Fertilisation

Question 1

what is coagulated?

Answer 1

ejaculated sperm

Question 2

why is ejaculated sperm coagulated?

Answer 2

to prevent loss, later liquifies

Question 3

what happens to the coagulated sperm?

Answer 3

it’s jelly-like, takes about 15 mins to liquify and the sperm swim out

Question 4

importance of sperm moving through cervical mucus?

Answer 4

removes seminal fluid, abnormally morphological sperm and cellular debris

Question 5

effect of progesterone on cervical mucus?

Answer 5

cervical mucus is less viscous in the absence of progesterone allowing sperm to pass

Question 6

what do cervical crypts do?

Answer 6

-ridges on the side of the cervix
that trap sperm which then swim round and round in the ridges and come out at different times
-increases the window of time that the sperm has to meet the egg – increases the chance of them being around when the egg is released

Question 7

when does fertilisation occur?

Answer 7

typically within 24-48 hours

Question 8

give a suggestion as to how the sperm finds and travels to the oocyte cumulus complex?

Answer 8

-chemo-attractants (pH and other factors) released from the oocyte cumulus complex may attract the sperm

Question 9

what are CatSper channels?

Answer 9

VGCC’s on the surface of the sperm which open in response to pH and other factors released from the egg

• sperm become hyperactivated
• forceful tail beats with increased frequency and amplitude mediated by Ca2+ influx via CatSper channels.

Question 10

what does hyperactivity mean?

Answer 10

means that means as the sperm gets near the egg it swims much faster

Question 11

where do the sperm and egg meet?

Answer 11

the ampulla (wide portion of the uterine tube, close to the fimbrial end)

Question 12

where does the embryo spend the first 5-6 days of its life?

Answer 12

uterine tube

Question 13

what is capacitation and how is it achieved?

Answer 13

• biochemical rearrangement of the surface glycoprotein and changes in membrane composition
• partly achieved by removing sperm from seminal fluid
• uterine/tubal fluid may contain factors which promote capacitation

Question 14

why is capacitation needed?

Answer 14

prepares the sperm to be able to undergo the acrosome reaction

Question 15

how long does capacitation take?

Answer 15

4-18 hours

Question 16

does every sperm undergo capacitation for the same length of time - what is the importance of this?

Answer 16

each sperm has a slightly different time to capacitate

-widening the window of time that capacitated sperm might meet the egg

Question 17

when does the sperm undergo the acrosome reaction?

Answer 17

when sperm comes into contact with zona cumulus complex, binds to ZP3 receptor

Question 18

what is the acrosome?

Answer 18

invagination of the sperm membrane to make a fluid-filled compartment that contains enzymes to digest though cells surrounding the egg

Question 19

what happens in the acrosome reaction

Answer 19

the acrosomal membrane on the sperm head fuses releasing enzymes that cut through the complex

Question 20

what breaks in ovulation?

Answer 20

basement membrane, blood pours into the middle

Question 21

what mix in ovulation?

Answer 21

theca and granulosa become mixed

Question 22

another name for the follicular phase (of the ovary)?

Answer 22

proliferative phase (of the uterus)

Question 23

another name for the luteal phase (of the ovary)?

Answer 23

secretory phase (of the uterus)

Question 24

what happens in the follicular/proliferative phase?

Answer 24

• dominated by oestrogen, levels go up causing endometrium proliferation
• LH surge, meiosis 1 completion, ovulation

Question 25

what happens in the luteal/secretory phase?

Answer 25

dominated by progesterone, which: - makes the endometrium secretory and receptive to implantation - supresses cilia in uterine tubes once oocyte has already passed. - makes cervical mucus viscous again to prevent further sperm penetration also some oestrogen secreted from CL, which helps maintain endometrium in luteal phase

Question 26

role of oestrogen in follicular vs luteal phase

Answer 26

follicular is proliferation of endometrium, luteal is maintenance of endometrium

Question 27

why would the CL need beta-HCG to survive?

Answer 27

because otherwise its essentially killing itself - it is producing progesterone, which will negatively feedback on the HPG axis, decreasing LH levels - less LH is able to bind to CL, so CL would die - hence beta-HCG from embryo binds to LH receptors on the CL to maintain its survival

Question 28

what happens as a consequence of the CL dying?

Answer 28

endometrium sheds, menstruation | -because CL stops making progesterone, which is needed to maintain the endometrium

Question 29

what is the zona pellucida?

Answer 29

secreted by the egg, impenetrable after the cortical reaction (inner layer)

Question 30

what is the Cumulus oophorus?

Answer 30

derived from granulosa cells, protects the egg (very outside layer)

Question 31

what is the corona radiata?

Answer 31

the innermost layer of cumula cells, in contact with the ZP | -formed by granulosa cells adhering to the oocyte before it leaves the ovarian follicle (middle layer)

Question 32

explain sperm binding and penetration?

Answer 32

- sperm comes into contact with the zona-cumulus complex, penetrates cumulus and comes into contact with ZP via ZP3 receptor - enzymes digest through ZP, sperm fuses with plasma membrane and taken in by phagocytosis - phospholipase Zeta activated by basal Ca2+ inside egg - PIP2 → DAG + IP3 - release of intracellular Ca2+, large Ca2+ spike - cortical reaction as wave of Ca2+ sweeps around egg - release of proteases, peroxides and hyaline prevents polyspermy

Question 33

ca2+ release causes what?

Answer 33

completion of meiosis II, expelling of the second polar body and the cortical reaction

Question 34

explain what syngamy is and what happens

Answer 34

it is the fusion of 2 nuclei - sperm nuclear membrane breaks down, the chromatin decondenses and chromosomes separate - 4-7 hours after sperm penetration the two sets of haploid chromosomes (male and female) become surrounded by distinct membranes forming two pronuclei - pronuclei synthesise DNA in preparation for the first mitotic division - pronuclei fuse, spindle forms and chromosomes line up - completion of mitosis - one cell zygote becomes a two cell embryo