Question

Arrange the following hormones in sequence of their secretion in a pregnant woman : hCG; LH; FSH; Relaxin.

Hint:

To easily remember this order, think of the biological timeline: FSH grows the egg, LH releases it, hCG signals that the embryo has implanted, and Relaxin loosens the ligaments for birth.

Answer 1

Concept: The timeline of human reproduction is tightly regulated by a succession of endocrine events. Hormonal tracking begins prior to conception with gametogenesis, progresses through the establishment of pregnancy, and concludes at parturition (childbirth). Step-by-Step Chronological Analysis:
• FSH (Follicle Stimulating Hormone): This hormone is secreted early in the menstrual cycle during the follicular phase. Its primary role is to stimulate the growth and development of primary ovarian follicles before conception can even occur. Thus, it acts first in the reproductive timeline.
• LH (Luteinizing Hormone): Secreted later in the follicular phase, a sharp rise known as the "LH surge" occurs around the middle of the cycle (day 14). This surge triggers ovulation, releasing the secondary oocyte so it can be fertilised.
• hCG (Human Chorionic Gonadotropin): Produced shortly after successful fertilisation and implantation. The developing blastocyst's outer trophoblast layer begins secreting hCG around day 7–9 post-fertilisation to maintain the corpus luteum. This makes it the earliest specific marker of pregnancy.
• Relaxin: Although present in trace amounts earlier, its secretion increases significantly during the late stages of pregnancy and peaks near the end of the third trimester. It is secreted to prepare the maternal pelvis for childbirth. Therefore, the correct chronological sequence based on their onset of action and primary secretion timeline is: \[ \text{FSH} \quad \rightarrow \quad \text{LH} \quad \rightarrow \quad \text{hCG} \quad \rightarrow \quad \text{Relaxin} \]