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Once fertilized, the ovum is referred to as a zygote, a single diploid cell. The zygote undergoes mitotic divisions with no significant growth (a process known as cleavage) and cellular differentiation, leading to development of a multicellular embryo. The formation of the male and female gametes (sex cells) through meiosis makes fertilization possible. The ovum, the female gamete, is relatively large (approximately 0.1 mm across in humans) and contains a cytoplasm rich with organelles and substances to be used during development. The Development of viable offspring requires the successful union of ovum and sperm, both of which are haploid (contain half the number of somatic chromosomes), to form a diploid cell. In many mammals, the sperm is required to break through a translucent, elastic coating of the ovum, known as the zona pellucida, before fertilization can take place.
The process of embryo development from fertilization to implantation and the formation of a gastrula include various steps
What is embryo development?
Human embryonic development, or human embryogenesis, is the development and formation of the human embryo.
What is embryo?
Embryo is the early developmental stage of an animal while it is in the egg or within the uterus of the mother.
stages of embryonic development:-
1. fertilization
- The merging of the female gamete (egg) with the male gamete (sperm) is known as fertilization (spermatozoa).
- The result is a formation called a zygote, which can arise naturally inside the female reproductive system or with the help of reproductive technology outside the human body.
- When a woman ovulates, one egg is released into her Fallopian tubes (or more in the case of fraternal twins).
- A woman's cervical mucus will thin at this period, allowing sperm to flow through more easily.
- Special secretions assist spermatozoa travel past the cervix to the uterine tube, where fertilization occurs between 24-72 hours after ejaculation in the vaginal canal.
2.Blastocyst Development
- The embryo is made up of a tiny number of cells that divide continuously inside a complicated structure called a blastocyst.
- It is made up of two types of cells: inner and outer cells, as well as fluids.
- During development, the blastocyst is enclosed in a protective coat called zona pellucida, which is similar to an egg shell.
- The outer cells, which will become the future placenta and associated tissues to support fetal growth in the uterus, are placed just under this layer.
- The blastocyst's inner cells will develop into various tissues and organs of the human body, including bones, muscles, skin, liver, and heart.
- The cells of the blastocyst expand quickly, undergo several modifications, and transform into highly specialized cells, resulting in a very tight structure.
- These alterations occur in humans during the first few days of development, just before implantation in the uterus.
- The zona pellucida splits at this point, releasing the blastocyst.
- It travels through the Fallopian tubes to the uterus, where it implants on day ten.
3. Blastocyst Implantation
- The blastocyst implants in the endometrium, the mucous membrane that borders the uterus, when it reaches the uterus.
- The future placenta will be formed by the blastocyst's exterior cells and the uterine inner lining working together.
- The placenta is a structure that provides nutrition to the newborn while also removing waste.
4. The Embryo Development Process
- The blastocyst develops into an embryo when it progresses through the final stages of the implantation process into the inner lining of the uterus.
- Internal organs and exterior structures grow throughout this time.
- The mouth, lower jaw, and neck appear, while the circulatory system begins to develop and a heart tube is formed.
- Arms, legs, fingers, toes, and eyes emerge, and arms, legs, fingers, toes, and eyes are formed.
- The brain and spinal cord have already developed, whereas the digestive tract and sensory organs are just beginning to grow.
- The cartilage is being replaced by the earliest bones.
- The embryo enters the ultimate stage of development, a fetus, after ten to twelve weeks of pregnancy.
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