Placentation

1. Placentation

2. Embryonic development • Pre-implantation • Free-floating • Endogenous reserves • Nutrients from surrounding environment • Histotropic • Implantation and placentation • Formation of intimate but temporary relationship with uterus • Provision of nutrients • Protection

3. Placenta • Transient organ • Metabolic interchange between maternal and fetal systems • Endocrine organ • Production of steroids • Production of protein hormones • Composition • Chorion (fetal compartment) • Modified uterine endometrium (maternal compartment)

4. Contact between chorion and endometrium • Site of metabolic exchange • Hormone production

5. Embryonic cellular differentiation • Blastcyst • Blastcoel • Fluid-filled cavity • Inner cell mass • Develops into fetus and part of placenta • Three distinct cell • Ectoderm • Mesoderm • Endoderm

6. Three embryonic cell layers • Ectoderm • Skin and hair • Nerve tissue • Part of chorion • Mesoderm • Muscles, bones, and organs • Part of chorion and allantois • Endoderm • Inner lining of the GI tract • Part of allantois and amnion

8. Origin of placenta • Conceptus • Embryo • Extraembryonic menbrane • Extraembryonic membranes • Originate from trophoblasts • 3 compartments • Amnion (endoderm and ectoderm) • Chorion (ectoderm and endoderm) • Allantois (endoderm and mesoderm)

10. Composition of placenta • Fetal component • Chorionic villus • Functional unit • Small, finger-like projections on the surface of chorion • Used for classification of placenta • Distribution

11. Chorionic villi distribution • Diffuse • Villi distributed over the entire surface of the chorion • Pigs • Horse placenta • Specialized villi called microcotyledons (microzones) • Formation of endometrial cups (eCG secretion)

12. Cotyledonary placenta • Large discrete button-like structures • Cotyledons • Abundant blood supply • Formation of placentome • Cotyledons (fetal) • Caruncles (maternal)

13. Zonary placenta (dogs and cats) • Broad zone of villi • Exchange • Pigmented zone • Either end of the central region of the zone (blood clots) • Transparent zone • Distal ends

14. Discord • Humans and primates • One or two distinctive disks on the one end of the placenta

15. Classification of placenta based on microscopic appearance • Number of placental layers separating the fetal blood from maternal circulation • Degree of intimacy • Prefix=maternal endometerium • Suffix=fetal membrane • Ranges anywhere from one to seven layers

16. Epitheliochorial placenta • Least amount of contact • Surface to surface contact • No invasion of the uterine endometrium by chorion • Pigs and horses

17. Epitheliochorial placenta • Some intimate between trophoblasts and endometrium • Ruminants • Syndesmochorial placenta • Formation of binucleated giant cells • Fusion of trophoblasts • Invasion and fusion with endometrium (trinucleated cells)

18. Endotheliochorial placenta • Complete erosion of endometrial epithelium and underlying interstitium • Exposure of maternal capillaries to the chorion • Embryos separated from actual maternal circulation

19. Hemochorial placenta • Primates • Actual contract between chorionic villi and maternal circulation • Fetal circulation separated from maternal circulation by three tissue layers • Direct exchange of materials from maternal circulation

20. Hemoendotherial placenta • Most intimate contact • Fetal circulation bathed in maternal blood

21. Exchange of materials • Three methods • Diffusion • Small molecules • Gases • Facilitated diffusion • Glucose • Amino acids • Active transport • Ions (Na, K, Ca)

22. Acts as a barrier • Maternal proteins • Hormones • Exception • Antibodies/immunoglobulins in hemochorial and hemoendotherial placenta • Lipids and fat-soluble vitamins • Cannot prevent entrance of toxic materials and infectious materials • Alcohol, opium, and other drugs • Birth defects (teratogenic agents) • Virus and bacteria

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

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

25. 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

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

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

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

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

30. 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