Chap.16 Animal development

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?? Development's phases for human beings.
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3- 4 days
Fig. 16.8 (a)
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Fig. 15.10 The sperm have reached the egg and
have surrounded it. However, only one sperm will
enter into fertilization.
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Table 16-1 Early stages of development 1.
Fertilization (??) 2. Cleavge (??) 3. Morula
(???) 3. Blastula (??) 3. Gastrulation (?????) 4.
Neurulation (?????)
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Migration of cells
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Fig. 16.3 The gradual development of a grog
embryo from the first cleavage toward the morula
stage.
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Frog
Chicken
Human
Fig. 16-4a A comparison of the development of
three vertebrates.
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Human
Chicken
Frog
Fig. 16-4b A comparison of the development of
three vertebrates.
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5-6 days
Fig. 16-8b
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Blustrula stage
Gratrulation stage
Fig. 16-5 a hen's egg.
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Table 16.2 Structures Produced by the three germ
layers Ectoderm All nervous tissue epidermis
of skin, parts of eyes and ears, hair, pituitary
gland, adrenal medulla Endoderm most linings of
digestive system, of respiratory system Mesoderm
muscle, cartilage, bone, blood, Kidneys and gonads
Fig. 16.1 Neurulation.
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Fig. 16-6 The basic tube-within-a tube structure
of most invertebrates and vertebrates.
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Fig. 16-6 The basic tube-within-a tube structure
of most invertebrates and vertebrates.
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Fig. 16-7 later development of membranes in the
chick embryo
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Fig. 16-7 later development of membranes in the
chick embryo
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?? Late stage of development of the allantois in
a chick embryo.
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Amnion
chorion
allantois
Yolk sac
Extraembryonic coelom
?? Early stage of development of the allantois in
a four-day-old chick embryo.
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?? Embryo of placental mammal.
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Fig. 16-4a A comparison of the development of
three vertebrates.
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Frog
Chick
Human
Fig. 16-4a A comparison of the development of
three vertebrates.
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?? various vertebrates embryos at the
organogenesis stage of development illustrating
similarity of gross structure.
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Fig. 16-2 Lens induction in the vertebrate eye.
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Fig. Schematic of the Saunders-Zwilling
hypothesis for the mutual interactions of the
apical extodermal ridge (AER) and mesoderm. The
AER stimulates mesodermal outgrowth, while an
apical ecotodermal maintenance factor (AEMF) from
mesoderm promotes the health and well being of
the AER. The zone of polarizing activity (ZPA)
may influence anterior-posterior determination.
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Fig. Experimental procedures (a, b) and results
(a', b') of grafting additional putative zones of
polarizing activity (ZPA) to different sites on
chick limb buds.
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Fig. In the normal limb (A), the zone of
polarizing activity is presumed to be the source
of morphogen, which would theoretically diffuse
across the limb to form a concetration curve, as
seen in B.
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Human development
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? At the beginning of the 2nd week, the embryo
has developed extensive membranes that lie in
close contact with the mother's tissues.
? Well into the 3rd week, the chorionic membrane
has continued to penetrate the mother's
endometrium. The balloonlike structure is the
yolk sac.
The embryo at the 4th week?. The dark lies
protected in its amniotic sac. The dark eye is
prominent and the enormous brain lies trucked
against the embryonic heart.
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?The human embryo is shown at 42 days with the
surrounding membrane removed .
It is about 16 mm long.
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At 6 weeks, with the amnion removed, the fingers
are apparent and the bulbous brain still
dominates the embryo. Notice the tail trucked
under the abdomen. The tiny pit above the arm
will become the ear.
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At about 7 weeks, the embryo afloat in its
amniotic fluid, is clearly anchored to its
placenta by the twisted umbilical cord through
which great blood vessels pass. The abdomen is
swollen due to the rapid growth of the liver, the
main blood-forming organ at this time.
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The 8-week embryo is shown here is front
view. The organs are now more or less complete.
The skeletal system is among the last to form,
but bones are now evident in the arms and legs.
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At 9 week lids have begun to grow down over the
eyes, and the outer ear begins to from. The fetus
may begin to move, wave its arms and legs, and
may even suck its thumb. It is now beginning to
fill its amniotic space and will assume the
typical upside-down fetal posture.
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At 10 weeks the skeleton is well along in its
development.
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At 14 weeks the fetus is e fist-sized. Ribs and
blood vessels are visible through the translucent
skin. The vigorous movements of the fetus can now
be felt by the mother. Refinements such as
fingerprints and fingernails have not yet
developed.
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By the end of 5 months the fetus is covered with
fine-downy hair and its head may have already
started to grow its own crop. The heart is
beating now at a rate of 120 to 160 times per
minute.
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Fig. 16-9 The development of the human embryo
showing relative size at different ages. Note
that at 4 weeks, every few features are clearly
distinguishable. The major organs have begun to
form. The embryo at this time is strangely
vulnerable to a variety of dangers from drugs to
radiation.
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Would you give a cigarette to your unborn
child? You do every time you smoke!
Fig. 16-11 A plea from a concerned citizen.
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Essay 16.1 Can humans regenerate missing parts?
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Essay 16.2 Wound healing.
Flesh wounds are dangerous. The protective
covering around the body has been broken, leaving
an opportunity for invasion, by dangerous
organisms. The body acts quickly by first
sealing blood vessels in a process called
clotting (??). Platelets (???) rush to the site,
where they interact with a blood protein called
fibrinogen to form the clot. Some of the
platelets releasing a substance called serotonin,
which constricts the blood vessels in the area.
Once the blood flow has stopped, the body begins
to respond to other chemicals (pyrogens) that
have been released in response to the trauma.
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An ethical concern

• ????,?????????????????
• Some couples found out that the eggs and sperm
  used were not theirs at all.
• Would you want to know if your baby bore your
  genes?
• What would you do if the baby didn't?
• Would your feelings for the baby change?

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• ?????!