Lecture 7: pregnancy and Parturition Flashcards
When do primary oocysts arrest during embryonic development
Prophase I of meiosis
What stage of oogenesis is gonadotropin independent
Mitosis and 1st meiosis division
What stage of oogenesis is gonadotropin dependent
After puberty when meiosis resumes to generate secondary oocyte—> mature ovum
Meiosis 2 occurs at ___
Fertilization
LH surge allows the ___ in the dominant follicle to be lifted
Meiotic arrest
When does fertilization occur
Time of second meiotic division
Describe the steps from LH surge to fertilization
- LH surge to lift meiotic arrest and generate secondary oocyte
- Ovulation occurs to generate optid
- Fertilization occurs and generates zygote that will briefly have male and female pro nucleus
What inhibits meiosis prior to ovulation
Oocyte inhibiting factor and luteinizing inhibiting factor
How does oocyte inhibiting factor inhibit meiosis prior to ovulation
Keeps oocyte in prophase 1
How does luteinizing inhibiting factor prevent meiosis prior to ovulation.
Prevents granulosa cells from becoming luteal tissue
Pre-ovulatory LH surge will breakdown what to release inhibition of meiosis
Breakdown of gap junctions between granulosal cells and oocyte
What happens after the breakdown of granulosal cells and oocyte
- Remove meiotic inhibition
- First polar body
- Haploid oocyte
- Fertilization
Where do dogs, cats, cow, sheep and primates ejaculate into
Cranial vagina
Where do pigs and camelids ejaculate into
Cervix
Where do horses ejaculate into
Uterus
What is fractionation of sperm
Methods that minimize sperm loss
Rodents fractionation of ejaculate
Produce cervical plug
Horse fractionation of ejaculate
Initial ejaculate is sperm-rich and subsequent ejaculate is viscous
Dog fractionation ejaculate
Have 3, final is thought to force sperm into uterus
Describe the sequence of events following deposition of spermatozoa into female tract
- Immediate transport into cervix/uterus
- Cervix- “priveleged path” removal of non-motile sperm, removal of some abnormalities
- Uterus- capacitation initiated
- Oviduct- docking to oviductal cells, capacitation completed, hyperactive motility
- Fertilization- acrosome reaction, spermatozoon penetrate oocyte, male and female pronuclei form
What part of female reproductive tract is the “privileged path” removals non-motile sperm and abnormalities
Cervix
Where is capacitation initiated
Uterus
Where is capacitation completed
Oviduct
What increases sperm motility
Ca2+ influx
Sperm motility in cervical canal requires what pH
Alkaline
Alkaline secretions in the semen from the male’s ___ elevate pH
Prostate
What is the role of estrogen in sperm motility
Makes cervix mucous watery, facilitating sperm motility
What is responsible for sperm transport in uterine cavity
Myometrial contractions
Natural conception lubrication causes what to happen to the sperm
Cholesterol withdrawal to expose acrosome cap, redistribute surface proteins, Ca2+ influx to increase motility
What is present in ejaculate that signals to the uterus to activate myometrial contractions
Prostaglandins
The myometrium is ___ primed tissue that helps provide sperm motility
Estrogen
Upon reaching the ovum what barriers must the sperm break through
Corona radiata and zona pellucida via acrosome cap
Oocytes are in meiotic arrest before ____
Ovulation
What are ZP molecules
Glycoproteins that occur on the zona pellucida
Where are ZP receptors located
On sperm
ZP specificity is one factor that limits ___
Fertilization to within species
What intimates the acrosomal reaction
ZP3 binding to ZP3 receptors
What is the function of ZP2
Hold the sperm in place
What happens once sperm penetrates the zona pellucida
Fertilin on sperm can bind fertilin receptors on the egg to influx Ca2+ into ovum this is called the zona reaction
What does the zona reaction result in
Spread of depolarization over the surface of the egg and immediate release of cortical granules which hardens the zona pellucida to block further ZP1-4 signaling from other sperm, preventing polyspermy
What is the 4-8 cell, non-differentiated pre hatching cells known as
Morula
What is a blastocyst
Result of fluid accumulation, pre-hatching
What two cell types occur prior to hatching
Trophoblasts and inner cell mass
What are trophoblasts responsible for
Establish communication between mother and fetus, regulate pregnancy
What do inner cell mass cells become
Somatic and germ tissue
How does hatching occur
Proteolytic enzymes weaken the zona pellucida and pressure increases within the blastocele
When does hatching occur in cows
9-11 days
When does hatching occur in sheep
7-8 days
When does hatching occur in swine
6 days
When does hatching occur in the bitch
13-15 days
When does hatching occur in the queen
10-12 days
Where does fertilization occur in female reproductive tract
Oviduct
Two oviducts/fallopian tubes attach to
Uterus
During artificial insemination where should sperm be placed in order to minimize retrograde sperm loss
Uterus
How long does migration of developing zygote and blastocyst take
Several days to weeks
Maternal recognition requires the distribution of ___ across a wide area of endometrium
Pregnancy factors
Pregnancy factors are required to rescue the ___ to maintain pregnancy
Corpus luteum
PGF2alpha induces what
Luteolysis
What do cows and ewe release from trophoblasts to block oxytocin receptors in uterus, thus inhibiting PGF2alpha
Interferon-tau
Interferon-tau allows ___to be recognized
Pregnancy
What is a reliable marker for conception in cows at days 17–20 post ovulation
Interferon-tau
What secretes interferon-tau
Trophoblasts
In sows ___ is released from trophoblast to recognize pregnancy
Estrogen
Describe the mechanism in how estrogen allows the sows to recognize pregnancy
Estrogen reroutes PGF2alpha back to uterus so it doesn’t act on CL and cause regression
Luteal oxytocin stimulates endometrium to secrete ___in non-pregnant females
Prostaglandins
___secretion is suppressed if there is an embryo present
Prostaglandin
what hormone remains high during pregnancy
Progesterone
is this graph indicative or not indicative of conceptus present
Conceptus is present, progesterone levels are high and PGF2alpha levels are low
Is this graph indicative or not indicative or conceptus present
no conceptus present, progesterone drops and PGF2alpha rises
What hormone is released by endometrial cups (horses) of placenta at day 40-70 days or pregnancy
Equine chorionic gonadotropin (eCG)
Soon after ovulation and early days of gestation what happens to progesterone levels
Drops
What reactivates progesterone levels in horses
Equine chorionic gonadotropin
What is the stimulus of release for eCG
Spontaneous release
What is the target of eCG
CL/ovary
What is the effect of eCG
LH-like characteristics in mares, enhances progesterone production by primary CL and triggers ovulation of additional follicles to create secondary CL
Which species lack luteotrophic mechanisms
Dogs and cats
How long does CL survive independent of pregnancy in dogs
60-70 days
In dogs, luteal function begins ___ and is supported by ___, followed later by ___
Autonomously, LH and prolactin
Relaxin ___luteal activity
Enhances
Relaxin enhances ___
Progesterone
T or F: a signal from the embryo in dogs and cats is not necessary because the CL are not lysed before normal pregnancy is established
True! CL survives 60-70 days
**unlike cows which require IFN-tau
How long does CL last in cats independent of pregnancy
35-40 days
Relaxin is a ___hormone
Placental
What hormones maintain CL in cats
Progesterone and relaxin
When does implantation adhesion occur
Blastocyst implantation begins when cell adhesion molecules adhere to the endometrium and trophoblasts enzymes erode the uterine wall
When does implantation invasion occur
Trophoblasts cells invade and blastocyst is embedded within the endometrium
___cells completely cover the developing embryo
Endometrial
When does implantation and invasion of endometrium occur
When endometrium is at its peak thickness and secretion
The placenta performs the functions of the ___system, the ___system, and ____ for the fetus
Digestive, respiratory and kidney
What structure prevents immunological rejection of fetus
Placenta
What essential pregnancy hormones does the placenta secrete
- Estrogen
- Progesterone
- Equine chorionic gonadotropin
In horses, what hormone maintains CL until placenta takes over function in last 2 trimesters
Equine chorionic gonadotropin
How is gestation maintained in all species
Progesterone
What structure takes over the corpus luteum later in gestation
Placenta
Progesterone inhibits ___contractions and maintains pregnancy
Myometrial contractions
___ blocks the formation of gap junctions during pregnancy
Progesterone
What prevents contractility of uterus during pregnancy
Progesterone
What promotes endometrial gland growth during pregnancy
Progesterone
What stimulates secretory activity of oviduct and endometrial glands to provide nutrients during pregnancy
Progesterone
What hormone has a thermogenesic effect during pregnancy
Progesterone
When does placenta take over control of CL in cows
6-8 months
When does placenta take over control of CL in ewe
50 days
When does placenta take over control of CL in mare
70 days
Where does progesterone synthesis start: mother, placenta or fetus?
Mother
Where is cholesterol converted to pregnenolone and then progesterone in pregnancy
Occurs in placenta
What is estriol
Estrogen that is derived from the placental-fetal unit
What is estriol useful to determine
Placental competency
Describe the steps and locations of estriol synthesis
- Starts in mother with cholesterol
- Cholesterol enters placenta and is converted to pregnenolone
- Pregnenolone travels from placenta to fetus
- Fetus converts pregnenolone to DHEA sulfate and then 16-OH DHEA-sulfate
- 16-OH DHEA sulfate returns to placenta and converted to estriol
- Estriol returns to mother
When during pregnancy does estrogen dramatically increase
End
What does peak estrogen at end of pregnancy do to prepare for baby
- Increased growth of myometrium- muscles for labor
- Development of ductile system of mammaries
- Relax and soften pelvic ligaments
- Stimulates prolactin release
What does estrogen inhibit at end of pregnancy
Lactation
How does estrogen inhibit lactation at end of pregnancy
- Antagonizes prolactin effect on mammary glands, suppressing milk synthesis
- Inhibits lactalbumin- required for lactose synthesis
What initiates stage 1 of parturition
Fetal adrenal corticoids
During stage 1 of parturition what is progesterone converted into
Estradiol
What happens to corpus luteum during stage 1 parturition
Luteolysis
What does PGF2alpha do during stage I parturition
Contributes to myometrial contractions
What stage does the preparation of Birth canal via lubrication and relaxation of pelvic ligaments occur
Stage 1
What happens during stage 2 parturition
Delivery, fetus passes through pelvic canal
What happens during stage III parturition
Fetal membranes are delivered
During stage III myometrial contractions and PGF2alpha surges occur to…
Reduce uterus size and release of membranes
What axis is activated towards end of pregnancy, stage I parturition
Fetal hypothalamus-pituitary adrenal axis
Fetal cortisol activates what enzyme to shunt synthesis from progesterone to estrogen
17-alpha hydroxylase
During conversion of progesterone to estrogen in stage I of parturition the myometrium becomes more active by
Increasing secretory activity of reproductive tract and opens the cervix
Fetal cortisol causes the placenta to produce ___
PGF2alpha
Fetal cortisol stimulates placenta to produce PGF2alpha which will stimulate release of ___loosening ligaments and softening birth canal
Relaxin
What two hormones contribute most to uterine contractions
Oxytocin and prostaglandins
Delivery of fetus through cervical canal is mediated by ___
Oxytocin
Labor is initiated when
Oxytocin receptor concentration reaches critical threshold