Embryology 2 - Fertilisation

Question 1

capacitation

Answer 1

glycoprotein and sterol coat acquired in epididymis is removed by proteases in the uterine/cervical fluid
causes cell membrane to become more permeable to calcium ions
indirectly, via cAMP, activate strong tail lashing and make the acrosome reaction possible later

Question 2

where does fertilisation take place

Answer 2

fallopian tube

Question 3

where can sperm wait until ovulation

Answer 3

bound to epithelial cells at medial end of fallopian tube

Question 4

where does the sperm meet the egg

Answer 4

at the zona pellucida of the oocyte

Question 5

what reaction occurs when the sperm meets the oocyte at the zona pellucida

Answer 5

acrosome reaction

Question 6

what happens during the acrosome reaction

Answer 6

acrosome membrane and plasma membrane fuse at many points
acrosomal contents spill out and can digest the zona pelludica

Question 7

process of fertilisation

Answer 7

acrosome reacted sperm burrow towards oocyte
one sperm reaches oocyte membrane and fuses with membrane - causes a wave of calcium entry which keeps repeating

Question 8

what sperm cells can fuse with oocyte membrane

Answer 8

only sperm that have undergone acrosome reaction

Question 9

effects of calcium waves

Answer 9

1. cortical granules are released - these alter the zona pellucida and make it impenetrable by sperm (and also block fusion)
2. meiosis of the oocyte resumes

Question 10

what forms male and female pronuclei

Answer 10

decondensed chromosomes

Question 11

typical reasons for assisted fertilisation

Answer 11

blocked/absent oviducts
blocked vasa deferentia/eferentia, impotence, low male fertility
female age

Question 12

typical stages of assisted fertilisation

Answer 12

superovulation
oocyte harvesting - follicular aspiration, laparoscopic or transvaginal - from carrying woman or donor
sperm harvesting - usually masturbation, can be aspiration from epidiymis or even testis for ICSI
capacitation of sperm (artificially)
mixing of sperm and oocytes
observation of early development (often genetic testing of one cell)
embryo transfer

Question 13

transvaginal oocyte harvesting

Answer 13

has largely replaced laparoscopy
with patient lying on back, knees up

Question 14

what is ICSI

Answer 14

intra-cytoplasmic sperm injection

Question 15

what does a new embryo have to do

Answer 15

grow much bigger - adult humans approx 1million times larger than a fertilised egg
create internal differences - so what is one cell becomes many cells types
organise the axes and the complex anatomy of the body

Question 16

activation of the embryonic genome

Answer 16

at the 4 cell stage:
mRNA synthesis from embryo’s own DNA begins
maternal mRNA is destroyed at an increasing rate

Question 17

first difference of embryonic cells

Answer 17

cells on inside of morula have contact all round. cells on outside have free surface

Question 18

morula

Answer 18

2 cells - 4 cells - morula
3rd division of cells

Question 19

trophoblast

Answer 19

makes placenta and some other extra-embryonic material

Question 20

inner cell mass

Answer 20

makes body itself plus some extra-embryonic membranes

Question 21

where does the blastocyst ‘hatch’ through

Answer 21

zona pellucida

Question 22

where does the early embryo live

Answer 22

unattached in journey down fallopian tube

Question 23

implantation

Answer 23

trophoblast of hatched blastocyst invades uterine epithelium

Question 24

what does the trophoblast develop into

Answer 24

the placenta