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Multilingual Illustrated DVD [Tutorial]

The Biology of Prenatal Development



Introducing the Multilingual Illustrated DVD
Explore the fascinating imagery and facts presented in The Biology of Prenatal Development at your own pace. Each clip from the program is accompanied by its corresponding written script. Select Play Movie to watch any clip. Select See Snapshots to view high resolution images. See the program script and subtitles in 88 languages by using the Choose Language drop-down menu and clicking Refresh. Subtitles are displayed in your chosen language and may be turned on and off by clicking the button found in the lower right corner of the movie player. A "full screen" option is also available by clicking the button.


 
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Chapter 15   5 Weeks: Cerebral Hemispheres

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.

Chapter 16   Major Airways

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

Chapter 17   Liver and Kidneys

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

The permanent kidneys appear by 5 weeks.

Chapter 18   Yolk Sac and Germ Cells

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.

Chapter 19   Hand Plates and Cartilage

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.

Embryonic Development: 6 to 8 Weeks

Chapter 20   6 Weeks: Motion and Sensation

By 6 weeks the cerebral hemispheres are growing disproportionately faster than other sections of the brain.

The embryo begins to make spontaneous and reflexive movements. Such movement is necessary to promote normal neuromuscular development.

A touch to the mouth area causes the embryo to reflexively withdraw its head.

Chapter 21   The External Ear and Blood Cell Formation

The external ear is beginning to take shape.

By 6 weeks, blood cell formation is underway in the liver where lymphocytes are now present. This type of white blood cell is a key part of the developing immune system.

Chapter 22   The Diaphragm and Intestines

The diaphragm, the primary muscle used in breathing, is largely formed by 6 weeks.

A portion of the intestine now protrudes temporarily into the umbilical cord. This normal process, called physiologic herniation, makes room for other developing organs in the abdomen.

Chapter 23   Hand Plates and Brainwaves

At 6 weeks the hand plates develop a subtle flattening.

Primitive brainwaves have been recorded as early as 6 weeks and 2 days.

Chapter 24   Nipple Formation

Nipples appear along the sides of the trunk shortly before reaching their final location on the front of the chest.

Chapter 25   Limb Development

By 6 1/2 weeks, the elbows are distinct, the fingers are beginning to separate, and hand movement can be seen.

Bone formation, called ossification, begins within the clavicle, or collar bone, and the bones of the upper and lower jaw.

Chapter 26   7 Weeks: Hiccups and Startle Response

Hiccups have been observed by 7 weeks.

Leg movements can now be seen, along with a startle response.

Chapter 27   The Maturing Heart

The 4-chambered heart is largely complete. On average, the heart now beats 167 times per minute.

Electrical activity of the heart recorded at 7 1/2 weeks reveals a wave pattern similar to the adult's.

Chapter 28   Ovaries and Eyes

In females, the ovaries are identifiable by 7 weeks.

By 7 1/2 weeks, the pigmented retina of the eye is easily seen and the eyelids are beginning a period of rapid growth.

Chapter 29   Fingers and Toes

Fingers are separate and toes are joined only at the bases.

The hands can now come together, as can the feet.

Knee joints are also present.

The 8-Week Embryo

Chapter 30   8 Weeks: Brain Development

At 8 weeks the brain is highly complex and constitutes almost half of the embryo's total body weight.

Growth continues at an extraordinary rate.

Chapter 31   Right- and Left-Handedness

By 8 weeks, 75% of embryos exhibit right-hand dominance. The remainder is equally divided between left-handed dominance and no preference. This is the earliest evidence of right- or left-handed behavior.

Chapter 32   Rolling Over

Pediatric textbooks describe the ability to "roll over" as appearing 10 to 20 weeks after birth. However, this impressive coordination is displayed much earlier in the low-gravity environment of the fluid-filled amniotic sac. Only the lack of strength required to overcome the higher gravitational force outside the uterus prevents newborns from rolling over.

The embryo is becoming more physically active during this time.

Motions may be slow or rapid, single or repetitive, spontaneous or reflexive.

Head rotation, neck extension, and hand-to-face contact occur more often.

Touching the embryo elicits squinting, jaw movement, grasping motions, and toe pointing.

Chapter 33   Eyelid Fusion

Between 7 and 8 weeks, the upper and lower eyelids rapidly grow over the eyes and partially fuse together.

Chapter 34   "Breathing" Motion and Urination

Although there is no air in the uterus, the embryo displays intermittent breathing motions by 8 weeks.

By this time, kidneys produce urine which is released into the amniotic fluid.

In male embryos, the developing testes begin to produce and release testosterone.

Chapter 35   The Limbs and Skin

The bones, joints, muscles, nerves, and blood vessels of the limbs closely resemble those in adults.

By 8 weeks the epidermis, or outer skin, becomes a multi-layered membrane, losing much of its transparency.

Eyebrows grow as hair appears around the mouth.

Chapter 36   Summary of the First 8 Weeks

Eight weeks marks the end of the embryonic period.

During this time, the human embryo has grown from a single cell into the nearly 1 billion cells which form over 4,000 distinct anatomic structures.

The embryo now possesses more than 90% of the structures found in adults.


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