32, 33, 34 - phys and induction of partirution Flashcards
what controls and influences gestational length?
controlled genetically
influenced by feto-maternal size ratio
cow gestation length?
variation?
280
+/- 14 d
longer in Bos indicus
mare gestation length?
variation?
340 days
320–360
sow gestation length?
114 d
doe and ewe gestation length?
150 days average for both
dow: 148-1555
ewe: 145-150
bitch gestation length and timing?
65 d from LH surge
+/- 1
also: 57 +/- 2 from cytological diestrus 1
queen gestation length and timing?
63 days from ovulation
hembra gestation length and timing?
variation?
334 d from breeding
320-360 variation
pregnancy is complex interplay btwn what entities?
dam, endometrium, myometrium
ovaries with CLs on them
placenta
fetus, fetal membranes
what hormone controls endometrial secretions in the bitch?
p4
what hormone maintains preg?
p4
how does p4 maintain pregnancy?
what mechanisms in the bitch?
endometrial gland secretions
uterine circulation
myometrial quiescence
cervical closure
what is a source of p4 in all species?
CL
the placenta is an additional source of p4 in what species?
mare
ewe
queen
what additional source of p4 is suspected in cattle?
adrenal gland
what must occur in the fetus and dam in order for parturition to occur?
fetal maturation - prep for extra uterine life
induction of lactation
cervical ripening - prep for passage of fetus
pelvic lig relaxation
myometrial contractility - evacuation of uterine contents
what is basic structure of myometrium?
smooth muscle structure
actin and myosin muscle fibers - slide across each other to contract
what enzyme is required for myometrial contraction?
what is it activated by?
MLC kinase
activated by calmodulin
what activates calmodulin in the myometrial muscle cells?
therefore, what is required to initiate the cascade that leads to myometrial contraction?
ionized calcium
influx of ionized Ca into the cells
what contributes to the Ca levels in the myometrial cells?
sarcoplasmic reticulum
extra cellular fluid compartment
what governs the influx of Ca into myometrial cells?
CAPS
what is the structure of CAPS?
what is the function of each component?
CAPS are made of 3 fraction associated proteins
2 are receptors: 1 for PG and 1 for oxytocin
3rd is formation of gap junctions to allow passage of Ca through junctions
when PG and oxy bind to the CAPS receptors, what do they induce?
the formation of more gap junctions and further Ca influx
describe the interaction btwn oxy and PG.
which is a better ecbolic agent?
oxy drives PG release
PG is stronger ecbolic agent
how is the myometrium prevented from contracting during pregnancy?
the contraction cascade is suppressed
what is the “rate limiting step” in a normal pregnancy, to begin the parturition cascade?
fetal hypoxia
b/c the fetus needs outgrow the supply capacity of the placenta
fetal hypoxemia triggers what hormonal cascade in the fetus, which leads to parturition?
hypoxia induces sec of CRH from hypothalamus
stim fetal pituitary to sec ACTH
stim fetal adrenal glands to sec cortisol
stim sec of PG in the placenta
in general, most end products of cascades are regulated by their own negative feedback mechanism.
in the fetus, at the time of parturition, this is suppressed by 3 mechanisms.
what are they?
- cortisol being released by fetus is highly protein bound
- some cortisol is inactivated to cortisone, which suppresses the cortisol receptor at the level of the pituitary gland, so cortisol cannot feedback and cause inhibition
- PG does not reach maternal circulation - it remains in the feto placental compartment, where it is neutralized by PG dehydrogenase
t/f
neither PG nor cortisol leave the feto-placental compartment to enter the maternal circulation at the time of parturition
true
both remain in the feto-placental compartmenet
what is the action of PG in the placenta?
PG upregulates the enzymes P450 and c17, which is responsible for the early conversion of early steroids to late steroids => p4 steroids to androgenic steroids
what is the role of fetal cortisol in the hormonal cascade at initiation of parturition?
induce enzymes that convert androgens into estrogens
after e2 prod inc, as a result of the fetal hormonal cascade, where does it go and what does it do?
e2 crosses the placenta into maternal circulation
induces the formation of CAPS in myometrial cells -> to prepare them for contraction ability
for species with the placental source of p4, what hormonal changes occur at initiation of parturition?
pathway changes from p4 production to e2 production
for animals that rely on the CL for p4 at the end of the pregnancy, what triggers luteolysis to end the pregnancy?
sec of oxytocin => stim sec of PG => luteolysis
where is oxy that lyses the CL at the end of pregnancy sec from?
from the placenta or the CL itself
where is PG sec from, after stimulation by oxy?
the endometrium
what hormone causes ripening or softening of the cervix?
relaxin
what is the mechanism of relaxin?
dissociation of collagen disuphide bonds => dissociation of fibers => cervix opens
what is the origin of relaxin?
placenta or CL
in addition to relaxin, what other molecules contribute to softening of the cervix?
metalloproteinases
what molecule is selectively up regulated in the cervical muscle cells to promote cervical softening?
cAMP
what cell influxes into the cervix?
what cytokine stimulates this movement?
result?
NTs influx into cervix under the stimulation of Interleukin 8
degranulate -> sec inflammatory mediators -> dec uptake of Ca into myometrial cells -> promotes relaxation
what happens to conc of Ca in myometrial cells during softening of cervix?
dec
what effect does e2 have on cervix?
softening -> opening
what stimulates the transition of the allanto-chorion into the cervix?
the inc pressure in the myometrium d/t contraction
what mechanical force helps push the cervix open as it ripens?
the allanto-chorion pushing on the cervix forces it to open
what stimulates stage 2 of labor?
the onset of abdominal pressure
subsequent the neuro endocrine reflex - Ferguson’s reflex
what is Ferguson’s reflex?
stretch receptors in the cervix and cranial vagina are activated
connect in posterior pituitary gland to oxy producing neurons loc in hypothalamus
stim sec of oxy -> further contraction
in response to pelvic filling, what voluntary action must occur?
mare must abdominal press
t/f
you can see uterine contractions from outside the body
false
you see abdominal contractions, NOT uterine contractions
what is stage 3?
expulsion of fetal membranes
what species expels a whole placenta rather than fetal membranes?
bitch
what is involved in separation of fetal membranes from the endometrium?
proteolytic enzymes leukocyte enzymes oxytocin PGs mechanical pull
what does the presentation of the fetus describe?
longitudinal axes of dam and fetus
how can a fetus appear if in a longitudinal presentation?
cranial or caudal longitudinal - axis of fetus parallel to axis of dam
head or butt facing out
what is a transverse presentation?
ventral if legs/belly first
dorsal if spine first
what does the position of fetus describe?
examples?
the portion of the maternal pelvis against which fetal spine lies
dorso-sacral
dorso-pelvic
dorso-ileal (Left or Right)
MC position of fetus at time of parturition?
dorso-sacral -> spine directed against sacrum of dam
what does posture of fetus describe?
what is MC / proper posture?
the angulation / flexion of head, neck and presenting limbs
head and forelimbs should be extended in most animals with both front limbs extended
what are sings of pre partum cow indicating she will calve soon?
what hormones is she under the influence of?
last week: vulva swells and lengthens 48-24 hours: cervical musus 24 h: tone of tail is poor udder development pelvic ligg relaxation
e2