Fertilisation and Pre-Implantation Development Flashcards
How, mechanistically, does LH surge cause ovulation?
- Changes gene expression in follicle
- Allows Cumulus-oocyte complex to penetrate the follicle
Describe the four layers (superficial to deep) of the overlying structures of the shaft of the penis
- Skin
- Smooth muscles (continuous w/ dartos [which does what?])
- Loose connective tissue (allows movement)
- Elastic tissue around the corpora (allows for changes in size)
Describe the venous drainage of the penis
- Superficial and deep dorsal veins drain
Describe the physiological mechanism of erection
- First, arousing stimuli (mechanical or pyschological)
- Increased parasympathetic nerve supply through pelvis (physiological sigh -> Huberman 6x girlfriends)
- Nitric oxide release relaxes smooth muscle of penile arteries
- Blood flows into lacunae of corpora cavernosum/spongiosum, filling tissue (venous outflow also reduced)
Orgasm vs ejaculation
- Orgasm: psychological sensation
- Ejaculation: release of semen (incl. muscle contractions of epididymis, vas deferens, ischiocavernosus/bulbospongiosus)
True or false: in a primordial follicle, follicular cells produce oestrogen and progesterone (although more of the former)
- False
- They produce oestrogen pre-ovulation (how?) and progesterone + estrogen post-ovulation, from the corpus luteum
How does ovulation affect cervical mucus?
- Pre-ovulation: white, thick
- Ovulation: clear-slippery, can nourish sperm (white, thick stuff is replaced by the real deal)
Where does sperm capacitation occur (how to remember this)? What happens there?
- Happens in isthmus of fallopian tube (makes sense; narrowing = maturation)
- Sperm becomes hyperactive, and prepare for acrosome reaction, helping to push through follicular cells and melting through the zona pellucida
How do oocytes prevent polyspermy?
- Cortical granules release Ca2+, hardening zona pellucida
- Na+ depolarisation electrically repels the losers
Describe pre-implantation development of the embryo
- First, a zygote genome forms. There is very little epigenetic modifications on these cells, so we have a full, pluripotent genome
- Then, the cells begin to divide within the zona pellucida, until we have a morula (=berry), where it’s a compact ball of cells that we can’t differentiate
- Then, a fluid-filled cavity forms in the centre, and we have trophoectoderm cells (~placenta) and an inner cell mass (~fetus); this is called a blastocyst (hole = blastocoel)
- Blastocyst hatches from the zona pellucida
Describe the three phases of implantation
- Apposition: embryo comes into contact with endometrium
- Adhesion: trophoblast cells anchor embryo to endometrial epithelium
- Invasion: syncytiotrophoblast cells burrow into the endometrium, anchoring the blastocyst
Describe two ways of assessing pregnancy status (earlier and later)
Earlier: blood (11 days)/urine (12-14 days) hCG test
Later: transvaginal ultrasound to detect fetal heartbeat
How does the dominant follicle have a superior LTV:CAC, and how does this make them dominant
- As a follicle gets bigger, it grows more granulosa cells
- This increases the levels of oestrogen and inhibin
- The inhibin starves the environment of FSH (higher CAC)
- But the dominant follicle has more upsells (less dependent on FSH, denser receptor expression), so it can still survive while others die (higher LTV:CAC)
