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