Coitus, fertilisation and pre-implantation

Question 1

What are the 4 phases in the human sexual response?

Answer 1

• EPOR
• Excitement sexual arousal - psychological and physical stimulation of erogenous zones. Tumescence and erection of penis and clitoris, engorgement of female tract
• Plateau intensification of arousal
• Orgasm series of involuntary muscular contractions in both sexes with intense pleasurable sensations
• Resolution - detumescence and time during which re-arousal is impossible (may not be true of women)

Question 2

What is the parasympathetic system predominantely associated with?

Answer 2

Erection

Question 3

What is the sympathetic system predominantely associated with?

Answer 3

Ejaculation

Question 4

How long is sperm viable for?

Answer 4

24 - 72 hours

Question 5

How long are oocytes viable for?

Answer 5

12 - 24 hours

Question 6

For fertilisation to occur when does coitus need to happen?

Answer 6

No more than 3 days befpre ovulation and no more than 1 day after

Question 7

In what trimester do most miscarriages occur?

Answer 7

1st 1 - 12 weeks

Question 8

When in pregnancy is there a 50% survival rate?

Answer 8

24 weeks (2nd trimester)

Question 9

At what week does pregnancy usually occur?

Answer 9

40th

Question 10

What percentage of unprotected intercourse results in development to the blastocyst stage?

Answer 10

20%

Question 11

WHat percentage of blastocysts fail to implant?

Answer 11

8 - 20%

Question 12

What percentage of human conceptions actually survive to a successful birth roughly?

Answer 12

~ 15 - 20% (possibly less)

Question 13

When does the embryonic period occur?

Answer 13

First 8 weeks

Question 14

When does the foetal period occur?

Answer 14

8 - 40 weeks

Question 15

What does the embryonic period include?

Answer 15

• Preimplantation embryo
• Implantation
• Differentiation and development of the organ systems

Question 16

What are the hair-like projections called that draw the oocyte into the fallopian tubes?

Answer 16

Fimbriae

Question 17

What structures beat the egg towards the interior of the duct?

Answer 17

Cilia

Question 18

Movement through the uterus and fallopian tubes is via what?

Answer 18

• Sperm’s own propulsions and uterine contractions

Question 19

What is passage of sperm intocervix dependant on?

Answer 19

Oestrogen-induced changes in mucus consistency

Question 20

What causes many sperm to die from vagina to fallopian tubes?

Answer 20

100 - 200 million dies due to:

• Acidic vaginal environment
• Length and energy requirements of trip

Question 21

What do femal tract secretions cause in sperm for them to be capable of fertilisation?

Answer 21

• Change from wavelike beats of sperm tail to whip-like action to propel sperm forward
• Sperm’s plasma membrane is altered so it is capable of fusing with surface membrane of egg (acrosome reaction)

Question 22

What is capacitation and what does it include?

Answer 22

Capacitation destabilises the sperm surface membrane to enhance fusion with oocyte

• Increase in Ca2+ permeability - rise in intracellular Ca2+
• Removal of membrane proteins (glycoproteins)
• Change in surface charge
• Depletion of cholesterol

Question 23

Where does fertilisation usually occur?

Answer 23

The ampulla of the uterine tube

Question 24

When does fertilsation usually occur?

Answer 24

Few hours after ovulation and within 24 - 48 hours of ovulation

Question 25

What prevents other sperm from fertilising the egg?

Answer 25

Space between plasma membrane and glycoprotein/zona pelucida change in composition creates insulating layer

Question 26

What is the front part of the head of the sperm called?

Answer 26

Acrosome

Question 27

What does the increase in Ca2+ from the sperm to egg cause?

Answer 27

- Fusion of corticol vesicles in egg which move towards the zona pellucida generating increase in space in viteline envelope creating insulating protective layer

Question 28

Describe the acrosome reaction

Answer 28

- Induced by sperm head contacting the zona pellucida and binding to glycoproteins ZP2 and ZP3 - Releases contents of acrosome which causes entry of more CA2+ - Sperm then digests a path through the zona pellucida (proteolytic enzymes)

Question 29

When does ovulatgion occur in relation to the LH peak?

Answer 29

1 day after

Question 30

How many days after the LH peak does implantation occur?

Answer 30

6 - 7 days after

Question 31

What rescues the corpus luteum?

Answer 31

Human chorionic gonadotropin (hCG) from implanted blastocyt (trophoblast) rescues corpus luteum (occurs 9 - 10 days after LH peak)

Question 32

What hormone maintains contraction of smooth muscle near where fallopina tubes enter the wall of the uterus?

Answer 32

Oestrogen

Question 33

What is the size of the morula in comparison with the original fertilised egg?

Answer 33

the same

Question 34

When does progesterone rise after fertilisation and what does it cause?

Answer 34

Plasma progesterone levels rise 3 - 4 days after fertilisation, smooth muscle relaxes and conceptus is allowed to pass into the uterus

Question 35

When do cavities develop between cells?

Answer 35

4 - 5 days after fertilisation

Question 36

For how long does the conceptus/blastocyst lie free in the uterine cavity?

Answer 36

Approx 3 days

Question 37

What do trophoblasts give rise to?

Answer 37

The placenta

Question 38

What does the trophoblast differentiate into?

Answer 38

- Inner cytotrophoblast | - Outer synctiotrophoblast (loses cell boundaries)

Question 39

What cells invade the endometrium?

Answer 39

Fingers of syncytiotrophoblast