Midterm 3 - Lecture 23 Flashcards
4 steps in pre-attachment embryonic development
- development within the Zona Pellucida
- hatching from the Zona Pellucida
- maternal recognition of pregnancy
- extra-embryonic membranes
Ootid
oocyte after the 1st meiotic division in which the 1st polar body is present
What is syngamy? Where does it occur? What does it give rise to?
fusion of the male and female pronuclei within the cytoplasm of a newly fertilized oocyte, giving rise to a zygote
Zygote
diploid cell resulting from the fusion of the male and female pronuclei
Embryo
animal in the early stages of development that has not taken on an anatomical form that is recognizable as a member of a species
Fetus
unborn young that possesses identifiable features of a given species
Conceptus
- a product of conception including:
1. embryo in early development (preimplantation)
2. fetus and placenta (postimplantation)
What occurs during fertilization to produce a zygote?
during fertilization syngamy occurs to produce a zygote that begins to go cleave (mitotic division) to give rise to blastomeres
What is cleavage?
Cleavage of blastomeres (2, 4, and 8-celled embryo) to form ball of cells within the zona pellucida referred to as a Morula
What is blastcoele development?
- two groups of cells form in the Morula - process of compaction
1. outer cells - adhesions create tight jxns btw cells
2. inner cells - connected by gap jxns btw cells - sodium is pumped into the intercellular spaces and water follows osmotically = fluid accumulation within the morula
- fluid accumulation causes outer cells to flatten and blastocoele forms
- two separate cellular components emerge
1. inner cell mass (ICM)
2. trophoblast
What is the process of compaction during blastcoele development?
two groups of cells form in the Morula - process of compaction
1. outer cells - adhesions create tight jxns btw cells
2. inner cells - connected by gap jxns btw cells
What 2 cellular components emerge during blastocoele development?
- inner cell mass
- trophoblast
What happens during blastocyst hatching?
- blastocyst eventually “hatches” from the Zona Pellucida
- Hatching caused by 3 factors
1. growth and accumulation of liquid within the blastocyst
2. enzymes from the trophoblast that degrade the ZP
3. contractions of the blastocysts
Do blastocysts form at the same time in all species?
No! There is variation
When doing embryo transfer, what is collected and transferred?
blastocysts
- if they have hatched it is too late
What does successful pregnancy maintenance require?
- high blood P4 concentrations
- PGF2a induced luteolysis must be prevented
- conceptus can play an active role in maintaining pregnancy
How do cows and ewes recognize pregnancy?
- blastocyst(s) produce interferon to prevent luteolysis; inhibits the oxytocin-receptor development so that oxytocin cannot stimulate PGF2a production by the uterine endometrium
How do sows recognize pregnancy?
- blastocysts produce estradiol to prevent luteolysis; cause PGF2a production by the uterine endometrium to be rerouted into the uterine lumen where it is destroyed
- # of conceptus is important
How do mares recognize pregnancy?
- proteins/estradiol synthesis and contact of the conceptus with endometrium prevents luteolysis
How do bitches and queens recognize pregnancy?
- does not require a signal from the conceptus; lifespan of the CL is longer than the gestation period
What 3 factors does luteolysis depend on?
- presence of oxytocin receptors on uterine endometrium
- oxytocin production by the large luteal cells
- PGF2a synthesis by uterine endometrium
What are the hormones of pregnancy?
- Early pregnancy factor
- Progesterone
- Equine Chorionic Gonadotropin
What are the hormones of parturition?
- Adrenal Corticotropin (ACTH)
- Estrogens
- Prostaglandin F2a
- Relaxin
- Oxytocin
Early Pregnancy Factor (EPF)
- a protein (chaperonin 10) expressed into the maternal circulation prior to embryonic attachment (human, cattle, sheep, pigs)
- shown to have immunosuppressive properties
- Early Pregnancy Test based on EPF
What is the dominant hormone of pregnancy?
Progesterone
Progesterone
- dominant hormone of pregnancy
- essential for embryonic/fetal development to prevent return to estrus and produce uterine environment appropriate for implantation
- provides the Progesterone Block that inhibits myometrial contractions during pregancny
Progesterone production
- P4 produced by CL in early pregnancy
- Placenta can eventually takeover P4 production
- Role of CL and Placenta in P4 production varies among species
How does the role of CL and Placenta in P4 production vary among species?
Ewe & Mare
- placenta takes over P4 in early gestation
Cow
- placenta takes over P4 in late gestation
Sow, Bitch & Queen
- Cl is the source of P4 through out gestation
*when the placenta takes over the major P4 production role, the CL continues to produce P4
Gestation Lengths: ewe, mare, cow, sow, bitch, queen
Ewe = 5 months
Mare = 11 months
Cow = 9 months
Sow = 3.8 months
Bitch = 2 months
Queen = 2 months
What is eCG produced by? When does eCG secretion peak? When do eCG secretions bottom out?
- eCG is a gonadotropin produced by the endometrial cups of the placenta
- endometrial cups begin to form and express eCG at the time of attahcment
- cup development and eCG secretion peaks midway through the 1st trimester
- cups regress and eCG secretion bottoms-out by ~Day 100 of Gestation
Where is eCG produced?
endometrial cups of the placenta
Role of eCG
- maintains CL production of P4 during the 1st trimester by maintaining the Primary CL
- as eCG increases the mare will ovulate to create an accessory CL which will takeover P4 production
- placenta assumes the major P4 producing role by ~day100
What effect does eCG have on other species?
strong FSH-like effect on other species and is often used as a part of superovulation protocols
CL P4 output of the mare in early gestation
- P4 from primary CL increases and then decreases
- eCG re-stimulates P4 production by primary Cl
- eCG continues to increase, accessory Cl forms and P4 increases
*after day 100 placenta assumes major P4 production
What does the uterine endometrium produce?
- various growth factors and cytokines that stimulate growth and development of the fetus in utero
