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Human embryonic development (HED) is the process of forming a human embryo. During the early stages of development, the embryo divides and differentiates its cells. In biology, the human body develops from a single-celled zygote to an adult. A sperm cell successfully penetrates and unites with an egg cell (ovum). The germinal stage of development begins when sperm and egg genetic material unite to produce a single cell termed a zygote. Human embryonic development lasts for eight weeks, after which the embryo becomes a foetus. Human embryology studies the first eight weeks of development. The average pregnancy lasts nine months or 40 weeks.
The germinal stage spans from fertilisation until implantation in the uterus. 10 days for the germinal stage. At this stage, the zygote begins to cleave. The blastocyst is then deposited in the uter Embryogenesis continues with gastrulation, when the embryo’s three germ layers develop (histogenesis), and then neurulation and organogenesis.
The foetus has more distinguishable outward characteristics and growing organs than the embryo. Throughout embryogenesis, gene expression, cell development, and differentiation are coordinated spatially and temporally. Other animals, notably chordates, go through a similar process.
Stages of development
A successful pregnancy has various phases. To fertilise an egg, a man’s sperm must enter it. In the end, a blastocyst is formed. The blastocyst must enter the uterine endometrium. The implanted blastocyst grows into an embryo, then a foetus.
Fertilization
Fertilization is the uniting of a female and male gamete (egg) (spermatozoa). The result is a zygote, which can arise naturally within the female reproductive system or artificially outside the human body.
Ovulating women release one egg into their Fallopian tubes (or more in the case of fraternal twins). During this period, a woman’s cervical mucus thins to allow sperm to pass more easily.
After spermatozoa ejaculation, specific secretions assist them to swim through the cervix to the uterine tube where fertilisation occurs within 24-72 hours.
The fertilised egg or zygote then moves toward the uterus, dividing into a blastocyst.
Blastocyst Growth
After fertilisation, a tiny number of cells called blastocysts continually divide to become the embryo. It is made up of inner and exterior cells, and fluids. During development, the blastocyst is protected by a translucent shell called zona pellucida. The outer cells form the future placenta and accompanying tissues to support foetal development in the uterus. The blastocyst’s inner cells develop into bones, muscles, skin, liver, and heart.
The blastocyst cells proliferate rapidly, changing into more specialised cells, resulting in a highly compact shape. These alterations occur in humans during the first few days of development, before implantation. The blastocyst is released when the zona pellucida (eggshell) splits. In the uter, it implants about day ten.
Implantation
The blastocyst implants in the endometrium, the mucous membrane lining the uterus. The blastocyst’s outer cells and the uterine inner lining will become the placenta. The placenta is an organ that feeds and excretes the infant.
Embryo Development
The blastocyst develops into an embryo after implantation into the uterine lining. This is when internal and external organs develop. The mouth, lower jaw, and throat form, while the blood circulation system develops and a heart tube forms. Arms, legs, fingers, toes, and eyeballs form. The brain and spinal cord are already established, but the digestive and sensory organs are still developing. First bones replace cartilage.
After ten to twelve weeks of pregnancy, the embryo develops into a foetus.
Fetal Development
By the 12th week of fertilisation, the embryo has reached the foetal stage. The foetus has established all of the baby’s organs and structures, but they must continually develop.
The foetus’ upper and lower extremities are fully grown at three months. The reproductive organs and ears and teeth have evolved. End of the month, the foetus is 5 inches long and has finished expanding most of its circulatory and urinary systems.
The foetus is six months old and is around 12 inches long. The foetus grows and changes position, reacting to noises and stimuli. The body can grow up to 14 inches long.
At eight months, the foetus is born. The baby’s brain is rapidly developing, allowing them to see and hear, but not breathe. The newborn can weigh 5 lbs. In the 9th month of pregnancy: the baby responds to stimuli and moves the complete body but the space surrounding the new human being becomes too small.
If the baby hasn’t moved within the uterus, now is the moment to drop into the pelvis and face the world.
Human Embryo Development Stages IVF
An embryo is produced when sperm fertilises an egg in the fallopian tube. The embryo continues to grow (via cell division) as it travels back down the fallopian tube towards the uterus. About 5-6 days after conception, the embryo enters the uterine cavity. It is currently a blastocyst, a 100-cell embryo.
A blastocyst develops in a laboratory during IVF. Ovarian egg retrieval, sperm fertilisation, and embryo creation. The blastocyst develops in 5–6 days from an embryo. Embryos that survive this stage of development have a high implantation potential.
Conclusion
A fertilised egg grows into a blastocyst, an embryo, and finally a foetus. Human embryonic development begins with a single cell that divides into a mass of numerous cells. Embryogenesis is the scientific word for the process of embryo development. This is the process that occurs after conception.
