Chimera

Early Embryonic Development

By Kingkhan

  • Zygote

    Zygote
    A diploid cell resulting from the fusion of two haploid gametes; a fertilized ovum.

  • Morula

    Morula
    A solid ball of cells resulting from division of a fertilized ovum, and from which a blastula will be formed

  • Blastocyst

    Blastocyst
    A thin walled hollow structure that contains a cluster of cells (inner cell mass) from which the embryo arises; this leaves a space within the called the amniotic cavity.

  • Implantation

    Implantation
    The attachment of the blastocyst to the wall of the uterus at the start of pregnancy and typically occurs 7-9 days after fertilization.

  • Gastrulation

    Gastrulation
    During gastrulation several important things occur. First the three primary germ layers are formed followed by the formation of the basic body plan which includes physical construction of the primary body axes. Due to the movements of gastrulation, cells are moved to new positions allowing them to interact with cells that were not near them before which furthers differentiation.

  • Musculoskeletal Somitogenesis

    Musculoskeletal Somitogenesis
    The first somites begin to form and continue to be added in sequence as pairs. Somites give rise to many different connective tissues including cartilage, bone, muscle, and tendon.

  • Heart

    Heart
    The heart begins to beat in humans between day 22-23 marking the formation of the first embryonic organ.

  • Bodily Formation

    Bodily Formation
    By stage 14 (around day 32) there is an observable heart, liver, umbilical cord, mesonephric ridge which manifest externally from the embryo as bulges. The first appearance of the future cerebral hemispheres is visible after the cerrebellar plate differentiates into an intermediate layer.

  • Stage 23: End of Organogenesis Period

    Stage 23: End of Organogenesis Period
    The embryo now has a developed head, nose, eyes, external acoustic meatus, and external ears. The trunk of the body has straightened and the upper limbs are longer and bent at the elbow while the hands and feet are turned inwards. The extraembryonic coelom is no longer visible after being lost by fusion with the expanding amniotic cavity. This marks the end of the organogenesis period and the embryo is classified as a fetus afterwards.