Fused Heart Tube : By the 25th day of gestation, a "heart" is already pumping and circulating blood through a network of vessels. These initial heartbeats come from a very different organ than the one seen in an adult. The early heart is really only a simple tube twisted back on itself because there is not enough room to grow. However, by the 5th week, the twisted tube fuses and becomes a two-chambered heart with one atrium and one ventricle.
Prenatal or antenatal development is the process in which a human embryo or fetus (or foetus) gestates during pregnancy, from fertilization until birth. Often, the terms fetal development, foetal development, or embryology are used in a similar sense.
After fertilization, the process of embryogenesis, (the early stages of prenatal development) begins. By the end of the tenth week of gestational age the embryo has acquired its basic form and the next period is that of fetal development where the 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.
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