What is the function of the embryonic disc?
The embryonic disc (or embryonic disk) forms the floor of the amniotic cavity. It is composed of a layer of cells – the embryonic ectoderm, derived from the inner cell mass and lying in apposition with the endoderm. Section through embryonic disc of a parti-coloured bat.
What is embryonic disc formation?
In humans, the formation of the embryonic disc occurs after implantation and prior to embryonic folding (between about day 14 to day 21 post-fertilization). The embryonic disc is derived from the epiblast layer, which lies between the hypoblast layer and the amnion.
What happens in the 3rd week of embryonic development?
The third week is concerned with establishing left and right handedness, the craniocaudal axis, as well as the conversion of the bilaminar disc into a trilaminar embryo. Additionally, there is further specialization of the extraembryonic structures that will continue to support the embryo during the intrauterine phase.
What are embryonic discs called?
Definition of embryonic disk 1a : blastodisc. b : blastoderm. 2 : the part of the inner cell mass of a blastocyst from which the embryo of a placental mammal develops. — called also embryonic shield.
What are the three parts of the embryonic disk?
nervous system development The embryonic disk soon acquires three layers: the ectoderm (outer layer), mesoderm (middle layer), and endoderm (inner layer).
Why is the amnion important for the embryo?
Lined with ectoderm and covered with mesoderm (both are germ layers), the amnion contains a thin, transparent fluid in which the embryo is suspended, thus providing a cushion against mechanical injury. The amnion also provides protection against fluid loss from the embryo itself and against tissue adhesions.
What are embryonic layers?
germ layer, any of three primary cell layers, formed in the earliest stages of embryonic development, consisting of the endoderm (inner layer), the ectoderm (outer layer), and the mesoderm (middle layer).
What is the importance of the three germ layers formed during the third week?
The second and third weeks of embryological development are crucial, involving the implantation of the blastocyst into the uterine wall; the establishment of three distinct germ layers – the mesoderm, endoderm and ectoderm – through gastrulation; and encompass the beginnings of the neurulation process, resulting in …
Which results in the lateral folding of the embryonic disc?
Lateral folding of the embryo is primarily the product of rapid growth of the ectodermal and mesodermal germ layers. As these layers expand, they begin begin to fold toward the midline and fuse. The ventrolateral body wall is thus created.
What are three functions of the amnion?
Amniotic fluid is responsible for: Protecting the fetus: The fluid cushions the baby from outside pressures, acting as a shock absorber. Temperature control: The fluid insulates the baby, keeping it warm and maintaining a regular temperature. Infection control: The amniotic fluid contains antibodies.
What are the function of the amnion chorion and allantois in birds and mammals?
The allantois is characteristic of reptiles, birds, and mammals, and lies between two other extraembryonic membranes: the amnion, the innermost layer, which covers and protects the embryo; and the chorion, which is the outermost layer, housing the embryo and all the other extraembryonic membranes.
What are the 3 layers of the embryo?