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Hormones of pregnancy

Hormones of pregnancy. Pregnancy. Preparation of uterus Steroid hormones Fertilization Coitus Gamete transfer Capacitation of sperms Fusion of gamates. Embryonic development Preimplantation Implantation Placentation Differentiation of cells Organogenesis.

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Hormones of pregnancy

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  1. Hormones of pregnancy

  2. Pregnancy • Preparation of uterus • Steroid hormones • Fertilization • Coitus • Gamete transfer • Capacitation of sperms • Fusion of gamates

  3. Embryonic development • Preimplantation • Implantation • Placentation • Differentiation of cells • Organogenesis

  4. Must alter cyclic changes in the ovarian steroid hormones • Progesterone • High • Must maintain the CL • Most species • Some can maintain pregnancy without CL after certain stage (placental progesterone)

  5. Luteolysis • Destruction of the CL • Reinitiation of reproductive cycle • Two types • Active • Passive • Active luteolysis • Production of luteolytic agent (PGF2a) • Uterus • Passive luteolysis • Loss of luteotropic agents

  6. Active luteolysis Ovarian artery • Communication from uterus to ovary • Approximately 4 days before estrus, the uterus begins to produce PGF2a, • PGF2adiffuses into the bloodstream feeding the ovary bearing the CL (ovarian artery). Uterine vein PGF2a Large black arrows indicate direction of PGF2a flow

  7. Progesterone • From uterus to ovary • Interaction between PGF2a and its receptor • Large luteal cells • Decreased production of progesterone • Death of the luteal cells • Elevated intracellular Ca level • Constriction of blood vessels • Release of oxytocin. Oxytocin PGF2a PGF2a

  8. Progesterone • From ovary to uterus (and back to the ovary) • Oxytocin • Reaches the uterus and stimulates production of more PGF2a • Increasing amount of estradiol from the large follicle • Increased production of PGF2a by uterus through increased sensitivity to oxytocin Oxytocin PGF2a PGF2a

  9. Progesterone • From ovary to uterus (and back to the ovary) • Positive feedback loop • Uterine production of PGF2a • Production of oxytocin by the CL • Ultimately leads to corpus luteum regression • Reinitiation of reproductive cycle Oxytocin PGF2a PGF2a

  10. Local regulation of reproductive cycle Progesterone • Progesterone production by CL • Begins to decline. • Initiated by increased production of PGF2a • Increased production of PGF2a • Ablated when pregnancy has been initiated, resulting in continued Progesterone production by the CL and pregnancy maintenance Pregnancy PGF2a

  11. Maternal recognition of pregnancy • Two types • Anti-luteolytic • Diversion of PGF2a secretion • Inhibition of PGF2a secretion • Luteotropic • Maintenance of the CL by providing necessary hormone • Gonadotropin

  12. Early embryonic development Uterotubal Junction Ampullary- isthmic Junction Isthmus Ampulla • Zygote • Begins to divide as it moves through the oviduct towards the uterus • Numbers of cells increase after each division • The size of the embryo does not (cell size decreases by approximately 20 % after each division)

  13. Early embryonic development 8-cell embryos 2-cell embryo • Cells of the embryo remain within the zona pellucida as they divide • The size of the nucleus increases • All chromosomes remain intact • In cows, the embryo divides three to four times (approximately one division a day) while in the oviduct • Usually at the 16-cell or morula stage when it reaches the uterus

  14. Early embryonic development • Morula stage • All the cells of the embryo are in a tightly packed clump • Cells on the inside of the clump • Different from those on the outside • Cells inside begin to further pack themselves together and form a mass of cells called the inner cell mass (ICM), located at one end of the embryo Morula-stage embryo Blastocyst-stage embryo ICM Blastcoele

  15. Early embryonic development • The ICM • Develops into the fetus • The outer layer of cells lining the zona pellucida • Trophoblast • Placenta • Formation of a fluid-filled cavity • Blastcoele • Blastocyst Morula-stage embryo Blastocyst-stage embryo ICM Blastcoele

  16. Early embryonic development • Cells in the ICM and trophoblast • Continue to divide • Blastacoele continues to accumulate fluid • Hatching • Floats freely until it attaches itself within lumen of the uterus Hatched blastocyst Zona

  17. Attachment and establishment of pregnancy Embryo ICM ICM Placenta • After hatching • Rapid growth and development phase. • In cows, the blastocyst begins to rapidly elongate around 13 days after estrus, transforming from an ~3 mm spherical blastocyst into a long, thread-like form (around 25 cm in length) in 3 to 4 days • The elongation of the bovine embryo • Due to rapid proliferation of trophoblast cells • Cells in the ICM divide slowly during elongation

  18. Attachment and establishment of pregnancy Inner cell mass Uterine endometrium Trophoblast layer • Cattle and sheep • Attachment of trophoblast to the uterine wall • Superficial with some fusion between uterus and trophoblast cells

  19. PGF PGF PGF PGF Implantation and establishment of pregnancy Non-Pregnant • Conceptus (embryo plus placental tissue) • Produces interferon-tau (IFN-t) as it elongates • Prevents production of PGF2a by endometrium of the uterus Endometrium PGF Uterine vein PGF PGF PGF Pregnant Conceptus IFN-t IFN-t IFN-t IFN-t Endometrium Uterine vein

  20. Diversion of PGF2a secretion • Pigs • Non-pregnant • Endocrine factor • Conceptus • Divert secretion(exocrine) • Estradiol • Increased production during 11-12 days post coitus • Conceptus

  21. Diversion of PGF2a secretion • Local factor rather than systemic factor • Conceptus must be present in both uterine horns

  22. Secretion of luteotropic substances • Species with passive luteolysis • Primates • Secretion of glycoprotein hormone • Syncytiotropoblast • Human chorionic gonadotropin (hCG) • Basis of pregnancy test • Secretion begins around 10 days after ovulation

  23. hCG • Luteotropic hormone • LH-like activity • Binds to LH receptors in the CL • Maintenance of progesterone production • Increased lifespan during early stage of pregnancy • Production • Peaks around 9 to 14 weeks of pregnancy • CL loses its function during this time • Switch in steroidogenesis (placenta) • Declines gradually thereafter

  24. Neuroendocrine system • Rodents and rabbits • Coitus as stimulus • Physical contact • Physical stimulation of reproductive tract (cervix) • Release of prolactin by the anterior pituitary gland

  25. Neuroendocrine system • Prolactin • Luteotropic hormone • Switch to placental hormones • Placental lactogen • CL • Eventually dies • Steroid production by placenta

  26. Horses • Recognition of pregnancy • Movement of embryo within the uterus • 12-14 times a day during day 12-14 of pregnancy • Eventual lock-down of the embryo • Production of glycoprotein • eCG • Cause luteinization of the large follicle • Formation of secondary CL • FSH-like activity in other mammals • Loss of both CLs • Placental progestigens

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