Embryonic Development

It is the prenatal stage that begins at conception and lasts through the second week.  In this stage zygote begins to have cell reproduction. Consequently, the zygote becomes a multi celled ball that attaches itself to the wall of the uterus of the mother.

The process of organogenesis takes place in the embryonic period. The formation of the nasal structure is a part of organogenesis and thus occurs in embryonic period.

Around the 9th day, cells from the hypoblast spread around the blastocoele, forming the exocoelomic or Heuser's membrane. When the blastocoele is surrounded by this membrane, it is referred to as the primary yolk sac or exocoelomic cavity.

The chorion laeve forms from the mural (abembryonic) pole of the embryo trophoblast.

Blue nevus is a true mesodermal structure and second most common intraoral nevi.

The human embryo has the protection cover of the Amniotic cavity.

It is formed by the outer cell mass which later develops into the placenta. It forms the outer wall of the blastocyst.

The eye lens is derived from ectoderm which is the outermost germ layer formed during the embryo development.

Germinal epithelium of the ovary possesses cuboidal cells.

These are extra embryonic membranes providing protection and nourishment to the growing foetus The eutherian placenta is derived from the layers.

The grey crescent is a pigmented region opposite the sperm entry point in amphibian zygotes. It marks the future dorsal side and specifically corresponds to the region where the dorsal lip of the blastopore will form during gastrulation. This area contains important organizational factors that establish the embryonic body axis.

Mesolecithal eggs have moderate yolk quantity (between oligolecithal and macrolecithal). They undergo holoblastic cleavage (complete division) but it is unequal - the vegetal pole (yolk-rich) divides slower than the animal pole. This is characteristic of amphibians like frogs. Meroblastic (incomplete) cleavage occurs in macrolecithal eggs.

Gastrulation is the embryonic stage where the blastula reorganizes into three germ layers (ectoderm, mesoderm, endoderm). This process forms the archenteron (primitive gut cavity), which eventually becomes the digestive tract. Heart, brain, and lungs form later during organogenesis (neurulation and subsequent development), not during gastrulation itself.