Gametes & Fertilization

Question 1

spermatozoa

Answer 1

sperm cells; simple cells designed for motility

Question 2

semen

Answer 2

sperm + seminal fluid

Question 3

where is the site of ejaculation in dogs, ruminants, horses, and pigs

Answer 3

dogs: vaginal
ruminants: vaginal
horses: cervix/uterine body
pigs: cervix

Question 4

what is the path of sperm transit

Answer 4

testis –> efferent ducts –> epididymis –> ductus deferens –> colliculis seminalis –> pelvic urethra –> penis –> urethral process

Question 5

where are the two sites of sperm storage

Answer 5

epididymis
ductus deferens

Question 6

where does sperm travel after ejaculation

Answer 6

site of fertilization (ampulla of the oviduct)

Question 7

oocyte

Answer 7

egg cell; released from ovulation into the oviduct

Question 8

polar body

Answer 8

inactivated nucleus that results from an unequal mitotic division

Question 9

what is unique about horse oocytes after ovulation

Answer 9

if not fertilized, will remain in the oviduct and accumulate

Question 10

what are the stages of gamete transport

Answer 10

1. urethral phase
2. uterine phase
3. oviductal phase
4. zygotę/embryo transport

Question 11

urethral phase

Answer 11

male ejaculation of sperm into vagina/cervix

majority of sperm gets lost at this stage

Question 12

uterine phase

Answer 12

sperm enter uterus and travel into one of the uterine horns

rapid and slow sperm transport

Question 13

rapid sperm transport

Answer 13

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

Question 14

slow sperm transport

Answer 14

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

Question 15

oviductal phase

Answer 15

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

Question 16

zygote/embryo transport

Answer 16

once fertilized, the zygote begins to divide as it travels down the oviduct to the uterus

Question 17

what species have a long oviduct transit

Answer 17

dogs and horses

enters the uterus at the blastocyst stage

Question 18

what species have a short oviduct transit

Answer 18

pigs, ruminants

enters the uterus at the 4, 8, or 16 cell embryo stage

Question 19

what are the major sites of sperm loss during fertilization

Answer 19

1. retrograde flow after ejaculation
2. phagocytosis by leukocytes in the uterus

female tract will select morphologically normal, motile sperm

Question 20

steps of fertilization

Answer 20

1. sperm maturation and capacitation
2. penetration of zona pellucida
3. sperm-egg recognition
4. acrosomal reaction
5. fusion of sperm and oocyte plasma membranes
6. blocks to polyspermy
7. fusion of male and female pronuclei
8. embryonic development

Question 21

sperm maturation and capacitation

Answer 21

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

Question 22

sperm-egg recognition

Answer 22

species specific receptors on oocyte surface recognize sperm binding
- IZUMO ligand on sperm binds to JUNO receptor on egg

Question 23

acrosomal reaction

Answer 23

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

Question 24

fusion of sperm and egg membranes

Answer 24

once inside the oocyte, sperm releases oscillin (sperm factor) that stimulates PLC activity

causes an influx of Ca into oocyte –> facilitates cortical reaction

Question 25

what are the two blocks to polyspermy

Answer 25

1. oocyte depolarization
2. cortical reaction

Question 26

oocyte depolarization

Answer 26

FAST block

upon sperm binding, oocyte membrane depolarizes to prevent other sperm from binding

Question 27

cortical reaction

Answer 27

SLOW block

cortical granules located along the periphery of the egg fuse with the oocyte membrane and release hydrolytic enzymes into the perivitelline space (between zona pellucida and oocyte membrane) to prevent additional sperm from entering

Question 28

fusion of male and female pronuclei

Answer 28

male and female pronuclei fuse together to form a pronuclear zygote

first cleavage division occur ~24 hours later