Exam 5: Placentation, Gestation, and Parturition Flashcards
What is the placenta?
Fusion of fetal membranes to endometrium
Organ of physiologic exchange
What does the size and function of the placenta change with?
Stage of pregnancy
When is the placenta expelled?
After parturition
How is the placenta classified?
Gross shape and distribution of villi
Microscopic structure of feto-maternal barrier
Loss of maternal tissue at parturition
What is the function of villi?
To bring fetal vessels into close proximity to maternal blood vessels
What kind of placenta do mares and sows have?
Diffuse
What kind of placenta do ewes, does, and cows have?
Cotyledonary
What kind of placenta do bitches and queens have?
Zonary
What kind of placenta do primates and rodents have?
Discoid
Describe diffuse placenta
Attachement dispersed everywhere
Describe cotyledonary placenta
Multiple focal areas of attachment
Describe zonary placenta
Placenta attaches in a specific circular zone all around the fetus
Describe discoid placenta
Very large, single area of attachment where all of the exchange occurs
What forms placentomes?
The fusing of fetal cotyledons and maternal carunlces
What are maternal caruncles?
Specialized projections of uterine mucosa
What are the maternal caruncles like in the cow?
Convex
What are the maternal caruncles like in the ewe and doe?
Concave
What is the name given to the functional unit of a cotyledonary placenta?
Placentome
What are the degrees of invasiveness?
Epitheliochorial
Endotheliochorial
Hemochorial
Describe epitheliochroial
Pig, horse, cow, ewe, and doe Least intimate (more layers), both maternal and fetal epithelium
Describe endotheliochorial
Dog and cat
Complete erosion of endometrial epithelium
Fewer layers
Describe hemochorial
Primates and rodents
Chorionic epithelium is in direct apposition to maternal pools of blood
Most intimate
What are the degrees of intimacy?
Deciduate
Adeciduate
Describe deciduate
Dog, cat, rodents, and primates
Portion of endothelium is shed with placenta
Describe adeciduate
Pig, horse, cow, sheep, and goat
Endometrium is left intact at time of placenta expulsion
What are the placental functions?
Metabolic exchange
Substitutes for fetal GI tract, lung, kidney, liver, and endocrine glands
Produce hormones
What do the hormones produced by the placenta do?
Stimulate ovarian function
Maintain pregnancy
Stimulate mammary function
Assist in delivery of fetus
What is the role of the placenta in pregnancy maintenance?
None in bitch, queen, camels, sow, and doe
Placenta takes over from primary (ovarian) source in cow, ewe, and mare
When does the placenta take over in cows? Ewes? Mares?
6-8 mos
50 days
70 days
What is unique to a pregnant mare? What does it do?
Endometrial cups
Produce eCG
Describe placental circulation
Two circulation parallel to each other
Blood does not intermingle between dam and fetus
Is close enough for gas and nutrient exchange to occur
What is freemartinism?
Blood can be co-mingled between twins of cattle
What is the gestation length of a cow?
283 days
What is the gestation length of a mare?
Approximately 344, but it is the most variable
When does placental takeover of P4 production in cows and mares?
150 days
What are the origins of amniotic fluid?
Fetal urine
Secretions from respiratory tract and buccal cavity
Maternal circulation
What are the functions of amniotic fluid?
Protects fetus from external shock
Prevents adhesion between fetal skin and amniotic membrane
Assists in dilating cervix and lubricating birth passages during birth
What are the origins of allantoic fluid?
Fetal urine
Secretory activity of allantoic membrane
What are the functions of allantoic fluids?
Brings allantochorion into close apposition with endometrium during initial steps of attachment
Stores fetal excretory products not readily transferred back to the mother
Helps to maintain osmotic pressure of fetal plasma
What are the functions of fetal fluids?
Protect and bathe the fetus
Lubrication of birth canal
Elimination of waste
Maintains osmotic pressure of fetal plasma and prevents fluid loss of maternal circulation
What can be present in fetal fluids?
Hippomanes
What species has allantoic caliculi?
Horse
What are the stages of parturition?
1: Initiation of myometrial contractions
2: Expulsion of fetus
3: Expulsion of fetal membranes
What occurs in stage I of parturition?
P4 block have been removed via PGF
P4 converted to estrogen
What occurs in stage II of parturition?
Strong myometrial and abdominal contractions expel fetus
What are the mechanical forces of the dilation of cervix (stage I of labor)?
Regular uterine contractions
What is the period of dilation of cervix?
Beginning of uterine contractions until cervix is fully dilated and continuous with vagina
What are related events to dilation of cervix?
Maternal restlessness
Elevated pulse and respiratory rates
Changes in fetal position and posture
What are mechanical forces of expulsion of fetus (stage II of labor)?
Strong uterine and abdominal contractions
What is the period of expulsion of fetus?
From complete cervical dilation to end of delivery of fetus
What are related events to expulsion of fetus?
Maternal recumbency and straining
Rupture of allantochorion and escape of fluid from vulva
Appearance of amnion at vulva
Rupture of amnion and delivery of fetus
What are the mechanical factors of expulsion of fetal membranes (stage III of labor)?
Uterine contractions decrease in amplitude
What is the period of expulsion of fetal membranes?
Following delivery of fetus to expulsion of fetal membranes
What are related events to expulsion of fetal membranes?
Maternal straining ceases
Loosening of chorionic villi from maternal crypts
Inversion of chorioallantois
Straining and expulsion of fetal membranes
Know parturition cascade
Know parturition cascade
What happens with 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
Describe the immune status of the fetus
Fetus synthesizes little to no antibodies
Acquires antibodies from dam in utero or from colostrum
What is the immune status related to?
Impermeability of epitheliochorial placenta to antibodies
