7. fertilisation & oocyte maturation (lecture)

Question 1

what does oocyte undergo?

Answer 1

meiosis I

Question 2

what happens during meiosis I of oocyte?

Answer 2

nuclear membrane disappears

1st polar body separates and enters perivitelline space

Question 3

what is the perivitelline space

Answer 3

space between the zona pellucida and the cell membrane of an oocyte or fertilized ovum

Question 4

what happens after appearance of 1st polar body in the perivitelline space?

Answer 4

second meiotic division takes place, and stops in metaphase II

Question 5

what is the process of 1st polar body appearing and second meiosis stopping at metaphase II called?

Answer 5

maturation of oocyte nucleus

Question 6

what happens to the mitochondria during cytoplasmic maturation?

Answer 6

dispersed throughout cytoplasm

Question 7

what happens to the endoplasmic reticulum during cytoplasmic maturation?

Answer 7

accumulates in oocyte cortex (outer)
protein and lipid synthesis –> cortical granules
immature oocyte: cortical granules displaced throughout cytoplasm

Question 8

what happens to the cortical granules during oocyte maturation?

Answer 8

becomes cortical (peripheral) instead of displaced throughout cytoplasm

Question 9

what is the function of lipid droplets (synthesised by ER) during cytoplasmic maturation?

Answer 9

provide energy (meiosis, maturation, fertilisation and early embryo development)

Question 10

function of cytoskeleton during cytoplasmic maturation?

Answer 10

microfilaments migrate toward oocyte cortex

Question 11

how many sperm does it take to ‘get pregnant’?

Answer 11

average 200-300 million per ejaculate
300 reach fertilisation site
1 sperm required for fertilisation, but 299+ sacrificed to disperse the zona pellucida

Question 12

how long do sperm survive for?

Answer 12

up to 5 days in female genital tract

Question 13

how long does oocyte survive for?

Answer 13

6-24 hours before phagocytosis

Question 14

what is the fertile period?

Answer 14

sperm deposition up to 3 days prior to ovulation or on the day of ovulation

Question 15

how long does it take oocyte to travel to Fallopian tube? from where?

Answer 15

oocyte takes 3-4 days to travel from ovary (abdominal cavity) to body of uterus (pelvic cavity)

Question 16

how does oocyte travel from ovary to body of uterus?

Answer 16

ciliar and Fallopian tube peristalsis

Question 17

what does sperm need to penetrate to get to oocyte?

Answer 17

penetrate corona radiata (follicular cells) and zona pellucida (glycoprotein membrane)

Question 18

what does sperm undergo in order to penetrate corona radiata and zona pellucida?

Answer 18

capacitation

Question 19

where does sperm undergo further maturation post ejaculation?

Answer 19

in female reproductive tract (6-8 hours)

Question 20

what is capacitation of sperm?

Answer 20

sperm cell membrane changes to allow fusion with oocyte cell surface

Question 21

what changes does the sperm undertake during capacitation?

Answer 21

removal or protein coat (head of sperm)

acrosomal enzymes are exposed

Question 22

how does the tail movement of sperm change with capacitation?

Answer 22

tail movement changes from beat to whip-like action

Question 23

how far does the sperm move per hour?

Answer 23

3mm/hour

Question 24

what does the plasma membrane of the epididymal spermatozoa contain? (within epididymus)

Answer 24

a complement of surface molecules (proteins and carbohydrates)

Question 25

what do the surface molecules in epididymal sperm become coated with? (post ejaculation)

Answer 25

seminal plasma proteins that mask portions of the membrane molecules

Question 26

what happens to the seminal plasma coatings of the sperm when exposed to female reproductive tract environment? (capacitation)

Answer 26

seminal plasma coatings along with some surface molecules are removed - exposing portions of the molecules that can bind to zona pellucida of oocyte

Question 27

aside from the whip like action of the sperm moving 3mm/hour, what else helps the transport of sperm along the female reproductive tract?

Answer 27

contraction of female genital organs

Question 28

how are the acrosome on sperm when the sperm contacts corona radiata?

Answer 28

sperm has intact acrosome

Question 29

what happens when sperm contacts corona radiata? (acrosome rection)

Answer 29

sperm pushes through granulosa (follicular) cells of corona radiata

Question 30

what do proteins on sperm head bind to when pushed through granulosa (follicular) cells of corona radiata?

Answer 30

sperm head bind to ZP3 proteins of zona pellucida (ZP)

Question 31

what happens when sperm head binds to ZP3 proteins of zona pellucida (ZP)?

Answer 31

key signalling mechanism involves intracellular Ca2+

acrosomal enzymes digest path through ZP

Question 32

what happens after acrosomal enzymes digest path through ZP?

Answer 32

1 sperm penetrates: fusion of plasma membranes (egg and sperm)

Question 33

what happens after fusion of plasma membranes (egg and sperm)?

Answer 33

sperm moves into cytoplasm: oocyte and sperm –> zygote

Question 34

what happens after formation of zygote?

Answer 34

polyspermy blocked (cortical reaction) - prevent other sperms from fertilising within oocyte