Human Endocrine System

Pineal gland secretes a hormone called melatonin. Melatonin plays a very important role in the regulation of a 24-hour (diurnal) rhythm of our body. For example, it helps in maintaining the normal rhythms of sleep-wake cycle, body temperature. In addition, melatonin also influences metabolism, pigmentation, the menstrual cycle as well as our defense capability.

Parathyroid hormone (PTH) and thyrocalcitonin (TCT) profoundly influence the metabolism of calcium. Thyrocalcitonin reduces calcium levels in the blood. When the blood calcium level is too low, PTH is released to bring the calcium level back up to normal.

Step 1: Understanding the Concept:
The placenta acts as a temporary endocrine gland during pregnancy. it secretes several hormones essential for maintaining the pregnancy and supporting fetal development.
Step 2: Detailed Explanation:
1. hCG (Human Chorionic Gonadotropin): Produced early by the placenta; it's what pregnancy tests detect. 2. hPL (Human Placental Lactogen): Produced by the placenta to regulate metabolism. 3. Estrogens and Progestogens: The placenta takes over the production of these from the corpus luteum to maintain the uterine lining. 4. LH (Luteinizing Hormone): This hormone is secreted by the Anterior Pituitary Gland, not the placenta. Its primary role is to trigger ovulation in a non-pregnant cycle.
Step 3: Final Answer
LH is the hormone not secreted by the human placenta.