Stages of Human Development

Question 1

Embryonic Stage

Answer 1

End of 2nd week after conception to end of 8th week; developing organs are MOST susceptible to major structural defects as result of teratogen with time of greatest susceptibility depending on organ system; examples = CNS most affected from beginning of 3rd week to beginning of 6th week; heart affected from middle of 3rd week to middle of 6th week

Question 2

Germinal Stage

Answer 2

Conception to implantation, occurring 8-10 days later; exposure to teratogen may only damage a few cells having little to no effect on development or may affect many cells and lead to organism’s death

Question 3

Fetal Stage

Answer 3

Beginning of 9th week until birth; organ systems less affected but exposure can still cause less severe effects especially for external genitalia and brain; prolonged exposure during this time tends to cause growth retardation and lowered IQ