Coitus, fertilisation & preimplantation Flashcards
Identify the main phases of human sexual response.
4 phases - EPOR model
1) Excitement sexual arousal: psychological and physical stimulation of erogenous zones. Tumesence and erection of penis and clitoris, engorgement of female tract
• Parasympathetic -erection
• Sympathetic -ejaculation
2) Plateau intensification of arousal
3) Orgasm series of involuntary muscular contractions in both sexes with intense pleasurable sensations
4) Resolution detumescence and time during which re-arousal is impossible (may not be true of women)
Which of the uterine/ovarian cycles is fixed ? Which is variable ? How does this affect day of ovulation, and the length of the entire cycle ?
- Length of the luteal phase is fixed at approximately 14 days (pretty much regardless of length of total cycle)
- Follicular phase varies
- Menstrual phase varies
This means that the whole cycle is variable, may be 25, 28, 35 days etc. The day of ovulation also changes (e.g. may be on day 11, 14, 21).
How long are sperm viable for ? Oocytes ? How does this affect fertilisation ?
• Sperm are viable for 24 – 72 hours
• Oocytes are viable for 12 – 24 hours
For fertilisation to occur, coitus must occur no more than 3 days before ovulation (since sperm can survive 3 days) and no more than 1 day after (since occytes can survive one day).
Other guidelines say:
• Sperm are viable for 4-6 days
• Oocytes are viable for 24-48 hours
so for fertilisation to occur, sperm introduction should be between 5 days before and one day after ovulation.
Is control of development of the fetus maternal, or fetal ?
Initially, maternal. After fertilisation, control of development will switch from maternal to foetal (the embryo must communicate with the mother to convert her whole physiology from a cyclic state to a pregnant one)
State the trimesters of pregnancy.
- First Trimester weeks 1 -12
- Second Trimester weeks 13 – 28
- Third Trimester weeks 29 – 40
At which stage of pregnancy do most miscarriages occur ?
• First Trimester weeks 1 -12, most miscarriages occur
At 24 weeks, what is the survival rate for early prematurity ?
• At 24 weeks 50% survival rate for early prematurity.
When does parturition typically occur ?
Parturition at about 40 weeks from LMP
What proportion of all pregnancies miscarry ?
10-15 % of all pregnancies miscarry
For couple:
– using no contraception
– trained to detect 6 most fertile days around ovulation
How many will be pregnant after two cycles ? How many will be pregnant by 6 months ? How many will be pregnant after 1 year ? How many will be subfertile ?
For couple:
– using no contraception
– trained to detect 6 most fertile days around ovulation
- 50% pregnant after 2 cycles
- 85% pregnant after 6 months
- Half the remaining couples were pregnant after 1 year
- Leaves ~5 % subfertile
What proportion of unprotected intercourse results in development to the blastocyst stage ? What about IVF ?
Only 20 % of unprotected intercourse results in development to the blastocyst stage (Similar success rate for IVF)
What are causes of failure of unprotected intercourse in resulting in a normal birth ?
- Pre-implantation and post-implantation failure occurs frequently - spontaneous abortion
- Blastocysts fail to implant
What proportion of blastocysts will fail to implant ?
• 8-20% of blastocysts fail to implant
What proportion of clinically detected pregnancies will fail in the first 12 weeks (ie in 1st trimester) ?
Clinically detected pregnancies 15 – 20 % will fail in the first 12 weeks (ie in 1st trimester)
What proportion of human conceptions survive to successful birth ?
• Possible that less that 15 – 20% of human conceptions survive to successful birth
Define embryonic period.
• Embryonic period – 8 weeks (1 to 8)
- Preimplantation embryo (fertilised developing embryo which has not implanted yet)
- Implantation
- Differentiation and development of the organ systems
Define feteal period.
• Foetal period 8 – 40 weeks
- Differentiation continues
- Growth
What is the clinical significance of the embryonic period ?
Mother may not know that she is pregnant during this sensitive period.
– She may not avoid harmful influences that may affect the development of the embryo (alcohol, tobacco, prescription drugs).
Describe the events of the ovum immediately following ovulation.
At ovulation:
• Egg extruded onto surface of ovary.
• Smooth muscle of fimbriae cause them to pass over ovary while cilia beat in waves toward interior of Fallopian tube.
Describe the physiological events occurring following ejaculation in coitus.
• Ejaculation deposits semen into vagina then move down into cervix.
• Passage into cervical mucus dependent on oestrogen-induced changes in mucus consistency (to allow sperm to move through it)
• Sperm can reach uterus minutes/hours after ejaculation.
– But can survive 1-2 days within cervical mucus before release to enter uterus.
• Movement through uterus and fallopian tubes is via sperm’s own propulsions (activity of tail) AND smooth muscle uterine contractions.
How many sperm die from the vagina to the Fallopian tubes ? Why ?
• Sperm mortality from vagina to fallopian tubes is large.
– Several hundred million to 100-200 (reason for large number of sperm in ejaculate)
Because:
• Vaginal environment is acidic.
• Length and energy requirements of trip.
Define capacitation.
the process in which the spermatozoon, after it reaches the ampulla of the fallopian tube, undergoes a series of changes that lead to its ability to fertilize an ovum.
Describe the process of capacitation.
• Action of female tract secretions on sperm over several (6-8) hours.
– Essential for them to be capable of fertilisation
• Causes:
– 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).
• Capacitation destabilises the sperm surface membrane to enhance fusion with oocyte
- Increase in Ca2+ permeability - rise in intracellular Ca2+
- Removal of membrane proteins (glycoprotein)
- Change in surface charge
- Depletion of cholesterol
Where does fertilisation usually occur ?
• Normally occurs in ampulla of the uterine tube.