Fertilization, Maternal Recognition of Pregnancy and Placentation Flashcards
What needs to occur for fertilization?
Sperm needs to encounter oocyte
What is the general range of sperm viability?
Hours to days
Roughly how much sperm is lost via retrograde flow?
~50%
Where do the non-motile sperm get removed after breeding?
The cervix
Where is capacitation initiated?
The uterus.
Where is capacitation completed?
The oviduct.
What reaction must take place in order for fertilization to occur?
The acrosome reaction.
In what 3 species is the semen deposited in the uterus?
Pig
Alpaca
Horse
In what 5 species is semen deposited in the vagina?
Cows Goats Sheep Dogs Cats
Where do sperm mature?
Through the epididymus
Where is maximal sperm fertility achieved?
Only after residing in the female tract for a period of time
What are the changes that occur to sperm for final maturation?
Capacitation
What is the rapid phase of sperm transport?
Muscle contractions help the sperm arrive at the oviduct in minutes where they await the oocyte.
What is the sustained phase of sperm transport?
Sperm delivered continually from reservoirs.
NOTE: This is critical for animals the ovulate several oocytes.
What 2 areas are considered “reservoirs” for sperm?
Cervix
Uterotubual junction
What is the site of fertilization?
The Ampullary-isthmic junction
What is capacitation?
Stripping of the seminal plasma proteins by uterine factors.
What is the result of capacitation?
Hyper-activated sperm with unmasked ZP (zona pellucida) binding sites
What are the 3 layers of cells that act as a barrier to fertilization?
Cumulus cells
Zona Pellucida
Oolemma (oocyte membrane)
What is the function of the zona pellucida?
Prevents polyspermy
What initiates the acrosome reaction?
Binding of the sperm to the zona pellucida.
How is polyspermy prevented?
Once sperm binds to the oolemma, the zona pellucida hardens to prevent other sperm from binding.
What is syngamy?
Fusion of male and female pronuclei to form a zygote.
How many cells are in a zygote?
One
How many cells are in an embryo?
Many
Before the embryo can attache to the uterus, what 4 steps must first occur?
Develop within ZP
Hatch from ZP
Maternal recognition of pregnancy
Formation of extra-embryonic membranes
What is the site of fertilization in the cow?
The ampullaristhmic junction.
What is totipotency?
The ability of a single blastomere to develop into a fully formed individual animal.
Up to what stage is each blastomere totipotent?
8-16 cell stage
How many cells are in a morula?
16+ cells
What is the first fetal membrane you see at birth?
Amnion
Why do you not see the chorion first at birth?
Because it is attached to the dam.
What is the term if you see the chorion first at birth?
Red bag
NOTE: This is BAD, the chorion has been decomposing.
What are the 2 main goals of maternal recognition of pregnancy?
Preservation of the primary CL
Maintain high levels of progesterone
What must maternal recognition of pregnancy occur before?
Before luteolysis
What is the mechanism of maternal recognition of pregnancy in the cow?
Interferon-tau from trophoblast cells inhibits oxytocin receptor synthesis so no PGF2a is released.
What is the mechanism of maternal recognition of pregnancy in the sow?
The blastocyst produces estradiol which re-routes PGF2a where it is destroyed.
What is so different about equine maternal recognition of pregnancy?
The embryo needs to migrate everywhere to signal pregnancy.
What is different about maternal recognition of pregnancy in cats and dogs vs our large animal species?
The CL has a similar lifespan in bot pregnant and non-pregnant animals.
What membrane is the origin of the placenta?
The chorioallantois.
What type of placenta does a horse have?
Diffuse
NOTE: Sow also has diffuse
What type of placenta does a ruminant have?
Cotyledonary
What type of placenta does a primate have?
Discoid
What type of placenta does a dog or cat have?
Zonary
What is the point of attachment of the placenta to the dam?
Chorionic villi
How many layers of tissue exist between the maternal and fetal blood in an epitheliochorial placenta?
6 layers total; 3 maternal and 3 fetal
NOTE: Embryo ALWAYS has 3 layers.
How many layers of tissue exist between the maternal and fetal blood in an endotheliochorial placenta?
5 layers total; 2 maternal and 3 fetal
NOTE: Embryo ALWAYS has 3 layers.
How many layers of tissue exist between the maternal and fetal blood in a hemochorial placenta?
4 layers total; 1 maternal and 3 fetal
NOTE: Embryo ALWAYS has 3 layers.
What type of placenta does a sow have?
Diffuse
What 6 species have an epitheliochorial placenta?
Pig Horse Camelid Cow Sheep Doe
What 2 species have an endotheliochorial placenta?
Dog
Cat
What 2 species have a hemochorial placenta?
Primates
Rodents
What is an additional mechanism of maternal recognition of pregnancy that we find in the horse?
Endometrial cups
What is produced by the endometrial cups?
Equine chorionic gonadotropin (eCG)
How does the placental induce parturition?
Convets P4s to estrogen
How does the placenta assist parturition?
Secretes relaxin and estrogen
How does the placental help maintain pregnancy?
Placenta secretes P4
What is the placenta’s role in pregnancy maintenance?
In the cow, sheep, and mare the placenta takes over from the ovaries at various times.
