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Embryonic development and implantation. Pregnancy Preparation of uterus –Steroid hormones Fertilization –Coitus –Gamete transfer –Capacitation of sperms.

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Presentation on theme: "Embryonic development and implantation. Pregnancy Preparation of uterus –Steroid hormones Fertilization –Coitus –Gamete transfer –Capacitation of sperms."— Presentation transcript:

1 Embryonic development and implantation

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 (PGF 2  ) Uterus Passive luteolysis –Loss of luteotropic agents

6 From ovary to uterus (and back to the ovary) –Positive feedback loop Uterine production of PGF 2  Production of oxytocin by the CL –Ultimately leads to corpus luteum regression Reinitiation of reproductive cycle PGF 2  Progesterone Oxytocin PGF 2 

7 Progesterone production by CL –Begins to decline. –Initiated by increased production of PGF 2  –Increased production of PGF 2  Ablated when pregnancy has been initiated, resulting in continued Progesterone production by the CL and pregnancy maintenance PGF 2  Progesterone Pregnancy

8 Maternal recognition of pregnancy Two types –Anti-luteolytic Diversion of PGF 2  secretion Inhibition of PGF 2  secretion –Luteotropic Maintenance of the CL by providing necessary hormone –Gonadotropin

9 Early embryonic development 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) Ampulla Isthmus Ampullary- isthmic Junction Uterotubal Junction

10 Early embryonic development 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 2-cell embryo 8-cell embryos

11 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 ICM Blastcoele Morula-stage embryo Blastocyst- stage embryo

12 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 ICM Blastcoele Morula-stage embryo Blastocyst- stage embryo

13 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

14 Attachment and establishment of pregnancy 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 ICM Embryo Placenta

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

16 Implantation and establishment of pregnancy Conceptus (embryo plus placental tissue) –Produces interferon-tau (IFN-  ) as it elongates Prevents production of PGF 2  by endometrium of the uterus IFN-  PGF Uterine vein Non-Pregnant Pregnant Conceptus Endometrium Uterine vein Endometrium

17 Diversion of PGF 2  secretion –Pigs Non-pregnant –Endocrine factor Conceptus –Divert secretion(exocrine) –Estradiol Increased production during 11-12 days post coitus –Conceptus

18 Diversion of PGF 2  secretion –Local factor rather than systemic factor Conceptus must be present in both uterine horns

19 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

20 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

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

22 Neuroendocrine system –Prolactin Luteotropic hormone Switch to placental hormones –Placental lactogen –CL Eventually dies –Steroid production by placenta

23 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

24 Placental lactogen Some species –Type of placentation Ruminants Humans Rodents Produced by fused cells –Syncytiotropoblast –Binucleated/trinuclea ted cells

25 Proteins related to pituitary GH and prolactin –Close to GH in humans –Close to prolactin in rodents –50-50 in cows

26 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

27 No known receptor(s) for placental lactogen –Interacts with GH receptor –Interacts with prolactin receptor

28 Pattern of secretion –Different between cattle and sheep Degree of fusion between tropoblasts and endometrium

29 GH-Variant –Human only –Acts like GH Tissue growth Nutrient metabolism –Affects function of insulin Pregnancy-induced diabetes

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

31 Estrogens –Limited production Limited 17  -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


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