Lecture 25: Maternal Recognition of the Preg & Placentation (Exam 2) Flashcards
What must happen before the embryo can attach to the uterus
- Dev w/in the zona pellucida
- Sub sequently hatch from the ZP
- Undergo MRP
- Form extraembryonic membranes
What is present in the ootid
- Male & female pronuclei along w/ the first & second polar bodies are present
When does an ootid become a zygote? What does it become after that?
- After syngamy
- Will then undergo cleavage to give rise to daughter cells (2 - celled = Blastomeres)
What happens after a blastomere is formed
- Cleavage division continues
- A 4 cell embryo gives rise to an 8
- After the 8 celled stagea ball of cells is formed (morula)
What happens after the egg is a morula
- Divide a develops into a blastocyst that consists of an inner cell mass, a cavity (blastocoele), & a single layer of cells (Trophoblast)
What happens after a blastocyst is formed
The rapidly growing blastocyst hatches from the zone pellucida & forms a hatched blastocyst that is free floating w/in the uterus
What is totipotent
- Each blastomere
- Up to 8-16 cell stage
Define totipotency
The ability of a single blastomere to dev into a fully indiv animal
What 3 forces govern the hatching of blastocyst
- Growth & fluid accumulation w/in the blastocyst
- Production of enzymes by the trophoblastic cells
- Contraction of the blastocyst
What happens after an embryo hatches
Incredible conceptus growth
Describe a ruminant blastocyst
- Filamentous
- Thread like structure
Describe a mare blastocyst
Remains spherical
What accounts for the rapid expansion of the blastocyst? List the different parts
- Extraembryonic mems of the preattachemnt embryo
- Yolk sac
- Chorion
- Amnion
- Allantois
Why is the extra embryonic mems impt
Essential to facilitate attachment to the uterus
What are the attachments times for cow, mare, sow, & ewe embryos
- Cow: Day 18 - 22
- Mare: D 36 - 45
- Sow/Ewe: D 15 - 18
What gives rise to the chorion & amnion
- Trophoblast
- Primitive endoderm
- Mesoderm
What does the yolk sac dev from
The primitive endoderm
What does the allantois fuse w/
The chorion & the chorion will eventually attach to the uterus
What does the amnion do
Provides a fluid-filled protective sac for the dev fetus
While the embryo is dev in the uterus what prevents luteolysis from occurring
Maternal recognition of preg
Describe maternal recognition of preg
- Preservation of the primary corpus luteum
- Must occur before luteolysis
- Maintains high levels of progesterone
- In most cases it is a conceptus mediated by biochemical signs
How does luteolysis occur
- Oxytocin receptors appear in the endometrium in the late luteal phase (~10 to 12 days of increasing progesterone)
- The corpus luteum contains large amounts of oxytocin
- Oxytocin release stimulates a pulse of PGF2a release
- PGF2a stimulates more oxytocin (POS FEEDBACK)
How does MRP occur in ruminants
- Interferon tau (INF-T) is produced by trophoblastic cells
- This inhibits oxytocin receptor synthesis
- Which then inhibits the release of PGF2a
How does MRP occur in the sow
- Blastocyst produces estrogen
- Estrogen re routes PGF2a release into the uterine lumen where it is destroyed
- PGF2a is changed from endocrine to exocrine (& dies)
How does MRP occur in the mare?
- Blastocyst migration through the uterine lumen
- Reduced synthesis of PGF2a
- Occurs btw/ Days 12 - 14
- Embryo roams through the uterus til MRP
Describe MRP for dogs & cats
- Prob doesn’t req a signal from the conceptus
- The bitch’s CL has a similar lifespan when pregnant & not preg
- The queen’s CL has a similar lifespan when preg & induced to ovulate w/out conception
What is the origin of the placenta in all domestic animals
The chorioallontois
How does the placenta dev in mares
- Chorionic girdle cells are trophoblast cells that stop and make endometrial cups that produce pregnant mare serum gonadotropin (eCG)
- ECG has FSH & LH like activity so it helps to luteinize the accessory & secondary corpor lutea
What is the function of the placenta
- Temporary organ of metabolic interchange
- Temporary endocrine organ ( Maintain preg & induce parturition)
What are the placental characteristics
- Functional unit = chorionic villi
- Villi may be grouped together into microscopic groups (microcotyledons) or macroscopic groups (cotyledons)
What are the classifications of placenta based on distribution of chorionic villi
- Diffuse
- Cotyledonary
- Microcotyledonary
- Zonary
- Discoid
What are the classifications of placenta based on the # of tissue layers btw/ the maternal & fetal blood
- Epitheliochorial
- Endotheliochorial
- Hemochorial
Describe a diffuse placenta
- Almost the entire surface of the allantochorion is involved in formation of the placenta
- Horses, pigs, & camelid
Describe cotyledonary placenta
- Multi discrete areas of attachment (placentomes) are formed by interaction of patches of allantochorion w/ endometrium
- Fetal portions are called cotyledons
- Maternal contact sites are caruncles
- Cotyledons + caruncles = placentome
- Found in ruminants
Define zonary placentas
- The area of attachment is complete or incomplete band of tissue surround the fetus
- Seen in carnivores (dogs, cats, seals, bears, & elephants)
Define a discoid placenta
- The area of attachment is discoid in shape
- Seen in primates & rodents
T/F: The sow has microcotolydeans
False the mare does
What are the two types of cotyloledens
- Cows are convex
- Sheep & goats are concave
What is the placenta attachment to the mother called
Caruncle
What is the placenta attachment to the fetus called
The cotyledon
What is the placentome
The caruncle + the cotyledon
Describe a epitheliochorial placenta
- Least intimate
- Both maternal & fetal epithelium are intact
- Pig, horse, cow, ewe, & doe
Describe a endotheliochorial placenta
- No endometrial epithelial cells
- Complete erosion of the endometrial epithelium
- Dogs & cats
Describe a hemochorial placenta
- All layers broken down
- Fetal tissue sitting in blood
- Chorionic epithelium is in direct apposition to maternal pools of blood
- Primates & rodents
Why is epitheliochorial clinically impt
B/c all these animals are the ones we rush to give colostrum to. All the layers made it difficult to get maternal antibodies while in utero so they get it through colostrum
T/F: The more layers in the placenta the easier it is for maternal antibodies to cross
False; the less layers
What are the function of placenta
- Metabolic exchange
- produces hormones
What do the hormones from the placenta do
- Stimulate ovarian fxn - like ECG in mares
- Maintain preg - Secretes P4 in certain species
- Stimulate mammary function - secretes lactogen in ewes
- Assist in parturition - relaxiin
What are the roles of placenta in maintenance of preg
- Has none in the bitch, queen, camel, sow, & goat
- Placenta takes over from primary (ovarian) source of progesterone in the cow, ewe, & mare @ various times
