The Menstrual Cycle | 3D Animation (2/2)

Summary

The menstrual cycle initiates with bleeding, signaling the start of the follicular phase where low estrogen and progesterone levels lead to uterine lining breakdown. The pituitary gland's follicle-stimulating hormone stimulates follicle development, with one becoming dominant and increasing estrogen levels. This rise inhibits further follicle development, while the thickening uterine lining prepares for potential pregnancy. The ovulatory phase is marked by a hormone surge causing the dominant follicle to release an egg. The luteal phase follows, with the formation of the corpus luteum, which secretes hormones to further thicken the uterine lining. If fertilization occurs, progesterone supports early pregnancy; otherwise, the cycle returns to menstruation.

Takeaways

• 🩸 Menstrual bleeding marks the start of the menstrual cycle and the first day of the follicular phase.
• 🌡 Low levels of estrogen and progesterone at the beginning of the follicular phase trigger the breakdown and shedding of the uterine lining.
• 💉 The pituitary gland releases follicle-stimulating hormone (FSH), which stimulates the development of multiple follicles in the ovaries.
• 🥚 Each follicle contains an immature egg and produces estrogen, with one becoming the dominant follicle as it grows faster than the others.
• 📈 The dominant follicle's growth leads to a significant rise in estrogen levels, which in turn inhibits FSH secretion.
• 🌀 The fall in FSH allows smaller follicles to die off, while estrogen ensures the uterine lining thickens in preparation for potential pregnancy.
• 🚀 The ovulatory phase is initiated by a surge in luteinizing hormone (LH) and FSH, leading to the release of an egg from the dominant follicle.
• 🥚 Ovulation typically occurs 16 to 32 hours post-LH surge, around day 14 of the menstrual cycle, with the egg entering the fallopian tube.
• 🌕 The luteal phase follows ovulation, with a decrease in LH and FSH levels, and the formation of the corpus luteum from the ruptured follicle.
• 🌱 The corpus luteum produces estrogen and progesterone, further thickening the uterine lining to support early pregnancy if fertilization occurs.
• 🔄 If fertilization does not occur, the corpus luteum breaks down 9 to 11 days post-ovulation, causing a drop in hormone levels and returning to the menstrual phase.

Q & A

What event marks the beginning of the menstrual cycle?

The menstrual cycle begins with menstrual bleeding, which is the first day of the follicular phase.

Why do the levels of estrogen and progesterone start low at the beginning of the follicular phase?

Low levels of estrogen and progesterone cause the breakdown and shedding of the uterus's thickened lining, leading to menstrual bleeding.

What role does the pituitary gland play during the early follicular phase?

The pituitary gland sends follicle-stimulating hormone to the ovaries, stimulating the development of 5 to 20 follicles.

What is the significance of the dominant follicle?

The dominant follicle grows faster than the others and produces more estrogen, which inhibits the secretion of follicle-stimulating hormone and causes smaller follicles to die off.

How does estrogen affect the lining of the womb?

Estrogen ensures that the lining of the womb thickens with nutrients and blood, preparing it for a potential fertilized egg to grow.

What triggers the beginning of the ovulatory phase?

The ovulatory phase begins with a rise in the levels of luteinizing hormone and follicle-stimulating hormone.

What happens during ovulation?

During ovulation, the most prominent follicle pops open and releases its egg, which then enters the fallopian tube and starts its journey toward the uterus.

When does ovulation typically occur in the menstrual cycle?

Ovulation usually occurs 16 to 32 hours after the beginning of the surge in hormones, around day 14 of the menstrual cycle.

What is the role of the corpus luteum during the luteal phase?

The corpus luteum, formed from the ruptured follicle, produces estrogen and progesterone, which cause the uterus lining to thicken even more in preparation for potential pregnancy.

What happens if fertilization does not occur after ovulation?

If no fertilization occurs, the corpus luteum breaks down between 9 and 11 days after ovulation, leading to a drop in estrogen and progesterone levels and the start of menstruation.

How does progesterone support early pregnancy if fertilization occurs?

Progesterone produced by the corpus luteum supports early pregnancy by maintaining the thickened uterine lining and creating a suitable environment for the fertilized egg to implant.