♦♦♦ Regulation of menstrual cycle controlled by the following substances:
1. Main hormones: 1) GnRH. 2) FSH. 3) LH.
2. Assistant hormones: 1) Inhibin. 2) Activin. 3) PGs.
♦♦♦ Chemistry: decapeptide (10) aminoacids.
♦♦♦ Source: secreted from arcuate nucleus of the hypothalamus in a pulsatile manner then reaches the anterior pituitary via hypophyseal portal circulation.
♦♦♦ Metabolism: locally.
♦♦♦ Half life: < 1 minute.
♦♦♦ Action: ↑ production & release of pituitary gonadotrophins.
♦♦♦ Control: 2 hypothalamic centers
– Tonic center: * Controls continuous basal gonadotrophins level.
* Responds by –ve feedback to sex hormones.
– Cyclic center: * Induces midcyclic peak of gonadotrophins.
* Responds by +ve feedback to estrogen.
* Under control of cerebral cortex, diet, & emotion.
♦♦♦ Chemistry: glycoprotein (α subunit is non-specific & β-subunit is specific).
♦♦♦ Source: basophils of ant. pituitary in response to small amount of GnRH on short intervals.
♦♦♦ Half life: 30 minutes.
♦♦♦ Metabolism: liver.
♦♦♦ Action: (acts only on granulosa cells of Graffian follicle):
a) Stimulates aromatase enzyme activity in granulosa cells (main action).
b) Stimulates proliferation of granulosa cells.
c) Stimulates formation of LH receptors on granulosa cells.
d) ↑ number & sensitivity of its own receptors on granulosa cells.
♦♦♦ Control: GnRH & feedback mechanism by high level of estrogen.
♦♦♦ Chemistry: glycoprotein (α-subunit is non-specific & β-subunit is specific).
♦♦♦ Source: basophils of anterior pituitary in response to large amount of GnRH on long intervals.
♦♦♦ Half life: 20 minutes.
♦♦♦ Metabolism: liver.
♦♦♦ Action: (acts on all cells of Graffian follicle & corpus luteum)
a) Stimulates theca cells to produce androgen from cholesterol (androgen is substrate for
aromataze enzyme in granulosa cells to convert it to estradiol).
c) Completion of reduction division of oocyte.
d) Ovulation & maintanence of corpus luteum.
e) ↑ its own receptors on granulosa cells of the dominant follicles.
f) Stimulates synthesis of PGs within the pre-ovulatory follicles.
♦♦♦ Control: GnRH & feedback mechanism (+ve feedback of high estradiol level just before ovulation leading to LH surge).
♦♦♦ Nature: water soluble glycoprotein hormone.
♦♦♦ Source: granulosa cells.
♦♦♦ Action: inhibits FSH secretion (not affecting GnRH) & may be involved in the process of follicular atresia.
♦♦♦ Secreted from the ovary & stimulates FSH secretion.
♦♦♦ Locally acting substances secreted as autocrine or paracrine secretion.
♦♦♦ Its main actions are;
a) Stimulate proteolytic enzymes: leading to lysis of collagen on the surface of ovulatory follicle.
b) Inhibit collagen synthesis in the ovulatory follicle.
c) ↑ Activity of peri-follicular smooth muscles that ↑ intra-follicular pressure and so rupture of the follicle & ovulation.
Special notes on hormonal control
♦♦♦ 2 cell theory of steroidogenesis:
– Theca cells: under the effect of LH, cholesterol is converted to androstenedione then
diffuses to granulosa cells.
– Granulosa cells: under the effect of FSH, androstenedione is converted to estrone (E1)
via aromatase enzyme then estrone estradiol (E2).
♦♦♦ After ovulation:
– If pregnancy occurs, HCG secreted from syncytiotrophoblast of the fetus has LH-like
action and so; it maintains pregnancy till the 3rd month (time of
complete placental formation).
– If pregnancy doesn’t occur:
a) endometrial shedding occurs due to:
– Withdrawal of luteal support due to –ve feedback of progesterone on LH.
– Rising level of PGf2α.
b) Release of the anterior pituitary from the –ve feedback so, new cycle starts.
This HD video is e-lecture on Physiology of Menstruation primary meant for undergraduate and postgraduate students of obstetrics & gynaecology by Prof. Ajit Virkud from Mumbai, India
FSH & LH AND THE REGULATION OF THE REPRODUCTIVE ORGANS by Professor Fink
In this video lecture, Professor Fink describes the Regulation of the Reproductive Organs (Ovaries & Testes) by the Gonadotropic Hormones (Follicle Stimulating Hormone; FSH & Luteinizing Hormone (LH). Included in the detailed discussion is the Negative Feedback Loop involved in regulating circulating plasma Estrogen, Progesterone in the Female & Testosterone levels in the Male. The Menstrual Cycle is reviewed and the efficacy of Birth Control Pills (Oral Contraceptives) are explained by a Negative Feedback on the Pituitary Gland. A contrast is made between the continuous release of FSH & LH in the male versus a cyclical release of FSH & LH in the female. Reference is made to the GnRH, Pre-Ovulatory Phase and Post-Ovulatory Phase, Ovarian Follices, follicle cells, Ovulation, Corpus Luteum, Inhibin, Spermatogenesis, and Human Chorionic Gonadotropin (HCG).
The Menstrual Cycle – CRASH! Medical Review Series
The Menstrual Cycle
What is the menstrual cycle? The menstrual cycle refers to the regular changes in the activity of the ovaries and the endometrium that make reproduction possible.
Female Reproductive System – Menstrual Cycle, Hormones and Regulation
The ovarian cycle | Reproductive system physiology | NCLEX-RN | Khan Academy
Human Physiology – Menstrual Cycle: Ovarian Cycle
Ovulation & the menstrual cycle – Narrated 3D animation
Menstrual cycle its details and its physiology
Physiology Of Menstruation
By: Nur Afiqah Binti Jasmi (11-2013-031) & Luqman Hakim Bin Mohd Jais (11-2013-170)
Dokter Pembimbing: Dr. Harianto Wijaya Sp.OG