Ovarian cycle

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  • Estradiol has negative feedback on FSH release and almost stops LH secretion – however both are still synthesized and stored in the gonadotropes. At midcycle, the pituitary gonadotropes become more sensitive to GnRH and the graafian follicle releases a maximum level of estradiol, which now effects a positive feedback effect on GnRH, causing gonadotropes to release LH and some FSH as well
  • Relaxin causes dilation of cervix, softens symphysis pubis in preparation for birth
  • Branches of arcuate arteries enter basalis layer, where they ascend to functionalis layer as spiral arteries.
  • Lacunae are thin-walled, dilated segments of the capillary bed. Spiral arteries give off numerous capillaries.
  • The layer of trophoblast closest to the inner cell mass is called the cytotrophoblast and consists of an irregular layer of ovoid, mononucleated cells thatundergo extensive proliferation.
    At day 8, the portion of the cytotrophoblast that pushes into the endometrium differentiates into the syncytiotrophoblast. The syncytiotrophoblast is formed by the fusion of cytotrophoblast cells, forming a multinucleated syncytium possessing microvilli at its surface.
  • The syncytiotrophoblast forms spaces, or lacunae which will shortly become filled with maternal blood
  • The syncytiotrophoblast invades the endometrium (decidua) and ruptures the maternal arterial and venous blood vessels. The maternal blood flows from the arterial vessels into spaces (lacunae) that form at day 9 within syncytiotrophoblast. The maternal blood is drained by the ruptured veins and returns to the mother’s circulatory system.
  • By day 13, the cytotrophoblast cells grow into the syncytiotrophoblast to form primary villi.
  • By day 16, the extraembryonic mesoderm derived from the inner cell mass invades the center of the primary villi, producing secondary villi.
  • By day 21, fetal vessels (part of the umbilical circulation) grow into the secondary villi, forming tertiary villi.
  • Cytotrophoblastic shell anchors blastocyst to decidua – cytotrophoblast cells migrate out from tertiary villi to surround blastocyst
  • Placenta Functions as lungs, GI tract and kidneys for the fetus!
  • Chorion laeve forms chorionic sac
  • decidual prolactin has trophic effects on CL; relaxin softens cervix and pubic symphysis; prostaglandins help to prevent immunologic rejection of fetus
  • Ovarian cycle

    1. 1. Ovarian cycleOvarian cycle Menstrual cycleMenstrual cycle PlacentationPlacentation Department of the Histology, Cytology and EmbryologyDepartment of the Histology, Cytology and Embryology Tatiana GlobaTatiana Globa State University of Medicine and Pharmacy “Nicolae Testemitanu”State University of Medicine and Pharmacy “Nicolae Testemitanu”
    2. 2. Ovarian cycle has 2 phasesOvarian cycle has 2 phases • FOLLICULAR PHASEFOLLICULAR PHASE – consists of the development of a primordial follicle into a mature or Graafian follicle • LUTEAL PHASELUTEAL PHASE – consists of the formation of the corpus luteum, a major-secreting gland • At the middle of the ovarian cycle the OVULATIONOVULATION takes place
    3. 3. Follicular Phase Luteal Phase
    4. 4. Endocrine Control of Follicular Development & Ovulation GnRH (12 hrs. after LH peak) - Inhibin
    5. 5. Fate of Corpus Luteum (CL) without fertilization • FSH and LH release is inhibited by the progesterone and estradiol released by the CL • Without LH, the CL lasts for ~14 days before it degenerates
    6. 6. GnRH LH maintains the corpus luteum Progesterone & estrogen from CL inhibits GnRH, slowing the release of FSH and LH Without LH, the CL degenerates Junqueira et al. 8th ed. Appleton and Lange X X
    7. 7. Fate of Corpus LuteumFate of Corpus Luteum withwith fertilization & implantationfertilization & implantation • Chorionic gonadotropinChorionic gonadotropin (hCG) produced by the placenta will support the CL for ~ 6 months • also estrogen, IGF-I and II (from ovary), LH, prolactin (from ant. pituitary) and insulin contribute to formation and maintenance • CL grows to a diameter of 5 cm • Continues to secrete progesterone • Decreases in size during last 3 months • Begins to secrete relaxin in preparation for birth
    8. 8. Menstrual cycleMenstrual cycle The endometrium is directly controlled by OVARIAN hormones (estrogen, progesterone), not by pituitary hormones Menstrual cycle has 3 phases: • Proliferative phaseProliferative phase is regulated by estrogens • Secretory phaseSecretory phase is under the control of progesterone • Menstrual phaseMenstrual phase results from a decline in the ovarian secretion of progesterone & estrogens
    9. 9. Stratum Functionalis Stratum Basalis Myometrium Endometrium (glands present; dependent on ovarian hormones for appearance & maintenance) Uterine lumen
    10. 10. Arcuate Arteries (myometrium) Uterine artery Spiral arteries (in endometrium – dependent on ovarian hormones for growth & maintenance) Vascular Supply of Myometrium & EndometriumVascular Supply of Myometrium & Endometrium
    11. 11. Spiral arteries: dependent upon estradiol for growth, progesterone for maintenance Capillary bed with dilated portions of capillary wall (lacunae)
    12. 12. PROLIFERATIVE PHASE (days 4 – 14 of cycle) MENSTRUAL CYCLE 4
    13. 13. Proliferative phase - under control of estradiol (follicular phase of ovarian cycle) - glands in s. basalis under go mitosis - stroma, glands, spiral arteries grow toward lumen s. basalis
    14. 14. Proliferative phase: day 4 – day 14 of menstrual cycle
    15. 15. Hormonal control of endometrial changes during the menstrual cycle: SECRETORY PHASESECRETORY PHASE (days 14 – 28 of cycle)
    16. 16. Secretory phase - under control of progesterone (luteal phase of ovarian cycle - uterine glands coiled, larger lumens - secrete glycogen, mucin
    17. 17. Secretory phase: day 14 – 28 of menstrual cycle
    18. 18. Gestational hyperplasiaProliferative: day 9 Secretory: day 15 Secretory: day19 Pregnancy
    19. 19. Hormonal control of endometrial changes during the menstrual cycle: MENSTRUAL PHASEMENSTRUAL PHASE (days 1 – 4 of cycle)
    20. 20. Menstruation At end of luteal phase of ovarian cycle, Progesterone  Spiral arteries to constrict
    21. 21. Menstrual phaseMenstrual phase - the involution of the corpus luteum results from a decrease in blood levels of steroid hormones, leading to an ischemic phase. - a reduction in the normal blood supply-causing intermittent ischemia-and the consequent hypoxia determine the necrosis of the functional layer of the endometrium, which sloughs off during the menstrual phase.
    22. 22. Blastocyst Blastocyst = inner cell mass (embryo) + outer shell (trophoblast) Fertilization 1 2 3 4 5 6 7 8 9 Morula
    23. 23. Placenta Implanted in the wall of the uterus Composed of fetal portion (chorion) and maternal portion (decidua) Exchange of gases, nutrients waste products without any mixing of maternal & fetal blood
    24. 24. Functions of placenta Act as • respiratory organ • excretory organ • nutritive organ • protective organ • endocrine organ (progesterone, estrogens, human chorionic gonatotropin, melanin spreading factor, other hormones also manufactured by the hypothalamus & pituitary.
    25. 25. This is a circumvallate placenta in which the membranes double back for a short distance over the fetal surface when the chorionic plate is too small. There may be increased fetal loss with this condition.
    26. 26. The maternal surface of a normal term placenta is seen here. Note that the cotyledons that form the placenta are reddish brown and indistinct.
    27. 27. Placenta • The morpho-functional unit is cotyledon. Placenta has about 15-25 cotyledons. • Proliferation of the trophoblast, growth of chorionic mesoderm & blood vessel development give rise to: - primary chorionic villi – a mass of cells - secondary villi – composed of a core of mesenchyme surrounded by an inner layer of cytotrophoblast & an outer layer of syncytiotrophoblast - tertiary villi – blood vessels have developed in the cores
    28. 28. Inner cell mass (embryo) Uterine lumen Syncytiotrophoblast secretes proteolytic enzymes Maternal decidua
    29. 29. 9 days Maternal capillary Uterine lumen Maternal decidua
    30. 30. Maternal blood enters lacunae Uterine gland Syncytiotrophoblast Uterine lumen Extraembryonic mesoderm Cytotrophoblast Maternal decidua Blastocyst is now completely embeddedBlastocyst is now completely embedded within the endometriumwithin the endometrium
    31. 31. Cytotrophoblast grows into syncytiotrophoblast: (Maternal decidua)
    32. 32. Extraembryonic mesoderm invades primary villi: Maternal decidua
    33. 33. (Intervillous spaces) Fetal vessels grow into secondary villi: Outer cytotrophoblast shell Maternal decidua
    34. 34. 21 days Maternal decidua Human Embryology, Larsen, 1993 Churchill Livingstone
    35. 35. Fetal Maternal Small tertiary villi will sprout from larger ones to increase surface area for exchange
    36. 36. Placenta – low magnification = Intervillous space (maternal blood)
    37. 37. Villus from early pregnancy (during 3rd Cytotrophoblast Syncytiotrophoblast Mesenchyme (embryonic CT) Fetal capillaries
    38. 38. Villi from late pregnancy – 7th month By 4th month, cytotrophoblast begins to thin out and is no longer obvious syncytial knot
    39. 39. Placental barrier • Syncytiotrophoblast • Cytotrophoblast • Basement membrane of trophoblast • Connective tissue of the chorionic villus • Basement membrane of endothelium • Cytoplasm of endothelial cell
    40. 40. Placental Barrier Intervillous space (maternal blood) O2, H2O, electrolytes, carbohydrates, lipids, proteins, antibodies CO2, H2O, hormones, metabolic waste products
    41. 41. Placental structure and vascular dynamics Fetal side Maternal side
    42. 42. Placental Hormones Syncytiotrophoblast secretes: 1. Human chorionic gonadotropin (HCG) - detected 6 days after ovulation (pregnancy test) - keeps CL alive 2. Placental lactogen – lactogenic and growth stimulating properties for mammary gland (a.k.a. hCS: human chorionic somatomammotropin) 3. Estradiol (made in cooperation with fetal adrenal cortex) 4. Progesterone Cytotrophoblast also secretes: IGF I and II; various other growth factors that stimulate cytotrophoblast growth, plus hCG, estradiol, progesterone
    43. 43. etal portion of he placenta = CHORION . chorionic plate . chorion frondosum (villi) . chorion laeve (villi that were here earlier have degenerated) Chorionic plate Ham and Cormack, 8th ed. J.B.Lippencott
    44. 44. Maternal portion of he Placenta = DECIDUA 1. Decidua basalis 2. Decidua capsularis 3. Decidua parietalis Ham and Cormack, 8th ed. J.B.Lippencott
    45. 45. Decidual cells – glycogen, lipid for early embryonic nourishment; later, produce decidual prolactin (trophic effects on CL), prostaglandins (prevent immunologic rejection of fetus)of fetus), relaxin (dilates cervix and softens pubic symphysis) upper portion of decidua (near fetus)
    46. 46. Giant cells: multinucleated, trophoblast derivatives that migrate into the decidua. Establish cleavage plane for separation of placenta from endometrium after birth.
    47. 47. Fusion by 5th month (form cotyledons(form cotyledons Placental septae

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