Understanding Hormones in Later Pregnancy

Pregnancy is a complex process regulated by various hormones produced by different organs, including the ovaries, placenta, and pituitary gland. The question asks specifically about a hormone secreted by the ovary during the later phase of pregnancy.

Hormones and Their Sources During Pregnancy

Let's examine the options and their sources during pregnancy:

• Lactogen: This refers to Human Placental Lactogen (hPL), also known as human chorionic somatomammotropin (hCS). It is primarily secreted by the placenta. hPL affects the mother's metabolism and plays a role in preparing mammary glands for lactation.
• Relaxin: This hormone is secreted by the corpus luteum of the ovary and also by the placenta and uterus. While the corpus luteum is crucial in early pregnancy for producing progesterone and estrogen, it continues to produce Relaxin throughout pregnancy. Relaxin is particularly important in the later phase for relaxing pelvic ligaments and softening the cervix, preparing the body for childbirth.
• Human chorionic gonadotropin (hCG): This hormone is secreted by the developing embryo and later the placenta. hCG is primarily active in the early stages of pregnancy, maintaining the corpus luteum. Its levels peak early and then decline.
• Estrogen: Estrogen is produced by the corpus luteum (part of the ovary) in early pregnancy and then predominantly by the placenta throughout pregnancy. The placenta produces large amounts of estrogen in the later phases. While the ovary (via the corpus luteum) contributes early on, the placenta is the major source later.

Analyzing the Options for Later Pregnancy and Ovary Secretion

We are looking for a hormone secreted by the ovary in the later phase of pregnancy. Based on the sources:

• Lactogen is from the placenta.
• hCG is primarily from the placenta and is highest in early pregnancy.
• Estrogen is primarily from the placenta in later pregnancy, though the corpus luteum (ovary) produces it early.
• Relaxin is secreted by both the corpus luteum (ovary) and the placenta, and its role in preparing for birth is significant in the later phase. The corpus luteum of the ovary continues to secrete Relaxin throughout pregnancy.

Considering the options and the role of the ovary in secreting hormones in the later phase, Relaxin is the most appropriate answer among the choices provided that fits the criteria of being secreted by the ovary (via the corpus luteum) and having a significant function in the later stages of pregnancy.

Therefore, the hormone secreted by the ovary (specifically the corpus luteum within the ovary) which plays a crucial role in the later phase of pregnancy is Relaxin.

Revision Table: Key Pregnancy Hormones

Additional Information: The Corpus Luteum's Role

The corpus luteum is a temporary endocrine gland formed in the ovary after ovulation. In a non-pregnant cycle, it degenerates. However, if pregnancy occurs, hCG secreted by the embryo rescues the corpus luteum, and it continues to produce progesterone and estrogen for the first few weeks, maintaining the pregnancy. The corpus luteum also produces Relaxin throughout pregnancy, even after the placenta takes over the primary production of progesterone and estrogen later on. The continued secretion of Relaxin by the corpus luteum makes it an important hormone from the ovary in the later phase.