Question

Figure 14.8 Whi ch of the following statements about hormone regulation of the female reproductive cycle is false? a. \(\mathrm{LH}\) and FSH are produced in the pituitary, and estrogen and progesterone are produced in the ovaries. b. Estrogen and progesterone secreted from the corpus luteum (CL) cause the endometrium to thi cken. c. Follicles produce high levels of progesterone. d. Secretion of \(\mathrm{Gn} \mathrm{RH}\) by the hypothalamus is inhibited by high levels of estrogen.

Short answer

a) LH and FSH are produced in the pituitary, and estrogen and progesterone are produced in the ovaries. b) Estrogen and progesterone secreted from the corpus luteum cause the endometrium to thicken. c) Follicles produce high levels of progesterone. d) Secretion of GnRH by the hypothalamus is inhibited by high levels of estrogen. Answer: c) Follicles produce high levels of progesterone.

Step-by-step solution

Statement A

LH and FSH are produced in the pituitary, and estrogen and progesterone are produced in the ovaries. This statement is true. LH and FSH are secreted by the anterior pituitary gland, and they regulate the development, growth and maturation of the follicles in the ovaries. Estrogen and progesterone, on the other hand, are steroid hormones produced by the ovaries that are essential for the menstrual cycle, pregnancy, and development of secondary sexual characteristics in females.

Statement B

Estrogen and progesterone secreted from the corpus luteum cause the endometrium to thicken. This statement is also true. After ovulation, the corpus luteum is formed from the remains of the dominant follicle. It secretes estrogen and progesterone which help in thickening and maintaining the endometrium to prepare the uterus for implantation of a fertilized egg.

Statement C

Follicles produce high levels of progesterone. This statement is false. In the early to mid-follicular phase, follicles primarily produce estrogen, which stimulates the growth and maturation of the dominant follicle. Progesterone production is minimal during the follicular phase. It is only after ovulation when the corpus luteum forms, progesterone production increases significantly.

Statement D

Secretion of GnRH by the hypothalamus is inhibited by high levels of estrogen. This statement is true. GnRH is released from the hypothalamus and stimulates the pituitary to release LH and FSH. When estrogen levels are high, it acts as a negative feedback to inhibit the release of GnRH, thereby controlling the levels of LH and FSH in the blood. In conclusion, the false statement is: c. Follicles produce high levels of progesterone.

Key concepts

Hormone Regulation

The orchestration of the female reproductive cycle relies heavily on a delicately balanced hormonal interplay. Hormones serve as chemical messengers, shuttled through the bloodstream to target organs, eliciting precise responses necessary for reproductive processes. Key players include luteinizing hormone (LH) and follicle-stimulating hormone (FSH) which originate from the pituitary gland. These hormones trigger the ovaries to produce estrogen and progesterone.
Their production is a dynamic process. During the initial stages of the menstrual cycle, FSH fosters the development of ovarian follicles, each containing an egg. These follicles, in turn, secrete estrogen, which prepares the uterus lining for potential pregnancy and, consequently, influences the release of yet more LH and FSH in a complex feedback loop.
Estrogen levels peak leading up to ovulation, signaling a temporary feedback inhibition of gonadotropin-releasing hormone (GnRH) from the hypothalamus and, thus, moderating LH and FSH levels. This interplay exemplifies hormone regulation's pivotal role in managing the reproductive cycle's various phases, ensuring each step occurs in a timely, coordinated fashion.

Menstrual Cycle

The menstrual cycle is a monthly series of events aimed at preparing the female body for pregnancy. Spanning approximately 28 days, the cycle can be divided into several phases: the follicular phase, ovulation, and the luteal phase.
During the follicular phase, FSH promotes the growth of ovarian follicles. A surge in LH then leads to ovulation—the release of an egg from the most mature follicle. Subsequently, the ruptured follicle morphs into the corpus luteum during the luteal phase and secretes progesterone and estrogen. These hormones are vital for the thickening of the endometrium, the uterine lining, preparing it for a fertilized egg. If fertilization does not occur, the corpus luteum degrades, hormone levels drop, and the endometrium is shed during menstruation.
Understanding the menstrual cycle is essential, as it dictates not just fertility but also many aspects of a woman's health. Aberrations in the cycle can signal underlying health issues, hence why grasp of its mechanics is important not only for reproductive health but for overall well-being.

Endocrine System

The endocrine system is composed of glands that release hormones into the bloodstream, controlling various bodily functions. In the reproductive domain, the hypothalamus, pituitary gland, and ovaries form a triumvirate that masterminds the menstrual cycle by secreting and responding to hormones.
At the helm is the hypothalamus, which releases GnRH. This hormone prompts the pituitary gland to secrete LH and FSH — critical for follicle development and the ensuing release of estrogen and progesterone from the ovaries. The ovaries' response culminates in the menstrual cycle's progress, reflecting this system's sequence of command.
Without the precise timing and release of these hormones, the reproductive cycle would falter, emphasizing the vital role of the endocrine system in maintaining female reproductive health. By regulating hormones, the endocrine system not only controls the reproductive cycle but impacts mood, energy levels, and overall vitality, playing a formidable role in an individual's quality of life.