To answer the question regarding the hormones secreted by the placenta to maintain pregnancy, we will follow these steps:
### Step-by-Step Solution:
1. **Understand the Role of the Placenta**:
- The placenta is an organ that forms during pregnancy, connecting the developing fetus to the uterine wall. It facilitates the exchange of nutrients, gases, and waste between the mother and fetus. Importantly, it also has an endocrine function, meaning it secretes hormones that are crucial for maintaining pregnancy.
2. **Identify Key Hormones Secreted by the Placenta**:
- The main hormones secreted by the placenta that are essential for maintaining pregnancy include:
- **Human Chorionic Gonadotropin (HCG)**: This hormone is crucial for maintaining the corpus luteum, which in turn secretes progesterone necessary for sustaining the uterine lining.
- **Human Placental Lactogen (HPL)**: This hormone prepares the mother's body for childbirth and lactation by promoting the development of mammary glands.
- **Progesterone**: While primarily an ovarian hormone, during pregnancy, the placenta also produces progesterone to maintain the endometrium.
- **Estrogen**: Similar to progesterone, estrogen levels rise significantly during pregnancy due to secretion by the placenta, supporting fetal development and preparing the body for childbirth.
3. **Distinguish Between Other Hormones**:
- It is important to differentiate between hormones that are not secreted by the placenta and do not play a role in maintaining pregnancy:
- **Oxytocin**: Secreted during labor to induce contractions, not for maintaining pregnancy.
- **Relaxin**: Secreted by the ovaries, primarily during the later stages of pregnancy to aid in childbirth, not for maintaining pregnancy.
- **Prolactin**: While important for milk production, it is not secreted by the placenta.
- **Glucocorticoids and Mineralocorticoids**: These are secreted by the adrenal glands and are not related to the maintenance of pregnancy.
4. **Conclusion**:
- The hormones that are secreted by the placenta to maintain pregnancy are HCG, HPL, progesterone, and estrogen. Therefore, the correct answer is the option that includes these four hormones.
