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Multilingual Illustrated DVD [Tutorial]
The Biology of Prenatal Development
Table of Contents
- THE EMBRYONIC PERIOD (THE FIRST 8 WEEKS)
- EMBRYONIC DEVELOPMENT: THE FIRST 4 WEEKS
- Chapter 3 – Fertilization
- Chapter 4 – DNA, Cell Division, and Early Pregnancy Factor (EPF)
- Chapter 5 – Early Stages (Morula and Blastocyst) and Stem Cells
- Chapter 6 – 1 to 1 1/2 Weeks: Implantation and Human Chorionic Gonadotropin (hCG)
- Chapter 7 – The Placenta and Umbilical Cord
- Chapter 8 – Nutrition and Protection
- Chapter 9 – 2 to 4 Weeks: Germ Layers and Organ Formation
- Chapter 10 – 3 to 4 Weeks: The Folding of the Embryo
- EMBRYONIC DEVELOPMENT: 4 TO 6 WEEKS
- Chapter 11 – 4 Weeks: Amniotic Fluid
- Chapter 12 – The Heart in Action
- Chapter 13 – Brain Growth
- Chapter 14 – Limb Buds and Skin
- Chapter 15 – 5 Weeks: Cerebral Hemispheres
- Chapter 16 – Major Airways
- Chapter 17 – Liver and Kidneys
- Chapter 18 – Yolk Sac and Germ Cells
- Chapter 19 – Hand Plates and Cartilage
- EMBRYONIC DEVELOPMENT: 6 TO 8 WEEKS
- Chapter 20 – 6 Weeks: Motion and Sensation
- Chapter 21 – The External Ear and Blood Cell Formation
- Chapter 22 – The Diaphragm and Intestines
- Chapter 23 – Hand Plates and Brainwaves
- Chapter 24 – Nipple Formation
- Chapter 25 – Limb Development
- Chapter 26 – 7 Weeks: Hiccups and Startle Response
- Chapter 27 – The Maturing Heart
- Chapter 28 – Ovaries and Eyes
- Chapter 29 – Fingers and Toes
- THE 8-WEEK EMBRYO
- THE FETAL PERIOD (8 WEEKS THROUGH BIRTH)
- Chapter 37 – 9 Weeks: Swallows, Sighs, and Stretches
- Chapter 38 – 10 Weeks: Rolls Eyes and Yawns, Fingernails & Fingerprints
- Chapter 39 – 11 Weeks: Absorbs Glucose and Water
- Chapter 40 – 3 to 4 Months (12 to 16 Weeks): Taste Buds, Jaw Motion, Rooting Reflex, Quickening
- Chapter 41 – 4 to 5 Months (16 to 20 Weeks): Stress Response, Vernix Caseosa, Circadian Rhythms
- Chapter 42 – 5 to 6 Months (20 to 24 Weeks): Responds to Sound; Hair and Skin; Age of Viability
- Chapter 43 – 6 to 7 Months (24 to 28 Weeks): Blink-Startle; Pupils Respond to Light; Smell and Taste
- Chapter 44 – 7 to 8 Months (28 to 32 Weeks): Sound Discrimination, Behavioral States
- Chapter 45 – 8 to 9 Months (32 to 36 Weeks): Alveoli Formation, Firm Grasp, Taste Preferences
- Chapter 46 – 9 Months to Birth (36 Weeks through Birth)
|Between 4 and 5 weeks,
the brain continues
its rapid growth
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.
|In the respiratory system, the right and left main stem bronchi are present and will eventually connect the trachea, or windpipe, with the lungs.|
|Note the massive liver
filling the abdomen
adjacent to the beating heart.
The permanent kidneys appear by 5 weeks.
|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.|
|Also by 5 weeks,
the embryo develops
and cartilage formation begins
by 5 1/2 weeks.
Here we see the left hand plate and wrist at 5 weeks and 6 days.
|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.|
|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.|
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.|
|At 6 weeks the hand plates
develop a subtle flattening.
|Primitive brainwaves have been recorded as early as 6 weeks and 2 days.|
|Nipples appear along the sides of the trunk shortly before reaching their final location on the front of the chest.|
|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.|
|Hiccups have been observed
by 7 weeks.
Leg movements can now be seen, along with a startle response.
|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.
|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.|
|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.
|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.
|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.|
|Pediatric textbooks describe
the ability to "roll over"
10 to 20 weeks after birth.
However, this impressive
is displayed much earlier
in the low-gravity environment
of the fluid-filled
Only the lack
of strength required
to overcome the higher
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.|
|Between 7 and 8 weeks, the upper and lower eyelids rapidly grow over the eyes and partially fuse together.|
|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.
|The bones, joints,
and blood vessels
of the limbs
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.
|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.