Final answer:
The placenta is the organ that secretes hormones necessary for fetal survival. It develops during early pregnancy and gradually takes over as the endocrine organ of pregnancy, secreting hormones like hCG, estrogens, and progesterone.
Step-by-step explanation:
The organ that secretes hormones necessary for fetal survival is the placenta. The placenta develops during early pregnancy and gradually takes over as the endocrine organ of pregnancy.
It secretes several hormones, including hCG, estrogens, and progesterone, which maintain the pregnancy, stimulate maternal and fetal development, and mediate the transmission of maternal hormones into fetal blood and vice versa.