Menstrual Cycle: Phases and Hormonal Changes

• The menstrual cycle is a recurring series of physiological changes in the female reproductive system

• It is essential for sexual reproduction

• It occurs in females of reproductive age

• The cycle prepares the uterus for pregnancy

• The cycle occurs roughly every 28 days but varies among individuals

• The regularity and duration of the cycle can be influenced by factors such as stress, diet, and overall health

Phases of the Menstrual Cycle

• The menstrual cycle is typically divided into four main phases

• These phases are menstruation, the follicular phase, ovulation, and the luteal phase

Menstruation Phase

• This phase marks the beginning of the menstrual cycle
• It is characterized by the shedding of the uterine lining (endometrium)
• The endometrium sheds when fertilization does not occur
• The shedding results in menstrual bleeding, commonly known as a period
• Menstruation typically lasts for 3 to 7 days
• Hormone levels, specifically estrogen and progesterone, are low during menstruation
• Cramps caused by uterine contractions are common during menstruation

Follicular Phase

• This phase overlaps with menstruation and continues until ovulation
• It is characterized by the development of follicles in the ovaries
• Follicle-stimulating hormone (FSH) stimulates follicular growth
• Developing follicles produce estrogen
• The rising estrogen levels cause the uterine lining to thicken
• A dominant follicle becomes more sensitive to FSH
• The dominant follicle matures and prepares to release an egg

Ovulation Phase

• This phase involves the release of a mature egg from the dominant follicle
• It is triggered by a surge in luteinizing hormone (LH)
• LH surge occurs due to high levels of estrogen produced by the dominant follicle
• Ovulation typically occurs around day 14 of a 28-day cycle
• The egg is released from the ovary and enters the fallopian tube
• The egg is viable for fertilization for approximately 24 hours

Luteal Phase

• This phase begins after ovulation and lasts until the start of the next menstruation
• The ruptured follicle transforms into a corpus luteum
• The corpus luteum secretes progesterone and estrogen
• Progesterone prepares the uterine lining for implantation of a fertilized egg
• If fertilization occurs, the corpus luteum continues to produce progesterone to support the early stages of pregnancy
• If fertilization does not occur, the corpus luteum degenerates
• The degeneration of the corpus luteum leads to a decrease in progesterone and estrogen levels which causes the endometrium to shed
• The shedding of the endometrium marks the beginning of the next menstrual cycle

The menstrual cycle is a recurring process essential for sexual reproduction in females, preparing the uterus for pregnancy. The cycle consists of menstruation, the follicular phase, ovulation, and the luteal phase. Menstruation involves shedding the uterine lining when fertilization doesn't occur and typically lasts 3-7 days.