Embryo 40 Day Old Heart and Liver: Computer Generated Image from Micro-MRI, actual size of embryo = 8.0 mm - This image of the embryo presented from the left-dorsal side shows the internal organs during the sixth week of embryonic development. This age is calculated from the day of fertilization. The prominent C-shaped curvature of the spinal cord (in red) remains. The chambered heart, marked in red, can be seen from the backside perspective. The liver is highlighted in violet. Veins and blood vessels connect the heart to the brain to supply nutrients and oxygen.
Prenatal development is the process in which an embryo and later fetus develops during gestation. Prenatal development starts with fertilization the first stage in embryogenesis which continues in fetal development until birth.
In human pregnancy, prenatal development, also known as antenatal development, is the development of the embryo following fertilization, and continued 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 many organs become fully developed. This fetal period is described both topically (by organ) and chronologically (by time) with major occurrences being listed by gestational age.
In other animals the very early stages of embryogenesis are the same as those in humans. In later stages, development across all taxa of animals and the length of gestation vary.
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