Presentation is loading. Please wait.

Presentation is loading. Please wait.

Embryonic development and implantation

Similar presentations

Presentation on theme: "Embryonic development and implantation"— Presentation transcript:

1 Embryonic development and implantation

2 Pregnancy Preparation of uterus Fertilization Steroid hormones 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 Active luteolysis Passive luteolysis
Reinitiation of reproductive cycle Two types Active Passive Active luteolysis Production of luteolytic agent (PGF2a) Uterus Passive luteolysis Loss of luteotropic agents

6 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 Progesterone Oxytocin PGF2a PGF2a

7 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

8 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

9 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)

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

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 Morula-stage embryo Blastocyst-stage embryo ICM Blastcoele

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 Morula-stage embryo Blastocyst-stage embryo ICM Blastcoele

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
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

15 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

16 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 PGF PGF Uterine vein PGF PGF

17 Diversion of PGF2a secretion
Pigs Non-pregnant Endocrine factor Conceptus Divert secretion(exocrine) Estradiol Increased production during days post coitus

18 Diversion of PGF2a 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 Production 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 Production of glycoprotein
Movement of embryo within the uterus 12-14 times a day during day 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 steroidogenesis
Cholesterol Lipoproteins from circulation No De Novo synthesis Progesterone Replace CL in some species Maintenance of pregnancy Precursor for fetal adrenal steroids

25 Estrogens Limited production Androgens from fetal adrenal gland
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


Download ppt "Embryonic development and implantation"

Similar presentations

Ads by Google