Early Embryonic Development

Timeline created by 20ssipes
  • Day 1: Menstrual Phase

    Day 1: Menstrual Phase
    Female's menstrual cycle experiences initial changes. The follicles in the ovaries begin to develop and the uterus's endometrium begins to fade away.
  • Day 1: Also Fertilization

    This is the fusion of the egg and sperm to form the diploid zygote. This process occurs naturally within the body's reproductive organs.
  • Day 2: Morula Development

    Day 2: Morula Development
    Cells mitotically divide to form a solid ball of cells (It has a mulberry like appearance).
  • Day 4: Blastocyst

    The blastocyst contains an outer trophectoderm layer, and inner cell mass, and a blastocoele (fluid filled). The inner cell mass will go on to develop into the entire embryo. This stage is followed by blastocyst hatching and then implantation.
  • Day 7: Implantation

    Day 7: Implantation
    This is when the fertilized egg attaches to the female's uterus. The conceptus is called a blastocyst, and it is by this adhesion that the embryo receives the initial oxygen and nutrients.
  • Day 13: Stage 6- Chorionic Cavity

    Day 13: Stage 6- Chorionic Cavity
    The bilaminar embryo is now about .2mm diameter in size. The embryo has developed the three embryonic spaces- amniotic, primitive yolk sac, and the chorionic cavity. This occurs towards the end of week two.
  • Day 16: Stage 7: Gastrulation

    Day 16: Stage 7: Gastrulation
    The epiblast layer has now formed three distinct layers- the ectoderm, mesoderm, and endoderm. The primitive streak is now beginning to form and starts burrowing from the ectoderm into the mesoderm. The inner cell mass is being converted into the trilaminar embryonic disc.
  • Day 23: First Heartbeat

    Around days 22-24, you will be able to identify the baby's heartbeat for the first time. This marks the first embryonic organ formed in the embryo.
  • Day 25: Stage 12- Development

    At this stage, the embryo experiences more drastic development. Neural secondary neurulation begins, the ependymal separates from the amniotic fluid, and the liver stroma and hepatic trabeculae forms.
  • Day 27- Neural Development

    The neural tube is now completely closed and the entire ventricular system is separated from the amniotic fluid. The ventral roots of the spinal cord begin their early stages of development.
  • Day 29: Respiratory Development

    The cochlear part of the otic vesicle elongates. The right and left lungs (which are still small buds at this stage), push into the primordia of pleural cavity.
  • Day 31- Visible Body Changes of Embryo

    Day 31- Visible Body Changes of Embryo
    The heart, liver, umbilical cord, and the mesonephric ridge are all seen externally in the form of a bulge. The heart's development begins in the mesoderm of the trilaminar embryonic disc, but when this disc folds, it gets pushed into the chest cavity.
  • Day 33: Vascular Development

    The vision lens pits close and the vertebral arteries begin taking formation. All arteries from the proatlantal to the 6th intersegmental artery begin to form.
  • Day 36: More respiratory Development

    The Pleuroperitoneal foramen closes, and the lungs/heart begin their decent of getting pushed into the thorax (closer to the correct anatomical position). During weeks six and seven, the nerve fibers approach the lingual epithelium.
  • Day 43: Pancreas Development

    During weeks 7-20, more pancreatic hormones are constantly being secreted when needed (specifically maternal insulin in small amounts). During week 7, the liver continues expanding and eventually causes the halt of of the heart/lung's decent.
  • Day 47: Vision

    During stages 19-21, the eyelids develop and begin to cover the eye while the palebral fissure develops. The oral cavity is also formed following the breakdown of the oral membrane. During weeks 7-8, the cornea, anterior chamber, pupillary membrane, lens, and retina also begin to form.
  • Day 51: Development of Gastrointestinal Tract

    Here, the gastrointestinal tract anal membrane forms its hole. In addition, the formation of the anterior communicating artery in the vascular system develops.
  • Day 54: Sensory Development

    In stages 22, the embryo begins to develop its sensory organs- migratory streams of neurons from the subventricular zone of olfactory bulb goes towards future claustrum. The embryo's finger and toe limbs begin to lengthen as well.
  • Day 56- Last Day before Termed "Fetus" (Stage 23)

    The embryo's abdominal wall is forming three distinct muscle layers with myotube orientation uniform in all muscles. The axial skeleton vertebral column is now made up of 33 or 34 cartilaginous vertebrae and is 20-33 mm in total length. This is the final stage of embryonic development and now the baby will be called a fetus.