Fertilization Flashcards
Describe ovum development in fetal life.
-primary germ cells originate by yolk sac & migrate to developing ovary (genital ridge)
-differentiate to oogonia (2N) & multiply via mitosis
-prophase 1 = primary oocytes arrested until puberty
Describe the postnatal oocyte development.
-primary oocyte (meiosis I)
>duplicate DNA (interphase)
>crossing over
-meiosis resumed at ovulatory surge of LH (puberty)
*meiosis I = secondary oocyte (2n) & polar body
Describe polar body.
-degenerate
-after meiotic division
-reduced genetic material
-requires oocyte cytoplasm for embryo
Describe what happens in oogenesis at Meiosis II.
-secondary oocyte from meiosis I continues to meiosis II (ovulation) = arrested at metaphase II until fertilization
-result: ovum (n) & 2nd polar body
Describe ovulation.
-release oocyte from follicle
-oocyte + cumulus mass = move into infundibulum by fimbria
-meiosis continue to metaphase II
-fertilization in ampulla (6-12h)
Describe dogs ovulation.
-oocyte ovulate at prophase I instead of metaphase II
*(Before completion of meiosis I)
-maturation (metaphase II) finishes in oviduct
Describe sperm transit in fertilization.
-fertile sperm via epididymal transit
-move from site of deposition (insemination & natural) to uterine tube (mins/hrs) via contractions of female tract
-mil ejaculated, thou reach uterine tube, hund present for fertilization
Describe sperm reservoir.
-isthmus of uterine tube (near uterotubal junction)
-sperm adhere to epithelium = prolonged lifespan
-sperm released at time of ovulation
Describe ampulla, isthmus, infundibulum.
Uterus -> ovary
1. Isthmus
-sperm reservoir
2. Ampulla
-fertilization
3. Infundibulum
-collect oocytes
Describe sperm capacitation.
-acrosome reaction
-biochemical (non morphologic) changes in female tract before sperm fertilize
-remove seminal plasma to interact w female secretion
-HYPERMOTILITY
-change in membrane cholesterol
Describe acrosome reaction.
-essential for fertilization = allow sperm penetration into oocyte (zona pellucida)
-Ca dependent
-fusion of sperm PM w outer acrosomal membrane
-vesiculation over surface of sperm & acrosome
-release of acrosomal enzymes
Describe penetration of zona pellucida.
-sperm move between cumulus cells
-attach to zona pellucida (proteins for binding sites)
-fusion of sperm & oocyte membrane = DNA
-only acrosome intact sperm bind
-sperm motility + enzymes = zona penetration
Describe gamete fusion.
-oocyte membrane less species specific in binding than ZP
-acrosome reaction required before sperm fuse w oocytes (oolemma)
Describe blocks to polyspermy.
-ZP impermeable upon fert
-reorganization of ZP structure
-oocyte cortical granules release into perivitelline space after release soluble factors & DNA by sperm
Describe fertilization after the sperm penetrates into the oocyte.
-oocyte completes meiosis & expels 2nd polar body
-remaining haploid chromosomes enclosed in pro nucleus
-sperm nuclear envelope disintegrates
>DNA decondensation
>new envelope: pronucleus
-M & F pronuclei migrate to cell center
-nuclear envelope disperse
-fusion of chromosome & aggregate in prophase of 1st cleave division
-proximal centriole of sperm forms one of the zygotes centrioles
Describe the migration to the uterus.
-early cleavage in uterine tube
-zygote reach uterus in 4d in cow & 6d in horse & 8d in dog
-16 cell morula stage (cow, sheep)
-morula/early blastocyst (mares, dogs)
MARES:
-only fertilized zygotes transported thru uterine tubes
-zygote responsible for transport by secretion of PGE2
Describe early embryo development.
-mitotic divisions
-early division = no increase in cell mass ‘cleavage’
-metabolic support via maternal secretions
-zygotic protein synthesis = 2-16 cell stage (totipotent cells)
Describe the differentiation from the morula to the blastocyst stage.
-morula =
>ICM - polarized cell in blastocyst that form embryo
>trophoblast - form chorion (placenta)
—pump Na into intracellular space due to osmotic pressure & embryo is filled with water “blastocele” = cavity that surrounds embryo
Describe hatched blastocysts.
-hatch out of ZP (beginning of implantation)
>increase fluid in blastocele
>proteolytic enzymes from trophoblast
>blastocyst contraction
*7-10d in most species
*9-10d in mares
Describe extraembryonic membranes. (4)
- Yolk sac - nutrition & sex diff
- Amnion - mechanic protection, hydration, temp, fetus movement
- Allantois - secretion from embryo & gas exchange
- Chorion - (outermost) external layer of placenta that attaches to uterus + nutrition of embryo
Describe maternal recognition of pregnancy.
*due to prolong period of function of CL
1. Antiluteolytic =
-diversion or inhibition of PGF2a secretion
2. Luteotropic
-maintain CL
*mechanism not understood in mares
*preg & not preg cycle similar for first 14-16d
MARE = embryo motility
COW, SHEEP = IFNT
PIG = E2
MONKEY = chorionic gonadotropin
Describe the maternal recognition of pregnancy in ruminants.
-after hatching from ZP, blastocyst elongates
-trophoectoderm makes IFNT
>inhibits oxytocin receptor synthesis
>inhibits PGF2a
>stimulates endometrial glands
Describe the maternal recognition of pregnancy in swine.
-blastocyst makes E2
-E2 changes direction of PGF2a secretion by endometrium = away from uterine vasculature (endocrine) & sequester into uterine lumen (exocrine)
-PFG2a inactivated in lumen
-PGF2 metabolized to inactive metabolite
Describe the maternal recognition of pregnancy in horses.
-embryo enter uterus 6d after fert (transport via PGE2)
-embryo migrate thru both uterine horn & body
-movement mediated by uterus (max by day 10-12)
-prevention of movement = preg loss
Describe a embryo capsule.
-unique to equids
-polysaccharide membrane between trophoectoderm & ZP
-forms after embryo reaches uterus
-maintain shape for uterine migration
-gone by day 23
-not made in vitro
Describe the maternal recognition of pregnancy in llama.
-pregnancy in left uterine horn
-PGF2a synthesis/release inhibited
-embryo secrete estrogens
-blocks induction of endometrial COX2 expression = attenuation of PGF2a & CL rescue
