Download Fetal Development - County Central High School

Fetal Development
Fertilization
This occurs when a sperm has
penetrated the egg’s outer membrane
This typically occurs in the Fallopian
Tube of the female reproductive
system
Fertilization
Once the egg and the sperm join, the cell that is
produced (zygote) now contains 46 chromosomes
The cell division that begins in the early stages is
called cleavage and forms a blastocyst
Fertilization
When the zygote reaches the uterus, it
implants in the endometrium and that
is where it begins the rest of fetal
development
Development
Four days after fertilization, the zygote becomes an
embryo
For pregnancy to continue, the menstrual cycle
cannot happen - this is aided through the secretion
of hormones
Hormones!
hCG (human chorionic gonadotropic hormone) maintains the corpus luteum for the first three
months of pregnancy
This is what pregnancy tests are looking for
BACKTRACK
The corpus luteum is found in the ovary
and is secreting progesterone to help
maintain the endometrium, prevent
contractions, and firm the cervix...
Back to Hormones!
Progesterone and estrogen levels remain high and
fluctuate throughout the pregnancy to ensure the
endometrium is maintained
If LH, estrogen, or progesterone levels fall,
menstruation could be stimulated leading to a
miscarriage
What happens to the Reproductive
System?
Changes to the Reproductive System
The blastocyst gives rise to the chorion and amnion
The chorion produces hCG and will eventually
contribute to the placenta
The amnion becomes the amniotic cavity which is a
fluid filled sac that insulates the embryo and
protects it
Changes to the Reproductive System
The yolk sac forms beneath the embryo and is
where early blood cell formation occurs and later
becomes part of the digestive tract
The placenta is formed from cells of the embryo and
endometrium - this is the place where many wastes
and nutrients are exchanged between the mother
and the fetus
Changes to the Reproductive System
The placenta begins producing estrogen and
progesterone around the second trimester (4
months)
The placenta is richly supplied with blood vessels
and the allantois provides umbilical blood vessels
connecting the embryo to the placenta
Embryonic Development
Morphogenesis is the development of an organism
(or part of it)
During the first trimester, there are many changes
to the embryo
The blastocyst has flattened into a two layer disk by
the second week
Embryonic Development
This two layered structure forms a three layered
gastrula during gastrulation
These three layers are very important and will each
play a unique role later in development
Embryonic Development
Embryonic Development
Ectoderm - outer layer
Mesoderm - middle layer
Endoderm - inner layer
Embryonic Development
By the end of the first month:
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four chambered heart has formed
brain is visible
buds for limbs have formed
tiny fingers and toes have developed
Embryonic Development
By the second trimester, all the organs have formed
(not fully developed)
Organs begin developing in this trimester and a
skeleton begins to form
There is a small chance for a baby born at the end
of the second trimester to survive
Embryonic Development
During the third trimester, the embryo is known as a
fetus and is growing rapidly
Abortions
An abortion is the early termination of a pregnancy
In Alberta, this can occur as late as 24 weeks (the end
of the second trimester)
2 forms
Medical Abortion - use of medication
Surgical Abortion - use of a vacuum or medication
Sex Determination
Females have XX sex chromosomes while males
have XY sex chromosomes
The SRY (sex-determining region of the y
chromosome) is responsible for determining male
phenotype
Sex Determination
Hormone balance is essential during development
Too much estrogen in the blood can lead to a male
embryo with female characteristics while too much
testosterone can lead to a female embryo with male
characteristics
Birth
The process of labour is called parturition (the
parting of the fetus from the mother)
Relaxin is released from the placenta causing the
cervix to soften and pelvic muscles to relax allowing
the body to have a baby pass through it
Oxytocin is released from the pituitary and
stimulates uterine contractions
Lactation
During pregnancy, the breasts are preparing for the birth of the baby
through milk production
Prolactin is a hormone produced by the pituitary that stimulates the
production of milk
The milk is not released from the breast automatically - the suckling
of the baby stimulates receptors allowing for release
Oxytocin is also used here to stimulate muscle contractions of the milk
ducts allowing for the release of the milk
Lactation
Breast feeding is a very important role of the mother
if she can do it
She passes on many antibodies and immunities to
her child through her breast milk
Mother’s need to be careful though because they
pass on any toxins or medications in their bodies
through breast milk as well