Menstrual Cycle and Oral Contraceptives
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.
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.
Estrogen which causes:
1- Endometrial Proliferation
2- Thinning of cervical mucus to allow easier passage of sperm
FSH causing follicle maturation
Follicular phase length varies; however, the length of the luteal phase is fixed.
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.
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.
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.
The endometrium normally consists of glands and stroma.
The stroma consists of:
1. Basal layer.
2. Intermediate spongiosa layer.
3. Epithelial layer
Ferning indicates high levels of salt in the cervical mucus, which becomes maximally prominent just before ovulation when estrogen levels are in their maximum.
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.
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:
Merck Manuals Professional Edition. Female Reproductive Endocrinology - Gynecology and Obstetrics [Internet]. 2016 [cited 9 January 2016]. Available from: reproductive-endocrinology/female-reproductive-endocrinology
Dunn, Robert B et al. USMLE Step 1 Physiology Lecture Notes. [New York, N.Y.]: Kaplan Medical, 2011. Print.
Merck Manuals Professional Edition. Female Reproductive Endocrinology - Gynecology and Obstetrics [Internet]. 2016
[cited 9 January 2016]. Available from:
reproductive-endocrinology/female-reproductive-endocrinology (Figure 1).
Le T, Bhushan V, Sochat M, Sylvester P, Mehlman M, Kallianos K. First aid for the® USMLE.
Written by: Samaher AlHarbi
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