Question

During the human ovarian cycle, ovulation is stimulated by a. a decrease in $\mathrm{FSH}$ secretion. b. an increase in progesterone secretion. c. an increase in $\mathrm{LH}$ secretion. d. the presence of semen in the vagina. e. a decrease in estradiol concentration in the bloodstream.

Short answer

The stimulation of ovulation in the human ovarian cycle is caused by an increase in LH secretion. Thus, the correct answer is c. an increase in LH secretion.

Step-by-step solution

Understanding FSH

FSH or Follicle Stimulating Hormone influences the maturation of egg cells in ovaries. However, it does not trigger ovulation by itself, thereby eliminating option a.

Understanding Progesterone

Increased secretion of Progesterone occurs after ovulation. The role of this hormone is to thicken the lining of the uterus to prepare for a possible pregnancy, therefore, it does not stimulate ovulation, eliminating option b.

Understanding LH

Luteinizing Hormone or LH surges sharply immediately before and during ovulation, triggering the release of a mature egg from an ovary. This validates option c.

Ruling Out Other Options

Semen and estradiol do not stimulate ovulation. Estradiol helps in follicular growth, but its decrease does not lead to ovulation. So, options d and e can be eliminated.

Key concepts

Ovulation

Ovulation is a crucial phase in the human ovarian cycle. It's the process where a mature egg is released from an ovary, ready for potential fertilization. This usually occurs around the middle of a woman's menstrual cycle, about 14 days before the start of her next period. During this time, the follicle bursts, releasing the egg into the fallopian tube.
Once in the tube, the egg awaits fertilization by sperm. If fertilization does not occur, the egg will eventually disintegrate and be absorbed by the body. However, if fertilization happens, it can lead to pregnancy. Understanding ovulation is essential for those who are planning to conceive, as it highlights the fertile window when conception is most likely to occur.

Follicle Stimulating Hormone (FSH)

Follicle Stimulating Hormone (FSH) plays a fundamental role in the ovarian cycle by regulating the development of follicles in the ovaries. Each follicle contains an egg, and FSH helps stimulate their growth and maturation.
This hormone is produced by the pituitary gland and works in conjunction with Luteinizing Hormone, or LH, to promote the follicular phase of the cycle. While FSH is vital for egg development, it doesn't directly trigger ovulation. Instead, FSH prepares the egg for the possibility of ovulation by helping develop the follicle to its mature state.

• Promotes follicle growth
• Essential in the early stages of the ovarian cycle
• Works together with LH

Luteinizing Hormone (LH)

Luteinizing Hormone (LH) is key for inducing ovulation. A surge in LH levels triggers the release of a mature egg from the ovarian follicle, marking the process of ovulation. This sharp increase, often referred to as the "LH surge," is a critical indicator for the timing of ovulation.
The LH surge usually happens about 24 to 36 hours before ovulation, making this hormone instrumental in the cycle. For those tracking their fertility, monitoring LH levels can provide valuable insights into when ovulation is likely to occur, thus identifying the most fertile days.

• Triggers ovulation
• Causes the LH surge
• Indicates fertile period

Progesterone

Progesterone is a hormone that becomes prominent after ovulation. Following the release of the egg, progesterone levels rise to help prepare the lining of the uterus for a potential pregnancy. This thickened uterine lining is vital should the fertilized egg need to implant itself.
If pregnancy does not occur, progesterone levels will drop, leading to the shedding of the uterine lining during menstruation. Although important for supporting pregnancy, increased levels of progesterone do not initiate ovulation; instead, they aid in creating a welcoming environment for the developing embryo.

• Supports uterine lining preparation
• Rises after ovulation
• Essential for pregnancy maintenance

Estradiol

Estradiol is a form of estrogen critical to the ovarian cycle, especially during the follicular phase. It is produced by the developing follicles and serves several functions, most notably stimulating the growth and development of the uterine lining in preparation for a potential pregnancy.
It also plays a role in signaling the pituitary gland to release LH, leading to the LH surge and subsequent ovulation. While an increase in estradiol prepares the body for ovulation, a decrease is not known to stimulate the release of the egg. Therefore, its importance lies mainly in facilitating the early stages of the cycle and preparing for ovulation.

• Stimulates uterine lining growth
• Induces LH release
• Supports follicular development