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Overview of Fertilization Mechanisms
Sep 22, 2024
Notes on Fertilization Lecture
Introduction
Focus on fertilization after sperm ejaculation.
Follow the sperm to the egg in the female reproductive tract.
Egg Location
Egg is located in the
ampulla of the fallopian tube
.
The egg (secondary oocyte) is arrested in
metaphase II
before ovulation.
Surrounded by
granulosa cells
(Corona radiata).
Seminal Fluid Components
Seminal Vesicles
Contributes
60-70%
of seminal fluid.
Important components:
Fructose
: Energy source for sperm.
Prostaglandins
: Stimulate uterine contractions (retropulsion).
Coagulase
: Helps sperm latch onto vaginal walls.
Prostate Gland
Accounts for
30-40%
of seminal fluid.
Important components:
Citrate
: Energy source.
Prostate-specific antigen (PSA)
: Indicator for benign prostatic hyperplasia (BPH).
Sperm Structure
Head
: Contains nucleus with
23 chromosomes
and
acrosome
(hydrolytic enzymes).
Midpiece
: Contains mitochondria for ATP production.
Tail
: Flagellum (9+2 arrangement) enables movement.
Sperm Function in Female Reproductive Tract
Sperm movement facilitated by
alkaline fluid
; moves faster in alkaline.
Prostaglandins
cause uterine contractions, aiding sperm movement.
Coagulase
allows sperm to adhere within the vagina.
Fibrinolysin
helps release sperm after coagulation.
Capacitation
Process of sperm activation as it travels through the female tract.
Removes proteins and cholesterol, increasing motility (hypermotility).
Fertilization Process
Acrosomal Reaction
Binding
to
ZP3 receptors
on zona pellucida.
Calcium influx
triggers acrosome fusion, releasing enzymes (acrosin, proteases).
Enzymes break down zona pellucida for sperm penetration.
Fast Block to Polyspermy
Sodium ions
flow into the oocyte upon sperm binding, creating a positive charge that prevents additional sperm from binding.
Membrane Fusion
Alpha subunit
of sperm protein binds to oocyte membrane, leading to membrane fusion.
Nuclear material
from the sperm is released into the oocyte (ovum).
Slow Block to Polyspermy
Calcium influx activates
lysosomal enzymes
to degrade zona pellucida proteins and harden the membrane, blocking further sperm entry.
Completion of Meiosis
Calcium triggers the completion of
meiosis II
in the secondary oocyte.
Results in a definitive ovum and a polar body.
Formation of the Zygote
Fusion of male and female pronuclei results in a
zygote
(2N).
Conception has occurred, marking the start of embryonic development.
Conclusion
Summary of the fertilization process, emphasizing the intricate mechanisms involved.
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