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Ovarian Cycle

Sexual Cycles

  • Starts at puberty
  • Regular monthly cycle
  • Controlled by hypothalamus

Hypothalamus produces releasing factors act on cells of pituitary gland secrete gonadotropins:

    • FollicleStimulating Hormone (FSH)
    • Luteinizing hormone (LH)
  • At the start of each ovarian cycle, 5-12 primordial follicles begin to grow under influence of
  • Follicle-stimulating hormone.
  • Under normal conditions only one follicle reaches maturation and only one oocyte is discharged
  • The others degenerate and become atretic, so the majority of follicles degenerate w/o reaching  maturity When the follicle becomes atretic, the oocyte and surrounding follicular cells degenerate  and are placed by connective tissue forming
  • Corpus Atreticum
    • Duringgrowth of follicle, large numbers of follicle and theca cells are formed  which produce
    • Estrogens(stimulate pituitary gland to secrete luteinizing hormone)
  • LHis needed for:
  • Final stage of follicle maturation
  • Induced Shedding of the oocyte

OVULATION

OVULATION

  • Days immediately before ovulation, the Graafian Follicle increases rapidly in size under influence of FSH and LH (15 mm diameter)
  • Primary oocyte, which until this time has remained in its dictyotene stage, resumes and finishes its 1st meiotic division.
  • Surface of ovary begins to bulge locally and at the apex, an avascular spot appears STIGMA Result of local weakening and degeneration of  the ovarian surface, follicular fluid oozes out Through the stigma w/c gradually opens.
  • When more fluid escape, the tension in the follicle is released, with the oocyte and surrounding Cumulus oophorus cells break free and float out of the ovary Some cumulus oophorus rearrange around the Zona pellucida to form CORONA RADIATA
  • Ovulation – the moment the oocyte and its cumulus oophorus cells discharge from the ovary, the first meiotic division is completed and  secondary oocyte is starting its 2nd meiotic division.
  • Middle Pain – pain occurring near the middle of the menstrual cycle. Rise in BASAL BODY TEMPERATURE aid in determining when
  • release of oocyte occurs.

 CORPUS LUTEUM

  • After ovulation the follicular cells remaining in the wall of ruptured follicle are vascularized by surrounding vessels and become polyhedral. Under influence of LH it will develop yellowish pigment and change into LUTEAL CELLS forms CORPUS LUTEUM and secrete progesterone
  • PROGESTERONE with estrogenic hormones of theca cells causes uterine mucosa to enter the PROGESTATIONAL SECRETORY STAGE in preparation for implantation of the embryo.

OOCYTE TRANSPORT

  • Before ovulation, the fimbriae of the oviduct begin to cover the surface of the ovary and the tube itself begins to contract rhythmically Oocyte and surrounding cumulus/granulosa cells is  carried into the tube by sweeping movements of the fimbriae and by the motion of cilia on the  epithelial lining.
  • Once in tube the cumulus cells lose contact with oocyte by withdrawing their cytoplasmic process from zona pellucida. Once oocyte is in uterine tube, it is pushed toward the lumen by the contractions of muscular wall.
  • Fertilized oocyte reaches uterine lumen in 3- 4 days.

CORPUS ALBICANS

  • If fertilization fails to occur, corpus luteum reaches maximum development about 9 days after ovulation Corpus luteum decreases in size through degeneration of the luteal cells and forms a mass fibrotic scar tissue CORPUS ALBICANS Progesterone production decrease, precipitating menstrual bleeding.
  • If oocyte is fertilized, degeneration of corpus luteum is prevented by the gonadotropic hormone secreted by the trophoblast of developing embryo.
  • Corpus luteum continues to grow and forms CORPUS LUTEUM of PREGANANCY  (gravidities)
  • At the end of 3rd month the structure is 1/3 to ½ of the total size of the ovary Yellowish luteal Cells continue to secrete progesterone until end of 4th month, then regress slowly as secretio of progesterone becomes adequate for maintenance of pregnancy
  • Removal of corpus luteum if pregnancy before 4th month usually leads to abortion
  • Progestational compound taken orally form day 5 to 25 of menstrual cycle usually act as Contraceptives and inhibit ovulation almost 100% of the cases.

FERTILIZATION

  • Process by w/c male and female gametes fuse,itoccurs in ampullary region of uterine tube, the widest part of the tube and located near the ovary.
  • Spermatozoa can stay alive in female reproductive tract for 24 hours, secondary oocyte dies 12 to 14 hours after ovulation if not fertilized.
  • Rapid passage of spermatozoa in the vagina intouterus into uterine tubes is caused by Contractions of the muscle
  • Spermatozoa can’t fertilize oocyte unless they undergo:
    • CAPACITATION – period of conditioning in the female reproductive tract (7hours).A glycoprotein coat and seminal plasma proteins are removed from plasma membrane that overlies acrosomal region. Completion permits acrosome reaction.
    • ACROSOME REACTION  –occurs  in immediate vicinity of oocyte under influence of substance from corona radiata and oocytes.
  • During this process the ff are released:
    • Hyaluronidase – needed to penetrate corona radiata barrier
    • Trypsin-like substance – digestion of zona pellucida
    • Zona lysine – help spermatozoon cross zona pellucida

IN VITRO FERTILIZATION

  • Follicle growth is stimulated in the ovary by administration of gonadotropins:
    • hMG = stimulate growth
    • hCG = induce preovulatory changes
  • In vitro provides opportunity to alleviate infertility from variety of causes including occluded Oviducts hostile cervical mucus, immunity to spermatozoa,etc.
  • Risk of producing malformed offspring is low due tohigh resistant of preimplantic embryo to teratogens. Low success rate since only 20% of fertilized ova implant and develop to term.