Transcript Reproductive System Pt 2 Development

The Human Reproductive
Human Development
Objectives:
• Identify the four phases of the
menstrual cycle.
• Describe fertilization.
• Describe the function of the placenta.
• Outline the life cycle after birth.
Terms you need to know:
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Menstruation
Ovulation
Follicle
Implantation
Zygote
Placenta
Fetus
-Gastrulation
-Embryonic stem cells
-Differentiation
The Menstrual Cycle
• During the menstrual cycle, an egg develops
and is released from an ovary.
• The release of a mature egg from the ovary is
called ovulation.
• In addition, the uterus is prepared to receive a
fertilized egg (progesterone)
• If the egg is fertilized after ovulation, it is
implanted in the uterus and embryonic
development begins.
• If it is not fertilized it is discharged along with
the lining of the uterus.
The Menstrual Cycle
The menstrual cycle has four phases:
1. Follicular Phase
2. Ovulation
3. Luteal Phase
4. Menstruation
The Menstrual Cycle
-Begins when estrogen level in blood is low
1. Follicular Phase: (10 days) egg
develops.
• Pituitary gland to secretes Follicle
Stimulating Hormone (FSH).
• FSH causes a follicle to develop to
maturity.
Follicle: Cluster of cells surrounding egg to
help it develop.
Follicle produces estrogen, which causes
thickening in lining of uterus.
The Menstrual Cycle
2. Ovulation: (3-4 days) egg released into
fallopian tubes.
• High estrogen levels decrease secretions of
FSH (feedback!!!)
• Pituitary now secretes Leutinizing
Hormone (LH)which causes follicle to
rupture and release a mature egg into the
fallopian tubes.
The Menstrual Cycle
3. Luteal Phase (corpus luteum): (10-14)
days.
• After ovulation, LH causes broken follicle to
fill with cells forming the corpus luteum.
• Corpus luteum secretes progesterone which
further thickens uterine lining.
• Chances of fertilization are highest.
• If fertilized zygote will float down fallopian
tubes and implant itself in the lining of the
uterus
The Menstrual Cycle
4. Menstruation: (3-7 days)
• If fertilization does not occur, secretion of
LH decreases and the corpus luteum breaks
down.
• As corpus luteum breaks down, estrogen
and progesterone levels drop causing the
lining of the uterus to detach from the
uterine wall.
• This tissue, along with blood and an
unfertilized egg are discharged through the
vagina.
Fertilization
• Fertilization:
Process by
which sperm
(n) meets an
egg (n) in the
Fallopian
tubes of a
female’s
reproductive
system to form
a zygote (2n).
Early Development: Cleavage
• After fertilization, zygote begins a series
of mitotic divisions called cleavage.
• Cleavage and Fertilization take place in
the fallopian tubes.
• During cleavage, cells increase in number
but decrease in size.
• Early divisions of cleavage result in a solid
ball of cells called a morula.
• As cells divide further they form a sphere
filled with fluid called a blastula. The
fluid inside is called blastocoel
Early Development Cleavage
Early Development: Cleavage
• Morula
• Blastula
Early Development: Implantation
• About 6-7 days after fertilization, blastula
attaches itself to the lining of the uterine
wall.
• The developing embryo secretes an
enzyme that digests a path into the into
the soft tissue
• This process is known as implantation.
• Implantation marks the beginning of
pregnancy.
Early Development: Implantation
Early Development: Gastrulation
• A cluster of cells gradually forms within the
blastocyst.
• This cluster sorts itself out into three layers
of tissue in a process called gastrulation.
• In gastrulation, the embryonic stem cells
begin differentiating into the three cell
layers: endoderm, mesoderm, ectoderm.
• All organs and tissues of the embryo will be
formed by these three layers.
Gastrulation
• Each of these
germ layers
will have
special roles
to play in
building the
complete
animal. Some
are listed in
the table .
Ectoderm Mesoderm Endoderm
Skin
Notochord Lining of
gut
Early
backbone
Brain
Muscles
Spinal cord Blood
Lining of
lungs
Lining of
bladder
Liver
Neurons
Bone
Sense
receptors
Sex organs Pancreas
Gastrulation
Similarities in embryonic
development
• Human embryonic development is very
similar to embryonic development in
other vertebrates such as reptiles, birds,
fish and other mammals.
• These similarities are REAL
EVIDENCE that we share an
evolutionary history with these
organisms
Similarities in development reveal common ancestry
Early Development: Placenta
• By the end of the third week, the nervous
and digestive systems have begun to form.
• The developing embryo needs a supply of
nutrients and oxygen. It also needs a way to
eliminate CO2 and metabolic wastes.
• This is achieved by the placenta which
serves as a connection (via the umbilical
cord) between the mother and the
developing embryo.
• The placenta is the embryo’s organ of
respiration, nutrition, and excretion.
Question:
• Why do humans and other mammals have
the placenta? Why not have the blood
supply of the embryo join up with the blood
supply of the mother?
• Write you answer here.
Early Development:
The Placenta
• The placenta allows for the blood of the
mother and the blood of the embryo to pass
each other, but not to mix.
• They are separated by the placenta; across
this thin barrier, gases are exchanged CO2
and O2 and food and waste products diffuse.
• Almost everything that the mother takes into
her body passes through the placenta to the
embryo.
Later Development
• After 8 weeks of development, the embryo is
called a fetus.
• By the end of 3 months, most of the major
organs and tissues of the fetus are fully
formed. During this time the umbilical cord
forms and connects the fetus to the placenta.
• 6 months after fertilization, the tissues of the
fetus become more complex and specialized.
• More tissues begin to function.
Later Development
• After 6 months, the fetus may be able to
survive outside the uterus if life-supporting
machinery is available.
• Chances of survival are much better after three
more months in the uterus.
• Here fetus will double in mass, and the lungs
and other organs undergo a series of changes
to prepare for life outside the uterus.
• Premature babies (before 8 mo.) often have
breathing problems due to incomplete lung
development.
The Developing Fetus
Embryo at 6
weeks
Fetus at 14
weeks
Fetus at 38
weeks
Childbirth
• About nine months after fertilization, the fetus
is ready for birth.
• A complex set of factors affect the onset of
childbirth.
• One factor is the release of the hormone
oxytocin from the pituitary gland.
• Oxytocin stimulates the rhythmic muscle
contractions known as labor.
• Oxytocin is also important in the bonding of
mother and newborn baby.
Childbirth
• Labor contractions become more frequent and
more powerful.
• The opening of the cervix expands until it is
large enough for the head of the baby to pass
through it.
• At some point the amniotic sac breaks and the
fluid it contains rushes out of the vagina
(water breaks).
• Contractions of the uterus (and lots of pushing
from mom) force the baby (usually head first)
out through the vagina
Changes in Baby After Childbirth
• After birth, the baby may cry or cough to rid
the lungs of fluid.
• Breathing starts almost immediately and the
blood supply to the placenta begins to dry up.
• The umbilical cord is clamped and cut off with
a small piece attached to the baby. This soon
dries off and leaves scar called belly button.
• Body systems quickly adapt to life outside of
uterus. Supply their own oxygen, excrete their
own wastes, maintain own body temperature.
Changes in Mother
After Childbirth
• Within a few hours after birth, the pituitary has
released a burst of oxytocin to allow for strong
bonding between mom and baby.
• The pituitary also releases a hormone called
prolactin that stimulates the production of
milk in the breast tissues of the mother.
• Nutrients in the milk contain everything the
baby needs for growth and development
during the first year or so of life.
• Breast milk also contains antibodies from the
mother to help fight off pathogens.
A couple years later and they
look a bit like this
Internal vs. External Reproduction
• Internal Fertilization: • External Fertilization:
Some aquatic animals
Male releases sperm
directly into the female’s gather in large groups
during their breeding
body where the egg is
season.
fertilized.
• Females release eggs
• Most terrestrial (land
into water.
dwelling) animals use
internal fertilization.
• Males release sperm
over the eggs.
• Fertilization takes place
outside of the organism’s
body
Evolution often involves trade-offs
• Organisms that fertilize internally often
invest in fewer numbers of offspring.
• The offspring have a relatively higher chance
of survival than the offspring of external
fertilization.
• Rather than putting energy into a high number
of offspring, the investment is in increasing
the rate of survivability of the few offspring.
• Parental care is often (not always) involved to
increase the chances that the offspring will
survive.
Evolutionary trade-offs
• Organisms that fertilize externally hedge their
bets by producing large numbers of offspring.
• Although only a very small percentage of these
offspring survive, there is still a good chance
that many will make it to adulthood.
• In these organisms, resources and energy are
invested in producing large numbers of
organisms and not in the development and care
of offspring.
Male Fish Externally Fertilizing Eggs
Galapagos Tortoises Fertilizing Internally