Download Biology Chapter 43-2 Human Development

Biology Chapter 43-2 Human Development
VOCAB
Cleavages- mitotic cell divisions of the
zygote
Morula- four days after fertilization the
embryo is a solid ball of about 50 cells
Blastocyst – a fluid filled cavity forms in the center of the embryo transforming it into a
hollow structure
Implantation- when the blastocyst attaches itself to the wall of the uterus and beings to
grow inward
Gastrulation- a cluster of cells that sorts into two layers, which then produce a third
layer by process of cell migration
Ectoderm- one of the three cell layers formed by gastrulation
Develops into: epidermis of skin: hair and nails, nervous system, tooth enamel, lining of
mouth and nose
Mesoderm -one of the three cell layers formed by gastrulation
Develops into: skeleton, muscles, excretory system, circulatory system, gonards
Endoderm -one of the three cell layers formed by gastrulation
Develops into: digestive tract, respiratory system, liver, and pancreas
Amnion- one of the membranes that surround, protects, and nourishes the developing
embryo
Chorion- one of the membranes that surround, protects, and nourishes the developing
embryo
Placenta- the connection between mother and the developing embryo. It provide
nutrients and oxygen and eliminates carbon dioxide and metabolic wastes.
Fetus- the embryo after 8 weeks of development
Umbilical Cord- contains two arteries and one vein that contains the fetus to the placenta
Amniotic Sac- fluid filled sac that cushions and protects the developing fetus
Labor- a series of rhythmic contractions that expand the cervix so that it will be large
enough to allow the baby to pass through it
Early Development
The first few mitotic cells divisions of the zygote take place while the zygote is still in the
fallopian tube.
Four days after fertilization the embryo is a solid ball of about 50 cells called morula.
As the embryo grows, a fluid-filled cavity form in the center called the blastocyst.
After 6 to 7 days of fertilization the blastocyst attaches itself to the wall of the uterus and
begins to grow inward in a process called implantation
A cluster of cells gradually forms in the cavity of the blastocyst.
The cluster forms into two lays which then produce a third, by gastrulation:
Ectoderm- one of the three cell layers formed by gastrulation
Develops into: epidermis of skin: hair and nails, nervous system, tooth enamel, lining of
mouth and nose
Mesoderm -one of the three cell layers formed by gastrulation
Develops into: skeleton, muscles, excretory system, circulatory system, gonards
Endoderm -one of the three cell layers formed by gastrulation
Develops into: digestive tract, respiratory system, liver, and pancreas
These are known as the primary germ layers.
During implantation the outer layer of cells of the blastocyst produces the amnion and
chorion membrane.
At the end of the third week, the nervous system had begun to form and so has the tube
that will start the digestive system.
The chorion had grown into the uterine layer to form the placenta.
The placenta is the embryo’s organ of respiration, nourishment, and excretion.
After 8 weeks the embryo is know as a fetus.
By the end of 3 weeks development, most major organs and tissues are fully formed and
the umbilical cord is formed
The muscular system is developed and fetus may show signs of reflexes
The fetus is about 9cm and 15grams.
The amnion has developed into the fluid-filled amniotic sac.
Later Development
During the 4th, 5th, and 6th months, the tissues of fetus continue to become more complex
and specialized. A skeleton begins to form and a fetal heartbeat become strong enough to
be heard with stethoscope.
A layer of soft hair grows over the fetus’s skin.
The developing fetus will be about 35 cm in length and have a mass of about 700gramds
by the end of the 6th month.
The last 3 month the fetus doubles in mass and the lungs and other organs undergo
changes that help them for life outside the mother.
Childbirth
About 9 months after fertilization, at the end of full pregnancy, the fetus is ready for birth.
When the time comes oxytocin is released from the Pituary gland.
When the muscles around the uterus are stimulated, they begin rhythmic contractions that
expand the opening of the cervix so that it will be large enough for the baby to pass
though.
As the contractions continue, they get more powerful and more frequent, occurring every
minute or two.
In a process that last 2 to 16 hours, the baby is force toward the vagina as labor continues.
The amniotic sac breaks releasing the fluid.
As the baby meets the outside world, it may cough or cry to rid its lungs of the fluid.
The umbilical cord is clamped and cut, leaving a small piece attached to the baby that
will dry and fall off leaving the navel.
In a final series of uterine contractions, the placenta itself and the empty amniotic sac are
expelled from the uterus as the after birth.
After Childbirth Within a few hours, the Pituary hormone prolactin stimulates the
production of milk in the breast tissues of the mother. If the mother breastfeeds the baby
regularly, the milk is always ready then needed and seldom runs dry, yet stops when the
mother ends breastfeeding. Upon stimulation, the nerve cells in the breast transmit nerve
impulses to the hypothalamus. This cause the Pituary gland to release nearly 10 times the
amount of prolactin. The increased levels of prolactin enable milk production to keep up
with demand.