Fertilization

Question 1

Describe ovum development in fetal life.

Answer 1

-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

Question 2

Describe the postnatal oocyte development.

Answer 2

-primary oocyte (meiosis I)
>duplicate DNA (interphase)
>crossing over
-meiosis resumed at ovulatory surge of LH (puberty)
*meiosis I = secondary oocyte (2n) & polar body

Question 3

Describe polar body.

Answer 3

-degenerate
-after meiotic division
-reduced genetic material
-requires oocyte cytoplasm for embryo

Question 4

Describe what happens in oogenesis at Meiosis II.

Answer 4

-secondary oocyte from meiosis I continues to meiosis II (ovulation) = arrested at metaphase II until fertilization
-result: ovum (n) & 2nd polar body

Question 5

Describe ovulation.

Answer 5

-release oocyte from follicle
-oocyte + cumulus mass = move into infundibulum by fimbria
-meiosis continue to metaphase II
-fertilization in ampulla (6-12h)

Question 6

Describe dogs ovulation.

Answer 6

-oocyte ovulate at prophase I instead of metaphase II
*(Before completion of meiosis I)
-maturation (metaphase II) finishes in oviduct

Question 7

Describe sperm transit in fertilization.

Answer 7

-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

Question 8

Describe sperm reservoir.

Answer 8

-isthmus of uterine tube (near uterotubal junction)
-sperm adhere to epithelium = prolonged lifespan
-sperm released at time of ovulation

Question 9

Describe ampulla, isthmus, infundibulum.

Answer 9

Uterus -> ovary
1. Isthmus
-sperm reservoir
2. Ampulla
-fertilization
3. Infundibulum
-collect oocytes

Question 10

Describe sperm capacitation.

Answer 10

-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

Question 11

Describe acrosome reaction.

Answer 11

-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

Question 12

Describe penetration of zona pellucida.

Answer 12

-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

Question 13

Describe gamete fusion.

Answer 13

-oocyte membrane less species specific in binding than ZP
-acrosome reaction required before sperm fuse w oocytes (oolemma)

Question 14

Describe blocks to polyspermy.

Answer 14

-ZP impermeable upon fert
-reorganization of ZP structure
-oocyte cortical granules release into perivitelline space after release soluble factors & DNA by sperm

Question 15

Describe fertilization after the sperm penetrates into the oocyte.

Answer 15

-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

Question 16

Describe the migration to the uterus.

Answer 16

-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

Question 17

Describe early embryo development.

Answer 17

-mitotic divisions
-early division = no increase in cell mass ‘cleavage’
-metabolic support via maternal secretions
-zygotic protein synthesis = 2-16 cell stage (totipotent cells)

Question 18

Describe the differentiation from the morula to the blastocyst stage.

Answer 18

-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

Question 19

Describe hatched blastocysts.

Answer 19

-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

Question 20

Describe extraembryonic membranes. (4)

Answer 20

1. Yolk sac - nutrition & sex diff
2. Amnion - mechanic protection, hydration, temp, fetus movement
3. Allantois - secretion from embryo & gas exchange
4. Chorion - (outermost) external layer of placenta that attaches to uterus + nutrition of embryo

Question 21

Describe maternal recognition of pregnancy.

Answer 21

*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

Question 22

Describe the maternal recognition of pregnancy in ruminants.

Answer 22

-after hatching from ZP, blastocyst elongates
-trophoectoderm makes IFNT
>inhibits oxytocin receptor synthesis
>inhibits PGF2a
>stimulates endometrial glands

Question 23

Describe the maternal recognition of pregnancy in swine.

Answer 23

-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

Question 24

Describe the maternal recognition of pregnancy in horses.

Answer 24

-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

Question 25

Describe a embryo capsule.

Answer 25

-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

Question 26

Describe the maternal recognition of pregnancy in llama.

Answer 26

-pregnancy in left uterine horn
-PGF2a synthesis/release inhibited
-embryo secrete estrogens
-blocks induction of endometrial COX2 expression = attenuation of PGF2a & CL rescue