Question

Which of the following hormones is not produced by the placenta?

• A. \( \text{hCG} \)
• B. \( \text{hPL} \)
• C. \( \text{Thyroxine} \)
• D. \( \text{Estrogen} \)

Hint:

Placenta mainly secretes hCG, hPL, Estrogens, and Progesterone, whereas Thyroxine is secreted by the thyroid gland.

Answer 1

The Correct Option is C

Concept: The placenta is a temporary but highly important endocrine organ formed during pregnancy. It develops from fetal tissues and establishes physiological connection between mother and developing fetus. Apart from exchange of nutrients, respiratory gases, and metabolic wastes, the placenta also functions as an endocrine gland by secreting several hormones essential for maintenance of pregnancy and fetal development. The major hormones secreted by placenta include:

• Human Chorionic Gonadotropin (hCG)
• Human Placental Lactogen (hPL)
• Estrogens
• Progesterone

These hormones help in maintaining uterine lining, supporting fetal growth, preparing mammary glands, and regulating maternal metabolism during pregnancy.

Step 1: Analyze option (A) Human Chorionic Gonadotropin (hCG).
Human Chorionic Gonadotropin (hCG) is one of the earliest hormones secreted by the trophoblastic cells of the placenta after implantation. The primary function of hCG is to maintain the corpus luteum during early pregnancy so that progesterone secretion continues. Continuous progesterone secretion is essential for maintenance of the uterine endometrium and successful continuation of pregnancy. Therefore, hCG is definitely produced by the placenta.

Step 2: Analyze option (B) Human Placental Lactogen (hPL).
Human Placental Lactogen (hPL) is another important placental hormone. It is secreted during pregnancy and plays a major role in altering maternal metabolism to ensure adequate nutrient supply to the fetus. It also contributes to growth and development of mammary glands in preparation for lactation after childbirth. Hence, hPL is also produced by the placenta.

Step 3: Analyze option (C) Thyroxine.
Thyroxine is a hormone secreted by the thyroid gland located in the neck region. It contains iodine and plays an important role in regulating basal metabolic rate, growth, development, and overall metabolism of the body. Although thyroid activity may increase during pregnancy to meet metabolic demands, the placenta itself does not synthesize or secrete thyroxine. Therefore, Thyroxine is not a placental hormone.

Step 4: Analyze option (D) Estrogen.
During pregnancy, the placenta secretes estrogens in increasing amounts. Estrogens help in:

• Growth of uterus
• Development of mammary glands
• Increased vascularization
• Preparation of body for parturition

Hence, Estrogen is produced by the placenta.

Step 5: Determine the correct answer.
Among all the given options, Thyroxine is the only hormone which is not secreted by the placenta. Therefore, the correct answer is: \[ \boxed{\text{Thyroxine}} \]