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A fetus is a stage in the human development considered to begin nine weeks after fertilization. [4] [5] In biological terms, however, prenatal development is a continuum, with many defining features distinguishing an embryo from a fetus. A fetus is also characterized by the presence of all the major body organs, though they will not yet be ...
Human embryology is the study of this development during the first eight weeks after fertilization. The normal period of gestation (pregnancy) is about nine months or 36 weeks. The germinal stage refers to the time from fertilization through the development of the early embryo until implantation is completed in the uterus .
In humans, internal organs begin to develop within 3–8 weeks after fertilization. The germ layers form organs by three processes: folds, splits, and condensation. [6] Folds form in the germinal sheet of cells and usually form an enclosed tube which you can see in the development of vertebrates neural tube.
The development of the reproductive system is the part of embryonic growth that results in the sex organs and contributes to sexual differentiation. Due to its large overlap with development of the urinary system , the two systems are typically described together as the genitourinary system .
Plant development is the process by which structures originate and mature as a plant grows. It is studied in plant anatomy and plant physiology as well as plant morphology. Plants constantly produce new tissues and structures throughout their life from meristems [36] located at the tips of organs, or between mature tissues. Thus, a living plant ...
Neurulation forms the nervous system, and organogenesis is the development of all the various tissues and organs of the body. A newly developing human is typically referred to as an embryo until the ninth week after conception, when it is then referred to as a fetus.
In human pregnancy, prenatal development is also called antenatal development. The development of the human embryo follows fertilization , and continues as fetal development . By the end of the tenth week of gestational age , the embryo has acquired its basic form and is referred to as a fetus .
This article contains a list of organs in the human body. It is widely believed that there are 79 organs (this number goes up if you count each bone and muscle as an organ on their own, which is becoming a more common practice [1] [2]); however, there is no universal standard definition of what constitutes an organ, and some tissue groups' status as one is debated. [3]