Human embryogenesis is a complex process that occurs during the first eight weeks after fertilization. The stages of embryogenesis are described in more detail below. The process of embryogenesis begins with an egg or ovum being fertilized by a sperm cell to form a zygote. The zygote is surrounded by a strong membrane made up of glycoproteins, which the sperm has managed to penetrate. The zygote is formed 24 hours after the egg and sperm nuclei fuse. The zygote is a single diploid cell. Over the next three days, the zygote undergoes a number of cell divisions, a process referred to as cleavage. Once the embryo has reached the 8-cell stage, it undergoes another process called compaction, which involves the tight binding of the cells to create a compact sphere. After compaction, the embryo is made up of 16 cells, which is referred to as the morula. After one more day, a cavity referred to as the blastocele develops in the morula. Cells inside the blastocele compact and flatten to form a structure referred to as the blastocyst. Over the next week, the mass of cells rapidly divides, giving rise to a disc-shaped structure that has two layers. One of the layers goes on to become the embryo and the amniotic cavity, while the other layer develops into the yolk sac. Three weeks after ovulation, two types of cells arise from the streak which changes the two-layered disc into a three-layered one. These layers are referred to as the ectoderm, mesoderm and endoderm. The endoderm eventually gives rise to the tissue that forms a lining in the tonsils, lungs, bladder, digestive system, tongue and urethra. The mesoderm develops into the bones, lymph, heart, lungs, muscles, blood cells, spleen and genital organs. The ectoderm gives rise to the nails, skin, tooth enamel, mammary glands, pituitary gland, anus, mouth, sinuses, eye lens, the lining of the external and internal ear and the entire nervous system. Citations are important for a journal to get impact factor. Impact factor is a measure reflecting the average number of citations to recent articles published in the journal. The impact of the journal is influenced by impact factor, the journals with high impact factor are considered more important than those with lower ones. This information can be published in our peer reviewed journal with impact factors and are calculated using citations not only from research articles but also review articles (which tend to receive more citations), editorials, letters, meeting abstracts, short communications, and case reports.
