Fertilisation Flashcards
What is the mammalian egg structure?
Corona radiata = layer of follicle cells
Zona pellucida = extracellular matrix containing glycoproteins. Protects the egg and has a role in fertilisation
Vitelline membrane = cell membrane that surrounds the ooplasm
Ooplasm = contains cytoplasm nutrients and control elements for early embryo
Germinal vesicle = nucleus containing DNA
What is the mammalian sperm structure
Head = contains nucleus with sperm DNA, capped with acrosome
Acrosome = contains enzymes to penetrate egg membrane
Neck = contains centriole
Centriole = important for tail formation and movement, also important for embryo development
Midpiece = contains mitochondria to provide energy for movement (spiral around the mid piece)
Tail = drives sperm forwards
How does sperm penetrate the ovum?
Uses vigorous motility to burrow through the corona radiata
Sperm undergoes acrosomal reaction to dissolve through zone pellucida
Sperm plasma membrane exposed
Recognition proteins on the egg recognise sperm proteins
Sperm and ooctye plasma membrane fuse via attachment proteins
Sperm nucleus and other sperm components enter the ovum
DNA combines to form zygote
Plasma membrane changes structure and ZP blocks any polyspermy rapidly after fusion of DNA
What are the challenges for sperm as they go through the female reproductive tract?
Sperm enters through vagina which is highly acidic and kills any sperm not protected by seminiferous fluid
Sperm have to swim through cervix which is only open for a few days
Many sperm killed in cervical fluid or get lost/stuck in cervical walls
Sperm then have to choose which fallopian tube to swim through
Cilia in fallopian tube are wafting the egg in the opposite direction the sperm are swimming so they have to swim against a current
How many sperm make it to the egg?
30-40 sperm out of ~300,000,000
