Question

Describe the process of embryonic development from fertilization to the neurula stage. (Include interphase and the 4 phases of mitosis).

Answer 1

The embryonic development takes through several developmental stages, the sperm and ovum fuse to form the zygote. The zygote undergoes mitotic cleavage to form morula. Day four begins blastulation and cavities. There are now two different cell types, an inner and outer. The inner cells are called the inner cell mass, and the exterior is known as the trophoblast, which later helps form the placenta, and the inner cell mass becomes the embryo. The inner cell mass will further differentiate into the epiblast and the hypoblast. The hypoblast will become the primitive yolk sac, and the epiblast will become the amniotic sac. During this phase, the entity is a blastula, and the zona pelucida is now gone, allowing for growth and differentiation. During week three, tubes will form, and this is known as the gastrulation phase. Movements during gastrulation are dependent on differential cell adhesion, chemotaxis, chemokinesis, and planar polarity.During this time, there are three layers of cells which will make up different organ systems. These are known as the endoderm, mesoderm, and ectoderm. The ectoderm forms the epidermis, nails, hair, peripheral nervous system, brain, and spinal cord. The mesoderm forms the muscle, bone, connective tissue, notochord, kidney, gonads, and circulatory system. The endoderm forms the epithelial lining of the digestive tract, stomach, colon, liver, bladder, and pancreas. At sixteen weeks the primitive streak forms. The primitive streak establishes the midline of the body. The next stage in development is neurulation. At this time the notochord induces the ectoderm to form the neural plate which eventually forms the neural tube. The neural tube will become the brain and spinal cord. The mesoderm divides into the axial, paraxial, intermediate, and lateral plate mesoderm, which give rise to different body parts — the paraxial mesoderm forms somites, which differentiate into cartilage, muscle, bone, and dermis. The intermediate mesoderm becomes the urogenital system, and the lateral plate mesoderm becomes the heart and vessels. The endoderm becomes the gastrointestinal tract, and the ectoderm will meet the endoderm forming the mouth and the excretory organ. Mitosis consists of 4 phases : prophase, metaphase, anaphase and telophase. Two additional phases are interphase  and cytokinesis, occur before and after mitosis. Mitosis  is a cyclical process that continues throughout the life of an organism.Mitosis is  the process in which the nucleus of a eukaryotic cell divides. During this process, sister chromatids separate from each other and move to opposite poles of the cell. It happens in 4 phases , called prophase, metaphase, anaphase, and telophase.

Interphase refers to stages of the cell cycle other than mitosis. During interphase , cellular organelles double in number, the DNA replicates, and protein synthesis occurs. The chromosomes are not visible and the DNA appears as uncoiled chromatin.