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The Biology of Prenatal Development




THE BIOLOGY OF PRENATAL DEVELOPMENT

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Desenvolvimento Embrionário: 4 a 6 Semanas

Capítulo 11   4 Semanas: Líquido Amniótico

By 4 weeks the clear amnion surrounds the embryo in a fluid-filled sac. This sterile liquid, called amniotic fluid, provides the embryo with protection from injury.

Capítulo 12   O Coração em Ação

The heart typically beats about 113 times per minute.

Note how the heart changes color as blood enters and leaves its chambers with each beat.

The heart will beat approximately 54 million times before birth and over 3.2 billion times over the course of an 80-year lifespan.

Capítulo 13   O Crescimento do Cérebro

Rapid brain growth is evidenced by the changing appearance of the forebrain, midbrain, and hindbrain.

Capítulo 14   Brotos dos Membros

Upper and lower limb development begins with the appearance of the limb buds by 4 weeks.

The skin is transparent at this point because it is only one cell thick.

As the skin thickens, it will lose this transparency, which means that we will only be able to watch internal organs develop for about another month.

Capítulo 15   5 Semanas: Hemisférios Cerebrais

Between 4 and 5 weeks, the brain continues its rapid growth and divides into 5 distinct sections.

The head comprises about 1/3 of the embryo's total size.

The cerebral hemispheres appear, gradually becoming the largest parts of the brain.

Functions eventually controlled by the cerebral hemispheres include thought, learning, memory, speech, vision, hearing, voluntary movement, and problem-solving.

Capítulo 16   Vias Respiratórias Principais

In the respiratory system, the right and left main stem bronchi are present and will eventually connect the trachea, or windpipe, with the lungs.

Capítulo 17   Fígado e Rins

Note the massive liver filling the abdomen adjacent to the beating heart.

The permanent kidneys appear by 5 weeks.

Capítulo 18   Saco Vitelino e Células Germinativas

The yolk sac contains early reproductive cells called germ cells. By 5 weeks these germ cells migrate to the reproductive organs adjacent to the kidneys.

Capítulo 19   Placas da Mão e Cartilagem

Also by 5 weeks, the embryo develops hand plates, and cartilage formation begins by 5 1/2 weeks.

Here we see the left hand plate and wrist at 5 weeks and 6 days.