Coitus, fertilisation and pre-implantation Flashcards
What are the 4 phases in the human sexual response?
- 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)
What is the parasympathetic system predominantely associated with?
Erection
What is the sympathetic system predominantely associated with?
Ejaculation
How long is sperm viable for?
24 - 72 hours
How long are oocytes viable for?
12 - 24 hours
For fertilisation to occur when does coitus need to happen?
No more than 3 days befpre ovulation and no more than 1 day after
In what trimester do most miscarriages occur?
1st 1 - 12 weeks
When in pregnancy is there a 50% survival rate?
24 weeks (2nd trimester)
At what week does pregnancy usually occur?
40th
What percentage of unprotected intercourse results in development to the blastocyst stage?
20%
WHat percentage of blastocysts fail to implant?
8 - 20%
What percentage of human conceptions actually survive to a successful birth roughly?
~ 15 - 20% (possibly less)
When does the embryonic period occur?
First 8 weeks
When does the foetal period occur?
8 - 40 weeks
What does the embryonic period include?
- Preimplantation embryo
- Implantation
- Differentiation and development of the organ systems
What are the hair-like projections called that draw the oocyte into the fallopian tubes?
Fimbriae
What structures beat the egg towards the interior of the duct?
Cilia
Movement through the uterus and fallopian tubes is via what?
- Sperm’s own propulsions and uterine contractions
What is passage of sperm intocervix dependant on?
Oestrogen-induced changes in mucus consistency
What causes many sperm to die from vagina to fallopian tubes?
100 - 200 million dies due to:
- Acidic vaginal environment
- Length and energy requirements of trip
What do femal tract secretions cause in sperm for them to be capable of fertilisation?
- 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)
What is capacitation and what does it include?
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
Where does fertilisation usually occur?
The ampulla of the uterine tube
When does fertilsation usually occur?
Few hours after ovulation and within 24 - 48 hours of ovulation
What prevents other sperm from fertilising the egg?
Space between plasma membrane and glycoprotein/zona pelucida change in composition creates insulating layer
What is the front part of the head of the sperm called?
Acrosome
What does the increase in Ca2+ from the sperm to egg cause?
- Fusion of corticol vesicles in egg which move towards the zona pellucida generating increase in space in viteline envelope creating insulating protective layer
Describe the acrosome reaction
- 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)
When does ovulatgion occur in relation to the LH peak?
1 day after
How many days after the LH peak does implantation occur?
6 - 7 days after
What rescues the corpus luteum?
Human chorionic gonadotropin (hCG) from implanted blastocyt (trophoblast) rescues corpus luteum (occurs 9 - 10 days after LH peak)
What hormone maintains contraction of smooth muscle near where fallopina tubes enter the wall of the uterus?
Oestrogen
What is the size of the morula in comparison with the original fertilised egg?
the same
When does progesterone rise after fertilisation and what does it cause?
Plasma progesterone levels rise 3 - 4 days after fertilisation, smooth muscle relaxes and conceptus is allowed to pass into the uterus
When do cavities develop between cells?
4 - 5 days after fertilisation
For how long does the conceptus/blastocyst lie free in the uterine cavity?
Approx 3 days
What do trophoblasts give rise to?
The placenta
What does the trophoblast differentiate into?
- Inner cytotrophoblast
- Outer synctiotrophoblast (loses cell boundaries)
What cells invade the endometrium?
Fingers of syncytiotrophoblast
