Ch 27, L10

Uterine Cycle

• Occurs in the uterine wall where the embryo implants and develops.
• The uterine wall is receptive to implantation for about 6-7 days post ovulation.
• The uterine cycle is the monthly set of changes to the endometrium to prepare for potential embryo implantation.
• The process occurs in response to ovarian hormone levels.

Regulation of the Uterine Cycle

• The uterine cycle consists of three phases: menstrual, proliferative, and secretory.
• The menstrual phase sheds the functional layer of the endometrium.
• The proliferative phase rebuilds the functional layer of the endometrium.
• The secretory phase begins immediately after ovulation.
• Enrichment of blood supply and glandular secretion of nutrients prepares the endometrium to receive an embryo.
• Both the menstrual and proliferative phases occur prior to ovulation and correspond to the follicular phase of the ovarian cycle.
• The secretory phase lines up in time with the luteal phase of the ovarian cycle.

Days 0-4: Menstrual Phase

• Ovarian hormone levels are at their lowest.
• Gonadotropin levels begin to increase.
• The functional layer of the endometrium detaches and sheds..
• Menstrual flow lasts approximately 3-5 days.
• By day 5, growing ovarian follicles produce more estrogen.

Days 6-14: Proliferative (Preovulatory) Phase:

• Rising estrogen levels lead to the creation of a new functional layer.
• Estrogen increases the synthesis of progesterone receptors in the endometrium
• Cervical mucus thins out to facilitate sperm passage
• Ovulation happens at the end of this phase, around day 14.

Days 15-28: Secretory (Postovulatory) Phase

• This phase represents the most consistent phase in duration.
• The endometrium prepares for embryo implantation.
• Rising progesterone levels from the corpus luteum cause the functional layer to become a secretory mucosa
• Endometrial glands enlarge and secrete nutrients into the uterine cavity.
• A thickened mucus forms a cervical mucus plug that blocks sperm, pathogens, and debris from entering.

Days 15-28 (Continued)

• If fertilization does not occur, the corpus luteum degenerates, and progesterone levels decline.
• Endometrial cells die, and the functional layer sloughs off.
• The uterine cycle restarts on the first day of menstruation.

Effects of Estrogen and Progesterone

• They are female sex hormones, analogous to testosterone in males.

• Rising estrogen levels at puberty:

  • Promote oogenesis and follicle growth in ovaries.
  • Exhibit anabolic effects on the female reproductive tract.
  • Support the growth spurt in puberty for girls (between ages 11 and 12).
  • Promote secondary sex characteristics.
  • Spur Breast development and the deposition of subcutaneous fat, especially around hips and breasts.
  • Lead to the development of a lighter and wider pelvis.

• Progesterone works with estrogen to Regulate the menstrual cycle and promote changes in cervical mucus.

• During pregnancy, it inhibits uterine motility and helps prepare the breast for lactation.

• The placenta is the main source of progesterone, and estrogen during pregnancy, not the ovaries.

Female Sexual Response

• Initiated by touch and psychological stimuli.
• The clitoris, vaginal mucosa, bulbs of vestibule, and breasts engorge with blood; nipples become erect.
• Cervical and vestibular gland secretions lubricate the vestibule.
• Orgasm entails muscle tension, an increased pulse and blood pressure, and rhythmic contractions of the uterus, triggered by sympathetic stimulation.
• Females have no refractory period after orgasm and can experience multiple orgasms during a single sexual experience.
• Orgasm is not required for conception.
• Female libido is enabled by dehydroepiandrosterone (DHEA), an androgen produced by the adrenal cortex.