Exam 2: Lecture 25: Maternal Recognition Of Pregnancy And Placentation Flashcards
What has to happen before the embryo can attach to the uterus?
-Must develop within Zona Pellucida
-Susequently hatch from the ZP
-Undergo Maternal Recognition of Pregnancy (MRP)
-Form extraembryonic membranes
What are the steps of early embryogenesis?
-In ootid, male & female pronuclei along w/ 1st & 2nd polar bodies are present
-Fusion of male & female pronuclei into single diploid nucleus constitutes syngamy
-Shortly after, zygote undergoes cleavage (miotic divisions) & gives rise to daughter cells called blastomeres
-4 celled embryo give rise to 8-celled embryo
-After 8 celled stage, ball of cells is formed & this embryonic stage is referred to as a morula
-Cells of morula continue to divide & blastocyst develops consisting of inner cell mass (ICM), blastocoele, & trophoblast
-Finally, rapidly growing blastocyst hatches from zona pellucida & forms hatched blastocyst that is free-floating within the uterus
What are the cleavages/divisions of embryogenesis?
-Zygote (one cell following synamy)
-First division (cleavage) (two blastomeres, half size of zygote)
-Second division (cleavage) (four blastomeres, quarter size of zygote)
-Each blastomere is totipotent
What is totipotency?
-Ability of single blastomere to develop into fully formed individual animal
What are the 3 forces that govern the hatching of the blastocyst?
- Growth & fluid accumulation within blastocyst
- Production of enzymes by trophoblastic cells
- Contraction of blastocyst
What is this?
Zygote
What is this?
2-cell Embryo
What is this?
4-cell Embryo
What is this?
8-cell Embryo
What is this?
16-cell Embryo (Morula)
What is this?
Early Blastocyst
What is this?
Blastocyst
What is this?
Hatching Blastocyst
____ is a time of incredible conceptus growth
Post-hatching blastocyst growth
A ____ blastocyst remains spherical
Mare
A ____ blastocyst is filamentous, thread-like structure
Ruminant
____ accounts for the rapid expansion of the blastocyst & is essential to facilitate attachment to the uterus
Extraembryonic membrane development
What are the extraembryonic membranes of the preattachmnt embryo?
-Yolk sac
-Chorion
-Amnion
-Allantois
What gives rise to the chorion and amnion?
-Trophoblast, along with the primitive endoderm & mesoderm
____ develops from the primitive endoderm
The yok sac
The allantois will fuse with the chorion & the chorion will eventually attach to the uterus, while the amnion will
provide a fluid-filled protective sac for the developing fetus
While the embryo is developing in the uterus, what prevents luteolysis from occurring?
-Maternal recognition of pregnancy
What does maternal recognition of pregnancy do?
-Preserves the primary corpus luteum (CL)
-Maintains high levels of Progesterone
-In most cases, it is a conceptus mediated biochemical signal
____ must occur before luteolysis
Maternal Recognition of Pregnancy (MRP)
What is the positive feedback system of luteolysis?
-Oxytocin receptors appear in endometrium in late luteal phase
-Corpus luteum contains large amounts of oxytocin
-Oxytocin release stimulates a pulse of PGF2a release
-PGF2a stimulates more oxytocin
How does maternal recognition of pregnancy occur in ruminants?
-Interferon Tau (INF-T) produced by the trophoblastic cells inhibits oxytocin receptor synthesis thereby inhibiting PGF2a release
How does maternal recognition of pregnancy occur in the sow?
-Blastocyst produces Estrogen which re-routes PGF2a release into uterine lumen where it is destroyed
-PGF2a secretion is changed from endocrine to exocrine
How does maternal recognition of pregnancy occur in the mare?
-Blastocyst migration through uterine lumen (entire uterus several times) causes reduced synthesis of PGF2a
-Occurs between days 12-14
-PGE2? production by embryo
How does maternal recognition of pregnancy occur in the dog and cat?
-Probably doesn’t require a signature from conceptus
-The bitch’s CL has similar lifespan when pregnant & non-pregnant
-Queen’s CL has similar lifespan when pregnant & induced to ovulate without conception
When the embryo proper is in the middle of the embryo, the mare is ____ days pregnant
30 days
How does the placenta develop?
-In all domestic animals, the chorioallantois is the origin of the placenta
What do the endometrial cups in the mare do?
-Produce pregnant mare serum gonadotropin (PMSG) –> now called equine chorionic gonadotropin (eCG)
-eCG has FSH & LH like activity, so helps luteinize accessory & secondary corpora lutea
Will only have hCG in your system if
a placenta is present
Endometrial cups in the mare are in the _____ but made by _____
In the uterus, made by trophoblast cells
What is the function of the placenta?
-Temporary organ of metabolic interchange
-Temporary endocrine organe (maintenance of pregnancy, induction of parturition)
The functional unit of the placenta involves the _____
Chorionic villi
What are the microscopic groups placental villi can be grouped into
Microcotyledons
What are the macroscopic groups the placental villi can be grouped into
Cotyledons
Placental classification is based on
Distribution of the chorionic villi
-Diffuse
-Cotyledonary
-Microcotyledonary
-Zonary
-Discord
Number of tissue layers between maternal & fetal blood
-Epitheliochorial
-Endotheliochorial
-Hemochorial
What is a diffuse placenta?
-Almost entire surface of allantochorion involved in formation of placenta
What animals have a diffuse placenta?
-Horses
-Pigs
-Camelids
What is a cotyledonary placenta?
-Multiple discrete areas of attachments
-Fetal portions called coytledons
-Maternal contact sites are caruncles
-Cotyledon-caruncle complex is called a placentae
What animals have a cotyledonary placenta?
-Ruminants
What is a zonary placenta?
-Area of attachment is complete or incomplete band of tissue surrounding the fetus
What animals have a zonary placenta?
-Carnivores like dogs & cats
-Seals
-Bears
-Elephants
What is a discoid placenta?
-Area of attachment is discoid in shape
What animals have a discoid placenta?
-Primates
-Rodents
This is a ____ placenta
Discoid
What animals have a convex cotylendonary placenta and what animals have a convex cotyledonary placenta?
-Convex = cow, giraffe
-Concave = sheep, goat
What placenta is this?
-Cotylendonary (cow)
What type of caruncles?
Concave caruncles
Do cotyledons form early or late?
-Form very early
The caruncle is from the ____, the codyledon is from the _____, and the entire unit together is the _____
-Caruncle = dam (mom drives CAR)
-Cotyledon = baby (baby sleeps in COT)
-Entire unit together = placentome
What is clinically relevant regarding the placenta?
-The degree of invasiveness (number of tissue layers between fetal & maternal blood)
What is an epitheliochorial placenta?
-Last intimate, both maternal & fetal epithelium intact
What animals have an epitheliochorial placenta?
-Pig
-Horse
-Cow
-Ewe
-Doe
What is an endotheliochorial placenta?
-Complete erosion of endometrial epithelium
What animals have an endotheliochorial placenta?
-Dog
-Cat
What is a hemochorial placenta?
-Chorionic epithelium is in direct apposition to maternal pools of blood
What animals have a hemochorial placenta?
-Primates
-Rodents
What are all the tissue layers between fetus & dam?
-Fetal endothelial cells
-Fetal connective tissue
-Chorionic epithelial cells
-Endometrial epithelial cells
-Maternal connective tissue
-Maternal endothelial cells
Which placental type needs colostrum because there are too many tissue layers to receive maternal antibodies?
-Epitheliochorial
What placental type can have colostrum but it isn’t as important to receive it because there is some maternal antibody transfer?
-Endotheliochorial
What placental type does not need colostrum?
-Hemochorial
What is an example of an animal with this placenta?
Diffuse, epitheliochorial
-Horses (microcotyledonary)
-Pigs
What is an example of an animal with this placenta?
Cotyledonary, epitheliochorial
-Ruminants (cattle, sheep, goats, deer)
What is an example of an animal with this placenta?
Zonary, endotheliochorial
-Carnivores (dog, cat, ferret)
What is an example of an animal with this placenta?
Discoid, hemochorial
-Humans
-Apes
-Monkeys
-Rodents
What are the functions of the placenta?
-Metabolic exchange
-Produce hormones that stimulate ovarian function, maintain pregnancy, stimulate mammary function, assist in parturition
How does the placenta produce hormones that stimulate ovarian function?
Equine chorionic gonadotropin (eCG, PMSG) in mare
-Produced by endometrial cups of placenta (formed from trophoblastic cells)
-Serves as stimulus to primary CL & stimulates accessory CL’s
How does the placenta produce hormones that maintain pregnancy?
-Placenta secretes P4 in certain species
How does the placenta produce hormones that stimulate mammary function?
-Placenta secretes lactogen in ewes -> mammary
How does the placenta produce hormones that assist in parturition?
-Relaxin
What animals does the placenta not play a role in maintenance of pregnancy?
-Bitch
-Queen
-Camels
-Sow
-Goat (weird one)
Placenta takes over from primary (ovarian) source of Progesterone in
-Cow, ewe, & mare (at various times)
