Transcript From Fertilization to Development

Fertilization, Development
and Birth
G.Burgess 2010.
http://www.accessexcellence.org/AB/GG/blastocyst.html: Accessed Dec.4, 2001.
Fertilization
• completion of meiosis and the
development of a viable organism
• Ova and sperm on their own are not
able to live.
• Successful fertilization requires that no
more than one sperm fuses with an
egg
• Fertilization by more than one sperm is
polyspermy and almost always leads
to early death of the embryo.
Spermatozoa
Structure of Spermatozoa
• Acrosomal cap: encloses and protects DNA, also
contains hydrolytic enzymes to break through
zona pelludica of ovum.
• Mitochondria: used to generate ATP to move
flagellum
• Flagellum: propel spermatozoa through fluids
• Seman: composed of sperm and protective/ nutrient
fluids.
– Nutrient fluid from seminal vesicle
– Protective fluids
– prostate adds base fluid to protect sperm from
acids in vaginal canal
– Cowper’s gland adds base fluid to protect sperm
from acids in urethra
Release of Spermatozoa
• Path: epididymis, vas deferens, seminal
vesicle, prostate, Cowper’s gland,
urethra, vaginal canal, fallopian tube,
ovum
• Fluids in vaginal canal flow out,
preventing deformed/weak sperm from
entering fallopian tube
Capacitation
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The changing and activation of the
sperm
Makes sperm swim when released
into the female reproductive track
destabilizes the sperm’s membrane to
prepare for the acrosomal reaction
Factors for Successful
Fertilization
• mobility (constant propulsive force from
the sperm’s tail)
• zona-digesting enzymes
Stopping Polyspermy
• Polyspermy is the entrance of more
than one sperm into the ova during
fertilization.
– Cortical Reaction
Conception
Fertilization
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Fertilized Ovum: Zygote (2n)
Single cell
Ovulated ova are inactive (they have stopped maturing)
Entry of sperm causes;
– Completion of meiosis
• Acrosomal reaction: The entering of a sperm activates
the ova by releasing Nitric Oxide into the egg.
• Cortical reaction: causes a thickening of the membrane
around the ovum so that no other sperm may enter the
cell.
• Egg Activation: Activate DNA (combining of male and
female DNA) and beginning of metabolism
• Development activation: beginning of cell division
(cleavage)
Development:
• Cell division: mitosis (no growth in beginning/
only duplication of DNA/ cellular organelles/ and
cleavage)
– Type cleavage is determined by quantity of yolk:
ie.
• Humans & sea urchins have little yolk; do
symmetrical radial cleavage (form cells of equal
size)
• Chickens; cleavage is asymmetrical. (cells are of
different sizes)
– Human Zygote divides to 64 blastomeres(cells):
called a morula (single mass of cells)
• All cells are undifferentiated
• Twinning may occur during this time
Blastulation:
• Cells are cleaving, no growth
• Formation of Blastula
– a hollow ball (hollow area is called a
blastocoel).
Gastrulation (Gastrula)
• Formation of the primitive gut
• Develop; endo/ ecto and meso -derm
– Endoderm: inside layer
• Forms digestive tract
• Makes tissues of back of mouth, pharynx, esophagus, stomach,
and intestine
– Ectoderm: outside layer
• Forms skin
• Nails/hair/epidermis/ears, sweat glands, sensory cells
• Spinal cord/ nervous system
– Mesoderm: middle layer
• Forms: muscle/fat/ligaments/ bone
• Cells are beginning to differentiate
– Identified for individual tasks.
Neurulation:
• Cells of animal pole fold and pinch
inward forming a tube of cells that
stretches the length of the embryo
forming a neurula
– Development of spine and nervous system
– Determines head / thoracic cavity/
abdomen
– Determines segmentation
Pregnancy
• 280 days from time of first day of last
menstrual cycle.
• Blastocyst implants in endometrium and
begins formation of placental tissues
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Amnion:
Chorion:
Allantois:
Placenta:
• Endometrium: developed by mother’s tissue
• Chorionic villi: developed by embryonic tissue