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Menestrual cycle, fertilization & implantation


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Menestrual cycle, fertilization & implantation

  2. 2. • Monthly menstruation is an obvious marker that the various levels of interaction between -hypothalamus, - pituitary, - ovary & -uterus are functional.
  3. 3. Endocrine cycle Ovarian cycle Endometrial cycle
  4. 4. GnRH…………………..Hypothalamus Gonadotropins………..Pitutary -FSH -LH Steroids…………………Ovary -Estrogen -Progestrone
  5. 5.  GnRH -Gonadotropin Releasing Hormone  controlling factor for gonadotropin secretion  synthesized by neurosecretory cells in the hypothalamus  carried by hypophysial portal system to anterior lobe of pitutary  Unique among releasing hormones b/se 1. simultaneously regulates the secretion of 2 hormones (FSH & LH) 2. must be secreted in pulsatile fashion to be effective
  6. 6. Gonadotropins (FSH and LH) -produced by the anterior pituitary gonadotroph cells -responsible for ovarian follicular stimulation -FSH, LH, TSH, hCG all share identical α subunits and differ only in the structure of their β subunits
  7. 7.  The structural similarity between FSH, LH, and TSH. The α subunits are identical and the β subunits differ.
  8. 8. Follicle Stimulating Hormone (FSH) -stimulates development of ovarian follicles -stimulates production of estrogen by follicular cells Luetinizing Hormone (LH) -trigger for ovulation ( release of secondary oocyte) -stimulates follicular cells & corpus luteum to produce progesterone
  9. 9.  regulated at both endocrine and paracrine levels  Phases of ovarian cycle -Follicular (pre ovulatory) phase, -Ovulation, and -Luteal (post ovulatory) phase
  10. 10.  Oocytes in the ovary - 7 million present during fetal life , - 2 million present at birth , - 400,000 present at the onset of puberty, &  >99.9 % of follicles undergo atresia through a process of apoptosis  Only 400 follicles are normally released during female reproductive life
  11. 11. Development of ovarian follicle characterized by; -growth & differentiation of primary oocyte -proliferation of follicular cells -formation of zona pellucida -dev’t of theca folliculi
  12. 12. Occurs around mid cycle Triggered by a surge in LH production Mechanism of ovulation………..
  13. 13.  After ovulation the walls of ovarian follicle & theca folliculi develop in to glandular structure, corpus luteum, under LH influence  Corpus Luteum; -secrets progesterone & some estrogen -prepare endometrium for implantation  Fate of corpus Luteum; 1) If the oocyte is fertilized -enlarges to form corpus luteum of pregnancy -placenta takes over function by around 8-10 wks 2) If no fertilization occurred -involutes & degenerates 10-12 days after ovulation -subsequently transformed in to white scar tissue in the ovary….corpus albicans
  14. 14.  The functional layer of the endometrium is sloughed off & discarded with the menestrual flow  Origin of menstrual blood -arterial bleeding greater than venous  Mechanism of mensus…. rupture of arteriole of a coiled artery hematoma formation Superficial endometrium distends & ruptures Fissures develop in adjacent functionalis layer Blood & tissue fragments sloughed
  15. 15. Coincides with growth of ovarian follicles Controlled by estrogen 2 to 3 fold increase in the thickness of endometrium Phase of repair & proliferation Glands increase in number & length Spiral arteries elongate Length of cycle may vary among women
  16. 16.  Coincides with luteal phase of ovary  Progesterone dependant  Glandular epithelium secrete a glycogen rich material  Glands become wide, tortuous and saccular  Endometrium thickens  Spiral arteries become increasingly coiled  Direct arteriovenous anastomosis are prominent features  Length of cycle usually fixed ( 14 days)
  17. 17. 1) If fertilization does not occur; -the corpus luteum degenerates -estrogen & progesterone levels fall & the secretory endometrium enters an ischemic phase -menestruation occurs.
  18. 18. 2) If fertilization occurs; -Decidualization (transformation of secretory endometrium to decidua)  DECIDUA -a specialized, highly modified endometrium of pregnancy -a function of hemochorial placentation  Types of decidua 1. Decidua basalis 2. Decidua capsularis 3. Decidua parietalis
  19. 19.  Duration of flow 1-8 days (5 on average)  Frequency / cycle length 21-36 days (28 on average)  Amount of blood flow 10-80ml (50 on average)  Character of blood Dark, non-clotting blood  Degree of discomfort No dysmenorrhea
  21. 21.  The union of egg & sperm  Sequence of coordinated events 1. Passage of sperm through corona radiata 2. Penetration of the zona pellucida 3. Fusion of plasma membranes of the oocyte & sperm 4. Completion of the second meiotic division of oocyte & formation of female pronucleus 5. Formation of the male pronucleus 6. Fusion of pronuclei into a single diploid aggregation of chromosomes…….the ootid becomes a zygote
  22. 22. 10 microns (0.01mm) (0.05 to 0.1 microns) (0.5 to 1.5 microns) (5 microns) (5 to 8 microns) (60 microns) VIRUS BACTERIA RBC LYMPHOCYTE SPERM SIZE COMPARISONS 100 microns OVUM
  23. 23. SPERM NUCLEUS EGG NUCLEUS DIPLOID NUCLEUS (syngamy - syn = together; gamy = gametes) FERTILIZATION ZYGTOTE ( = yoke)
  24. 24. Usual site is the ampulla of the fallopian tubes Results when intercourse occurs during the 2 days preceding or on the day of ovulation Restores the normal diploid number of chromosomes Determines chromosomal sex of the embryo
  25. 25.  Zygote - a diploid cell with 46 chromosomes -undergoes cleavage into blastomeres  Morula..a solid mulberry-like ball of cells  The morula enters the uterine cavity about 3 days after fertilization  Gradual accumulation of fluid b/n the cells of the morula ……..early blastocyst
  26. 26. The Blastocyst 1. Earliest stages of blastocyst; -wall consists of single layer of ectoderm 2.As early as 4-5 days after fertilization; -58 cell blastula differentiatesinto 5 embryo producing cells(inner cell mass) 53 cells to form trophoblasts
  27. 27.  Takes place 6 or 7days after fertilization  Divided in to 3 phases 1) APPOSITION -initial adhesion of the blastocyst to the uterine wall 2) ADHESION -increased physical contact b/n the blastocyst & uterine epithelium, & 3) INVASION -penetration & invasion of syncytiotrophoblasts & cytotrophoblasts in to the endometrium , inner third of the myometrium & , uterine vasculature.
  28. 28.  Succesful implantation requires receptive endometrium  Uterine receptivity is limited to days 20-24 of the cycle  Implantation most commonly occurs on the upper posterior uterine wall  At the time of interaction with the endometrium, the blastocyst is composed of 100-250 cells.  By the 10th day the blastocyst becomes totally encased with in endometrium
  29. 29. Hmmm…! Life is a journey!