Endocrine Control Female Reproduction 4 Flashcards
Explain the production of sex hormones.
What is the role sex hormone binding globulin (SHBG) in female reproduction?
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High affinity binding protein for estrogens and adrogens
- androgens bind with higher affinity than estrogens
- bound hormones considered biologically inactive
- hormones that are free or loosely associated with albumin are biologically available
- Hepatic SHBG production increased by the following:
- estrogen
- thyroid hormone
- Production is decreased by the following:
- androgens
- obesity
- insulin
List the major peptides involved in female reproduction?
- Inhibin A and B
- Activin
- Follistatin
What is the role of Inhibin A and B in female reproduction?
- Inhibits FSH release
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Inhibin A
- present in both granulosa and theca cells
- secreted by the dominant follicle
- secreted by the corpus luteum
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Inhibin B
- secreted by granulosa cells of small antral follicles
- increases in response to FSH stimulation
- feeds back to modulate FSH release
- marker of gonadal reserve
What is the role of activin in female reproduction?
- homodimer of inhibin beta-subunits
- synthesized by the pituitary and ovary
- stimulates FSH release by local autocrine/paracrine rather than endocrine actions
- most circulating actiin is likely bound to follistatin
What is the role of follistatin in female reproduction?
- inhibits FSH release by binding and neutralizing activin
- acts locally to inhibit follicular growth
- autocrine/paracrine actions
Discuss the following stages of female development: menarche, adrenarche, and adult female.
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Menarche
- median age 12.6 in US
- occurs about 2 years after breast budding
- secular trend in age of menarche
- occurs at earlier ages over the centuries
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Adrenarche
- occurs between 6-8 years, prior to onset of puberty
- development of adrenal zona reticularis - androgen secreting compartment of adrenals
- results in secretion of adrenal androgen, DHEAS
- leads to development of pubic and axillary hair
- uncouple from gonadarche
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Adult female
- menstrual cycle 21-35 days in length
- cycle varies by no more than +/- 2 days
List the phases of the menstrual cycle.
- Ovarian follicular development
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Follicular phase
- early
- mid
- late
- Luteal phase
Describe the events during ovarian follicular development.
- Gonadotropin-independent and regulated by intraovarian growth factors
- Maturation of antral follicles and ovulation with resumption of meiosis requires FSH and LH
- A single dominant follicle emerges from growing follicle pool 5-7 days after to start of menses
- Other growing follicles become atretic
Describe the events during the follicular phase.
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Early follicular phase
- FSH increase persists from of last cycle
- dominant follicle is selected
- LH pulse frequency begins to increase in absence of negative feedback of effects of E2 and progesterone
- LH stimulates thecal cell T production, aromatized into E2 by adjacent granulosa cells of follicle
- aromatase activity increases with FSH-stimulated follicular growth
- Inhibin B increases follicular growth
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Mid follicular phase
- increasing GnRH pulse frequency
- synergizes with increasing ovarian E2 and inhibin B production
- suppresses FSH release
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Late follicular phase
- continued increase E2 production induces mid-cycle LH surge
- induces ovulation of the dominant follicle
- increased GnRH pulse frequency to ~1 pulse/hour
Describe the events of the luteal phase.
- Period after ovulation, usually 14 days
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Post ovulatory follicle
- lueinizes, forming corpus luteum
- secretes progesterone and E2
- feed back to slow GnRH pulse frequency
- as frequency slows, FSH release selectively increases and LH decreases
- stimulates follicular recruitment to the next cycle
- progesterone production falls in the face of decreasing LH levels
- without conception and hCG production, the embryo does not sustain the corpus luteum preogesterone production
Describe the events that occur in the endometrium during the menstrual cycle.
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Proliferation
- E2 or synthetic estrogens stimulate proliferation od endometrial, stromal, and epithelial cells
- estrogens also induce expression of progesterone receptors
- Ability of endometrium to respond to progesterone depends on estrogen induction of progesterone receptors
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Differentiation
- Prgestins such as progesterone or synthetic progestins induce differentiation of the poliferative endometrium
- P also prepares the endometrium for implantation of the embryo
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Menstruation
- In the absence of hCH produced by the embryo, P and E2 production by the corpus luteum stops
- this withdrawal of P and E2 leads to vasomotor changes in the endometrium and shedding of the endometrial lining
Describe the events that occur during menopause.
- cessation of ovarian follicular activity
- mean age 51-52 years
- ovarian estradiol virtually ceases at menopause
- ovarian androgen production continues from some years afterwards
- Androgens, primarily androstenedione can be aromatized extragonadally into estrogen