BIOL 2020U Lecture Notes - Ovulation, Clomifene, Erectile Tissue

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29 Jan 2013
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Structure of the Egg
0.1mm (100um) in diameter. Sperm's head is only 2.5um across
Haploid nucleus is surrounded by cytoplasm / with enzymes and organelles
Yolk droplets contain proteins and lipids
Outside plasma membrane is a glycoprotein coat called a jelly coat
Acrosome Reaction and Penetration of the Oocyte
Membrane
Acrosome reaction
o Contact of jelly coat and sperm
o Triggers Ca2+ to enter membrane of sperm
o Causes acrosome to burst / releases enzymes / digest jelly coat
// enzymes: hyluronidase + acrosin
o Sperm filament attaches to receptor on vitelline membrane
o Sperm and egg plasma membranes fuse
o Sperm nucleus enters egg, tail and middle piece remain outside
Depolarisation of membrane / blocks entry of more sperm
2° oocyte undergoes 2nd division of meiosis / produces ovum + second polar body
Nuclei (ovum + sperm) fuse forming a zygote
Female Infertility
Pituitary gland fails to produce FSH and prevents ovulation
o TREATMENT: Injections of FSH
o SIDE EFFECTS: May produce several eggs at the same time (→twins)
Too much oestrogen is secreted which inhibits FSH secretion
o TREATMENT: non-steroidal drugs (e.g. clomiphene) which oppose action of
oestrogen
Male Infertility
Semen contain too few sperm
o TREATMENT: natural/synthetic androgens such as testosterone
// Viagra (sildenafil) is an enzyme inhibitor → causes smooth muscle surrounding erectile
tissue to relax → more blood can be pumped into them during erection process
In Vitro Fertilisation (IVF)
FSH is injected in woman
Just before ovulation eggs are collected and matured
Fertilisation → collected sperm sample is added to collected mature egg
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