Transcript Female hormones to Fertilization 2016

Fertilization in animals can be
internal or external
Fertilization is the fusion of egg & sperm to form a
zygote (1 celled organism)
What type of organisms
would do each type?
Pros and Cons of each
type?
Human Egg Surrounded by Sperm
Fertilization involves mechanisms that prevent polyspermy
Cortical granules
11.4 Process of Fertilization
Step 1: Capacitation
• Wearing down of the
membrane surrounding
the sperm head.
• It becomes fragile as
the sperm travel
through cervical
mucus, uterus, &
oviducts in search of
• Requires about 6 to 8 hours
the egg.
11.4 Process of Fertilization
Step 2: Acrosome Reaction
• Release of acrosome enzymes
• Enzymes digest through surrounding follicle
cells and zona pellucida
• Success is the result
of hundreds of
sperm acrosomes
rupturing
11.4 Process of Fertilization
Step 3: Fusion of sperm head
• Sperm membrane fuses with plasma membrane of
the egg. Triggers fast block
• Opening of Na+ channels causing Na+ to flow into
egg depolarizing
the membrane.
• Prevents other
sperm from
fusing with
membrane.
• Occurs 1-3 sec after fusion
11.4 Process of Fertilization
Step 4: Cortical reaction
• E.R. releases Ca2+ into cytoplasm at site of sperm entry.
High Ca2+ concentration triggers cortical granule to
fuse with plasma membrane & release contents
• Enzymes digest binding proteins so no other sperm can
bind.
• granule cause the vitelline layer to separate from the
plasma membrane & water enters perivitelline space
• Vitelline membrane hardens preventing other sperm
from entering
• Return of normal voltage across egg plasma membrane
11.4 Process of Fertilization
Step 4: Cortical reaction
11.4 Process of Fertilization
Step 5: Meiosis of egg completed
• Ca2+ influx triggers
Step 6: Swelling of sperm & egg nucleus
• occurs about 20 minutes
after entry
• Contents merge creating
diploid nucleus
• Now called zygote
• “in vitro” means ‘in glass’ (i.e. a test tube).
• Can be used for women whose oviducts are blocked.
Photos taken from whereivf-fertilization.com
Procedure:
1. Hormone (FSH) is given
to increase development of
follicles so a larger
number can be harvested.
2. Ova are surgically
removed from Graffian
follicles prior to ovulation
3. Sperm are harvested from
the male
4. Fertilization and first few cell divisions
occur outside of the body in a petri dish or
test tube.
5. After about 5days (when the embryo has
reached the blastocyst stage) the embryo is
placed into the uterus and allowed to
implant.
6. Embryos can also be
frozen for later use if
the first attempt is
unsuccessful.
http://www.dreamstime.com/stock-image-vitro-fertilizationimage13398841
www.mountnittany.org
Click to see a National Geographic video of IVF
click here to go PBS.org to read
several articles on IVF
Click here for a news
interview on how embryos
are chosen
Read the following articles:
• Introduction to test tube babies
• Pros and Cons of IVF
• In vitro fertilization today
• Ethical Questions
Who owns the embryo - the ‘donors’ or the
laboratory?
Is it appropriate to “sell” ova or sperm to other
couples for the IVF process?
If ‘donor’ ova and/or sperm are used, who are the
legal parents?
What is to be done with frozen embryos that are no
longer needed?
From ZYGOTE to BLASTOCYST
The Beginning:
• Ovum is
fertilized in
the oviduct.
• The resulting
cell is called a
zygote
• 1st cleavage occurs
within 36 hours
resulting in 2 identical
cells.
• Zygote continues
movement along oviduct
and 2nd cleavage occurs
with in the next 36
hours resulting in 4
identical cells.
Two Cell Stage
Eight Cell Stage
Morula - Cluster of Cells
• Cleavage continues rapidly,
resulting in a solid ball of
cells. A hollow fluid filled
area develops inside this
ball of cells creating a
blastocyst.
• The blastocyst will implant
in the endometrium of the
uterine lining at
approximately day 5 or 8.
(it now has between 50 and
100 cells)
• This is essential for
pregnancy to continue.
Human development before implantation.
Upon Implantation:
Hormone action
• Embryo secretes a hormone that sends a signal
to mother’s reproductive system.
• This hormone is HCG.
(Human Chorionic Gonadotropin)
• Its function is to maintain the secretion of
progesterone and estrogen by the ovary.
• HCG can be detected in mother’s urine to
determine positive pregnancy test.
Effect of high level of Progesterone:
Protective mucus plug formed in the
cervix
Growth of the placenta
Enlargement of uterus
Ovulation and menstruation stopped
Enlargement and sensitivity of breasts.