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Placental lactogen

Placental lactogen. Some species Type of placentation Ruminants Humans Rodents Produced by fused cells Syncytiotropoblast Binucleated/trinucleated cells. Proteins related to pituitary GH and prolactin Close to GH in humans Close to prolactin in rodents 50-50 in cows. Function

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Placental lactogen

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  1. Placental lactogen • Some species • Type of placentation • Ruminants • Humans • Rodents • Produced by fused cells • Syncytiotropoblast • Binucleated/trinucleated cells

  2. Proteins related to pituitary GH and prolactin • Close to GH in humans • Close to prolactin in rodents • 50-50 in cows

  3. Function • Regulation of metabolism • GH-like activity • Much weaker than pituitary GH • Development of mammary gland • Prolactin-like activity • Maintenance of CL function • Rodents during early stage of pregnancy

  4. No known receptor(s) for placental lactogen • Interacts with GH receptor • Interacts with prolactin receptor

  5. Pattern of secretion • Different between cattle and sheep • Degree of fusion between tropoblasts and endometrium

  6. GH-Variant • Human only • Acts like GH • Tissue growth • Nutrient metabolism • Affects function of insulin • Pregnancy-induced diabetes

  7. Placental steroidogenesis • Cholesterol • Lipoproteins from circulation • No De Novo synthesis • Progesterone • Replace CL in some species • Maintenance of pregnancy • Precursor for fetal adrenal steroids

  8. Estrogens • Limited production • Limited 17a-hydroxylase activity • Abundant in fetal adrenal gland • Androgens from fetal adrenal gland • Converted to estrogens in the placenta • Production of estriol rather than estradiol • Secretion of estrone • Majority of placental estrogen in some species

  9. Parturition • Three stages • First stage • Initiation of myometrium contraction • Initiated by the fetus • Second stage • Expulsion of the fetus • Third stage • Expulsion of fetal membrane

  10. Parturition • First stage • Initiated by fetus • Distress • Maximum size that can be maintained • Lack of nutrients • Hypoxia • Activation of fetal hypothalamus-pituitary-adrenal axis • Release of ACTH by the fetal pituitary gland

  11. Fetal ACTH • Release of cortisol from fetal adrenal gland • Fetal cortisol • Removal of “progesterone block” • Contraction of myometrium • Conversion of progesterone to estradiol • 17a-hydroxylase • 17-20 lyase • Aromatase

  12. Fetal cortisol • Increase production of PGF2a by the endometrium • Further removal of progesterone block • Cause luteolysis • Stimulates contraction of myometrium • Synergism with estradiol

  13. Contraction of myometrium • Pushes the fetus toward cervix • Activation of the CNS • Secretion of oxytocin from the posterior pituitary gland • Oxytocin • Increased contraction of the uterine smooth muscle • Positive feedback • More contraction (pushing of fetus), increased oxytocin secretion • Entering of the fetus in the cervical canal • End of the first stage

  14. Expulsion of fetus • Relaxation of the cervix and pelvic ligaments • Relaxin • Secretion stimulated by PGF2a

  15. Role of estradiol on parturition • Increased overall secretory activity • Mucus production by cervix and vagina • Removal of cervical plug • Lubrication

  16. Rupture of fetal membrane • Loss of amniotic and allantonic fluid • Further lubrication • Fetus becomes hypoxic • Movement of the fetus • Stimulates further contraction of the myometrium • Increased strength of contraction

  17. Expulsion of the fetal membrane • Shortly after expulsion of the fetus • Dislodging of fetal membrane from the uterus • Vasoconstriction

  18. Mammary gland development • Cyclic changes in ovarian steroid hormones • Essential for mammary development • Estradiol • Development of mammary alveoli (secretory unit) • Progesterone • Development of mammary ducts

  19. Final stage of mammary gland development • Pregnancy • Ovarian/placental steroid hormones • Periparturient period • GH and prolactin • Placental lactogen? • Glucocorticoids

  20. Lactation • Parturition • Metabolic shift • Fetal growth to synthesis and secretion of milk • Mobilization of nutrients • Storage within the body • Fats • Triggered by changes in hormones

  21. Lactation and re-initiation of reproductive cycle • Lactating women • High prolactin • Low LH and estradiol • No ovulation • Lactation-induced anovulation/amenorrhea (infertility) • Women remain anovulatory as long as they breast-feed their babies • Increased survivability of the infants

  22. Lactational anestrus in the domestic species • Divert nutrients for lactation • Ensure the survival of offspring • Lactation stimuli/physical contact between mother and offsprings • Animals remain in anestrus (absence of estrus) until nutrient intake exceeds nutrient demand

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