Gametes & Fertilization Flashcards
spermatozoa
sperm cells; simple cells designed for motility
semen
sperm + seminal fluid
where is the site of ejaculation in dogs, ruminants, horses, and pigs
dogs: vaginal
ruminants: vaginal
horses: cervix/uterine body
pigs: cervix
what is the path of sperm transit
testis –> efferent ducts –> epididymis –> ductus deferens –> colliculis seminalis –> pelvic urethra –> penis –> urethral process
where are the two sites of sperm storage
epididymis
ductus deferens
where does sperm travel after ejaculation
site of fertilization (ampulla of the oviduct)
oocyte
egg cell; released from ovulation into the oviduct
polar body
inactivated nucleus that results from an unequal mitotic division
what is unique about horse oocytes after ovulation
if not fertilized, will remain in the oviduct and accumulate
what are the stages of gamete transport
- urethral phase
- uterine phase
- oviductal phase
- zygotę/embryo transport
urethral phase
male ejaculation of sperm into vagina/cervix
majority of sperm gets lost at this stage
uterine phase
sperm enter uterus and travel into one of the uterine horns
rapid and slow sperm transport
rapid sperm transport
rapid movement of sperm from site of ejaculation to oviduct
occurs by uterine and vaginal contraction
NONE of the rapidly transported sperm will become the fertilizing sperm
slow sperm transport
sperm undergo metabolic changes required to gain motility/fertilizing ability while traveling to oviduct
ONE will become the fertilizing sperm
significant loss as sperm are exposed to leukocytes and oxidative killing
oviductal phase
one sperm complete metabolic changes (capacitation), will bind to folds in the oviduct epithelium (in isthmus and ampulla) that induces them to slow metabolism
- binding will favor morphologically normal sperm
as egg travels into the oviduct - sperm get slowly released from epithelium
zygote/embryo transport
once fertilized, the zygote begins to divide as it travels down the oviduct to the uterus
what species have a long oviduct transit
dogs and horses
enters the uterus at the blastocyst stage
what species have a short oviduct transit
pigs, ruminants
enters the uterus at the 4, 8, or 16 cell embryo stage
what are the major sites of sperm loss during fertilization
- retrograde flow after ejaculation
- phagocytosis by leukocytes in the uterus
female tract will select morphologically normal, motile sperm
steps of fertilization
- sperm maturation and capacitation
- penetration of zona pellucida
- sperm-egg recognition
- acrosomal reaction
- fusion of sperm and oocyte plasma membranes
- blocks to polyspermy
- fusion of male and female pronuclei
- embryonic development
sperm maturation and capacitation
occurs during sperm transit to the oviduct
series of Ca dependent steps that results in cholesterol efflux from the membrane –> loss of cholesterol increases fluidity to allow for fusion with oocyte membrane
sperm-egg recognition
species specific receptors on oocyte surface recognize sperm binding
- IZUMO ligand on sperm binds to JUNO receptor on egg
acrosomal reaction
acrosome in sperm head releases hydrolytic enzymes that dissolve a pathway through the zona pellucida
requires motility for sperm to be able to travel through pathway into the perivitelline space
fusion of sperm and egg membranes
once inside the oocyte, sperm releases oscillin (sperm factor) that stimulates PLC activity
causes an influx of Ca into oocyte –> facilitates cortical reaction
