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16 Cards in this Set
- Front
- Back
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What is the major role of the HPO (Hypothalamus Pituitary Ovarian) axis?
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To drive the menstrual cycle
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What are the phases in the Ovarian Cycle and the Uterine/Endometrial Cycle?
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Ovarian Cycle:
1. Follicular phase (1-4days) 2. Luteal phase (last 14days) Uterine/endometrial cycle: 1. Menstrual phase (1-4d) 2. Proliferative phase (4-14d) 3. Secretory phase (14-28) |
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Explain how GnRH affects the functioning of the pituitary gonadotropes and why?
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Early follicular phase: gonadotropes are NOT very sensitive, producing a SMALL rise of LH
**The amt of GnRH release does not change so the change in sensitivity is due to the increase levels of estradiol in the late luteal phase. Laste Follicular phase: gonadotropes are MORE sensitive, producing a LARGER rise of LH |
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Describe the pulse pattern of GnRH and the pulse generator.
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The GnRh pulse pattern is every hour and every month (mid-cycle)
GnRH regulator is unknown but - pulse generator every hours is from arcuate nucleus of the hypothalamus. - pulse generator every month is in the preoptic area of the hypothalamus. |
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What are the effects of GnRH pulsatility on pituitary gonadotropes (vs constant)?
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Pulses spaced 60-90min UPREGULATE the GnRH receptors and thus stimulating the release of of LH/FSH.
Constant GnRH release will cause a DOWN-REGULATION of the GnRH receptors thus suppressing LH/FSH release. |
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What are the results of the monthly mid-cycle surge of GnRH?
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Partly responsible for the LH surge that leads to ovulation
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What cell signaling pathway does GnRH work through?
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PLC --> IP3 (for Ca that is responsible for LH/FSH exocytosis) and DAG (for PKC that is responsible for LH/FSH gene transcription)
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What consists in an ovarian follicle structure?
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1. Oocyte (egg)
2. Follicular cells **Types of egg and follicular cells present depend upon developmental state of the ovarian follicle. |
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Explain the functional roles of LH and FSH before and after ovulation
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Before ovulation:
1. Theca cells have LH receptors 2. Granulosa Cells have LH & FSH receptors **Both LH/FSH -stimulate follicular growth and maturation -support synthesis of estrogen (estradiol) After ovulation: 1. LH & FSH act on the cells of corpus luteum (which are cells remaining from a ruptured follicle) -LH causes luteinization -LH/FSH support the synthesis of estrogen & progestins/progesterone (in greater amts) |
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Estrogen synthesis in the ovaries is dependent upon...
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androgen synthesis
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Outline the steroidal biosynthetic pathways that occur in granulosa and theca cells of the ovaries
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Two-Cell Model of Estrogen Synthesis:
1. LH stimulates the theca cells to synthesize androstenedione and testosterone 2. These androgens diffuse to the granulosa cells 3. FSH stimulates the granulosa cells to produce aromatase, whose enzymatic activity leads to the synthesis of estradiol from the androgen precursors. 5. FSH also increases the activity of aromatase |
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What is luteinization?
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The process by which ruptured follicle is transformed into a corpus luteum and completely dependent on a LH surge.
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What is the corpus luteum composed of and their roles under LH/FSH influence?
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1. Granulosa lutein cells (modified granulosa cells)
-under LH produce the majority of progesterone during luteal phase -under FSH they convert androgens formed by the theca lutein cells into estrogens 2. Theca lutein cells (modified theca interna cells) -under LH they manufacture progesterone and androgens |
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What is the LH/FSH influence in protein synthesis?
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LH/FSH --> G linked protein --> AC --> cAMP --> PKA -->
1. stimulate enzymes for steroid synthesis -LDL receptor needed for Chol to be transported into the cell -Aromatase required for estrogen synthesis in the granulosa cells 2. increases cell division |
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Explain the roles of estrogens & progestins, in terms of negative & positive feedback within the hypothalamic‐pituitary‐ovarian axis
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Both have negative and positive feedback but depends on their concentration and duration of exposure of the steroid.
1. Through most of the menstrual cycle the net effect is negative feedback (estrogen both at low and high levels while progesterone only at high) 2. The END of the follicular phase (mid-cycle) the estradiol (and progesterone) level rises sharply and after it reaches a threshold for ~2days the HP axis REVERSES its sensitivity such that POSITIVE feedback occurs **This switch in feedback promotes the LH surge. |
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Explain the roles of inhibins & activins in terms of negative & positive feedback within the hypothalamic‐pituitary‐ovarian axis
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1. Inhibins: inhibit FSH secretion mainly during the luteal phase of the ovarian cycle (also during follicular phase)
-they are produced by the granulosa cells of the corpus luteum and also the granulosa cells 2. Activins: stimulate FSH secretion mainly during the last portion of the follicular phase -they are produced by the granulosa cells. |
