Transcript Development - MSU Denver

Development
Fertilization
• The haploid sperm joins with the haploid
egg to make a diploid zygote or embryo
• Fertilization occurs in the oviduct
• Sex of baby is determined at the time of
fertilization
Sperm fertilizing egg
Fertilization
• Fraternal twins are the result of 2 different
eggs fertilized by 2 different sperm
• Identical twins are the result of a single
egg/sperm that subsequently splits into
twins. These twins are genetically
identical.
• Ectopic pregnancy is a pregnancy in an
abnormal site, usually when the fertilized
egg gets stuck in the oviduct
Cleavage
• Day 1-4 pregnancy
• Mitosis division that occurs in oviduct as
embryo moves towards the uterus
Cleavage
Blastocyst
• Day 5
• In uterus
• Rearrangement of cells into outer cells
destined to become the placenta
• Inner mass of cells destined to become
the baby
Blastocyst
• Implantation occurs on day 7-8
• Blastocyst burrows its way into mom’s
endometrium for nourishment & protection
• Embryo secretes HCG, Human Chorionic
Gonadotropin, that serves to keep the
corpus luteum making estrogen and
progesterone.
HCG
• HCG is the basis for the do-it-at-home
pregnancy test
• Urine test
• Highly accurate
Gastrulation
• Week 2 pregnancy
• Germ layers form, which are layers of cells
destined to become certain organs
depending on their position
Gastrulation Germ Layers
• Ectoderm is outer layer destined to
become nervous tissue and skin.
• Mesoderm is middle layer destined to
become skeleton, muscles, heart, blood,
vessels….
• Endoderm is inner layer destined to
become lungs and digestive structures.
Cross section of embryo
Neurulation
• 3 weeks
• Embryo is 2mm long
• Neural tube forms resulting in brain and
spinal cord
Organogenesis
• Week 4
• All major organs, arm/leg buds, have
begun their formation
First Trimester
• Most organ development occurs during the
first trimester (3 months) of pregnancy
• This is the time when the embryo is most
susceptible to damage.
Embryo vs. Fetus
• By the end of the second month, the
embryo looks distinctly human, and is now
called a fetus
Growth
• Second and third trimesters are primarily
growth stages
Placenta
• Begins development at 4 weeks and
becomes fully functional by 12 weeks
• Provides nourishment and oxygen for
fetus, removes fetal waste and makes
estrogen and progesterone
Placenta
• Comprised of maternal tissue – the
endometrium
• Comprised of fetal tissue – the chorion
Placenta
• Umbilicus is comprised of arteries/vein
that link the fetus to the placenta
Fetal Amnion
• Sac surrounding fetus
• Filled with amniotic fluid that provides
protection, facilitates movement, and
keeps a warm temperature
• An amniocentesis is a sampling of this
fluid checking for chromosomal and
genetic abnormalities.
Gestation
• = pregnancy
• 9 full months; three trimesters
Childbirth
• Labor occurs when contractions are
regular and occurring about every 30 min.
• As contractions get stronger, amnion is
ruptured and amniotic fluid is released
(“water” breaking)
Childbirth
• Estrogen causes minor contractions
forcing the baby’s head against mom’s
cervix
• Stretching of the cervix causes the release
of OXYTOCIN which causes large
contractions
• Oxytocin is made in the hypothalamus but
released from the pituitary
Note the positive feedback cycle
Childbirth
• Relaxin, made by the placenta, relaxes
cervix and birth canal
Childbirth
• As the contractions occur even after the
baby is delivered, the afterbirth (placenta)
is passed.