MCAT Reproductive Systems
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When does oogenesis take place?
- before birth
- arrested at prophase I of meisosis
- 2 million at peak, born with around 400,000, only 400 released
What causes frozen prophase I oocytes to finish meiosis?
- After puberty, hormonal changes stimulate the first division and ovulation. This yields a polar body and a large secondary oocyte.
- second meitoic division only occurs when the oocyte has been fertilized by sperm which also produces a polar body.
Do sperm and egg nuclei fuse immediately?
No, oocyte has to complete meiosis
What cells produce testosterone and what hormone are they stimulated by?
What cells are stimulated by FSH?
Sustenacular/Sertoli - promote spergatogenisis
Where do sperm mature?
Epidydimis - this is called spermiogenisis - usually gain motility
What cells make and secrete estrogen?
What structure secretes progesterone?
- Corpus leuteum
- Placenta if pregancy takes place
What is ectopic pregnancy?
When implantation occurs in the fallopian tubes
What happens at the LH surge?
What hormone maintaines the endometrial lining?
Progesterone. This lining is important in pregnancy. If no progesterone is made, miscarrages are very likely.
3 phases of the overian cycle
- Follicular phase: primary follicle matures and secretes estrogen
- Ovulatory phase: secondary oocyte is released from the ovary. Triggered by LH surge
- Luteal phase: formation of the corpus luteum which secretes both progesterone and estrogen
At what phase is the endometrium when ovulation occurs?
What is GnRH, LH, FSH inhibitd by?
Negatively by estrogen, especially after ovulation when the corpus luteum contributes to feedback inhibition
What would happen if a woman was on the pill for prolonged periods of time?
- No menstruation
- Prevention of ovulation because LH and FSH would be inhibited (no LH surge)
Why does the corpus leuteum degenerate?
- Due to decreased levels of LH which keeps it alive
- LH reduced due to feedback by estrogen and progesterone
- This ensures that ovulation does not occur during pregnancy - this is also why estrogen and progesterone are high during pregnancy
Where is the chorion derived from?
What hormone does the zygote release?
- hCG (human chorionic gonadotropin)
- hCG take the place of LH in maintaining the corpus leuteum, which in turn maintains estrogen and progesterone production, and as a result, LH is not necessary b/c it is feedbacked
When does meiosis I and II occur in oocytes?
- Meiosis I - prior to ovulation (before birth)
- Meiosis II - after fertilization
Where does sperm bind to?
Bindin receptors via bindin which is found on the acrosomal process
Fast and slow blocks of polyspermy
- Fast: depolarization due to influx of sodium
- Slow: Ca influx (caused by depol) = cortical reaction which hardens the zona pellucida and increasing metabolism and protein synthesis
Does cleavage increase the size of the initial embryo?
Embryonic development stages
- blastula: which has the tropoblast (plancenta) and inner cell mass (embryo)
What happens if corpus luteum is removed during the first trimester?
- Menstruation will occur resulting in a miscarriage
- This is either because (1) progesterone levels are not maintained (2) LH levels are decreased which they should but (3) hCG not produced which maintains the corpus luteum.
When does the placenta take over in making progesterone?
- After the first trimester when it is developed
- this allows hCG release to be halted and corpus leuteum to be degenerated
- remember, estrogen and progesteroe levels are still high so LH and FSH are low so ovarian cycle does not continue
Ectoderm, Mesoderm, Endodermal tissue derivatives
- Endoderm: nervous system, skin, pituitary gland, cornea, lens, nasal, oral, anal epithelium
- Mesoderm: all muscle, bone, and connective tissue (including blood), cardiovascular and lymphatic system, kidneys, ureters, gonads, reproductive ducts
- Endoderm: GI tract and epithelia, GI glands (liver, pancrease, gallbladder, etc), respiratory epithelium, bladder, epithelial lining of urogenital organs
- Seminal vesicles: fructose (nourishment and energy)
- Prostage gland: fructose and coagulant
- Bulbourethral glands: alkaline (neutralize acid in vagina and urethra)
- Testes: sperm
What NS division is responsible for ejaculation and erection?
- "Point and Shoot"
- Erection - para
- Ejaculation - sympa
Do spermatoGONia devide by mitosis or meiosis?
What hormone directly stimulats division of spermatogonia?
LH causes ________ cells to secrete __________
FSH stimulates __________
Which male hormone inhibits FSH release?
inhibin which is produced by the sustenacular cells
Mullerian or Wolfian development by default?
- Mullerian resulting in female genitalia
- Y chromosome leads to the development of testes which causes male internal and external genetialia to develop by producing testosterone and mullerian inhibiting factor
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