17: physio of pregnancy Flashcards
after being deposited in the FM repro tract, where do sperm travel to?
how long does it take the sperm to get there?
approximately how many sperm make it to this location?
uterine tubes
arrive minutes to hours after deposition
a few hundred up to 3,000
what is the group of sperm called the deposit in the uterine tubes?
sperm reservoir
how is the sperm reservoir established?
what part of the uterine tube does this occur in?
sperm loosely bind to epithelial cells in the isthmus of the uterine tube
what happens to the sperm that is left behind in the uterus?
it gets flushed out
what is capacitation?
external sperm membrane changes to inc binding affinity to oocyte
t/f
all of the sperm are released at once from the uterine tube
false
they detach a few at a time, periodically
how many membrane changes occur to the sperm?
where do they occur?
2
once when the sperm is in the seminal fluid [allows sperm to bind to the uterine tubes]
a second time in the uterine tubes [allows binding to the oocyte]
what specific change occurs to the sperm which alters its membrane?
calcium channels open - rendering the sperm more “sticky”
how long do sperm survive in the cow tract?
1-2 days
how long do sperm live in the mare tract?
4-5 d
how long do sperm live in the camelid tract?
4-5 d
how long do sperm survive in the bitch tract?
3-10 d
bc sperm do not often survive the max number of days in the FM tract, why is important that we consider the possibility?
do not count on sperm surviving that number of days - so we must time oocyte readiness with sperm deposition - but acknowledge that it is possible for the sperm to live this long in case multiple breedings occur near the same time
what must occur for sperm-oocyte binding to occur?
capacitation
what region of the sperm binds to the oocyte?
the cytolemma of the post equitorial segment of the head of the sperm
what region of the oocyte does the sperm bind to?
the oolemma
what key reaction occurs within the sperm, after the sperm binds to the zona pellucida?
the acrosome reaction
what occurs during the acrosome reaction?
pores form btwn the outer acrosomal mem and the cytoplasmic mem of the sperm
the contents of the acrosomal vesicle escape over the apex of the sperm
what type of molecules are held within the acrosome?
what is the fxn?
a mixture of proteolytic enzymes
facilitate the entry of sperm through the ZP of the oocyte via a digestive process
how does the motion of the flagella change from before binding to after binding?
why does this change occur?
from rigid whip-like motion to an undulating motion
the change occurs to facilitate entry through the ZP
how does sperm freezing affect the outer acrosomal membrane?
what are the implications of this when breeding with frozen thawed semen?
freezing damages the outer acrosomal membrane
the acrosomes react pre maturely so the membrane is “leaky” => therefore they are shorter lived
MUST accurately time sperm deposition into FM tract with oocyte readiness
what is the purpose of the release of cortical granules?
prevents polyspermy
once the sperm gets through the ZP, what does it encounter?
oolemma
when the sperm and oocyte fuse, what type of cells is created?
a single cell that has a haploid nucleus from the sperm and a haploid nucleus from the egg
what happens to the genetic material in the sperm when it enters the oocyte?
it was condensed but it de condenses and and re forms chromosomes
where does the early embryo develop?
inside the uterine tube
what is the significance of the embryo remaining in the uterine tube?
the uterus needs a few days to be “cleaned out” and must prepare for the arrival of the embryo
what happens to the 2 haploid nuclei in oocyte?
they fuse and form a pro nuclei - a single diploid cell
what occurs in the diploid cell just before the pro nuclei forms? and what occurs to the cell just after?
the 2nd polar body exits
it divides into 2 cells to form the zygote
t/f
as the zygote divides, the rapidly increases in size
false - there is massive cell replication but no changes in overall size of the embryo
the cells divide in half - begins with one large cell and divides continually to smaller cells
cytoplasm divides and chromatin multiplies: chromatin does not multiply
what restricts the size of the embryo?
the ZP
after how many days post fertilization does the embryo arrive at the uterus?
day 5 or 6
why is it important for the embryo to remain in the uterine tube for the first few days post fertilization?
uterus is contaminated and is releasing PG - inflammatory process
NOT hospitable for the embryo to survive
why is it important that the CL remains refractory to PG for the first few days of its life?
b/c the uterus is producing PGs to “clean itself out” from post mating debris
what is the early name of the embryo?
once a cavity forms, what is the embryo called?
morula
blastocyst
what are cells w/in the blastocyst called?
blastomeres
how does the cavity in the blastocyst form?
blastomeres secrete fluid
what is the structure of the blastocyst? which part is the developing embryo?
cavity lined by cells with an inner cells mass in one area
the inner cell mass is the embryo
what is the importance of the high pressure w/in the blastocyst, due to the fluid?
it stretches the ZP - leads to its rupture
what is critical for the survival of the embryo, related to the environment of the uterus?
there must be synchrony of the endometrial fxn and embryonic stage
what hormones must the uterus be exposed to prior to the entrance of the embryo?
for how long?
e2
p4
for 3-6 days
why cannot you breed 70% of cows who ovulate with the first shot of PG during syncrhonization?
b/c the endometrium was not exposed to e2 or p4
why is the exposure to e2 important for the endometrium?
e2 induces receptors for p4, which arrives after ovulation
in the equine, what does movement into the uterus require?
movement into the uterus is linked to embryonic production of PGE2
where does the unfertilized oocyte remain in the horse?
in the uterine tube
for how long does the embryo remain in the uterine tube?
for a few months
how does the PGE2 help the embryo move into the uterus?
it causes the UTJ (utero tubal junction) to widen
what is the first priority of the developing embryo?
maternal recognition of pregnancy
what prevents luteolysis?
maternal recognition of pregnancy
in primates and humans, what triggers the maintenance of the CL?
maternal recognition of pregnancy
t/f
maternal recognition of pregnancy is required in dogs and cats for the maintenance of pregnancy?
false
the default setting for dogs and cats is pregnancy so the prevention of luteolysis is not necessary
why is maternal recognition of pregnancy necessary for domestic animals?
the uterus is programmed with mechanisms to return to estrus - this is the default setting
so the cycle must be halted and luteolysis must be prevented in order for FM to maintain pregnancy
what is the mechanism in primates/humans to maintain pregnancy?
embryo secretes luteotropyic substance to support the maintenance of CL
what substance is luteotrophic in primates/humans?
hCG
what day does the ruminant blastocyst hatch from the blastocyst?
day 12
how long is the ruminant embryo around day 16?
what shape is it?
as long as 1 uterine horn
long filamentous structure, fluid filled
where is the 16 day ruminant embryo located?
lines the uterine horn, ipsilateral to the horn on which she ovulated in
why is elongation of the embryo so important?
allows contact btwn trophoblastic cells of the embryo and the endometrium of the mather
why is contact btwn the embryo and endometrium so important?
endometrial cells would sec PG, which would trigger luteolysis
what suppresses PG sec from the endometrium in the ruminant?
interferon Tau ( iT)
what secretes iT in the ruminant?
trophoblasts of the embryo?
how does iT function?
inhibits oxytocin receptors cell production on endometrial cells
what does oxytocin do?
signals the release of PG from the endometrium
what occurs when oxytocin receptors are blocked?
PGF2a will NOT be sec from endometrium => luteolysis will NOT occur
what does maternal recognition require in the sow?
at least 2 expanded blastocysts in each horn to suppress luteolysis
how is PG transported to the CL in the cow, sheep, goats?
what is the vasculature arrangement?
what is the implication for maintaining preg?
PG released from the endometrium, into the uterine V
enters the ovarian A via counter current exchange
unilateral arrangement of blood vessels so PG from R horn reaches R ovary
inhibit PG prod on the side of the uterus ipsilateral to where CL is
how is the vasculature arrangement in the sow different than the ruminants?
sows have very large uterine horns
blood is exchanged btwn L and R sides b/c vessels anastomose
so…must px PG from both uterine horns or else the CLs on both ovaries will be destroyed
how does the arrangement of the conceptuses of fetal pigs prevent luteloysis?
how many conceptuses are necessary to accomplish this task?
blastocyst of pig becomes long and filamentous structure that stretches to cover the endometrium
need at least 2 expanded blastocysts to cover inner surface of each uterine horn in order to px the transmission of PG
how do pig embryos prevent PG from entering circulation and reaching the ovaries?
trophoblastic estradiol “redirects” PgF2a towards the uterine lumen, where it will not be absorbed into the vasculature
why are there necrotic tips at the end of each placenta of fetal pigs?
tips of blastomeres at the end of the chorionic membranes become necrotic b/c they develop too far before the maternal recognition of pregnancy occurs - development of the vasculature does not develop to the ends
what is the shape of the mare uterus?
what does this mean for the spread of PG?
what is the vasculature anatomy like?
T shaped
PG can reach anywhere from anywhere in the uterus
there is NOT counter current exchange of PgF2a [no local exchange via uterine V and ovarian A]
PG travels systemically to suppress production in the entire uterus
what is the shape of the mare embryo?
what is the significance of the shape?
spherical
important for the embryo to move throughout the uterus
why does the embryo need to move throughout the uterus of the mare?
must maintain regular contact with the entire endometrium
what additional envelope forms around the embryo?
where does it originate?
embryonic capsule
secreted by the embryo
what is the significance of the embryonic capsule?
unlike the ZP, it can grow with blastocyst expansion
will maintain spherical shape
what moves the embryo around the uterus?
uterine contractions
what tone does the uterus in the mare have?
how does this differ from other species?
it has enhanced tone - so the muscular contractions can carry the embryo all around the uterus
most species have flaccid uterus to allow embryo expansion / growth
equine:
what hormone makes uterus firm?
what hormone makes uterus flaccid?
- p4 makes uterus firm
- e2 makes uterus flaccid
during estrus, what is the tone of the equine uterus?
how does this compare to other species?
flaccid
in most other species, it is rigit
what does the tone of the mare uterus indicate regarding sperm deposition?
sperm gets deposited in the uterus
what is a dz, primarily of mares, that occurs after breeding?
post breeding endometritis
why can the equine embryo be detected via u/s 10 days into development?
what does this mean for mare management?
b/c the fluid body is so large that it can be detected
pregnancy can be detected before her next anticipated heat
what is the earliest detection of pregnancy in cow and other species?
25 days
how can the fluid sphere be used to determine the age and viability of the embryo?
the volume of fluid inside the uterus reflects the development - the size of the embryo is directly proportional to its growth and development
measure the diameter of the vesicle each day to track development - if fluid volume is too small, the embryo is likely NOT viable
when does implantation occur in primates?
7-8 days
what substance is sec by trophoblastic cells and is used to detect preg in primates?
hCG
what occurs around day 16 in mare embryo?
why does this occur?
embryo becomes too large to move
so fixation occurs
t/f
in the mare, fixation is the same thing as implantation
false
fixation if NOT Implantation
where does the embryo becomes stuck in the uterine horn?
at the narrowest portion of the uterine lumen =>
at the base of either uterine horn
t/f
fixation occurs on the same side where ovulation occurs
false
fixation loc is NOT influenced by which side that ovulation occurred on
t/f
during fixation, there is connection btwn the endometrium and the embryo surface
false
there is not connection
it is held in place b/c of its size
what is implantation?
the formation of a placenta
what is the purpose of the placenta?
to nourish the embryo - uterine milk from the uterine lumen is no longer enough to support the embryo
what occurs to initiate implantation?
functional binding of trophoblastic cells to the surface of the endometrium
around what day does implantation occur in most species?
around day 20
around what day does implantation occur in the horse?
day 35
t/f
maintenance of pregnancy is dependent on serum p4 in all species
true
t/f
initially, all animals depend on the CL for maintenance of early preg
true
which species depend on CL primarily for the entire duration of preg?
hembra
bitch
nanny
sow
when in pregnancy does the cow depend on the CL?
through day 200
then again for the last 30 days of the pregnancy
what is the function of p4 in the maintenance of preg?
to maintain the endometrium that can maintain placentation
why does exposure to PG abort pregnancy in many species but NOT the bitch?
b/c PG lyses the CL but the bitch CL is refractory to PG
what does the cow rely on beginning on day 200 of preg for p4?
an alternate source
unknown for certain
may be placenta or cow’s adrenal gland
how long does the ewe rely on the CL for maintenance of preg?
first 50 days
what is the feto placental unit?
what is the significance / role of the feto placental unit?
fxn is an endocrine organ - that requires a placenta and a living fetus
precursor molecules are produced in the fetus and are converted to a different compound or activated in the placenta
how sensitive is the mare CL to the effects of PG?
does the horse rely on the CL to maintain preg?
very sensitive
horse relies on CL for 35 days - prior to implantation
what occurs during implantation in the mare?
cells from the trophoblast, the outer membrane of the embryo, detach from the embryo and implant sub epithelially into the uterus of the mare
what are the cells like that implant into the mare uterus at implantation?
what is their signifncance
bi nucleated cells - stop dividing soon after arrival in the uterus
form clusters of cells that become endometrial cups
what do endometrial cells secrete?
eCG
t/f
endometrial cups are in the horse but their origin is embryonic?
true
eCG has what hormone like effect on the ovaries?
LH-like
what is the function of eCG sec by endometrial cups?
alternate source of LH that stimulates a GnRH surge which triggers a subsequent surge of LH
what is the significance of the LH surge triggered by eCG secreted by endometrial cups?
stimulates follicles on the ovaries to lutenize so mare develops several CLs
during what period in pregnancy does mare sec eCG from endo cups?
why is this significant for the maintenance of preg?
btwn 80-100 days
during this time, she will always have at least 1 CL that is young and refractory to PG luteolysis effects
this mechanism ensures that her preg is maintained
how long do CL waves maintain preg in mare?
about mid way through gestation
after the ovarian source of p4 in the mare expires, what does she rely on the maintain preg?
what is the source?
5a pregnanes
from the feto placental unot
where is 5a pregnanes formed?
the young developing adrenal gland prod a steroid precursor which is converted by placenta into 5a pregnanes
what type of molecule is 5a pregnanes?
a pregestogen
what hormone level is extremely high in the mare during preg?
what is the source?
e2
source: gonads of developing fetus - produces steroid precursor - converted by placenta into estrogen
why do horses require high sources of e2 during preg?
it is not essential to maintain preg - the purpose of high e2 is not known
t/f
the pregnancy and non pregnant hormone of the bitch are similar
true
what aspect of the preg hormone profile of a bitch differs from a non preg bitch profile?
p4 profile looks diff at term in preg bitch
non preg: p4 drops off gradually
preg: small luteolytic event occurs at preg [even though the CL is already almost dead]
what hormone is produced by the bitch placenta?
relaxin
what is significance of relaxin in the bitch preg from a management standpoint?
relaxin is a peptide hormone
it is easily measured and adapted to a snap test that can be offered in clinics for preg detection in bitch
t/f
the queen does not have a luteolytic mechanism?
true
how does the CL of the queen survive for the duration of pregnancy?
unknown
what happens to the CL if the queen is preg?
CL disappears and placenta takes over p4 prod until term
what does estrone suplhate indicate?
the presence of live fetus(es)
where does estrone sulphate originate?
it is a biproduct of placental metabolism
what is the activity of estrone sulphate?
it is inactive - it is conjugated e2 that does not have activity and indicates that the conceptus is alive
what technology renders the detection of estrone sulphate somewhat irrelevant?
u/s
now we can see the heart beat [or lack there of] to dx preg
