Menstruation

• The menstrual cycle is the monthly process by which an egg matures, is released from the ovary, travels through the fallopian tube to the uterus, and then leaves the body if it has not been fertilized.
• Amenorrhea means no periods or irregular periods.
• Ovulation is the release of an egg from the ovary.
• Pregnancy is a time of rapid growth and development for the fetus.
• Fertility refers to the ability to conceive and bear children.
• Menstrual cycle

  Regular changes in the activity of the ovaries and the endometrium that make reproduction possible
• Endometrium


  Layer of tissue lining the inside of the uterus consisting of a functional layer subject to hormonal changes and a thin basal layer
• Menstrual cycle

  Consists of two interconnected and synchronized processes: the ovarian cycle (development of ovarian follicles and ovulation) and the uterine or endometrial cycle (thickening and shedding of the functional endometrium in response to ovarian activity)
• Menarche refers to the onset of the first menstrual period usually occurring during early adolescence as part of puberty
• The menstrual cycle occurs on a monthly basis, pausing only during pregnancy until menopause when ovarian function declines and menstrual periods stop
• The monthly menstrual cycle can vary in duration from 20 to 35 days with an average of 28 days
• Each menstrual cycle begins on the first day of menstruation, usually referred to as day one of the cycle
• Ovulation, the release of the oocyte from the ovary, usually occurs 14 days before the first day of menstruation, meaning there are usually 14 days leading up to ovulation (pre-ovulatory phase) and 14 days following ovulation (post-ovulatory phase)
• Pre-ovulatory period

  Includes the ovarian follicular phase (weeks one and two of a four-week cycle) and is controlled by the hypothalamus and pituitary gland
• Ovarian follicular phase


  Controlled by the hypothalamus secreting gonadotropin-releasing hormone (GnRH) which stimulates the pituitary to release follicle-stimulating hormone (FSH) and luteinizing hormone (LH)
• GnRH is released in pulses during puberty, determining FSH and LH production by the pituitary to control maturation of ovarian follicles
• Ovarian follicles grow and compete for ovulation, with the dominant follicle continuing to grow and eventually undergo ovulation
• Granulosa cells in the follicles produce estrogen in response to FSH, leading to negative feedback on FSH production and selection of the dominant follicle
• Rising estrogen levels act as a positive feedback signal, stimulating the pituitary to secrete a surge of FSH and LH before ovulation
• Ovulation

  1. Positive feedback signal from the follicle leads to secretion of follicle stimulating hormone and luteinizing hormone by the pituitary

  2. Stimulation of rupture of the ovarian follicle and release of the oocyte
• Menstrual cycle

  Includes menstrual phase, proliferative phase, and secretory phase
• Menstrual phase

  Shedding of the old endometrial lining or functional layer, resulting in menstrual bleeding
• Proliferative phase

  High estrogen levels stimulate thickening of the endometrium, growth of endometrial glands, and emergence of spiral arteries
• Secretory phase

  Under the influence of progesterone, spiral arteries grow and become coiled, uterine glands secrete more mucus
• High estrogen levels

  Change the consistency of cervical mucus to be more hospitable to incoming sperm
• Progesterone

  Acts as a negative feedback signal on the pituitary, decreasing release of follicle stimulating hormone and luteinizing hormone
• Rising progesterone level

  Signals that ovulation has occurred and helps make the endometrium receptive to the implantation of a fertilized gamete
• Corpus luteum degeneration

  Results in a decrease in estrogen and progesterone levels, leading to menstruation
• Menstrual cycle begins on the first day of menstruation for an average 28-day cycle
• Ovulation usually occurs around day 14 of the cycle
• Luteal phase precedes the onset of menses by 14 days
• Changes in the ovary during the first 14 days are called the follicular phase
• Changes in the uterus during the first 14 days include the menstrual phase and the proliferative phase
• Changes in the uterus during the last 14 days include the secretory phase