Reproduction Flashcards
Cumulus cells
create an intracellular junction with the oocyte cell membrane. And they penetrate the zona pellucida
Which species has the largest sperm cells?
Drosophilla (fruit fly)
The spermatozoon are divided into 3 bits:
the head, mid piece and the tail
Sperm can be prevented from reaching the ova from
the vaginal area (acidic env/ leaking out), the cervix, and the fallopian tube
Fertilisation involves a number of selective barriers
- swim from vagina to oviduct
- penetrate the cumulus layer
- bind to and penetrate zona pellucida
- bind to and fuse with the plasma membrane
Three stages of fertilisation include
- Sperm preparation
- Sperm binding and fusion
- cortical reaction
Capacitation
- takes place in the oviduct
- mature sperm need to acquire capacity to fertilise
- lose cholesterol, phospholipids, and glycoproteins on surface
- sperm becomes less stable
Acrosome reaction
is the fustion of sperm plasma membrane and outer acrosomal membrane- creates pores
- this is induced by progesterone
- enzymes are released
- exposes acrosin
- exposes surface molecules for sperm binding
Sequence of events in fertilisation
- hyaluronidase from sperm breaks down hyaluronic matrix between cumulus cells (aided by whiplash movements)
- acrosome reaction occurs in cumulus cells
- sperm binds to zona pellucida
- …
Immediately after the sperm fuses with oolemma…
the tail stops beating
The microvilli on the oocyte plasma membrane…
engulf the sperm, starting at the equatorial segment
Swelling (fertilisation cone)
forms ….
Cortical reaction…
cortical granules fuse with the plasma membrane. Contents released into perivitelline space
Polyspermy is blocked via
Zona reaction - zp2 cleaved, oligosaccharides removed from ZP3) - this is a slow block
Membrane block- Juno receptor is gradually shed from the plasma membrane so other sperm cannot bind
Sperm contribution to the zygote
in most mammals, whole sperm enters oocyte, sperm mitochondria are destroyed,
Formation of zygote
In the pronucleate zygote, there is a male pronucleus (which forms once the sperm enters the oocyte) and a female pronucleus,
The zona pellucida does not need to be removed
before fertilisation
Cleavage is
a series of rapid cell divisions without cell growth
divisions are reductive - form a blastomeres
Blastomeres are
totipotent- the ability to form the placenta is a defining feature of totipotent cells
Cleavage timings differ between species
mouse have a gestation period of 19-20 days. Humans take 270-290 days.
Compaction and polarisation occurs at
the 8-cell stage. Spherical cells become flattened, E-cadehrin and B- cadherin are essential. Embryo becomes a closely bonded single entity.
Polarisation includes
forming a apical surface (microvilli), apical region (organelles), inner basal region (nucleus), and tight junctions form.
How is the blastocyst formed?
energy dependant pump system, Na+ pumped into blastocyst cavity, water is drawn into cavity by osmosis, cavity expands.
the blastocyst hatches from the zona pellucida 1-2 days after cleavage.
