Menstrual Cycle and Oral Contraceptives

Study guide:

Definition:
Menstruation (menses, or menstrual flow): periodic discharge of sloughed endometrium and blood from the uterine cavity through the vaginal canal, which happens due to different hormonal changes in the absence of pregnancy.

Basics: 

  • The normal menstrual cycle ranges from 21 to 35 days.

  • Day 1 of the cycle is the first day of bleeding (14 days post-ovulation).

  •  The menstrual flow normally lasts from 2 to 7 days (average is 4 days).

  • The amount of blood loss is usually between 30-50 ml and should NOT form clots; >80 ml in an abnormally high amount of blood loss.

  • A normal menstrual cycle consists of a menstrual, proliferative, and secretory phases.

            → Also can be divided into follicular, ovulatory, & luteal phases.

  • If fertilization does not occur, the corpus luteum involutes.

  • Progesterone and estradiol levels fall, and subsequently endometrial sloughing occurs (menses).

            → Due to the functional endometrium ischemia & necrosis.

Menstrual Cycle 

Estrogen which causes:

1- Endometrial Proliferation

2- Thinning of cervical mucus to allow easier passage of sperm 

FSH causing follicle maturation 

Follicular Phase

Ovulatory Phase

LH Surge 

Follicular phase length varies; however, the length of the luteal phase is fixed. 

Luteal Phase

Corpus luteum 

Progesterone which causes:

1- Endometrium maturation and preparation for implantation of the Blastocyst.
2- Increased production of estrogen by the adrenal glands.

3- Increase the basal body temprature. 

Organ:

Endometrium 

Cervix 

Changes:

  • Intermediate spongiosa layer and the epithelial layer form the transient functionalis layer, which is sloughed during menses.
     

  • Estrogen causes thickening and proliferation of the basal layer.
     

  • Glands will become coiled and torturous in response to estrogen.

Changes:

  • In the follicular phase, high levels of estrogen will increase the cervical vascularity causing edema.

  • With high estrogen levels, mucus will increase in quantity, elasticity, and salt concentration (ferning), which will aid in the sperm transport.

  • In the luteal phase, progesterone will cause the cervical mucus to be thicker and less elastic inhibiting the access of sperm. 

Notes:

  • The endometrium normally consists of glands and stroma.

  • The stroma consists of:
    1.  Basal layer.
    2.  Intermediate spongiosa layer.
    3.  Epithelial layer 

Notes:

  • Ferning indicates high levels of salt in the cervical mucus, which becomes maximally prominent just before ovulation when estrogen levels are in their maximum. 

Vagina 

Changes:

  • In the late follicular phase, high estrogen will cause squamous cells to mature and be cornified.
     

  • In the luteal phase, progesterone will cause number of cornified squamous cells will increase as well as the number of leukocytes and cellular debris.

​Reffrences: 

  1. Potter L, Hempenstall L, Mahmood H, İşler E, Potter L, Shahid S et al. The Menstrual Cycle | Geeky Medics [Internet]. Geeky Medics. 2011 [cited 9 January 2016]. Available from: http://geekymedics.com/the-menstrual-cycle/

  2. Merck Manuals Professional Edition. Female Reproductive Endocrinology - Gynecology and Obstetrics [Internet]. 2016 [cited 9 January 2016]. Available from: http://www.merckmanuals.com/professional/gynecology-and-obstetrics/female- reproductive-endocrinology/female-reproductive-endocrinology

  3. Dunn, Robert B et al. USMLE Step 1 Physiology Lecture Notes. [New York, N.Y.]: Kaplan Medical, 2011. Print.

  4. Merck Manuals Professional Edition. Female Reproductive Endocrinology - Gynecology and Obstetrics [Internet]. 2016

    [cited 9 January 2016]. Available from: http://www.merckmanuals.com/professional/gynecology-and-obstetrics/female-

    reproductive-endocrinology/female-reproductive-endocrinology (Figure 1).

  5. Le T, Bhushan V, Sochat M, Sylvester P, Mehlman M, Kallianos K. First aid for the® USMLE. 

Written by: Samaher AlHarbi     

                                                               

Reviewed by: Ghadah Al-Qahtani

                        Dana Alturaifi

 

                        Roaa Amer 

Format editor: Roaa Amer

Web Publisher: Adel Yasky