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Multilingual Illustrated DVD [Tutorial]

The Biology of Prenatal Development



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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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The Fetal Period (8 Weeks through Birth)

Chapter 37   9 Weeks: Swallows, Sighs, and Stretches

The fetal period continues until birth.

By 9 weeks, thumb sucking begins and the fetus can swallow amniotic fluid.

The fetus can also grasp an object, move the head forward and back, open and close the jaw, move the tongue, sigh, and stretch.

Nerve receptors in the face, the palms of the hands, and the soles of the feet can sense light touch.

"In response to a light touch on the sole of the foot," the fetus will bend the hip and knee and may curl the toes.

The eyelids are now completely closed.

In the larynx, the appearance of vocal ligaments signals the onset of vocal cord development.

In female fetuses, the uterus is identifiable and immature reproductive cells, called oogonia, are replicating within the ovary.

External genitalia begin to distinguish themselves as either male or female.

Chapter 38   10 Weeks: Rolls Eyes and Yawns, Fingernails & Fingerprints

A burst of growth between 9 and 10 weeks increases body weight by over 75%.

By 10 weeks, stimulation of the upper eyelid causes a downward rolling of the eye.

The fetus yawns and often opens and closes the mouth.

Most fetuses suck the right thumb.

Sections of intestine within the umbilical cord are returning to the abdominal cavity.

Ossification is underway in most bones.

Fingernails and toenails begin to develop.

Unique fingerprints appear 10 weeks after fertilization. These patterns can be used for identification throughout life.

Chapter 39   11 Weeks: Absorbs Glucose and Water

By 11 weeks the nose and lips are completely formed. As with every other body part, their appearance will change at each stage of the human life cycle.

The intestine starts to absorb glucose and water swallowed by the fetus.

Though sex is determined at fertilization, external genitalia can now be distinguished as male or female.

Chapter 40   3 to 4 Months (12 to 16 Weeks): Taste Buds, Jaw Motion, Rooting Reflex, Quickening

Between 11 and 12 weeks, fetal weight increases nearly 60%.

Twelve weeks marks the end of the first third, or trimester, of pregnancy.

Distinct taste buds now cover the inside of the mouth.
By birth, taste buds will remain only on the tongue and roof of the mouth.

Bowel movements begin as early as 12 weeks and continue for about 6 weeks.

The material first expelled from the fetal and newborn colon is called meconium. It is composed of digestive enzymes, proteins, and dead cells shed by the digestive tract.

By 12 weeks, upper limb length has nearly reached its final proportion to body size. The lower limbs take longer to attain their ultimate proportions.

With the exception of the back and the top of the head, the body of the entire fetus now responds to light touch.

Sex-dependent developmental differences appear for the first time. For instance, female fetuses exhibit jaw movement more frequently than males.

In contrast to the withdrawal response seen earlier, stimulation near the mouth now evokes a turning toward the stimulus and an opening of the mouth. This response is called the "rooting reflex" and it persists after birth, helping the newborn find his or her mother's nipple during breastfeeding.

The face continues to mature as fat deposits begin to fill out the cheeks and tooth development begins.

By 15 weeks, blood-forming stem cells arrive and multiply in the bone marrow. Most blood cell formation will occur here.

Although movement begins in the 6-week embryo, a pregnant woman first senses fetal movement between 14 and 18 weeks. Traditionally, this event has been called quickening.

Chapter 41   4 to 5 Months (16 to 20 Weeks): Stress Response, Vernix Caseosa, Circadian Rhythms

By 16 weeks, procedures involving the insertion of a needle into the abdomen of the fetus trigger a hormonal stress response releasing noradrenaline, or norepinephrine, into the bloodstream.

In the respiratory system, the bronchial tree is now nearly complete.

A protective white substance, called vernix caseosa, now covers the fetus. Vernix protects the skin from the irritating effects of amniotic fluid.

From 19 weeks fetal movement, breathing activity, and heart rate begin to follow daily cycles called circadian rhythms.

Chapter 42   5 to 6 Months (20 to 24 Weeks): Responds to Sound; Hair and Skin; Age of Viability

By 20 weeks the cochlea, which is the organ of hearing, has reached adult size within the fully developed inner ear. From now on, the fetus will respond to a growing range of sounds.

Hair begins to grow on the scalp.

All skin layers and structures are present, including hair follicles and glands.

By 21 to 22 weeks after fertilization, the lungs gain some ability to breathe air. This is considered the age of viability because survival outside the womb becomes possible for some fetuses.

Chapter 43   6 to 7 Months (24 to 28 Weeks): Blink-Startle; Pupils Respond to Light; Smell and Taste

By 24 weeks the eyelids reopen and the fetus exhibits a blink-startle response. This reaction to sudden, loud noises typically develops earlier in the female fetus.

Several investigators report exposure to loud noise may adversely affect fetal health. Immediate consequences include prolonged increased heart rate, excessive fetal swallowing, and abrupt behavioral changes. Possible long-term consequences include hearing loss.

The fetal respiratory rate can rise as high as 44 inhalation-exhalation cycles per minute.

During the third trimester of pregnancy, rapid brain growth consumes more than 50% of the energy used by the fetus. Brain weight increases between 400 and 500%.

By 26 weeks the eyes produce tears.

The pupils respond to light as early as 27 weeks. This response regulates the amount of light reaching the retina throughout life.

All components required for a functioning sense of smell are operational. Studies of premature babies reveal the ability to detect odors as early as 26 weeks after fertilization.

Placing a sweet substance in the amniotic fluid increases the rate of fetal swallowing. In contrast, decreased fetal swallowing follows the introduction of a bitter substance. Altered facial expressions often follow.

Through a series of step-like leg motions similar to walking, the fetus performs somersaults.

The fetus appears less wrinkled as additional fat deposits form beneath the skin. Fat plays a vital role in maintaining body temperature and storing energy after birth.

Chapter 44   7 to 8 Months (28 to 32 Weeks): Sound Discrimination, Behavioral States

By 28 weeks the fetus can distinguish between high- and low-pitched sounds.

By 30 weeks, breathing movements are more common and occur 30 to 40% of the time in an average fetus.

During the last 4 months of pregnancy, the fetus displays periods of coordinated activity punctuated by periods of rest. These behavioral states reflect the ever-increasing complexity of the central nervous system.

Chapter 45   8 to 9 Months (32 to 36 Weeks): Alveoli Formation, Firm Grasp, Taste Preferences

By approximately 32 weeks, true alveoli, or air "pocket" cells, begin developing in the lungs. They will continue to form until 8 years after birth.

At 35 weeks the fetus has a firm hand grasp.

Fetal exposure to various substances appears to affect flavor preferences after birth. For instance, fetuses whose mothers consumed anise, a substance which gives licorice its taste, showed a preference for anise after birth. Newborns without fetal exposure disliked anise.

Chapter 46   9 Months to Birth (36 Weeks through Birth)

The fetus initiates labor by releasing large amounts of a hormone called estrogen and thus begins the transition from fetus to newborn.

Labor is marked by powerful contractions of the uterus, resulting in childbirth.

From fertilization to birth and beyond, human development is dynamic, continuous, and complex. New discoveries about this fascinating process increasingly show the vital impact of fetal development on lifelong health.

As our understanding of early human development advances, so too will our ability to enhance health - both before and after birth.


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