Embryo 54 Day Nervous System and Internal Organs: Computer Generated Image from Micro-MRI, actual size of embryo = 26.0 mm - This image provides a left-sided view of the embryo undergoing its eighth week of development. The age is calculated from the day of fertilization. The primary focus of this image is on the internal organ structures of the embryo. The two major components of the central nervous system, the brain and the spinal cord are highlighted in brown. The three major parts of the brain can be observed. The largest part facing downwards is the forebrain. The narrow segment in the middle is the midbrain. The hindbrain connects the midbrain and spinal cord. The heart is marked in bright red and is situated alongside the lung, marked in orange. The structures below the lung are the stomach ( white ) and kidneys ( red orange. ) The red structure protruding outwards from the embryo is the umbilical cord, which serves as a mechanism for gas exchange, nutrient delivery and waste removal.
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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