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REPRODUCTIVE PHYSIOLOGY: Pregnancy and Parturition (Parturition (Fetal…
REPRODUCTIVE PHYSIOLOGY:
Pregnancy and Parturition
Pregnancy
development of embryo involves fusion of oocyte and spermatozoon within oviduct
spermatozoa that concentrated and stored in epididymis gradually change from oxidative (aerobic) to glycolytic (anaerobic) metabolism
sperm are ejaculated into vagina
movement through cervis is aided by estrogen-induced changes in cervical mucus
form channels that facilitate movement
emphasized in primate
thinning of mucus occurs just before ovulation
sperm
transport is rapid
not involved in fertilization
passing from vagina to fimbriated end of oviduct within minutes
sperm get damaged
undergo changes within female genital tract that are prerequisite for fertilization
capacitation
removal of glycoproteins from sperm cell surface
allows sperm to undergo acrosome reaction (release of hydrolytic enzymes from acrosomal cap)
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deposition of sperm before ovulation is preferred timing for producing maximal fertility
environment of female genital system is generally inhospitable to survival of sperm
wbc quickly attracted to uterine lumen because sperm cells are foreign
special reservoirs evolved to aid in survival of sperm during transport
include cervix & oviduct, latter involving areas at the uterotubule junction and within ampulla
progressively filled
when full, able to release a few sperm on a continuous basis
so fertilization can occur shortly after arrival of oocytes within oviduct
prerequisite of oocyte is that is must undergo first meiotic division before fertilization
once fertilization occurred, embryo develops to morula or early blastocyst stage within oviduct before moving to uterus
4-5 days
affords uterus time to finish inflammatory response involving removal of spermatozoa
allows endometrial glands time to secrete nutrients under influence of progesterone from developing CL
Extension of life span of CL in large domestic species and cats is essential for pregnancy maintenance
domestic animals
:cow2::goat::racehorse::pig2::sheep:
luteal activity is controlled by uterus
modification of uterine PGF2α synthesis & release is important for establishment of pregnancy
embryo produces substances that modify uterine production PGF2α
way for endometrium be informed regarding presence of embryo (pregnancy recognition)
estrogen synthesis
trophoblastin produced before day 14 of pregnancy in sheep and cattle
has close structural relationship to molecule interferon
movement of embryo in the tract
in mare:
moves throughout both horns before being fixed at day 16
in pigs:
minimal number of embryos need to be present (~4)
to occupy a sufficiently large area of endometrium
in litter-bearing animal:
use transuterine migration
maximize opportunity for fetal development
cats
:cat:
CL lasts for 35-40 days after ovulation regardless of the presence of pregnancy
early modification of luteal activity is not essential for establishment of pregnancy
implantation occurs at ~day 13
allows fetoplancental unit to influence & extend luteal activity that is compatible with pregnancy maintenance
relaxin
placental hormone produced beginning at about day 20 of gestation
synergizes with progesterone for the support of pregnancy
causes ligaments & associated muslces surrounding pelvic canal to relax
placental lactogen
have both somatotropic & lactogenic effects on the basis of growth hormone-like and prolactin-like properties
primates
rescue of CL at the onset of pregnancy involves the production of luteotropin called
chorionic gonadotropin
(CG)
produced by trophoblastic cells (
syncytiotrophoblasts
) of the embryo
must have intimate contact with interstitium of endometrium (implantation called interstitial)
embryo penetrates endometrium at ~8-9 days after fertilization
begins 24-48 hours after implantation, with immediate enhancement of luteal progesterone production
Placenta acts as endocrine organ
produce progesterone
in cattle, goats, pigs: progesterone is never produced enough to support pregnancy
production of estrogen require interaction between fetus & placenta
Parturition
Fetal cortisol initiates delivery through increased secretion of estrogen & thus PGF2α
progesterone maintain inactivity of myometrium and promote tightly contracted cervix
estrogen
influence uterine muscle by stimulating production of contractile protein & formation of gap junctions
induces oxytocin receptor formation in myometrium
fetal adrenal cortex
maturation initiate parturition
progressively sensitive to fetal adrenocorticotropic hormone
fetal cortisol induce placental enzymes that direct steroid synthesis away from progesterone to estrogen
FIRST STAGE:
involves presentation of fetus at internal os of cervix
myometrial contractions become less important
abdominal press take over
SECOND STAGE:
actual delivery process
THIRD STAGE:
involves delivery of fetal membranes
major PGF2α surge occur
important for expulsion of placental membranes & reduction of uterine size