Menstrual Cycle (7.1)

Question 1

Define and distinguish between uterine and ovarian cycle

Answer 1

Uterine cycle: The cyclical changes observed in the lining of the uterus.

Divided into proliferative (variable in length) and secretory (relatively consistent in length ~ 14 days)phases.

Proliferative phase – thin, watery cervical mucus. Aids sperm transport

Secretory phase - Thick, impenetrable

Ovarian cycle: The interval between successive ovulations. Associated with the maturation and release of a mature ovum.

Divided into follicular (1-14 days) and luteal (15-28 days) phases.

Question 2

Describe the endocrinology of the menstrual cycle

Answer 2

• FSH allows for the maturation of the follicle, in preparation for oocyte release.
• LH surge allows for ovulation.
• Oestogen allows for the proliferation of the endometrial lining.
• Progesterone allows for maintenance of the endometrium.

Question 3

Describe the feedback control of the HPO axis during the menstrual cycle

Answer 3

• Oestrogen creates a negative feedback loop on the HPO axis, inhibiting the hypothalamus and the anterior pituitary gland
• Mid-cycle the high levels of oestrogen create a positive feedback loop on the hypothalamus causing a mid-cycle LH surge
• High levles of progesterone creates negative feedback on gonadotrophin release
• Progesterone enhances the negative feedback of oestrogen and blocks the positive feedback of oestrogen

Question 4

Explain the temporal events of the menstrual cycle

Answer 4

Oestrogen mediated proliferation of the endometrial lining (stroma cells) and growth of spiral arteries:

uterine artery → arcuate artery → radial artery → spiral artery

1. Ovulation - seeing release of the oocyte from the mature ovum, in preparation for fertilisation.
2. Further growth and decidualisation (change from endometrial stroma to secretory decidual cells)
3. If fertilisation occurs then the endometrium is maintained via progesterone secretion from the corpus luteum (first 12-14 weeks) until the placenta develops.

Question 5

Describe the function and effects of sex steroids on endometrial structure and function

Answer 5

Endometrium: Glandular tissue. Columnar epithelium lining. Functionalis (sloughed off) and basalis (persistent) layers.

Oestrogen:

• Proliferation of endometrial stroma
• Growth of spiral arteries

Progesterone:

• Further proliferation of endometrial stroma
• Stimulates decidualisation of the endometrium
  
  • Decidual cells secrete glycogen droplets (polygonal) to provide nutrition for developing embryo and aids immune tolerance of the uterus.
• Maintenance of the endometrial lining

Question 6

Give examples of conditions associated with menstrual cycle dysregulation

Answer 6

• Endometrosis
• HPO disorders: Prolactinaemia, hyper/hypothyroidis, Cushing’s
• HPO dysfunction: Excessive exercise/eating disorder, excessive weight loss/gain, stress