Female Reproduction Flashcards
(30 cards)
What are the rolesof the female reproduction ?
– Production of the egg – Ovulation – Implantation of the egg – Pregnancy – Birth – Lactatio
What is the mechanism of action of LH on the theca cell in the ovary?
Increased cAMP via PKA and increases DNA transcription
Cholesterol —> pregnolone
What is the mechanism of action FSH on an granulosa cell in early to mid follicular phase?
Has only FSH receptor in early phase
Increased cAMP via PKA
This increases DNA transcription for enzymes
Summarize the 2 cell theory
Early follicular phase
- LH binds to its receptor on the thecal cell causing an increase in uptake of LDL’s into the cell as well as stimulating the conversion of cholesterol into pregnenolone.
- This leads to the production of androstenedione.
- This androstenedione leaves the thecal cell and moves into the granulosa
cell.
- The binding of FSH to its receptor on the granulosa cell increases the
production of the aromatase enzyme that converts androstendione into estradiol. This estradiol then diffuses into the blood
Late follicular phase:
- Granulosa cell acquires an LH receptor under the influence of FSH
- Granulosa cell can now synthesize progesterone from cholesterol
Summarize the feedback mechanisms of the hypothalamus
Hypothalamus • GnRH pulse generator • Changes in GnRH secretion (frequency & amplitude) to differentially modulate LH and FSH. • Slow freq GnR—>FSH • ↑ freq & amp GnRH—> LH
What are the feedback mechanisms of the anterior pituitary?
FSH-effect granulosa cells
LH—> the cal cells
What are the feedback mechanisms of the ovary?
Ovary • Granulosa cells—>estrogen • Thecal cells—>testoserone • Corpus luteum—>estrogen & progesterone • Ovary- inhibin
What is the role of estrogen in feedback mechanisms?
Estrogen normally has
negative feedback.
However just prior to ovulation: estrogen switches to positive feedback and mediates LH surge (in later slides)
What are the 3 organs in the hormonal responses in the female reproductive system?
Hypothalamus: GnRH Pituitary: LH and FSH
Ovary:
Egg- granulosa & thecal cells
Corpus luteum
Uterus & Vagina:
Changes in preparation for fertilization & pregnancy
Summarize the follicular and luteal phase
Two phases: Follicular & Luteal (phases separated by ovulation)
Follicular phase
• Development of follicleFSH
• Follicular phase from menses until
ovulation ~ 14 days. (interval variable)
Luteal phase • Development of corpus luteum • Luteal phase =14 days (fixed by finite lifespan of corpus luteum) Length of cycle is 28- 35 days
In general, FSH stimulates follicular growth in the ovary
LH, drives ovulation & progesterone secretion from the developing corpus luteum
What is the function of FSH in the menstrual cycle?
FSH increases in early follicular phase (&late luteal)
• Important for follicular development • Due to:
• Decreased inhibin & estrogen negative feedback on pituitary
• Decreased progesterone & estrogen negative feedback on hypothalamus
FSH declines until ovulation
• Due to increased estrogen secretion by granulosa cells of growing follicle.
• FSH decrease important for selection of dominant follicle.
Decreased FSH in luteal phase (not needed for follicle development in this phase)
Summarize the lutenizing hormone in the early follicular phase and prior to ovulation
Early follicular phase:
• LH secretion pulses ~ every 1 hour (constant amplitude)
Prior to ovulation:
- LH pulse frequency increases (conc increase).
- Estrogen secretion from gravid follicle peak to 150 -200 pg/ml for ~36 -50 hrs
• Estrogen switches to a brief positive- feedback effect on the pituitary to trigger the preovulatory surge of LH and FSH
What is the function of luteinizing hormone prior to ovulation?
Prior to ovulation:
• Increased estrogen stimulates LH in a surge ~ 10 to 12 hrs before ovulation.
• LH surgeLuteinization of granulosa cells & stimulates synthesis of progesterone responsible for the midcycle FSH surge
• LH surge alsorupture & ovulation (enzymes and hyperemia of follicle)
What are the functions of the estrogen and progesterone peaks?
ESTROGEN PEAKS TWICE IN CYCLE
Follicular phase: secreted by follicle. Levels proportional follicle size
(# of granulosa cells)
Luteal phase: Corpus luteum
secretes estradiol & also progesterone to facilitate implantation.
If no fertilization:
• Corpus luteum breaks down
• Estradiol & progesterone synth decline
• Menstrual cycle begins again
What are estrogens ?
For the majority of the cycle, the reproductive system functions in a classic endocrine negative feedback mode.
• Estrogens are a group of steroidal hormones secreted in large quantities by the ovaries
– β estradiol is the major hormone secreted by the ovaries in a non-pregnant female
– 12 times more potent than estrone – 80 times more potent than estriol
• Is carried in blood bound to albumin & sex hormone binding globulin(SHBG) proteins (loosely bound)
• Is cleared by the liver
What are the functions of the estrogens?
- Increase size of reproductive organs
- Increase number & activity of cilia in oviducts • Prepare endometrium at puberty
- Makes vaginal epithelium resistant to trauma • Causes H2O retention
- Ovarian & menstrual function
- Initiation of breast development at puberty & ductal proliferation • Protein synthesis, sex binding proteins
- Subcutaneous fat deposition (e.g. hips)
- Epiphyseal fusion
- Builds bone
- Decreases cholesterol levels
What are progestins?
• Progestins are a group of steroidal hormones
• Mostimportantisprogesterone
• Progesterone secreted in large amounts by - corpus luteum during luteal phase
- placenta
• Transported similarly to estrogens
• Liver very quickly breaks down to inactive forms
What are the functions of progesterone?
- Proliferation of uterine epithelium
- Aidsovulation
- Promotes development of lobules & alveoli in the breast & glandular proliferation
- In pregnancy - inhibits uterine excitability
What are the roles of progesterone just prior to ovulation?
Helps LH to surge
Role in FSH surge
Ovulation processes
Inhibits estrogen
What is the role of progesterone in ovulation?
Progesterone stimulate collagenase and prostaglandins
Collagenase breaks down wall—> stigma degeneration and swelling of follicle which both contribute to rupture and ovulation
Prostaglandins —> hyperemia—> swelling of follicle—> rupture and ovulation
Describe the uterine cycle
• The uterus, where a fertilized egg will implant, also undergoes cyclical changes.
• It has 3 distinctive phases (even though there 4 phases – the ischemic phase)
- menstrual
- proliferative
- secretory
• These phases are dictated by ovarian steroids (estradiol and progesterone)
Summarize the phases of the uterine cycle
Menses phases (2-7 days)
- Shedding of epithelium (preceded by short ischemic phase)
- Duetoabruptwithdrawalprogesteron
- Withinfollicularphaseofmenstrualcycle;progesterone,FSH,&LHarelow
Proliferative phase:
• Changes in vagina and thickening of uterus (epithelium, mucus, etc)
• Due to increased amounts of estrogen secreted from follicle.
Secretory phase:
• Preparation for implantation
• Increase in glycogen secreting glands an
Aside from hormones, what changes occur during the uterine cycle?
Temp increase
Keratinization. Acidity of vagina decreases at ovulation
At ovulation- mucus becomes thinner to allow passage of sperm
What are the age related changes of the uterine cycle?
- puberty
- reproductive maturity
- reproductive senescence (menopause)
