The Biology of Prenatal Development Student Study Guide
The Biology of Prenatal Development Student Study Guide is a two-sided, fold-out, poster quality study guide for educators to use in their classrooms. The study guide features stunning prenatal imagery depicting the entire prenatal development process, prenatal facts, and a prenatal development timeline that continues from front to back. It is best used as a companion to The Biology of Prenatal Development DVD. To purchase the student study guide visit EHD's Online Store.
The neural plate emerges by 2 weeks, 4 days.6 By 3 weeks the neural tube appears, marking the onset of brain and spinal cord development.7 Blood cells and blood vessels also form.8 By 3 weeks, 1 day the heart begins to beat in the newly forming circulatory system.9
Fingers begin to separate in the 6½-week embryo16 and are completely free by 7½ weeks,17 at which time the hands can touch.18 Handedness is evident by 8 weeks, when 75% of embryos exhibit right-hand dominance.19
By 9 weeks the face, palms of the hands, and soles of the feet can sense light touch.28 Most of the fetus is touch-sensitive by 13 to 14 weeks.29 Gender differences emerge as female fetuses move their jaws more than males.30
By 14 weeks a fetus touched near the mouth shows the same rooting reflex newborns use to find their mother’s nipple when breastfeeding.31
Around 19 weeks; movement, breathing, and heart rate begin to follow daily cycles called circadian rhythms.34 These biologic rhythms persist throughout childhood and adulthood.
Rapid Eye Movements (REM) are first seen in the 20-week fetus.37 After birth, REM are known to occur during the dream stage of sleep.38 By 23 weeks all skin layers and structures including glands and hair follicles are present.39
By 25 weeks the fetus responds to taste. Sweet substances placed in the amniotic fluid increase fetal swallowing. Bitter substances decrease swallowing and may alter facial expression.40 Between 25 weeks and birth, a brain growth spurt consumes 50% of fetal energy as brain weight increases 400 to 500%.41
By 24 weeks the eyelids reopen.44 By 25 weeks, highly developed eyes contain rods and cones.45 A total of 200 million rods will detect low levels of light as 14 million cones produce focused, color images.46 Eyes form tears by 26 weeks.47 By 27 weeks, pupils dilate and constrict in response to light — a reflex that persists throughout life.48
True alveoli, or air “pocket” cells, begin forming in the lungs by 32 weeks. Alveoli are the site for O2/CO2 exchange and will continue to develop until about age 8, with the greatest increase between birth and age 2.49
After months of listening to their mother’s voice, newborns prefer her voice over any other male or female voice.50
By 32 weeks the brain has most of its nearly 100 billion (1011) neurons.51 Each neuron eventually connects with up to 200,000 other neurons, creating an electrical network of incalculable complexity.52 These connections are called synapses.53 At birth most organs are just 5% of their adult size. However, the newborn’s brain and eyes are approximately 25%54 and 75%55 of their final sizes respectively.
Newborns show a preference for prose passages and lullabies heard during the last 6 weeks of pregnancy. These preferences for familiar experiences provide evidence of memory formation and learning before birth.56
Photo Credits: (left to right, top to bottom) Cover: EHD/The Biology of Prenatal Development (BPD) Video; LifeArt/Lippincott Williams & Wilkins; Getty Images (next 3); 0-4 Week Panel: Lennart Nilsson/Albert Bonniers Forlag AB, A Child Is Born, Dell Publishing Company; Centro Riproduzione Assistia (next 7); LifeArt (next 2); EHD/BPD. 4-8 Week Panel: EHD/BPD; Nilsson/Forlag (next 3); EHD/BPD. 8-16 Week Panel: EHD/BPD; Getty Images (next 2); Nilsson/Forlag. 16-24 Week Panel: Nilsson/Forlag; LifeArt; Getty Images; Nilsson/Forlag (next 2). 24-32 Week Panel: EHD/BPD; Create Health Centre for Reproduction and Advanced Technology; Nilsson/Forlag. 32-38 Week Panel: Getty Images; Create Health Centre; Getty Images (next 3). Back: Getty Images (all 5).
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This study guide is licensed to schools for use by educators and students only. May not be reproduced, resold, or redistributed without the express written consent of The Endowment for Human Development, Inc. All rights reserved.
Copyright © 2005 by The Endowment for Human Development, Inc.
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