Parturition Flashcards by Kendra Broadfoot

3 pre-partum steps?

-Formation of placenta
-Acquisition of the endocrine function of the placenta
-Initiation of parturition

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What are the two components of placenta classification?

-Distribution of chorionic villi
-# of tissue layers separating maternal and fetal blood

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What is the chorion?

The chorion is the fetal contribution to the placenta.

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What is the functional unit of the placenta?

The functional unit of the placenta is the chorionic villus.

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What are chorionic villi?

Chorionic villi are finger-like projections on the surface of the chorion that protrude towards the endometrium.

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What are the extraembryonic membranes? (3)

Amnion, allantois, chorion

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Types of placentas by distribution of chorionic villi

Diffuse, zonary, discoid, cotyledonary

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What defines a diffuse placenta?

Uniform distribution of villi throughout the chorion

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What species has a diffuse placenta?

Mare

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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

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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

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What species have a zonary placenta?

Cats and dogs

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What defines a discoid placenta?

Forms a regionalized disc. Consists of a round patch of chorionic tissue that forms the fetal-maternal interface

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What species have a discoid placenta?

Primates and rodents

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What defines a cotyledonary placenta?

Numerous, discrete button like structures called cotyledons

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What species has a cotyledonary placenta?

Ruminants

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Types of placentas named based off of number of tissue layers separating maternal and fetal blood

Epitheliochorial
Endotheliochorial
Hemochorial

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What species have an epitheliochorial placenta

sow and mare

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What species have an endotheliochorial placenta

dogs and cats

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What species have an hemochorial placenta

primates and rodenst

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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?

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?

1. Softening of the pelvic ligaments 2. Cervix softens and begins secreting mucus 3. swelling of the vulva 4. Udder swells- edema, fills with first milk 5. 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