Prenatal development

Embryo 44 Day Old Circulatory System: Computer Generated Image from Micro-MRI, actual size of embryo = 13.0 mm - This image presents a left-frontal perspective of the embryo during its seventh week of development. This age is calculated from the day of fertilization. The concentration of this image is on the circulatory system. The heart is indicated as a red, bulk-like structure. Blood vessels can be seen extending towards the brain and to the rest of the embryo's body. The umbilical cord, as observed potruding from the body, serves as a means of exchanging nutrients and wastes between the embryo and mother. The nerve endings surrounding the spinal cord are indicated in white.

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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