Human embryos

Human embryo

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A human embryo at 8 weeks gestation
Latin	Embryo humanus
Precursor	Zygote
System	Reproductive system

The human embryo is the early stage of human development that occurs from the time of fertilization until the end of the eighth week of gestation. During this period, the embryo undergoes significant growth and differentiation, laying down the foundational structures of the body.

Developmental Stages

The development of the human embryo is a complex process that can be divided into several key stages:

Fertilization

Fertilization occurs when a sperm cell from a male merges with an ovum from a female, forming a single cell known as a zygote. This process typically takes place in the fallopian tube.

Cleavage and Blastocyst Formation

Following fertilization, the zygote undergoes a series of rapid cell divisions known as cleavage. These divisions result in the formation of a multicellular structure called a blastocyst, which consists of an inner cell mass and an outer layer known as the trophoblast.

Implantation

Around six to seven days after fertilization, the blastocyst implants itself into the endometrium of the uterus. This marks the beginning of the embryonic period.

Gastrulation

Gastrulation is a critical phase where the three primary germ layers—ectoderm, mesoderm, and endoderm—are formed. These layers will give rise to all the tissues and organs of the body.

Neurulation

Neurulation is the process by which the neural tube is formed. The neural tube will eventually develop into the central nervous system, including the brain and spinal cord.

Organogenesis

During organogenesis, the major organs and structures of the body begin to form. This includes the development of the heart, limbs, eyes, and other essential systems.

Embryonic Structures

Several key structures are present during the embryonic period:

• Amnion: A thin membrane that forms the amniotic sac, providing a protective environment for the embryo.
• Chorion: The outermost membrane that contributes to the formation of the placenta.
• Yolk Sac: Provides early nourishment to the developing embryo before the placenta is fully functional.

Clinical Significance

Understanding embryonic development is crucial for diagnosing and managing congenital anomalies and for advancing reproductive technologies such as in vitro fertilization.

Ethical Considerations

The study and manipulation of human embryos raise significant ethical questions, particularly in the context of stem cell research and genetic engineering.

Also see

• Fetal development
• Embryology
• Prenatal development
• Zygote
• Stem cell