Parturition Flashcards
3 pre-partum steps?
-Formation of placenta
-Acquisition of the endocrine function of the placenta
-Initiation of parturition
What are the two components of placenta classification?
-Distribution of chorionic villi
-# of tissue layers separating maternal and fetal blood
What is the chorion?
The chorion is the fetal contribution to the placenta.
What is the functional unit of the placenta?
The functional unit of the placenta is the chorionic villus.
What are chorionic villi?
Chorionic villi are finger-like projections on the surface of the chorion that protrude towards the endometrium.
What are the extraembryonic membranes? (3)
Amnion, allantois, chorion
Types of placentas by distribution of chorionic villi
Diffuse, zonary, discoid, cotyledonary
What defines a diffuse placenta?
Uniform distribution of villi throughout the chorion
What species has a diffuse placenta?
Mare
Endometrial cups in mares; origin, what do they produce and when do they develop?
- Transitory structures à
endometrial cups (mm to
cm) - Trophoblastic and
endometrial origin - Produce eCG
- Develop between 35 and
60 days of pregnancy
What defines a zonary placenta? what are the zones
Band like zone of chorionic villi. Consists of 3 zones; transfer zone, pigmented zone, and relatively non vascular zone called the allantochorion
What species have a zonary placenta?
Cats and dogs
What defines a discoid placenta?
Forms a regionalized disc. Consists of a round patch of chorionic tissue that forms the fetal-maternal interface
What species have a discoid placenta?
Primates and rodents
What defines a cotyledonary placenta?
Numerous, discrete button like structures called cotyledons
What species has a cotyledonary placenta?
Ruminants
Types of placentas named based off of number of tissue layers separating maternal and fetal blood
- Epitheliochorial
- Endotheliochorial
- Hemochorial
What species have an epitheliochorial placenta
sow and mare
What species have an endotheliochorial placenta
dogs and cats
What species have an hemochorial placenta
primates and rodenst
What is special about the ruminant placenta in relation to the # of layers?
Ruminants have epitheliochorial placenta, with endometrial epithelium that
erodes and regrows –> syndesmochorial (maternal capillaries transiently exposed to chorionic epithelium)
What 4 hormones does the placenta produce?
P4, E2, relaxin, placental lactogen
What species is relaxin not produced in
Cows
What hormone is not sufficiently produced in the cow placenta?
P4
Why is progesterone essential for early embryonic development?
Progesterone is obligatory for early embryonic development.
What role does high progesterone play during pregnancy?
It maintains the “progesterone block,” inhibiting strong myometrial contractions throughout pregnancy
How does the role of the corpus luteum (CL) in maintaining pregnancy vary among species?
In some species, like the ewe, mare, and women, the CL is not needed for the entire gestation as the placenta takes over progesterone production.
What happens in the sow and rabbit if the CL is removed?
Removal of the CL results in termination of pregnancy regardless of the stage of gestation.
What effect does CL removal have in cows during gestation?
Removal of the CL up to 8 months of gestation results in abortion
What cascade occurs after the estrodiol is present
estradiol -> myometrial contractions -> pressure -> cervical stimulation -> oxytocin -> maximum pressure
What is another result of estradiol in the cascade?
Leads to secretion by placenta -> lubrication
What hormone does fetal cortisol produce
PGF2alpha ; which induces luteolysis
What does PGF2alpha lead to further excretion of?
PGE2 and relaxion … which leads to cervical dilation and pelvic ligament stretching
What does fetal cortisol activate to get progesterone converted to estradiol?
-Fetal cortisol activates
17a-hydroxylase,
17-20 desmolase, and aromatase that convert progesterone to estradiol
-This conversion removes the
“progesterone block”
What occurs during the fergusson reflex?
- Pressure is created on the
cervix as fetus moves into
the birth canal - This stimulates the afferent
sensory neurons and PVN
(paraventricular nucleus) - Oxytocin is secreted from
posterior pituitary lobe - Oxytocin stimulates
myometrial contractions
What happens in the lung as a result of fetal cortisol?
increased surfactant production by type 2 pneumocytes
What happens in the blood as a result of fetal cortisol?
conversion of fetal to adult hemoglobin
What happens in the liver as a result of fetal cortisol?
increased glycogen deposition
What happens in the pancreas as a result of fetal cortisol?
increased pancreatic islet cell response to glucose
What happens in the thyroid as a result of fetal cortisol?
increased activated of T3 generating enzymes
Placental cortisol actions (overall, increase, decrease)
Terminates progesterone block and initiates estrogen production leading to the onset of lactation
DECREASE
1. The presence or activity of the placental factors
2. Progesterone synthesis and secretion
INCREASE
1. Placental estrogen synthesis and secretion
2. Prostaglandin synthesis and secretion from
placenta and endometrium
What 5 events occur just before parturition?
- Softening of the pelvic ligaments
- Cervix softens and begins secreting mucus
- swelling of the vulva
- Udder swells- edema, fills with first milk
- Fetus moves into proper position
What causes softening of the pelvic ligaments
Due mainly to estrogens and relaxin; collagenase breaks down collagen which also “stretches” the pelvis
What leads to the cervix softens and begins secreting mucus
Increase water content in cervical tissue resulting in cervical plug release and lubrication of the birth canal
What leads to swelling of the vulva
Hyperaemia caused by estrogen
what causes udder swelling-edema, fills with first milk
Effect of prolactin, estrogens and glucocorticoids
What occurs for the fetus to move into proper position
Resting on thorax, front feet and head facing the cervix
Details of stage 1; dilation of cervix
- Variable in length
- Variable in clinical signs
- Increased myometrial activity/fetal movement
- Entry of fetus into cervical canal-reflex release of oxytocin
- Ends with the rupture of the chorioallantois-“breaking
water” (first water bag)
stage 2; expulsion of the fetus/active labour
- Pelvic location of fetus-further release of oxytocin
- Peak oxytocin levels occur during this stage
- Forceful uterine and abdominal contractions
- Amnion ruptures-lubricates vestibular vagina (second water bag)
- Ends with delivery of the fetus or fetuses
stage 3; expulsion of fetal membranes/afterbirth
- Variable in duration
- Continued uterine contractions
- Passage of the placenta
- In polytocous species, placentas are usually passed during labour or shortly after birth of the last offspring
