Fertility Hormones In Female Reproductive Cycle
Fertility hormones and their role in menstrual cycle
Female reproduction is dependent on fertility hormones estrogen and Progesterone.
Estrogen
Produced by ovary
All estrogens are steroid
The 4 naturally occurring estrogens in women are
Estrone (E1)
Estradiol (E2)(Predominant)
Estriol (E3)
Estetrol (E4)
Estradiol (E2)
- Before puberty, estradiol is secreted very low amount which has a very little physiological action
- At puberty, Estradiol is secreted in large quantities and result in following changes in the female body.
- It promotes the growth of internal and external genitalia
At Puberty
- Ovaries: Increase in size, the start of the ovarian cycle
- Fallopian Tube: It becomes functional, more ciliated, and motility increases
- Uterus: Enlarges, thickness increases, begins menstrual cycle
- Cervix: Enlarges and onset of the menstrual cycle
- Vagina: Increases in size and change in the epithelium
- Responsible for secondary sexual characteristics in women
In Adult woman
- Maintenance of pregnancy and parturition
- Breast development
Other actions of Estradiol
Effects on bones: Helps in enlarging hips and widens inlet of pelvic bone to facilitate childbirth, Maintain balance between bone formation and bone resorption
Effects on metabolism: It causes fat deposition in subcutaneous tissues like breast and thigh
Effects on water and electrolyte balance: Causes salt and water retention in body and causes premenstrual tension
Effects on CNS: It is responsible for estrus behavior and increases libido. Effects on vascular system: It is a vasodilator and has anti vasoconstrictor effect
Effects on skin: It makes skin soft and more vascular and makes sebaceous gland secretions thin . Thus synthetic estrogen is used in treatment of acne.
Estrogen is a major fertility hormone in females
Therapeutic uses:
Menopausal symptoms
Post menopausal osteoporosis
Atherosclerosis
Contraceptive with progestrone
Side effects
Uterine and breast cancer
Progestrone
It is a steroid component belongs to the class of fertility hormones called progestogens.
In non pregnant women progestrone is secreted by corpus leutum , a temporary endocrine gland that the female body produces after ovulation during second half of the menstrual cycle. After pregnancy by placenta and adrenal cortex
Functions of fertility hormones: Progesterone
It produces the secretory changes which prepare endometrium for the implantation of the fertilized ovum.
Cervical secretions become thick, tenacious and cellular
Promotes the growth of lobes and alveolar tissues in breasts
Antagonizes the action of estrogen by decreasing the excitability of myometrial cells
It helps in maintaining pregnancy
It inhibits ovulation probably by inhibiting release of GnRH (Gonadotropin releasing hormone) from hypothalamus.
Menstrual cycle
The menstrual cycle has 3 phases
Follicular phase (before the release of the egg)
Ovulatory phase (release of the egg)
Luteal phase (after the egg release)
Follicular phase
When follicular phase begins, levels of estrogen and progestrons are low,As a result, the top layers of the thickened lining of the uterus (endometrium) break down and are shed, and menstrual bleeding occurs
At this time the follicle stimulating hormone level increases slightly thus stimulating the development of several follicles in the ovary.
Each follicles contain an egg, later at this stage the follicle stimulating hormone decreases, only one follicle continues to develop and this follicle producecs estrogen.
Ovulatory Phase:
The ovulatory phase begins with surge in luteinizing hormone and follicle stimulating hormone levels.
Luteinizing hormone stimulates egg release which happens 16-32 hrs of surge begins
The estrogen level decreases during the surge and the progesterone level starts to increases
Luteal Phase
During the luteal phase the follicle stimulating hormone and luteinizing hormone decreases.
After the egg release, the rupture follicles closes and form corpus luteum, which produces progesterone.
During most of this phase the estrogen level is high , Estrogen and progesterone helps in thickening of lining in uterus for possible fertilization.
If the egg is not fertilized, the corpus luteum degenerates and no longer produces progesterone, the estrogen level decreases which causes shedding of the top lining of endometrium resulting in menstrual bleeding occurs.
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