Life Science 20002 補充 Development's phases for human beings

Life Science 2000 2補充 Development's phases for human beings.

Life Science 2000 3

Fig. 16.8 (a)

3- 4 days

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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 ( 受精 )

2. Cleavge ( 卵割 )

3. Morula ( 桑椹胚 )

3. Blastula ( 囊胚 )

3. Gastrulation ( 原腸胚形成 )

4. Neurulation ( 神經管形成 )

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囊胚期桑椹胚 Migration of cells卵割

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Fig. 16.3 The gradual development of a grog embryo from the first cleavage toward the morula stage.

卵割階段

Life Science 2000 8Fig. 16-4a A comparison of the development of three vertebrates.

Frog Chicken Human

Life Science 2000 9Fig. 16-4b A comparison of the development of three vertebrates.

Human Chicken Frog

Life Science 2000 10Fig. 16-8b

5-6 days

Life Science 2000 11Fig. 16-5 a hen's egg.

Blustrula stage

Gratrulation stage

Life Science 2000 12Fig. 16.1 Neurulation.

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

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Fig. 16-6 The basic tube-within-a tube structure of most invertebrates and vertebrates.


Fig. 16-6 The basic tube-within-a tube structure of most invertebrates and vertebrates.

Life Science 2000 15Fig. 16-7 later development of membranes in the chick embryo

絨毛膜

羊膜

尿囊膜

卵黃囊

Life Science 2000 16Fig. 16-7 later development of membranes in the chick embryo

Life Science 2000 17補充 Late stage of development of the allantois in a chick embryo.

Life Science 2000 18補充 Early stage of development of the allantois in a four-day-old chick embryo.

Amnion

Extraembryonic coelom

Yolk sac

chorion

allantois


補充 Embryo of placental mammal.



Frog Chick Human


補充 various vertebrates embryos at the organogenesis stage of development illustrating similarity of gross structure.


Fig. 16-2 Lens induction in the vertebrate eye.


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.


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.


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.



Human development


← 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.


↑The human embryo is shown at 42 days with the surrounding membrane removed .

It is about 16 mm long.


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.


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.


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.


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.


At 10 weeks the skeleton is well along in its development.


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.


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.


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.


Fig. 16-11 A plea from a concerned citizen.

Would you give a cigarette to your unborn child?

You do every time you smoke!


Essay 16.1 Can humans regenerate missing parts?這隻手曾被鱷魚咬斷，再重新接回來，並用這些裝置固定住。

幾年前，有位年青的男孩，不小心切斷小手指頭。於醫院，通常會將斷掉的部份，再重新接回來。但由於醫療人員的疏失，包紮後，忘了進行接縫的手術。過了幾天，當這個疏失被發覺後，醫生急忙來看情況。令他們吃驚的是，這個手指有自行再生回來的趨勢。

目前，對小孩而言，醫院普遍採用此再生的方法來處理相同的案例。


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 ( 凝血 ).

Platelets ( 血小板 ) 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. 這可以促進地區的血液循環，引入更多的白血球。


An ethical concern• 試管嬰兒，抽取夫妻的精子和卵子進行

體外受精。• 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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Life Science 20002 補充 Development's phases for human beings