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Biology of Reproduction, Gamete Interaction
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text: Human Reproductive Biology 2nd Edition
- R.E. Jones: Read pages 161-181 for this lecture
XIX. Gamete Interaction back to XVIII. Fertilization Systems
A. Sperm competition
B. One spermatozoon fertilizes
1. after capacitation and activation
2. Hyaluronic Acid
a. cements together cells of the Cumulus Oophorus
i. sperm must penetrate between these cemented cells
(1) Acrosome Reaction necessary for this
3. Acrosome Reaction
a. sperm plasma membrane and outer acrosomal membrane
fuse at distinct points
i. now called composite membrane
b. openings formed in composite membrane
c. enzymes are released through these openings
i. hyaluronidase
d. hyaluronidase dissolves the hyaluronic acid cement
and allows the activated sperm through
e. shedding of the composite membrane
f. Corona penetrating enzyme also in acrosome
g. Inner acrosomal membrane attaches to Zona Pellucida
i. protein receptors on zona pellucida
for inner acrosomal membrane
h. Other enzymes from acrosome left on the outer margin
of inner acrosomal membrane
i. Acrosin
(1) protease that digests
part of the zona pellucida
ii. Neuramidase
(1) dissolves Neuramininc acid a component
of the zona pellucida
i. inner acrosomal membrane fuses with the
Vitelline Membrane
(1) Cortical Vesicles:
contain Cortical Granules
j. an opening forms at the point of fusion
k. Chromosomes and Centriole enter into Ooplasm
l. Cortical Granules expelled into the Perivitelline Space
i. membranes of cortical vesicles and vitelline
membrane fuse releasing granules
m. Cortical Granules contain:
i. factors which chemically/structurally change zona
pellucida to block sperm penetration
ii. acrosin inhibitor
iii. cortical granule protease
(1) keeps inner acrosomal membrane from binding
to vitelline membrane
iv. i-iii prevent multiple fertilizations
= polyspermy
C. Ovum Activation
1. Sperm penetration causes Ovum Activation
2. Ends 2nd Meiotic Arrest
3. 2nd polar body formed
a. 2o Oocyte ® Ootid + Polar Body
D. Nuclear Membranes Dissolve
1. Sperm + Ootid
2. ® Pronuclei
E. Fusion of Pronuclei = Conception
1. ® Zygote (2N)
2. 12 h from Ovum Activation to fusion of Pronuclei
a. all happens in the fallopian tubes
b. mitosis begins immediately