Ciclo menstrual - Biologia - Ensino Médio

Summary

Professor Rafaela Lima delivers an informative lesson on the menstrual cycle, explaining its various phases and hormonal regulation. She outlines the cycle’s stages, including menstruation, the follicular phase, ovulation, and the luteal phase, emphasizing the role of hormones like FSH, LH, estrogen, and progesterone in regulating the process. The cycle typically lasts 28 days, though it can vary. The lesson also covers how the endometrium thickens for pregnancy and sheds when fertilization doesn’t occur, resetting the cycle. The content is aimed at helping students understand the physiological changes and hormonal influence that drive the reproductive cycle.

Takeaways

• 😀 The menstrual cycle, also known as the uterine cycle, is a recurring event that prepares the uterus for pregnancy.
• 😀 The cycle begins with menstruation, which is the shedding of the uterine lining (endometrium).
• 😀 The menstrual cycle lasts on average 28 days, but this can vary between women and across cycles.
• 😀 Hormones, such as FSH, LH, estrogen, and progesterone, regulate the stages of the menstrual cycle.
• 😀 Menstruation marks the start of the cycle, where the endometrium is shed due to the absence of pregnancy.
• 😀 The follicular phase involves the development of a follicle in the ovary, leading to the maturation of an egg (oocyte).
• 😀 Ovulation occurs around day 14 of the cycle, when the egg is released from the follicle into the fallopian tube.
• 😀 After ovulation, the luteal phase begins, where progesterone prepares the endometrium for potential embryo implantation.
• 😀 If fertilization does not occur, the corpus luteum degenerates, progesterone levels drop, and menstruation resumes.
• 😀 If fertilization occurs, the embryo implants into the thickened endometrium, and progesterone levels remain high to support the pregnancy.
• 😀 The menstrual cycle repeats monthly until menopause, when the ovarian reserve is depleted and the cycle ends.

Q & A

What is the menstrual cycle, and why is it considered cyclical?

The menstrual cycle, also known as the uterine cycle, is a recurring series of events that occur in a woman's body each month. It is considered cyclical because it continuously renews itself, starting with menstruation and ending when a new cycle begins. It involves hormonal changes and physiological processes in the ovaries and uterus.

What is the role of the endometrium in the menstrual cycle?

The endometrium is the lining of the uterus, and its primary role in the menstrual cycle is to prepare for the possible implantation of a fertilized egg. During the cycle, the endometrium thickens and becomes nutrient-rich to support a potential pregnancy. If no pregnancy occurs, the endometrium sheds during menstruation.

How long does a typical menstrual cycle last, and does it vary between women?

A typical menstrual cycle lasts about 28 days, but this can vary among women. Some women may have cycles that are slightly shorter or longer, such as 30 days or even shorter than 28 days. The variation is natural and depends on individual hormonal and physiological factors.

What triggers ovulation during the menstrual cycle?

Ovulation is triggered by a peak in the luteinizing hormone (LH) around day 14 of the cycle. This hormone surge causes the mature follicle in the ovary to release an egg, which is then available for fertilization by sperm.

What hormones regulate the menstrual cycle, and what are their functions?

The menstrual cycle is primarily regulated by four key hormones: FSH (Follicle Stimulating Hormone), LH (Luteinizing Hormone), estrogen (estradiol), and progesterone. FSH stimulates the growth and maturation of the egg within the ovary. LH triggers ovulation. Estrogen promotes the thickening of the endometrial lining. Progesterone supports the maintenance of the endometrial lining for implantation in the luteal phase.

What happens during the follicular phase of the menstrual cycle?

The follicular phase begins after menstruation and lasts until ovulation. During this phase, FSH stimulates the growth of ovarian follicles, each containing an egg. Estrogen is produced by the developing follicles, which also stimulates the thickening of the endometrial lining in preparation for a potential pregnancy.

What is the function of progesterone during the luteal phase?

Progesterone plays a crucial role during the luteal phase by maintaining the thickness of the endometrial lining. It ensures the uterus remains prepared to receive and nourish a fertilized egg. If pregnancy does not occur, progesterone levels drop, leading to the shedding of the endometrial lining, which results in menstruation.

What happens if fertilization does not occur after ovulation?

If fertilization does not occur after ovulation, the corpus luteum (the structure formed from the ruptured follicle) degenerates. This leads to a drop in progesterone levels, causing the endometrial lining to break down and be shed, resulting in menstruation. The cycle then restarts.

How does the body detect whether fertilization has occurred or not?

The body detects whether fertilization has occurred through the presence of a fertilized egg. If fertilization occurs, the embryo releases hormones that signal the body to maintain high levels of progesterone to prevent the shedding of the endometrial lining. If no fertilization occurs, progesterone levels drop, triggering the breakdown and shedding of the lining.

What marks the end of the menstrual cycle and the beginning of menopause?

The end of the menstrual cycle is marked by the cessation of regular ovulation and menstruation. This occurs naturally as a woman ages, leading to menopause, which typically happens around age 50. During menopause, the ovaries no longer produce eggs, and hormone levels (particularly estrogen and progesterone) significantly decline, ending the reproductive cycle.