The chorion is the outermost fetal membrane
The fetal membranes are biological membrane, membranes associated with the developing fetus. The two chorioamniotic membranes are the amnion and the chorion, which make up the amniotic sac that surroun ...
(gestational sac), and
The yolk sac is a membranous wikt:sac, sac attached to an embryo, formed by cells of the hypoblast adjacent to the embryonic disk. This is alternatively called the umbilical vesicle by the Terminologia Embryologica (TE), though ''yolk sac'' is far ...