Download Trimester

Fertilization and Development
Be 21 - Be 30
Cruz, Canlas, Daroya, Estabaya,
Hubilla, Jimenez, Patubo,
Ramirez, Regala, Tuppil
Theories…
• Preformation –
sperm already
has all the organs
even before
fertilization
• Epigenesis –
animal develops
from a shapeless
egg
Fertilization
How in the world does it occur??!!
Fertilization
• Conception (start of gestation – carrying of
offspring in womb)
• Joining of egg and sperm (zygote)
• Sperm Capacitation
• Acrosomal Reaction
• Cortical Reaction
Sea Urchins
• External fertilization
• Sperm Capacitation – display
hyperactivated motility
• Prepares sperm for Acrosomal reaction
Sea urchins
• Acrosome – vesicle at the tip of sperm;
releases contents by exocytosis
• Acrosomal reaction – release of hydrolytic
enzymes
• Acrosomal Process – elongated structure
that penetrates jelly coat of egg
• Has proteins that adhere to vitelline layer (has
protein receptors) of egg
Sea Urchins
Fast Block to Polyspermy
• Spem and egg membranes fuse
• Neuron-like electrical response from
plasma membrane of egg
• Sodium ions flow into the egg
– Membrane potential
• Depolarization
Cortical Reaction
•
•
•
•
Changes in cortex of egg (outer part)
Egg’s ER releases Ca2+ into cytosol
High concentration of Calcium ions
Cortical granules fuse with plasma
membrane
– Content released in perivitelline layer (osmotic
gradient)
• Fertilization membrane – hardened
vitelline layer (slow block to polyspermy)
Sea Urchins
Fertilization in Mammals
• Egg cloaked in follicle cells
• Zona Pellucida – like jelly coat in sea
urchins
• Has protein receptors (ZP3) for sperm head
• Sperm releases acrosome by exocytosis
and fuse membrane with egg
• Depolarization – fast block to polyspermy
• Cortical reaction – hardens zona pellucida
Fertilization in Mammals
Fertilization in Mammals
Fertilization in Mammals
• Unlike sea urchin, sperm and egg nucleus
don’t fuse immediately
• Envelopes of both nuclei disperse
• Chromosomes from two gametes share
common spindle apparatus during first
mitotic division
After fertilization….
PREGNANCY??!!
During Pregnancy…
• Mother’s organs get squished
• Heart and lungs work harder to support
both mother and baby
• Stomach rotated about 45 degrees so can
only hold small amounts of food
• Baby needs food
First Trimester
• Cleavage(after 36 hours)- series of mitotic
divisions
• Embryo from this point until after nine weeks
• Organogenesis (formation of organs)
• Blastocyst(after 5 days)- fluid-filled
• Trophoblast- outer layer of cells (membrane systems)
• Inner cell mass- inner cells (embryo and fetus)
• Implantation in the endometrium (lining of
uterus)
• Trimester – in three parts
First Trimester
• 4 weeks – stop of menstrual period
• 5 weeks – beating heart; working placenta
and umbilical cord
• Waste and nutrient transfer
• Human chorionic gonadotropin- hormone checked
in pregnancy test and to detect fetal disorders
• 7 weeks – own blood cells; start moving
First Trimester
• 9 weeks – Fetus (until birth)
• 9 weeks – all organ, muscle and nerves
are in place and functioning
• 10 weeks – fingers and toes
• 11 weeks – functioning liver, kidneys,
intestines, brain and lungs
• 12 weeks – vocal chords, brain, pain,
urine, thumb sucking
Second Trimester
•
•
•
•
•
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13 weeks – fingerprints
14 weeks – first hair
15 weeks – taste
16 weeks – grasp, kick, somersault
18 weeks – genitals
20 weeks – hear and recognize mom’s
voice
Second Trimester
• 22 weeks – hear, fingernails
• 26 weeks – touch
Third Trimester
• 27 weeks – open eyes
• 31 weeks – preference in music
• 38-40 weeks – ready to go out (end of
gestation)
Baby is foreign…
right???
Trophoblast
• Thought of as a shield for the embryo
• Has composition that can trigger immune
response from mother
• Counteract attacks from mother’s immune
system
– Block action of IL-2
– If too subtle, can cause abortion
BABY
DELIVERY!!!
Delivery
• Parturition (birth) happens when certain
hormones trigger contractions (labor)
• Cervix dilates after thinning
• Umbilical cord - connection of baby to
mother (BVs, respiration, etc.)
– Cut after delivery
• Placenta removed
What happens when
baby is born??
MILK!!
• Lactation – postnatal care
• Decrease levels of progesterone
– Prolactin secretion
• Oxytocin – control mammary glands to
secrete milk
Sources
• http://www.vivo.colostate.edu/hbooks/pathphys/r
eprod/fert/fert.html
• http://www.baby2see.com/development/first_trim
ester.html
• http://www.baby2see.com/development/second_
trimester.html
• http://www.baby2see.com/development/third_tri
mester.html
• Campbell, N.A, et al (1999). Biology. 5th edition.
N.Y.: Pearson Edication, Inc. – Bejamin
Cummings.
• http://www.medterms.com