Coitus, fertilisation and implantation

Question 1

what is the EPOR model of sexual response

Answer 1

excitement- sexual arousal, tumesence and erection, engorgement,

plateau- intensification of arousal

orgasm- involuntary muscular contractions with intense pleasure

resolution- rearousal may be impossible

Question 2

what is the length of the luteal phase

Answer 2

14 days

follicular phase is more variable

Question 3

what is the time window for fertilisation

Answer 3

3 days before ovulation up to 1 day after

Question 4

what percentage of pregnancies miscarry

Answer 4

10-15%

Question 5

what proportion of couples are subfertile?

Answer 5

5%

Question 6

what proportion of intercourse results in a blastocyst

Answer 6

20%

Question 7

what proportion of blastocysts fail to implant

Answer 7

15%

Question 8

what percentage of clincally detected pregnancies fail

Answer 8

15-20%

Question 9

what proportion of conceptions survive until birth

Answer 9

20%

Question 10

how long is the embryonic period

Answer 10

8 weeks

Question 11

how long is the foetal period

Answer 11

8-40 weeks

Question 12

what is the function of cumulus cells

Answer 12

aid transport from the surface of the ovary

cling to the ciliated surface of the fimbriae

Question 13

why is sperm mortality high

Answer 13

acidic vagina

length and energy requirement of trip

Question 14

describe capacitation

Answer 14

change from wavelike beats to whip like action to propel sperm
sperm plasma membrane is altered
destabilisation to enhance fusion with oocyte
increase in Ca permeability, removal of membrane proteins
depletion of cholesterol

Question 15

where does ferlisation normally occur

Answer 15

ampulla

Question 16

what does the sperm bind to

Answer 16

zona pellucida

Question 17

what does a rise in Ca inside the sperm cell trigger

Answer 17

exocytosis of the acrosome which contains hydrolytic enzymes

Question 18

what glycoproteins are involved in the acrosome reaction

Answer 18

ZP3 and ZP2

Question 19

describe the acrosome reaction

Answer 19

fusion of the acrosome plasma membranes
releases contents of the acrosome, causes entry of more calcium
sperm digest the zona pellucida

Question 20

describe fertilisation

Answer 20

1. The sperm cell weaves past follicular cells and binds to the zona
   pellucida.
2. A rise in [Ca2+]i
   inside the sperm cell triggers the exocytosis of the
   acrosome (acrosomal reac/on) which contains hydroly/c
   enzymes.
3. Hydroly/c enzymes contained in the acrosomal cap are released.
   These enzymes locally dissolceolve the zona pellucida. The whiplike
   ac/on of the tail pushes the sperm head towards the oocyte
   membrane.
4. With the head of the sperm now on lying sideways, microvilli on
   the oocyte surround the sperm head. The two membranes fuse.
   The contents of the sprem-cell enter the oocyte; the sperm-cell
   membrane remains behind.
   A rise in [Ca2+]i
   inside the oocyte triggers the cor/cal reac/on, in
   which there is exocytosis of granules that previously lay
   immediately beneath the plasma membrane. The enzymes
   released lead to changes in the zona-pellucida proteins, causing
   the zona-pellucida to harden, preven/ng the entry of other
   sperm cells.
5. The rise in [Ca2+]i
   inside the oocyte induces the comple/on of the
   oocyte’s second meio/c division and the forma/on of the second
   polar body, which usually lies next to the first polar body.
6. The sperm head enlarges to become the male pronucleus.
7. The male and female pronuclei fuse.
   a. Sperm contributes its nuclear material and centrioles
   b. All other organelles are present in the oocyte cytoplasm
   c. Mitochondrial DNA inherited exclusively via maternal route

Question 21

how long does it take for the blastocyst to reach the uterine cavity

Answer 21

5 days

Question 22

when does hCG get secreted

Answer 22

from 9 days onwards

Question 23

what are totipotent cells

Answer 23

can form all the cell types in a body, plus
the extraembryonic, or placental, cells. Embryonic cells
within the first couple of cell divisions a^er fer/liza/on
are the only cells that are to/potent.

Question 24

what are pluripotent cells

Answer 24

can give rise to all of the cell types that
make up the body; embryonic stem cells are considered
pluripotent.

Question 25

what are multipotent cells

Answer 25

can develop into more than one cell
type, but are more limited than pluripotent cells; adult
stem cells and cord blood stem cells are considered
mul/potent.

Question 26

what does the trophoblast form

Answer 26

the placenta

inner cytotrophoblast and outer syncytiotrophoblast which invade the endometrium

Question 27

what is the cortical reaction

Answer 27

a rise in Ca inside the oocyte triggers exocytosis of granules that lay immediately beneath the plasma membrane
this leads to changes to the zona which hardens to prevent entry of sperm

Question 28

what triggers the completion of the oocytes second meiotic division

Answer 28

rise in Ca

Question 29

what forms the male pronucleus

Answer 29

the head of the sperm enlarging

Question 30

what surrounds the sperm head when it lies sideways against the oocyte

Answer 30

microvilli

this causes the two membranes to fuse

Question 31

when does implantation happen

Answer 31

day 7