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Nine-week-old human embryo from an ectopic pregnancy. Organogenesis is the development of the organs that begins during the third to eighth week, and continues until birth. Sometimes full development, as in the lungs, continues after birth. Different organs take part in the development of the many organ systems of the body.
Gestational age: 7 weeks and 0 days until 7 weeks and 6 days old. 50–56 days from last menstruation. Embryonic age: Week nr 6. 5 weeks old. 36–42 days from fertilization. The embryo measures 13 mm (1 ⁄ 2 in) in length. Lungs begin to form. The brain continues to develop. Arms and legs have lengthened with foot and hand areas distinguishable.
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. The next period is that of fetal development where ...
An embryo of a gestational age of 9 weeks and 0 days. The head is directed to the right in the image. The heart is discerned in the center of the embryo. A hand is visible slightly above. Even before the fetal stage begins, a six-week-old human embryo can arch its back and neck. [6]
Carnegie stages. In embryology, Carnegie stages are a standardized system of 23 stages used to provide a unified developmental chronology of the vertebrate embryo. The stages are delineated through the development of structures, not by size or the number of days of development, and so the chronology can vary between species, and to a certain ...
Anatomical terminology. [ edit on Wikidata] An embryo is the initial stage of development for a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male sperm cell. The resulting fusion of these two cells produces a ...
A lateral and ventral view of an embryo showing the third (inferior) and fourth (superior) parathyroid glands during the 6th week of embryogenesis. Once the embryo reaches four weeks of gestation, the parathyroid glands begins to develop. [7] The human embryo forms five sets of endoderm-lined pharyngeal pouches.
The embryo, meanwhile, proliferates and develops both into embryonic and extra-embryonic tissue, the latter forming the fetal membranes and the placenta. In humans, the embryo is referred to as a fetus in the later stages of prenatal development. The transition from embryo to fetus is arbitrarily defined as occurring 8 weeks after fertilization.