Placentation, Gestation, Parturition Flashcards
Placenta
Organ of physiologic exchange
- fusion of fetal membranes to endometrium
- size/functions change with pregnancy stages
- expelled after parturition (stage 3)
Placenta is classified based on
Gross shape and distribution of villi
- microscopic structure of feto-maternal barrier
Villi function
Bring fetal vessels into close proximity to maternal blood vessels
Diffuse
Attached everywhere
- mare and sow
Cotyledonary
Attachment occurs in small, multiple focal areas
- ewe, doe, cow
Zonary
Attachment occurs in a specific circular zone around the fetus
- bitch and queen
Discoid
Attachment occurs in one large single area (large cotyledon)
- primates and rodents
Convex villi
Cow, giraffe
Concave villi
Sheep, goat
Fetal _____ fuse with maternal ______ to form ______
Cotyledons; caruncles; placentomes
Maternal caruncles
Specialized projections of uterine mucosa
- convex in cow, concave in ewe/doe
Functional unit
Placentome
Utero verdin
Dark green fluid
Binucleate giant cells
Move from fetal side across junction, into maternal side to secrete substances (pregnancy specific protein B) that are used to detect pregnancy
- basis for pregnancy blood test
Epitheliochorial
Least intimate, both maternal and fetal epithelium are intact
- greatest barrier
- pig, horse, cow, ewe, doe
Endotheliochorial
Complete erosion of endometrial epithelium
- dog, cat
Hemochorial
Chorionic epithelium is in direct apposition to maternal pools of blood
- intimate, close attachment
- primates, rodents
Degree of invasiveness is important for transfer of _____
Maternal antibodies
- need to colostrum is high in pigs, cows, ewes
Deciduate
Portion of endothelium is shed with placenta
- dog, cat, rodents, primate
Adeciduate
Endometrium is left intact at time of placenta expulsion
- pig, cow, horse, sheep, goat
Placental functions
- metabolic exchange
- substitutes for fetal GIT, lung, kidney, liver, endocrine glands
The placenta produces hormones that _____
- stimulate ovarian functions
- maintain pregnancy
- stimulate mammary function
- assist in delivery of fetus
In which species does the placenta NOT have a role in pregnancy maintenance?
- bitch
- queen
- camels
- sow
- doe
The placenta takes over from primary (ovarian) source of progesterone in _______
Cow, ewe, and mare
- cow: 6-8 mos
- ewe: 50 days
- mare: 70 days
Endometrial cups are unique to the _____
Mare
- produce equine chorionic gonadotropin
- temporary structure
- embed and invade maternal endometrium
- could measure eCG level to determine pregnancy (is highest around 80 days)
Placental circulation
2 circulations parallel to each other
- blood does not intermingle between dam and fetus
- close enough for gas and nutrient exchange to occur
Freemartinism
Blood can be co-mingled between twins of cattle but rarely of other species
- anastomosis of fetal circulation
- mascinulizes female = sterility
What species has the most variable gestation length?
Mare
- 340-360 days
Placental takeover of P4 production in the cow and mare
150 days
Gestation lengths
- cow: 283 days
- ewe: 152 days
- doe: approx 230 days
- sow: 114 days
- dog: 58-68 days
- cat: 64-67 days
- camelids: 11 months
Amniotic fluid
- origin: fetal urine, secretions from respiratory and buccal cavity, maternal circulation
- functions: protects fetus from external shock, prevents fetal skin adhesion to membrane, dilates cervix and lubricates birth passage
Allantoic fluid
- origin: fetal urine, secretions of allantoic membrane
- functions: brings allochorion into close apposition with endometrium, stores fetal excretory products not transferred to mother, maintains osmotic pressure of fetal plasma
Fetal fluids
Function to protect and bathe the fetus
- lubricate birth canal
- elimination of waste
- maintains osmotic pressure of fetal plasma, prevents fluid loss to maternal circulation
Hippomanes
Allantoic calculi, similar to bladder stones
- do not serve physiologic purpose
- seen occasionally in cattle, common in equines
Stage 1 of parturition
Initiation of myometrial contractions
- P4 block has been removed via PGF
- P4 converted to E2
Stage 2
Expulsion of fetus
- strong myometrial and abdominal contractions expels fetus
Stage 3
Expulsion of fetal membranes
Active straining is due to
Abdominal contractions
Fetal stress drives the ____
Parturition cascade
Myometrial contractions
Uterus is transformed from P4 dominated “relaxed” state to an “active” state
- PGF synthesis and release is increased
- act jointly to initiate uterine contractions needed to dilate the cervix and deliver the fetus
Immune stats
Fetus synthesizes little to no antibodies
- acquires antibodies from dam while in utero (rat, human)
- secretes antibodies in colostrum (farm animals)
- related to impermeability of epitheliochorial placenta to antibodies
