In her human development class, Dr. Smith shows students several photographs of prenatal development. The fetus is protected from toxins by the placenta 15. Every human organism that is conceived originally has the potential to develop either a male or a female reproductive system. The fetus reaches the age of viability at around 32 weeks after conception.
All major organs begin to form between the second and the eighth week after conception.
Sex differentiation is determined at conception by the inheritance of X and Y chromosomes. Sex differentiation begins around the 7th or 8th week with the development of male and female external genitalia. Males and females begin with identical tissue that can evolve into male or female reproductive systems depending on genetic and hormonal factors. The earliest period in which nerves are connected to muscles and make them contract is the fetal period.