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The placenta is a temporary organ that develops during pregnancy, connecting the fetus to the mother's blood supply. It secretes several hormones, which are crucial for maintaining a healthy pregnancy. Some of the major hormones secreted by the placenta are: 1. Human Chorionic Gonadotropin (hCG): This hormone is produced early in pregnancy and helps to maintain the corpus luteum, which in turn produces progesterone needed to sustain the pregnancy. 2. Progesterone: Produced in large amounts during pregnancy, progesterone helps to maintain the uterine lining and suppresses the mother's immune response so that the fetus is not rejected. 3. Estrogens: These hormones are responsible for promoting the growth of the uterus, breasts, and other maternal tissues during pregnancy. 4. Human Placental Lactogen (hPL): This hormone helps to regulate the mother's metabolism and glucose levels to ensure a constant supply of nutrients for fetal development. 5. Relaxin: This hormone helps to relax the pelvic ligaments in preparation for childbirth and also acts on the mammary glands to prepare them for lactation.

Endocrine glands are responsible for producing and secreting hormones directly into the bloodstream without the use of ducts. These hormones play specific roles in regulating various physiological processes in the body. The placenta is considered an incomplete endocrine gland because it has a limited hormone repertoire. While it does produce and secrete a range of hormones that are essential for the maintenance of pregnancy, it does not produce all the hormones necessary for overall bodily functions. Additionally, the placenta is a temporary organ, which means it only functions during pregnancy and is not involved in hormone regulation throughout a person's entire life. Its primary function is to support fetal development, so its endocrine role is focused on this goal without covering all the hormonal needs of the organism. For these reasons, the placenta is considered an incomplete endocrine gland. By identifying the hormones secreted by the placenta and understanding the concept of an endocrine gland, we can now appreciate why the placenta is considered incomplete in this context. It plays a crucial but limited role in hormone regulation during pregnancy, supporting the growth and maintenance of the fetus.