18/06/2026
The menstrual cycle is a monthly series of changes in the ovaries and uterus that prepares a woman for pregnancy. The average cycle lasts 28 days and is divided into four stages:
Menstrual Phase
Follicular (Proliferative) Phase
Ovulatory Phase
Luteal (Secretory) Phase
1. Menstrual Phase (Day 1–5)
Definition
The menstrual phase is the period during which the superficial layer of the uterine lining (endometrium) is shed and discharged through the va**na as menstrual blood.
Cause
If fertilization does not occur, the corpus luteum degenerates, causing a sharp decline in estrogen and progesterone levels. This hormonal withdrawal leads to constriction of spiral arteries supplying the endometrium.
Changes Occurring
Spiral arteries constrict.
Endometrial tissue becomes ischemic and necrotic.
Functional layer of the endometrium breaks down.
Blood, mucus, and tissue are expelled through the va**na.
Hormonal Changes
Estrogen levels are low.
Progesterone levels are low.
FSH begins to rise to stimulate new follicular growth.
Characteristics
Duration: 3–7 days.
Average blood loss: 30–80 mL.
Menstrual fluid contains blood, mucus, endometrial tissue, and prostaglandins.
Clinical Features
Lower abdominal cramps (dysmenorrhea).
Backache.
Fatigue.
Mood changes.
2. Follicular (Proliferative) Phase (Day 6–13)
Definition
This phase begins after menstruation and ends with ovulation. It is characterized by follicular growth in the o***y and regeneration of the endometrium.
Ovarian Changes
Follicle Development
Under the influence of FSH:
Several primary follicles begin to grow.
One follicle becomes dominant (Graafian follicle).
Other follicles undergo atresia.
Estrogen Production
The growing follicle secretes increasing amounts of estrogen.
Uterine Changes
Endometrial Regeneration
Estrogen stimulates:
Repair of the endometrium.
Growth of endometrial glands.
Increase in blood vessels.
Thickening of the uterine lining.
The endometrium increases from approximately 1–2 mm to about 4–6 mm.
Hormonal Changes
FSH stimulates follicular growth.
Estrogen gradually rises.
LH remains low initially but begins to increase.
Importance
This phase prepares the uterus for possible implantation and prepares the o***y for ovulation.
3. Ovulatory Phase (Day 14)
Definition
Ovulation is the release of a mature o**m from the Graafian follicle.
Mechanism
Estrogen Peak
High estrogen levels stimulate the hypothalamus and pituitary gland.
LH Surge
A sudden surge in LH occurs approximately 24–36 hours before ovulation.
Follicular Rupture
The mature follicle ruptures and releases the o**m into the peritoneal cavity near the fimbriae of the fallopian tube.
O**m Capture
The fimbriae sweep the o**m into the fallopian tube.
Hormonal Changes
LH reaches its highest level.
Estrogen peaks just before ovulation.
FSH rises slightly.
Signs and Symptoms of Ovulation
Mittelschmerz (mid-cycle pain).
Increased cervical mucus.
Clear, slippery, stretchy mucus (Spinnbarkeit).
Slight rise in basal body temperature.
Increased libido.
Importance
Ovulation is the most fertile period of the menstrual cycle. The o**m remains viable for about 24 hours after release.
4. Luteal (Secretory) Phase (Day 15–28)
Definition
The luteal phase begins after ovulation and ends when menstruation starts.
Ovarian Changes
Formation of Corpus Luteum
After ovulation:
The ruptured follicle transforms into the corpus luteum.
Corpus luteum secretes progesterone and small amounts of estrogen.
Hormonal Changes
Progesterone
Progesterone becomes the dominant hormone and:
Maintains the endometrium.
Suppresses uterine contractions.
Thickens cervical mucus.
Estrogen
Continues to support endometrial growth.
Uterine Changes
Secretory Transformation
Progesterone causes:
Endometrial glands to become coiled and enlarged.
Increased glycogen secretion.
Increased blood supply.
Thick, soft, nutrient-rich endometrium.
The endometrium becomes highly receptive to implantation.
If Fertilization Occurs
The embryo produces human chorionic gonadotropin (hCG).
hCG maintains the corpus luteum.
Progesterone production continues.
Menstruation does not occur.
If Fertilization Does Not Occur
Corpus luteum degenerates into corpus albicans.
Estrogen and progesterone levels fall.
Endometrial breakdown begins.
Menstruation starts, initiating a new cycle.