L4.3.4: Uterine Cycle

• Phases

  • Menstrual Phase
  • Proliferative (Estrogen) Phase
  • Secretory (Progesterone) Phase
• MENSTRUAL PHASE — SHEDDING

  ● Menstrual bleeding, menses, period

  ● Discharge of bloody fluid containing endometrial cells, glandular secretions, and blood cells

  ● Result of previous menstrual cycle.
• MENSTRUAL PHASE — SHEDDING

  ● Due to strong vasoconstriction and proteolytic activity, the functional stratum of endometrial tissue dies and is discharged during menstrual bleeding.

  ○ The site of implantation is the endometrium

  ○ Endometrium thickens as it readies for implantation of the fertilized egg

  ○ Since there is no fertilized egg, the functional stratum of the endometrial tissue dies and is discharged/sloughed off.
• MENSTRUAL PHASE — SHEDDING

  ● Endometrium becomes very thin, but due to low estrogen levels, hypophysis secretes more FSH.

  ● FSH stimulates secretion of estrogen (proliferation signal).
• PROLIFERATIVE (ESTROGEN) PHASE — BUILDING

  ● Endometrium starts to thicken due to the increased release of estrogen from the follicles through the influence of FSH.

  ● Increase the thickness of the endometrium.
• SECRETORY (PROGESTERONE) PHASE

  ● Through the influences of LH, the endometrial lining achieves its full thickness which then prepares the reproductive tract for a possible fertilization to occur as the egg by this time is already mature.

  ● If there is a fertilized egg, the endometrium remains intact. However, if there is no presence of a fertilized egg, the endometrium will be sloughed off as part of the menstrual phase.