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生前発育の生物学

The Biology of Prenatal Development
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Chapter 1   Introduction

The dynamic process by which the single-cell human zygote(zī΄gōt)[1] becomes a 100 trillion (1014) cell adult[2] is perhaps the most remarkable phenomenon in all of nature.

Researchers now know that many of the routine functions performed by the adult body become established during pregnancy – often long before birth.[3]

The developmental period before birth is increasingly understood as a time of preparation during which the developing human acquires the many structures, and practices the many skills, needed for survival after birth.

Chapter 1   Introduction

1 個の細胞であるヒト接合子が 100 兆個の細胞を持つ大人となる このダイナミックな過程は 多くの自然現象の中でも 最も驚くべきものといえましょう

ヒトの大人が使う 通常の機能の多くが 妊娠中に出来上がっており その多くは出生のずっと以前 に確立されていることが 研究者により解明されています

出生前の発育期は 発育中のヒトが 出生後に必要となる 多くの機能を取得し 技能をみがいていく その準備期間として 徐々に理解されています

Chapter 2   Terminology

Pregnancy in humans normally lasts approximately 38 weeks[4] as measured from the time of fertilization,[5] or conception,[6] until birth.

During the first 8 weeks following fertilization, the developing human is called an embryo,[7] which means "growing within."[8] This time, called the embryonic period,[9] is characterized by the formation of most major body systems.[10]

From the completion of 8 weeks until the end of pregnancy, "the developing human is called a fetus," which means "unborn offspring." During this time, called the fetal period, the body grows larger and its systems begin to function.[11]

All embryonic and fetal ages in this program refer to the time since fertilization.[12]

Chapter 2   Terminology

ヒトの妊娠期間は 受精または受胎から出生まで 通常約38 週です

受精後最初の8 週においては 発育中のヒトは 胎芽と呼ばれます これは「中で育つ」 という意味です この時期は胎生期と呼ばれ 殆どの器官が 形成されるのが特徴です

8 週の終わりから 妊娠終了までの間 「発育中のヒトは 胎児と呼ばれます」 「おなかの中のこども」 という意味です この時期は胎児期と呼ばれ 身体が成長し 各器官も 機能し始めます

当プログラムにおける 胎生および胎児年齢は 受精時を基点としています

 

Click any superscript in the text to view footnote. Click any footnote number to view source text. Click on any author name to view the full reference in the Bibliography. Then click your browser’s back button to return to source footnote.


[1] Gasser, 1975, 1.
[2] Guyton and Hall, 2000, 2; Lodish et al., 2000, 12.
[3] Vindla and James, 1995, 598.
[4] Cunningham et al., 2001, 226; O’Rahilly and Müller, 2001, 92.
[5] O’Rahilly and Müller, 1987, 9.
[6] Spraycar, 1995, 377 & 637.
[7] O’Rahilly and Müller, 2001, 87.
[8] Quote from Ayto, 1990, 199.
[9] Human development during the 8-week embryonic period has been divided into a series of 23 stages called Carnegie Stages. These stages are well described in O’Rahilly and Müller, 1987. Because human growth is unique and dependent on multiple factors, different embryos may reach a certain developmental milestone or a certain size at slightly different ages. This internationally-accepted staging system provides a way to describe development independent of age and size. Each of the 23 Carnegie Stages has specific structural features. As we describe various milestones of development, the Carnegie Stage at which they occur will be noted by a designation such as: [Carnegie Stage 2]. See Appendix B for additional information relating embryonic staging and age assignments.
[10] Moore and Persaud, 2003, 3.
[11] Quotes from Moore and Persaud, 2003, 3: “After the embryonic period (eight weeks), the developing human is called a fetus.“ Also see O’Rahilly and Müller, 2001, 87.
[12] This convention, termed “postfertilization age“ by O’Rahilly, has been long preferred by embryologists. [see Mall, 1918, 400; O’Rahilly and Müller, 1999b, 39; O’Rahilly and Müller, 2001, 88 & 91.] Obstetricians and radiologists typically assign age based on the time elapsed since the first day of the last menstrual period prior to fertilization. This is correctly termed “postmenstrual age“ and begins 2 weeks before fertilization occurs. To summarize: postmenstrual age = postfertilization age + 2 weeks. Therefore, postmenstrual age equals approximately 2 weeks at the time of fertilization. The commonly used term “gestational age“ has been used with both age conventions and is best either avoided or carefully defined with each use.

Page 3

The Embryonic Period (The First 8 Weeks)

Embryonic Development: The First 4 Weeks

Chapter 3   Fertilization

Biologically speaking, "human development begins at fertilization,"[13] when a woman and a man each combine 23 of their own chromosomes through the union of their reproductive cells.

A woman's reproductive cell is commonly called an "egg" but the correct term is oocyte (ō´ō-sīt).[14]

Likewise, a man's reproductive cell is widely known as a "sperm," but the preferred term is spermatozoon (sper´mă-tō-zō´on).[15]

Following the release of an oocyte from a woman's ovary in a process called ovulation (ov´yū-lā´shŭn),[16] the oocyte and spermatozoon join within one of the uterine tubes,[17] which are often referred to as Fallopian tubes.

The uterine tubes link a woman's ovaries to her uterus or womb.

The resulting single-celled embryo is called a zygote,[18] meaning "yoked or joined together."[19]

The Embryonic Period (The First 8 Weeks)

Embryonic Development: The First 4 Weeks

Chapter 3   Fertilization

生物学上では 「ヒトの発育は受精を もって始まります」 男性と女性の 生殖細胞の結合により 各々が持つ23 組の染色体が 組み合わされるのです

一般に 女性の生殖細胞は 「卵子」と呼ばれますが 正しい用語は 「卵母細胞」です

同様に 男性の生殖細胞は 通常「スパーム」(精子) として知られていますが 「スパーマトゾン」(精子)という 呼び方のほうが好ましいでしょう

排卵と呼ばれる過程において 女性の卵巣より卵母細胞が放出され 卵母細胞と精子が 卵管の一つの中で結びつきます 卵管はファロピーオ菅 という名でも知られています

卵管は女性の卵巣を 子宮につなぐ器官です

その結果としてできた 1 個の細胞である胎芽は 「つながれた」という意味の 接合子と呼ばれます

Chapter 4   DNA, Cell Division, and Early Pregnancy Factor (EPF)

DNA

The zygote's 46 chromosomes[20] represent the unique first edition of a new individual's complete genetic blueprint. This master plan resides in tightly coiled molecules called DNA. They contain the instructions for the development of the entire body.

DNA molecules resemble a twisted ladder known as a double helix.[21] The rungs of the ladder are made up of paired molecules, or bases, called guanine, cytosine, adenine, and thymine.

Guanine pairs only with cytosine, and adenine with thymine.[22] Each human cell contains approximately 3 billion (3×109) base pairs.[23]

The DNA of a single cell contains so much information that if it were represented in printed words, simply listing the first letter of each base would require over 1.5 million (1.5×106) pages of text![24]

If laid end-to-end, the DNA in a single human cell measures 3⅓ feet or 1 meter.[25]

If we could uncoil all of the DNA within an adult's 100 trillion (1014) cells, it would extend over 63 billion (6.3×1010) miles. This distance reaches from the earth to the sun and back 340 times.[26]

Cell Division

Approximately 24 to 30 hours after fertilization, the zygote completes its first cell division.[27] Through the process of mitosis, one cell splits into two, two into four, and so on.[28]

Early Pregnancy Factor (EPF)

As early as 24 to 48 hours after fertilization begins, pregnancy can be confirmed by detecting a hormone called "early pregnancy factor" in the mother's blood.[29]

Chapter 4   DNA, Cell Division, and Early Pregnancy Factor (EPF)

DNA

この接合子の46 組の染色体が 新しく生まれる個体の 完全なる遺伝子の 唯一無比の青写真の始まりです このマスタープランには DNA と呼ばれる分子が らせん状に びっしりと からまっているのです DNA には身体全体の発達に対する 綿密な指示が組み込まれています

DNA 分子は 一見 らせん階段のようですが これは2 重らせん構造 として 知られています 2 重らせん構造の各々の鎖は 塩基と いう分子の対により構成されています 塩基にはグアニン シトシン アデニン チミンの4種類あります

グアニンはシトシンとのみ結合し アデニンはチミンとのみ 対になります ヒトの細胞ひとつひとつに およそ30 億にも及ぶ これらの塩基対が含まれています

1 個の細胞のDNA は 膨大な情報を含んでおり 仮に それを印刷した形で 表そうとした場合には 各塩基の最初の文字を 書き出すだけでも 150 万ページという 膨大な数になってしまいます

1 個のヒト細胞のDNA を 端から端まで広げてみた場合 その長さは 3-1/3 フィート およそ1 メートルとなります

大人の100 兆にもおよぶ細胞の 全DNA のらせんを解いて 伸ばしてみた場合 630 億マイル以上という 長さになります この距離は 地球と太陽間の 340 往復に値します

Cell Division

受精後 24 ~ 30 時間たって 接合子は最初の 細胞分裂を完了します 有糸分裂過程において 1 個の細胞が2 個に 2 個の細胞が4 個に となっていきます

Early Pregnancy Factor (EPF)

受精が始まって 早ければ 24 ~ 48 時間以内に 母親の血清中にある「早期妊娠要因」 というホルモンによって 妊娠を確認することができます

 

 


[13] Quote from Moore and Persaud, 2003, 16; From O’Rahilly and Müller, 1987, 9: “Fertilization is the procession of events that begins when a spermatozoon makes contact with an oocyte or its investments and ends with the intermingling of maternal and paternal chromosomes at metaphase of the first mitotic division of the zygote.“ See Carlson, 2004, 3; O’Rahilly and Müller, 2001, 8. [Carnegie Stage 1]
[14] O’Rahilly and Müller, 2001, 25: “The term ‘egg’ should be discarded from human embryology.“ From O’Rahilly and Müller, 1987, 9: “The term ‘egg’ is best reserved for a nutritive object frequently seen on the breakfast table.“
[15] O’Rahilly and Müller, 2001, 23-24.
[16] O’Rahilly and Müller, 2001, 30.
[17] Dorland and Bartelmez, 1922, 372; Gasser, 1975, 1; Mall, 1918, 421; O’Rahilly and Müller, 2001, 31.
[18] Gasser, 1975, 1; O’Rahilly and Müller, 2001, 33.
[19] Quote from Saunders, 1970, 1; Spraycar, 1995, 1976.
[20] Guyton and Hall, 2000, 34.
[21] Guyton and Hall, 2000, 24; Watson and Crick, 1953, 737.
[22] Guyton and Hall, 2000, 24; Lodish et al., 2000, 103; Watson and Crick, 1953, 737.
[23] Lodish et al., 2000, 456.
[24] See Appendix A.
[25] See Appendix A; Alberts et al., 1998, 189.
[26] See Appendix A.
[27] Hertig, 1968, 26; Hertig and Rock, 1973, 130; (cited by O’Rahilly and Müller, 1987, 12); Shettles, 1958, 400.
[28] Guyton and Hall, 2000, 34.
[29] Moore and Persaud, 2003, 33 & 60; Morton et al., 1992, 72; Nahhas and Barnea, 1990, 105.

Page 4

Chapter 5   Early Stages (Morula and Blastocyst) and Stem Cells

By 3 to 4 days after fertilization, the dividing cells of the embryo assume a spherical shape and the embryo is called a morula (mōr´ū-lă).[30]

By 4 to 5 days, a cavity forms within this ball of cells and the embryo is then called a blastocyst.[31]

The cells inside the blastocyst are called the inner cell mass and give rise to the head, body, and other structures vital to the developing human.[32]

Cells within the inner cell mass are called embryonic stem cells because they have the ability to form each of the more than 200 cell types contained in the human body.[33]

Chapter 5   Early Stages (Morula and Blastocyst) and Stem Cells

受精後3 ~ 4日までには 胎芽の分割された細胞は 球状を呈し これは 桑実胎芽と呼ばれます

4 ~ 5 日までには 分割球内で腔を形成し 胎芽盤胞と呼ばれる 状態に変化します

胎芽盤胞内の細胞は 内細胞塊と呼ばれ 頭や身体 発育中のヒトに不可欠な 組織等に分化します

内細胞塊の細胞は 胎芽性幹細胞(ES細胞) と呼ばれます このES細胞が ヒトの身体の有する 200 種以上の細胞に分化する 能力を備えているのです

Chapter 6   1 to 1½ Weeks: Implantation and Human Chorionic Gonadotropin (hCG)

After traveling down the uterine tube, the early embryo embeds itself into the inner wall of the mother's uterus. This process, called implantation, begins 6 days and ends 10 to 12 days after fertilization.[34]

Cells from the growing embryo begin to produce a hormone called human chorionic gonadotropin (human kō-rē-on'ik gō'nad-ō-trō'pin), or hCG, the substance detected by most pregnancy tests.[35]

HCG directs maternal hormones to interrupt the normal menstrual cycle, allowing pregnancy to continue.[36]

Chapter 6   1 to 1½ Weeks: Implantation and Human Chorionic Gonadotropin (hCG)

卵管内から下降した 初期の胎芽は 母親の子宮内膜に接着します この着床と呼ばれる過程は 受精後 約6 日目に開始し 10 ~ 12日頃に完了します

成長を続ける胎芽の細胞からは HCG(ヒト絨毛性ゴナドトロピン) というホルモンを分泌し始めます HCG は 妊娠検査薬で 探知できる成分です

HCG は母体のホルモンに 指示を送り 通常の月経周期を停止させ 妊娠の継続を促します

Chapter 7   The Placenta and Umbilical Cord

Following implantation, cells on the periphery of the blastocyst give rise to part of a structure called the placenta (plă-sen'tă), which serves as an interface between the maternal and embryonic circulatory systems.

The placenta delivers maternal oxygen, nutrients, hormones, and medications to the developing human; removes all waste products; and prevents maternal blood from mixing with the blood of the embryo and fetus.[37]

The placenta also produces hormones and maintains embryonic and fetal body temperature slightly above that of the mother's.[38]

The placenta communicates with the developing human through the vessels of the umbilical (ŭm-bil'i-kăl) cord.[39]

The life support capabilities of the placenta rival those of intensive care units found in modern hospitals.

Chapter 7   The Placenta and Umbilical Cord

着床後に 胎芽盤胞の周囲の細胞は 将来胎盤となる栄養膜細胞 に分化します 胎盤は 母体と胎児の循環系の インターフェイスの 役割を果たします

胎盤を通して発育中のヒトには 母体の酸素 栄養 ホルモン 薬品等が届けられ 廃棄物が除去されます また 母体の血液が 胎芽や胎児側に移動するのを防ぎます

胎盤は ホルモンを分泌し 胎芽や胎児の体温を 母体より やや高く維持します

胎盤は 臍帯の血管を通じて 発育中のヒトと 情報を伝達しています

胎盤の生命維持装置 としての役割は 近代的な病院の集中治療室 の機器に匹敵するでしょう

 

 


[30] Gasser, 1975, 1; O’Rahilly and Müller, 2001, 37; Spraycar, 1995, 1130: “Morula“ is derived from the Latin word morus meaning “mulberry.“ [Carnegie Stage 2]
[31] O’Rahilly and Müller, 2001, 39. [Carnegie Stage 3]
[32] Gasser, 1975, 1; O’Rahilly and Müller, 2001, 39; Sadler, 2005, 6.
[33] Alberts et al., 1998, 32. For a discussion and definition of embryonic stem cells see the website of the National Institutes of Health: http://stemcells.nih.gov/infoCenter/stemCellBasics.asp#3
[34] O’Rahilly and Müller, 2001, 40; Implantation begins with attachment of the blastocyst at about 6 days after fertilization. [Attachment of the blastocyst to the inner wall of the uterus is a transient event and is the hallmark of Carnegie Stage 4.] See also Adams, 1960, 13-14; Cunningham et al., 2001, 20; Hamilton, 1949, 285-286; Hertig, 1968, 41; Hertig and Rock, 1944, 182; Hertig and Rock, 1945, 81 & 83; Hertig and Rock, 1949, 183; Hertig et al., 1956, 444. [Carnegie Stage 5]
[35] Chartier et al., 1979, 134; Cunningham et al., 2001, 27; O’Rahilly and Müller, 2001, 43.
[36] Cunningham et al., 2001, 20 & 26-27; O’Rahilly and Müller, 2001, 31.
[37] Hertig, 1968, 16; Cunningham et al., 2001, 86 & 136; For a detailed description of the placenta see Hamilton and Boyd, 1960. For a detailed description of the placenta vasculature see Harris and Ramsey, 1966. This separation of maternal and fetal blood is almost but not quite perfect as a small number of fetal cells may be found in the maternal circulation and vice-versa. See Cunningham et al., 2001, 96 & 136.
[38] Liley, 1972, 101; O’Rahilly and Müller, 2001, 78-79.
[39] For a detailed description of umbilical cord formation see Florian, 1930.

Page 5

Chapter 8   Nutrition and Protection

By 1 week, cells of the inner cell mass form two layers called the hypoblast and epiblast.[40]

The hypoblast gives rise to the yolk sac,[41] which is one of the structures through which the mother supplies nutrients to the early embryo.[42]

Cells from the epiblast form a membrane called the amnion (am-nē-on),[43] within which the embryo and later the fetus develop until birth.

Chapter 8   Nutrition and Protection

1 週までには 内細胞塊の細胞は 胎芽盤葉下層と 胎芽盤葉上層と呼ばれる 2 層に分化します

胎芽盤葉下層は 卵黄嚢を形成し 初期の胎芽に 母体の栄養を 与えることになります

胎芽盤葉上層の細胞は 羊膜に分化します ここで 胎芽 そして後には胎児が 出生まで発育するのです

Chapter 9   2 to 4 Weeks: Germ Layers and Organ Formation

By approximately 2½ weeks, the epiblast has formed 3 specialized tissues, or germ layers, called ectoderm, endoderm, and mesoderm.[44]

Ectoderm gives rise to numerous structures including the brain, spinal cord, nerves, skin, nails, and hair.

Endoderm produces the lining of the respiratory system and digestive tract and generates portions of major organs such as the liver and pancreas.

Mesoderm forms the heart, kidneys, bones, cartilage, muscles, blood cells, and other structures.[45]

By 3 weeks the brain is dividing into 3 primary sections called the forebrain, midbrain, and hindbrain.[46]

Development of the respiratory and digestive systems is also underway.[47]

As the first blood cells appear in the yolk sac,[48] blood vessels form throughout the embryo, and the tubular heart emerges.[49]

Almost immediately, the rapidly growing heart folds in upon itself as separate chambers begin to develop.[50]

The heart begins beating 3 weeks and 1 day following fertilization.[51]

The circulatory system is the first body system, or group of related organs, to achieve a functional state.[52]

Chapter 9   2 to 4 Weeks: Germ Layers and Organ Formation

およそ2 週半までには 胎芽盤葉上層は 3 層性胎芽盤 または 胎芽葉を形成します これらは 外胎芽葉 内胎芽葉 中胎芽葉と呼ばれます

外胎芽葉は 多くの器官に分化します 脳 脊椎 神経 皮膚 爪 髪の毛などです

内胎芽葉は 呼吸器系や 消化器系に分化し 肝臓や すい臓などの 主要器官を形成します

中胎芽葉が形成するのは 心臓や腎臓 骨 軟骨 筋肉 血球 その他の組織です

3 週までには 脳 は3 つの主要部分に分かれます つまり 前頭葉 中頭葉 後頭葉です

呼吸器と消化器系の発達も 進行中です

最初の血球が 卵黄嚢に現れると 胎芽全体に 血管が形成され 管状心臓が現れます

殆ど時を同じくして 急速に発育する心臓は 個別の心室が 発達するにつれて 自然に折り込まれていきます

受精後3 週と 1 日で 心臓が 鼓動を打ち始めます

最初に機能を備える身体組織 または 関連器官のグループは 循環器系です

Chapter 10   3 to 4 Weeks: The Folding of the Embryo

Between 3 and 4 weeks, the body plan emerges as the brain, spinal cord, and heart of the embryo are easily identified alongside the yolk sac.

Rapid growth causes folding of the relatively flat embryo.[53] This process incorporates part of the yolk sac into the lining of the digestive system and forms the chest and abdominal cavities of the developing human.[54]

Chapter 10   3 to 4 Weeks: The Folding of the Embryo

3 ~ 4 週目までには 身体組織の特徴が現れ 胎芽の脳 脊椎 および心臓が 卵黄嚢とともに かなりはっきりと 分かるようになります

急速な成長により 比較的平らな胎芽が折り込まれ この過程により 卵黄嚢の一部が 消化器官の裏張りに 取り込まれ 発育中のヒトの 胸と 腹腔を形成します

 

 


[40] O’Rahilly and Müller, 2001, 39.
[41] Moore and Persaud, 2003, 50; O’Rahilly and Müller, 2001, 82. [Carnegie Stages 5 & 6]; In humans, the term “yolk sac“ has fallen out of favor among some embryologists (including O’Rahilly and Müller) because it is not a nutrient reservoir and does not contain yolk. The technically preferred term is umbilical vesicle. This structure plays a vital role in the transfer of nutrients from mother to embryo before placental circulation becomes fully functional.
[42] Campbell et al., 1993, 756; Kurjak et al., 1994, 437; O’Rahilly and Müller, 2001, 82.
[43] O’Rahilly and Müller, 1987, 29; O’Rahilly and Müller, 2001, 43. [Carnegie Stages 4-5]
[44] O’Rahilly and Müller, 2001, 14 & 135. [Carnegie Stage 7]; It should be noted there are many examples of organs derived from multiple germ layers. For instance, the liver is largely derived from endoderm but contains blood vessels and blood cells derived from mesoderm and nerves of ectodermal origin.
[45] Moore and Persaud, 2003, 80 & 83; Sadler, 2005, 9.
[46] Bartelmez, 1923, 236; Müller and O’Rahilly, 1983, 419-420 & 429; O’Rahilly and Gardner, 1979, 123 & 129; O’Rahilly and Müller, 1984, 422; O’Rahilly and Müller, 1987, 90; O’Rahilly and Müller, 1999a, 47 & 52. [Carnegie Stage 9]
[47] DiFiore and Wilson, 1994, 221; Fowler et al., 1988, 793; Grand et al., 1976, 793-794 & 796 & 798; O’Rahilly, 1978, 125; O’Rahilly and Boyden, 1973, 238-239; O’Rahilly and Müller, 1984, 421; O’Rahilly and Tucker, 1973, 6 & 8 & 23; Streeter, 1942, 232 & 235.
[48] Carlson, 2004, 117.
[49] Gilmour, 1941, 28; O’Rahilly and Müller, 1987, 86. [Carnegie Stage 9]
[50] Campbell, 2004, 14; Carlson, 2004, 116 & 446; Navaratnam, 1991, 147-148; O’Rahilly and Müller, 1987, 99. [Carnegie Stage 10]
[51] Campbell, 2004, 14; Carlson, 2004, 430; De Vries and Saunders, 1962, 96; Gardner and O’Rahilly, 1976, 583; Gilbert-Barness and Debich-Spicer, 1997, 650; Gittenger-de Groot et al., 2000, 17; van Heeswijk et al., 1990, 151; Kurjak and Chervenak, 1994, 439; Navaratnam, 1991, 147-148; O’Rahilly and Müller, 1987, 99; Wisser and Dirschedl, 1994, 108. [Carnegie Stage 10, possibly late Stage 9]
[52] Moore and Persaud, 2003, 70: “The cardiovascular system is the first organ system to reach a functional state.“
[53] Moore and Persaud, 2003, 78.
[54] Gasser, 1975, 26; Moore and Persaud, 2003, 78.

Page 6

Embryonic Development: 4 to 6 Weeks

Chapter 11   4 Weeks: Amniotic Fluid

By 4 weeks the clear amnion surrounds the embryo in a fluid-filled sac.[55] This sterile liquid, called amniotic (am-nē-ot'ik) fluid, provides the embryo with protection from injury.[56]

Embryonic Development: 4 to 6 Weeks

Chapter 11   4 Weeks: Amniotic Fluid

4 週までには 無色の羊膜が 液体に満たされた嚢にある 胎芽を取り囲みます この無菌の液体は 羊水と呼ばれ 胎芽を損傷から守ります

Chapter 12   The Heart in Action

The heart typically beats about 113 times per minute.[57]

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

The heart will beat approximately 54 million (5.4×107) times before birth and over 3.2 billion (3.2×109) times over the course of an 80-year lifespan.[58]

Chapter 12   The Heart in Action

通常1 分間に113 回の 心拍数があります

血液が心室に出入りすると 心臓の色が変化することに 気づきましたか

心臓は 出生前に およそ5,400 万回も脈打ち 約80 年という一生を通じて 32 億回もの心拍数があります

Chapter 13   Brain Growth

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

Chapter 13   Brain Growth

急速な脳の発達は 前脳 中脳 後脳の変化により分かります

Chapter 14   Limb Buds

Upper and lower limb development begins with the appearance of the limb buds by 4 weeks.[59]

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.[60]

Chapter 14   Limb Buds

4 週までには 肢芽の出現とともに 上肢と下肢の発育が始まります

この時点の皮膚は 細胞1個の厚みしかなく 透明色をしています

皮膚が厚みを増すにつれて 透明感は失われます ですから 器官の発達を 観察できるのも あと1 ヶ月のみとなります

Chapter 15   5 Weeks: Cerebral Hemispheres

Between 4 and 5 weeks, the brain continues its rapid growth and divides into five distinct sections.[61]

The head comprises about one-third of the embryo's total size.[62]

The cerebral (ser'ĕ-brăl) hemispheres appear,[63] gradually becoming the largest parts of the brain.[64]

Functions eventually controlled by the cerebral hemispheres include thought, learning, memory, speech, vision, hearing, voluntary movement, and problem-solving.[65]

Chapter 15   5 Weeks: Cerebral Hemispheres

4 ~ 5 週の間に 脳は急速な成長を続け 5 つのはっきりと識別できる 部分に分かれます

頭は 胎芽全体の大きさの 約 1/3を占めます

大脳半球が現れ 次第に 脳の大半を 占めるようになります

大脳半球が制御する ことになる機能は 思考 学習 記憶 言語 視力 聴覚 随意運動 および問題解決などです

 

 


[55] Gasser, 1975, 30; O’Rahilly and Müller, 2001, 80.
[56] O’Rahilly and Müller, 2001, 81.
[57] van Heeswijk et al., 1990, 153.
[58] See Appendix A.
[59] Gasser, 1975, 49 & 59; O’Rahilly and Gardner, 1975, 11; O’Rahilly and Müller, 1985, 148 & 151; O’Rahilly and Müller, 1987, 143; Streeter, 1945, 30; Uhthoff, 1990, 7 & 141. [upper and lower limb buds: Carnegie Stages 12 & 13]
[60] Moore and Persaud, 2003, 486; O’Rahilly, 1957, 459; O’Rahilly and Müller, 2001, 165. For information about the first-trimester, direct-imaging technique used in this program (called embryoscopy), see Cullen et al., 1990.
[61] O’Rahilly and Müller, 1999a, 134; Sadler, 2005, 106. [Carnegie Stage 15]
[62] Laffont, 1982, 5.
[63] Bartelmez and Dekaban, 1962, 25; Campbell, 2004, 17; O’Rahilly and Gardner, 1979, 130; O’Rahilly et al., 1984, 249; O’Rahilly and Müller, 1999a, 115; van Dongen and Goudie, 1980, 193. [Carnegie Stage 14]
[64] Moore, 1980, 938.
[65] Guyton and Hall, 2000, 663-677.

Page 7

Chapter 16   Major Airways

In the respiratory system, the right and left main stem bronchi (brong'kī) are present[66] and will eventually connect the trachea (trā´kē-ă), or windpipe, with the lungs.

Chapter 16   Major Airways

呼吸器官では 左右の主気管支幹が見られ 最終的には 気管が 肺につながります

Chapter 17   Liver and Kidneys

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

The permanent kidneys appear by 5 weeks.[67]

Chapter 17   Liver and Kidneys

脈打つ心臓の横にある腹部を 大きな塊の肝臓が占めている ことに注意してください

永久腎臓は5 週までに現れます

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.[68]

Chapter 18   Yolk Sac and Germ Cells

卵黄嚢は 胎芽細胞と呼ばれる 初期の生殖細胞を含んでいます 5 週までに これらの胎芽細胞は 腎臓の横にある 生殖器官に移動します

Chapter 19   Hand Plates and Cartilage

Also by 5 weeks, the embryo develops hand plates,[69] and cartilage formation begins by 5½ weeks.[70]

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

Chapter 19   Hand Plates and Cartilage

5 週までに 胎芽では 手板が発達し 軟骨の形成は5 週半 までに始まります

ここでは 5 週 6 日目に 左の手板と手首が見られます

 

 


[66] Moore and Persaud, 2003, 245; O’Rahilly and Boyden, 1973, 239; O’Rahilly and Müller, 2001, 291; Sparrow et al., 1999, 550.
[67] Angtuaco et al., 1999, 13; Lipschutz, 1998, 384; Moore and Persaud, 2003, 288; O’Rahilly and Müller, 1987, 167 & 182; O’Rahilly and Müller, 2001, 301; Sadler, 2005, 72. [Carnegie Stage 14]
[68] O’Rahilly and Müller, 2001, 23; Waters and Trainer, 1996, 16; Witschi, 1948, 70, 77 & 79.
[69] O’Rahilly and Müller, 1987, 175; Streeter, 1948, 139. [Carnegie Stage 15 ]
[70] O’Rahilly and Gardner, 1975, 4. [Carnegie Stages 16 and 17 ]

Page 8

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.[71] Such movement is necessary to promote normal neuromuscular development.

A touch to the mouth area causes the embryo to reflexively withdraw its head.[72]

Embryonic Development: 6 to 8 Weeks

Chapter 20   6 Weeks: Motion and Sensation

6 週までに大脳半球は 脳の他の部分と比べ 急激な発達をします

胎芽は 自発的な反射運動を始めます この運動は 正常な神経筋発達を 促すために必要です

口の周囲に触れると 胎芽は 反射的に頭をすくめます

Chapter 21   The External Ear and Blood Cell Formation

The external ear is beginning to take shape.[73]

By 6 weeks, blood cell formation is underway in the liver where lymphocytes are now present.[74] This type of white blood cell is a key part of the developing immune system.

Chapter 21   The External Ear and Blood Cell Formation

外耳が形成され始めます

6 週までに 肝臓では血球の形成が 行われています リンパ球が見られます この種類の白血球は 免疫系の発達に 重要な役割を果たします

Chapter 22   The Diaphragm and Intestines

The diaphragm (dī'ă-fram), the primary muscle used in breathing, is largely formed by 6 weeks.[75]

A portion of the intestine now protrudes temporarily into the umbilical cord. This normal process, called physiologic herniation (fiz-ē-ō-loj'ik her-nē-ā'shŭn), makes room for other developing organs in the abdomen.[76]

Chapter 22   The Diaphragm and Intestines

横隔膜は 呼吸の際に使われる 主要な筋肉ですが 6 週までに 大体形成されます

今のところ 腸の一部が 一時的に臍帯へ突出しています これは正常な過程であり 生理的ヘルニアと呼ばれますが この突出により腹部器官の 発達する余裕が生まれるのです

Chapter 23   Hand Plates and Brainwaves

At 6 weeks the hand plates develop a subtle flattening.[77]

Primitive brainwaves have been recorded as early as 6 weeks and 2 days.[78]

Chapter 23   Hand Plates and Brainwaves

6 週までに 手板は かすかに平になります

胎芽の脳波は 早ければ6 週 日で 記録されます

 

 


[71] Birnholz et al., 1978, 539; de Vries et al., 1982, 301 & 304: “The first movements were observed at 7.5 weeks postmenstrual age.“ [or 5½ weeks postfertilization age]; Humphrey, 1964, 99: earliest reflex 5½ weeks; Humphrey, 1970, 12; Humphrey and Hooker, 1959, 76; Humphrey and Hooker, 1961, 147; Kurjak and Chervenak, 1994, 48; Visser et al., 1992, 175-176: “Endogenously generated fetal movements can first be observed after 7 weeks postmenstrual age (i.e. 5 weeks after conception);“ Natsuyama, 1991, 13; O’Rahilly and Müller, 1999a, 336: 5½ weeks postfertilization; Sorokin and Dierker, 1982, 723 & 726; Visser et al., 1992, 175-176; Natsuyama, 1991, 13: Spontaneous movement observed by “Carnegie stage 15“ (about 33 days postfertilization); Hogg, 1941, 373: Reflex activity begins at 6½ weeks [adjusted to postfertilization age].
[72] Goodlin, 1979, D-128.
[73] Karmody and Annino, 1995, 251; O’Rahilly and Müller, 2001, 480; Streeter, 1948, 190.
[74] Kurjak and Chervenak, 1994, 19.
[75] de Vries et al., 1982, 320.
[76] Gilbert-Barness and Debich-Spicer, 1997, 774; Grand et al., 1976, 798; O’Rahilly and Müller, 1987, 213; Sadler, 2005, 66; Spencer, 1960, 9; Timor-Tritsch et al., 1990, 287.
[77] O’Rahilly and Müller, 1987, 202-203.
[78] Borkowski and Bernstine, 1955, 363 (cited by Bernstine, 1961, 63 & 66; O’Rahilly and Müller, 1999a, 195; van Dongen and Goudie, 1980, 193.); Hamlin, 1964, 113. For a summary of in utero fetal encephalography (measuring brainwaves) in the near- term fetus using abdominal and vaginal electrodes see Bernstine et al., 1955.

Page 9

Chapter 24   Nipple Formation

Nipples appear along the sides of the trunk shortly before reaching their final location on the front of the chest.[79]

Chapter 24   Nipple Formation

乳首が体幹の側面にそって現れ まもなく最終的な場所である 胸の前面に落ち着きます

Chapter 25   Limb Development

By 6½ weeks, the elbows are distinct, the fingers are beginning to separate,[80] and hand movement can be seen.

Bone formation, called ossification (os'i-fi-kā'shŭn), begins within the clavicle, or collar bone, and the bones of the upper and lower jaw.[81]

Chapter 25   Limb Development

6 週半までに 腕が 識別できるようになり 指が分かれ始め 手の動きを見ることができます

骨化と呼ばれる骨の形成は 鎖骨および 上顎と下顎の骨から 始まります

Chapter 26   7 Weeks: Hiccups and Startle Response

Hiccups have been observed by 7 weeks.[82]

Leg movements can now be seen, along with a startle response.[83]

Chapter 26   7 Weeks: Hiccups and Startle Response

7 週までに しゃっくりが 観察されます

この頃には足の動作や 驚愕反応が見られます

Chapter 27   The Maturing Heart

The four-chambered heart is largely complete.[84] On average, the heart now beats 167 times per minute.[85]

Electrical activity of the heart recorded at 7½ weeks reveals a wave pattern similar to the adult's.[86]

Chapter 27   The Maturing Heart

4室の心臓は 大体完成します この頃の平均心拍数は 1 分間167 回です

7 週半に記録された 電気的活動は 大人のものと似通った 波形を表しています

Chapter 28   Ovaries and Eyes

In females, the ovaries are identifiable by 7 weeks.[87]

By 7½ weeks, the pigmented retina of the eye is easily seen and the eyelids are beginning a period of rapid growth.[88]

Chapter 28   Ovaries and Eyes

女の胎芽の場合 7 週までに 卵巣が識別できます

7 週半までに 眼の色素上網膜が 簡単に観察でき 瞼は 急速な成長期を迎えます

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.[89]

Knee joints are also present.[90]

Chapter 29   Fingers and Toes

指は 離ればなれになり 足の指は 付け根のみで結合し

この頃になると 手足を合わせます

ひざの関節も見られます

 

 


[79] O’Rahilly and Müller, 1985, 155: “The nipple appears at stages 17 and 18.“ [41-44 days postfertilization]; Wells, 1954, 126.
[80] O’Rahilly and Müller, 2001, 221; Streeter, 1948, 187.
[81] Carlson, 2004, 189; O’Rahilly and Gardner, 1972, 293; O’Rahilly and Gardner, 1975, 19; O’Rahilly and Müller, 2001, 385; Sperber, 1989, 122 & 147. [Carnegie Stage 19]
[82] de Vries et al., 1982, 305 & 311; Visser et al., 1992, 176.
[83] de Vries et al., 1988, 96; Visser et al., 1992, 176.
[84] Cooper and O’Rahilly, 1971, 292; James, 1970, 214; Jordaan, 1979, 214; Streeter, 1948, 192; Vernall, 1962, 23: “The four chambers of the heart and the associated major vessels are externally apparent in a close approximation to their adult positions.“ [Carnegie Stage 18]
[85] van Heeswijk et al., 1990, 153.
[86] Straus et al., 1961, 446 (cited by Gardner and O’Rahilly, 1976, 571.):  “…an electrocardiogram with the classical P, QRS, and T configuration has been obtained from a 23mm human embryo (Straus, Walker, and Cohen, 1961).“
[87] O’Rahilly and Müller, 2001, 320. [Carnegie Stage 20]
[88] Andersen et al., 1965, 646; O’Rahilly, 1966, 35; O’Rahilly and Müller, 1987, 259; Pearson, 1980, 39; Streeter, 1951, 193. [Carnegie Stage 22] Pigment within the retina is present from about 37 days postfertilization per O’Rahilly, 1966, 25. [Carnegie Stage 16]
[89] Streeter, 1951, 191; reiterated by O’Rahilly and Müller, 1987, 257.
[90] O’Rahilly and Gardner, 1975, 11; O’Rahilly and Müller, 1987, 262.

Page 10

The 8-Week Embryo

Chapter 30   8 Weeks: Brain Development

At 8 weeks the brain is highly complex[91] and constitutes almost half of the embryo's total body weight.[92]

Growth continues at an extraordinary rate.

The 8-Week Embryo

Chapter 30   8 Weeks: Brain Development

8 週までには 脳は かなり複雑になり 胎芽の全重量の約半分を 占めるようになります

成長は 驚くべきペースで続きます

Chapter 31   Right- and Left-Handedness

By 8 weeks, 75 percent 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.[93]

Chapter 31   Right- and Left-Handedness

8 週までには 胎芽の75% が 右利きの優勢を表します 残りの25% は 左利きの優勢と どちらでもない 場合とに均等に分かれます これが 右利き左利き行動の 最初の証拠です

Chapter 32   Rolling Over

Pediatric textbooks describe the ability to "roll over" as appearing 10 to 20 weeks after birth.[94] However, this impressive coordination is displayed much earlier in the low-gravity environment of the fluid-filled amniotic sac.[95] Only the lack of strength required to overcome the higher gravitational force outside the uterus prevents newborns from rolling over.[96]

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.[97]

Touching the embryo elicits squinting, jaw movement, grasping motions, and toe pointing.[98]

Chapter 32   Rolling Over

小児科学の本によると 「寝返り」をする能力は 生後10 ~ 20 週に現れる とありますが この素晴らしい協調は それよりずっと前に 羊水に満たされた嚢の中という 低重力環境で見られるのです ただ 子宮から出た後ですと 高重力に対するだけの力がないので 新生児は 寝返りが打てないのです

胎芽は この頃 一層 活動的になります

動作は 緩慢だったり 早かったり 1回であったり 繰り返されたり 自発的であったり 反射的であったりと 様々です

頭の回転 首の伸長 手と顔の接触等が より頻繁に起こります

胎芽を触ると 眼を細めたり 顎を動かしたり 何かをつかむ様な動きをしたり 足指を伸ばしたりします

Chapter 33   Eyelid Fusion

Between 7 and 8 weeks, the upper and lower eyelids rapidly grow over the eyes and partially fuse together.[99]

Chapter 33   Eyelid Fusion

7 ~ 8 週の間に 上瞼と下瞼が急速に発達し 部分的には まだくっついています

Chapter 34   "Breathing" Motion and Urination

Although there is no air in the uterus, the embryo displays intermittent breathing motions by 8 weeks.[100]

By this time, kidneys produce urine which is released into the amniotic fluid.[101]

In male embryos, the developing testes begin to produce and release testosterone (tes-tos´tĕ-rōn).[102]

Chapter 34   "Breathing" Motion and Urination

子宮には空気がないのですが 8 週までには 胎芽に 間欠呼吸動作が見られます

この時期までに 腎臓は尿を生成し 羊水に放出します

男の胎芽では 発達中の睾丸が テステステロンを 生成および分泌し始めます

Chapter 35   The Limbs and Skin

The bones, joints, muscles, nerves, and blood vessels of the limbs closely resemble those in adults.[103]

By 8 weeks the epidermis, or outer skin, becomes a multi-layered membrane,[104] losing much of its transparency.

Eyebrows grow as hair appears around the mouth.[105]

Chapter 35   The Limbs and Skin

四肢の骨 関節 筋肉 神経 および血管は 大人の組織と非常に 似通っています

8 週までに 外側の 皮膚にあたる外皮は 数層の厚みをもった膜となり 透明感を殆ど失います

口の周囲に毛が現れると 眉も発達します

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 (109) cells[106] which form over 4,000 (4×103) distinct anatomic structures.

The embryo now possesses more than 90 percent of the structures found in adults.[107]

Chapter 36   Summary of the First 8 Weeks

8 週で 胎生期は終了します

この間に ヒトの胎芽は 1 個の細胞から およそ10 億個の細胞に成長し 4,000 の個別の特徴を有する 解剖学的構造を形成します

胎芽は この時点で 大人に見られる 構造の90% 以上を 備えています

 

 


[91] O’Rahilly and Müller, 1999a, 288: “The brain at [Carnegie] Stage 23 is far more advanced morphologically than is generally appreciated, to such an extent that functional considerations are imperative.“
[92] Jordaan, 1979, 149.
[93] Hepper et al., 1998, 531; McCartney and Hepper, 1999, 86.
[94] Bates, 1987, 534.
[95] de Vries et al., 1982, 320; Goodlin and Lowe, 1974, 348; Humphrey, 1970, 8.
[96] Liley, 1972, 101.
[97] de Vries et al., 1982, 311.
[98] Humphrey, 1964, 102; Humphrey, 1970, 19.
[99] Process described by Andersen et al., 1965, 648-649; O’Rahilly, 1966, 36-37; O’Rahilly and Müller, 1987, 261. [Carnegie Stage 23]
[100] Connors et al., 1989, 932; de Vries et al., 1982, 311; McCray, 1993, 579; Visser et al.,1992, 177.
[101] O’Rahilly and Müller, 2001, 304; Windle, 1940, 118; (Windle reports urine formation begins at nine weeks.)
[102] Moore and Persaud, 2003, 307; Waters and Trainer, 1996, 16-17.
[103] O’Rahilly and Gardner, 1975, 15: ”By the end of the embryonic proper (Stage 23, 8 postovulatory weeks), all of the major skeletal, articular, muscular, neural, and vascular elements of the limbs are present in a form and arrangement closely resembling those of the adult.“ See O’Rahilly, 1957, for a summary of joint types and a description of limb joint development during the embryonic period. See Gray et al., 1957, for a detailed examination of the bones and joints of the hand throughout the embryonic and fetal periods.
[104] Hogg, 1941, 407; Pringle, 1988, 178.
[105] Hogg, 1941, 387; O’Rahilly and Müller, 2001, 169.
[106] Pringle, 1988, 176.
[107] O’Rahilly and Müller, 2001, 87: “It has been estimated that more than 90% of the more than 4500 named structures of the adult body become apparent during the embryonic period (O’Rahilly).“

Page 11

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[108] and the fetus can swallow amniotic fluid.[109]

The fetus can also grasp an object,[110] move the head forward and back, open and close the jaw, move the tongue, sigh,[111] and stretch.[112]

Nerve receptors in the face, the palms of the hands, and the soles of the feet can sense light touch.[113]

"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.[114]

The eyelids are now completely closed.[115]

In the larynx, the appearance of vocal ligaments signals the onset of vocal cord development.[116]

In female fetuses, the uterus is identifiable[117] and immature reproductive cells called oogonia (ō-ō-gō′nē-ă) are replicating within the ovary.[118]

External genitalia begin to distinguish themselves as either male or female.[119]

The Fetal Period (8 Weeks through Birth)

Chapter 37   9 Weeks: Swallows, Sighs, and Stretches

胎児期は 出生まで続きます

9 週までには 指しゃぶりが始まり 胎児は 羊水を嚥下できます

胎児は 物をつかんだり 頭を前後に動かし 顎を開いたり閉じたり 舌を動かし ため息をついたり 伸びをすることができます

顔や手のひら 足裏にある神経受容体は 軽い接触を感じることができます

「足裏への軽い接触に反応して」 胎児は 股間部節と膝を曲げ また 足指を丸めたりもします

この頃には 瞼は かたく閉じられています

声帯発達の始まりの兆候として 喉頭に声帯靱帯が現れます

女の胎児では 子宮が 識別できるようになり 卵原細胞と呼ばれる 未成熟の生殖細胞が 卵巣内で複製されています

外性器においては 男女の区別ができる ようになります

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 percent.[120]

By 10 weeks, stimulation of the upper eyelid causes a downward rolling of the eye.[121]

The fetus yawns and often opens and closes the mouth.[122]

Most fetuses suck the right thumb.[123]

Sections of intestine within the umbilical cord are returning to the abdominal cavity.[124]

Ossification is underway in most bones.[125]

Fingernails and toenails begin to develop.[126]

Unique fingerprints appear 10 weeks after fertilization. These patterns can be used for identification throughout life.[127]

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

9 ~ 10 週にかけての 急激な成長により 体重が75% 増加します

10 週までには 上瞼を刺激することにより 眼球を下方に向けます

胎児は 頻繁にあくびをし 口を開けたり閉じたりします

殆どの胎児は 右指をしゃぶっています

臍帯内の腸の部分は 腹腔内に戻ります

骨の殆どの部分において 骨化が進んでいます

手足の爪が発達します

受精後10 週で 唯一無比の指紋が現れます 指紋は 人の一生を通じて 認証のため使われます

Chapter 39   11 Weeks: Absorbs Glucose and Water

By 11 weeks the nose and lips are completely formed.[128] 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.[129]

Though sex is determined at fertilization, external genitalia can now be distinguished as male or female.[130]

Chapter 39   11 Weeks: Absorbs Glucose and Water

11 週までには 鼻と唇が 完全に出来上がります その他の身体部分に関しては ヒトのライフサイクルの 各段階によって その外観が変わってきます

腸は 胎児の飲み込んだ グルコースと水を 吸収し始めます

受精時において 性別は決定されていますが 外性器の男女の区別が 出来るようになるのは この頃です

 

 


[108] Liley, 1972, 103.
[109] Campbell, 2004, 24; de Vries, 1982, 311; Petrikovsky et al., 1995, 605.
[110] Robinson and Tizard, 1966, 52; Valman and Pearson, 1980, 234.
[111] de Vries et al., 1982, 305-307.
[112] de Vries et al., 1982, 311.
[113] Humphrey, 1964, 96; Humphrey, 1970, 16-17 (cited by Reinis and Goldman, 1980, 232); Humphrey and Hooker, 1959, 77-78.
[114] Robinson and Tizard, 1966, 52; Quote from Valman and Pearson, 1980, 234.
[115] Andersen et al., 1965, 648-649; O’Rahilly and Müller, 2001, 465; Pearson, 1980, 39-41.
[116] O’Rahilly and Müller, 1984, 425. See also Campbell, 2004, 29.
[117] O’Rahilly, 1977a, 128; O’Rahilly, 1977b, 53; O’Rahilly and Müller, 2001, 327.
[118] O’Rahilly and Müller, 2001, 25 & 322.
[119] Campbell, 2004, 28 & 35; O’Rahilly and Müller, 2001, 336.
[120] Brenner et al., 1976, 561.
[121] Goodlin, 1979, D-128; Humphrey, 1964, 102.
[122] de Vries et al., 1982, 309.
[123] Hepper et al., 1991, 1109.
[124] Grand et al., 1976, 798; Pringle, 1988, 178; Sadler, 2005, 66; Spencer, 1960, 9. [Pringle reports the bowel returns into the abdomen during the ninth or tenth week.]
[125] Cunningham et al., 2001, 133.
[126] O’Rahilly and Müller, 2001, 170-171.
[127] Babler, 1991, 95; Penrose and Ohara, 1973, 201; For an overview of ridge formation in the skin of the hands see Cummins, 1929.
[128] Timor-Tritsch et al., 1990, 291.
[129] Koldovský et al., 1965, 186.
[130] O’Rahilly and Müller, 2001, 336; Wilson, 1926, 29.

Page 12

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 percent.[131]

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.[132]

Bowel movements begin as early as 12 weeks and continue for about 6 weeks.[133]

The material first expelled from the fetal and newborn colon is called meconium (mĭ-kō'nē-ŭm).[134] It is composed of digestive enzymes, proteins, and dead cells shed by the digestive tract.[135]

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.[136]

With the exception of the back and the top of the head, the body of the entire fetus now responds to light touch.[137]

Sex-dependent developmental differences appear for the first time. For instance, female fetuses exhibit jaw movement more frequently than males.[138]

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.[139] This response is called the "rooting reflex" and it persists after birth, helping the newborn find his or her mother's nipple during breastfeeding.[140]

The face continues to mature as fat deposits begin to fill out the cheeks[141] and tooth development begins.[142]

By 15 weeks, blood-forming stem cells arrive and multiply in the bone marrow. Most blood cell formation will occur here.[143]

Although movement begins in the 6-week embryo, a pregnant woman first senses fetal movement between 14 and 18 weeks.[144] Traditionally, this event has been called quickening.[145]

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

11 ~ 12 週にかけて 胎児の体重は およそ60% 増加します

12 週をもって 妊娠初期が終わります

はっきりとわかる味覚芽が 口内を覆います 出生時までには 味覚芽は 舌と口蓋の 後部に残るのみとなります

早ければ 12 週に便通が始まり 6 週間ほど続きます

胎児および新生児の結腸 からの最初の排出物は 胎便と呼ばれます 胎便は 消化酵素と タンパク質および 消化器官からの死細胞で 出来ています

12 週までに 上肢は 身体の大きさに最終的に 釣り合った長さになります 下肢が最終的に 釣り合った長さになるには もう少し時間がかかります

背中と頭上を除き 胎児全体の身体は 軽い接触に反応します

ここで初めて 性差による発達の違いが現れます たとえば 女の胎児の顎の動作は 男の胎児より頻繁です

初期の体をすくめる 反応とは対照的に この時点における口の周囲の刺激は 刺激を受けた方向に顔を向け 口を開けるという動作を促します 「ルーティング反射」 と呼ばれるこの反応は 出生後も継続し 授乳の際 新生児が母親の乳首を 見つけるのに役立ちます

脂肪沈着が 頬を覆うにつれて 顔立ちが しっかりとしてきます 歯の発達も 始まります

15 週までには 血液を 形成する幹細胞が達して 骨髄内で増殖します 殆どの血球形成は ここで行われます

動きは 6 週間の胎芽で 既に始まっているのですが 妊婦が胎動を初めて感じるのは 14 ~ 18 週にかけてです 従来から胎動感と呼ばれています

 

 


[131] Brenner, 1976, 561.
[132] Lecanuet and Schaal, 1996, 3; Miller, 1982, 169; Mistretta and Bradley, 1975, 80.
[133] Abramovich and Gray, 1982, 296; Ramón y Cajal and Martinez, 2003, 154-155, report visualizing defecation (bowel movements) with ultrasound in utero in all 240 fetuses studied between 15 and 41 weeks [postmenstrual age].
[134] O’Rahilly and Müller, 2001, 257; For a description of meconium by Aristotle see Grand et al., 1976, 791.
[135] Grand et al., 1976, 806.
[136] Moore and Persaud, 2003, 105.
[137] Lecanuet and Schaal, 1996, 2; Reinis and Goldman, 1980, 232.
[138] Hepper et al., 1997, 1820.
[139] Mancia, 1981, 351.
[140] Bates, 1979, 419.
[141] Poissonnet et al., 1983, 7; Poissonnet et al., 1984, 3: In a study of 488 fetuses, Poissonnet’s group found that adipose tissue (fat) appears in the face from 14 weeks postfertilization. By 15 weeks, fat appears in the abdominal wall, back, kidneys, and shoulders. By 16 weeks, fat is also present throughout the upper and lower limbs.
[142] Pringle, 1988, 178. [Thirteenth week postfertilization]
[143] Pringle, 1988, 179.
[144] Sorokin and Dierker, 1982, 720; Leader, 1995, 595: “Some pregnant women reported fetal flutters as early as 12 weeks (quickening).“ Women also tend to accurately recognize fetal movement at earlier fetal ages during second and subsequent pregnancies as compared to first pregnancies.
[145] Spraycar, 1995, 1479; Timor-Tritsch et al., 1976, 70.

Page 13

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 noradrenalin, or norepinephrin (nor-ep'i-nef'rin), into the bloodstream.[146]

In the respiratory system, the bronchial tree is now nearly complete.[147]

A protective white substance, called vernix caseosa (ver'niks caseo'sa), now covers the fetus. Vernix protects the skin from the irritating effects of amniotic fluid.[148]

From 19 weeks fetal movement, breathing activity, and heart rate begin to follow daily cycles called circadian (ser-kā'dē-ăn) rhythms.[149]

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

16 週までには 胎児の腹腔に 針を差し込む処置を 行うことにより ホルモンのストレス反応を誘発し ノルアドレナリンや ノルエピネフリンを 血中に放出するようになります

呼吸器官では この頃に器官支樹の 形成が完了します

胎脂と呼ばれる 白い保護物質が 胎児を覆います 胎脂は 羊水の刺激から 皮膚を保護します

19 週以降の胎児の動きでは 呼吸活動が始まり 心拍は日周性の 概日リズムに支配されます

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[150] within the fully developed inner ear. From now on, the fetus will respond to a growing range of sounds.[151]

Hair begins to grow on the scalp.

All skin layers and structures are present, including hair follicles and glands.[152]

By 21 to 22 weeks after fertilization, the lungs gain some ability to breathe air.[153] This is considered the age of viability because survival outside the womb becomes possible for some fetuses.[154]

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

20 週までには 聴覚器官である うずまき官が 大人の大きさに達します 内耳もその頃には 完全に発達しています この頃からは 胎児は 幅広い音に対して 反応するようになります

頭皮には毛が生えはじめ

毛嚢や皮脂腺などの 皮膚の層や構造が 形成されています

受精後 21 ~ 22 週までには 肺は 空気を取り込む能力を ある程度備えています これにより 子宮の外での生存が 胎児によっては可能となるので この時点を生育可能な 年齢とみなします

 

 


[146] Giannakoulopoulos et al., 1999, 494 & 498-499; Glover and Fisk, 1999, 883; Smith et al., 2000, 161. Cortisol levels also rise after invasive procedures following 21 weeks postfertilization - see Giannakoulopoulos et al., 1994, 80.
[147] DiFiore and Wilson, 1994, 221-222; Pringle, 1988, 178. [There is some disagreement among experts regarding when the bronchial tree is complete. Some say completion occurs as early as 16 weeks postfertilization while others say it occurs after birth.]
[148] Campbell, 2004, 48; Moore and Persaud, 2003, 107; O’Rahilly and Müller, 2001, 168.
[149] de Vries et al., 1987, 333; Goodlin and Lowe, 1974, 349; Okai et al., 1992, 391 & 396; Romanini and Rizzo, 1995, 121; For a description of the circadian system, see Rosenwasser, 2001, 127; From Vitaterna et al., 2001, 92: Glossary: “Circadian: A term derived from the Latin phrase “circa diem,“ meaning “about a day;“ refers to biological variations or rhythms with a cycle of approximately 24 hours.“
[150] Lecanuet and Schaal, 1996, 5-6; Querleu et al., 1989, 410.
[151] Glover and Fisk, 1999, 882; Hepper and Shahidullah, 1994, F81; Querleu et al., 1989, 410; Sorokin and Dierker, 1982, 725 & 730; Valman and Pearson, 1980, 233-234.
[152] Pringle, 1988, 180.
[153] Hansen and Corbet, 1998, 542.
[154] O’Rahilly and Müller, 2001, 92, report the age of viability as 20 weeks postfertilization; Draper et al., 1999, 1094, report a survival rate of 2% at 20 weeks postfertilization, 6% at 21 weeks, and 16% at 22 weeks. Moore and Persaud, 2003, 103, report viability at 22 weeks; Wood et al., 2000, 379, report survival rates of 11% at 21 weeks, 26% at 22 weeks and 44% at 23 weeks (postfertilization weeks) based on premature birth data from the United Kingdom during 1995. Cooper et al. 1998, 976, (Figure 2) report infants with a birth weight over 500 grams experienced survival rates (all approximate) of 28% at 21 weeks postfertilization, 50% at 22 weeks, 67% at 23 weeks, and  77% at 24 weeks. Draper et al., 2003, updated their previously published survival tables for premature infants and now report an overall survival rate of 7% at 20 weeks, 15% at 21 weeks, 29% at 22 weeks, 47% at 23 weeks and 65% at 24 weeks. [All ages corrected to reflect postfertilization age.] These survival tables are available online at http://bmj.bmjjournals.com/cgi/content/full/319/7217/1093/DC1. Their methodology is described in their earlier paper (Draper et al., 1999, 1093-1094.) Note: These published survival tables reflect postmenstrual ages. Hoekstra et al., 2004, e3, report a survival rate of 66% at 23 weeks and 81% at 24 weeks “gestational age“ [not specifically defined] for premature births from 1996 to 2000 at their center in Minneapolis, Minnesota.

Page 14

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[155] and the fetus exhibits a blink-startle response.[156] This reaction to sudden, loud noises typically develops earlier in the female fetus.[157]

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.[158] Possible long-term consequences include hearing loss.[159]

The fetal respiratory rate can rise as high as 44 inhalation-exhalation cycles per minute.[160]

During the third trimester of pregnancy, rapid brain growth consumes more than 50 percent of the energy used by the fetus. Brain weight increases between 400 and 500 percent.[161]

By 26 weeks the eyes produce tears.[162]

The pupils respond to light as early as 27 weeks.[163] This response regulates the amount of light reaching the retina[164] 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.[165]

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.[166]

Through a series of step-like leg motions similar to walking, the fetus performs somersaults.[167]

The fetus appears less wrinkled as additional fat deposits form beneath the skin.[168] Fat plays a vital role in maintaining body temperature and storing energy after birth.

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

24 週までには 瞼が再び開き 瞬き-驚愕反応が 胎児に現れます 突然の大きな音に対する反応は 通常 女の胎児に早く見られます

大きな音は 胎児の健康に 悪影響を及ぼすと 調査によっては 報告しています 直接の結果として 長期にわたる心拍数の増加 過度の胎児の嚥下 突発的な行動の変化 長期の影響では 聴覚の喪失 などが挙げられます

胎児の呼吸速度は 1 分間に44 回の吸入-呼気 となります

妊娠後期において 胎児の消費するエネルギーの 50% が 脳の発達に費やされます 脳の重量は400 ~ 500% 増加し

26 週までには 眼から 涙が生成されます

瞳孔は 早ければ27 週に 光に対して反応します 網膜に到達する光の調節を 生涯行うわけです

嗅覚に必要な 全要素も機能しています 未熟児における研究を通じて 受精後26 週には においを察知できることが 分かっています

羊水に甘い物質を投与すると 胎児の嚥下回数が増え 逆に 苦い物質があると 嚥下回数が低下します 表情の変化も しばしば見られます

歩行に似通った ステップを踏む動作で 胎児は 180度の転換を行います

皮膚の下で体脂が増えるにつれ 胎児の体の皺も 少なくなります 脂肪は 体温維持と 出生後のエネルギー貯蔵に 重要な役割を果たします

 

 


[155] Open eyes are visualized by 4D ultrasound following 22 weeks postfertilization per Campbell 2002, 3; De Lia, 2002, personal communication; O’Rahilly and Müller, 2001, 465. For a detailed ultrastructural study of the union between the upper and lower eyelids see Andersen et al., 1967, 293.
[156] Birnholz and Benacerraf, 1983, 517 (cited by Drife, 1985, 778); See also Campbell, 2002, 3: Professor Stuart Campbell correctly points out that the eyes of the fetus are closed most of the time and a true blink requires the eyes to be open. Perhaps the “blink-startle“ response would be more accurately termed “squint-startle.“
[157] Lecanuet and Schaal, 1996, 9.
[158] Visser et al., 1989, 285.
[159] Gerhardt, 1990, 299; Petrikovsky et al., 1993, 548-549; Pierson, 1996, 21 & 26.
[160] Natale et al., 1988, 317.
[161] Growth of the human brain, 1975, 6; Mancuso and Palla, 1996, 290.
[162] Isenberg et al., 1998, 773-774.
[163] Robinson and Tizard, 1966, 52.
[164] Noback et al., 1996, 263.
[165] Lecanuet and Schaal, 1996, 3.
[166] Lecanuet and Schaal, 1996, 3; Liley, 1972, 102; Moore and Persaud, 2003, 219; Reinis and Goldman, 1980, 227.
[167] Liley, 1972, 100.
[168] England, 1983, 29.

Page 15

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.[169]

By 30 weeks, breathing movements are more common and occur 30 to 40 percent of the time in an average fetus.[170]

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.[171]

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

28 週までに 胎児は 高調音と低調音を 区別できるようになります

30 週までには 呼吸が ごく通常の活動となり 平均の胎児において 30 ~ 40% の割合で起こります

妊娠の最後の4 ヵ月において 胎児には 休みを間に入れた 協調した活動が見られます これらの行動の状況は いよいよ複雑さを増す 中枢神経の働きを 反映しています

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

By approximately 32 weeks, true alveoli (al-vē'ō-lī), or air "pocket" cells, begin developing in the lungs. They will continue to form until 8 years after birth.[172]

At 35 weeks the fetus has a firm hand grasp.[173]

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.[174]

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

32 週頃までには 空気の「ポケット」細胞である 肺胞が 肺で発達し始めます 出生後 8 歳まで その形成は続きます

35 週になると 胎児は 確かな把握反射ができます

胎児が様々な物質に さらされることにより 出生後の味覚の好き嫌いに 影響を与えるようです たとえば 胎児の母親が リコリスキャンディを味付けする アニスを食べたとすると 生まれてきた子供は アニスが好きになり アニスにさらされていない 新生児は嫌悪を示します

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

The fetus initiates labor[175] by releasing large amounts of a hormone called estrogen (es´trō-jen)[176] and thus begins the transition from fetus to newborn.

Labor is marked by powerful contractions of the uterus, resulting in childbirth.[177]

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.

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

エストロゲンと呼ばれる ホルモンを大量に放出し 胎児は 陣痛を誘発し 胎児から新生児への 移行が始まります

強い子宮の収縮により 陣痛が起こり 出産に至るのです

受精から誕生 そしてその後 ヒトの発達は ダイナミックで 継続的であり 複雑です この驚異的な過程についての 新しい発見により 一生を通じての健康に 胎児の発育が 大きな影響を与えることが 分ってきています

初期のヒトの発達に対する 理解が進むにつれて 出生前と出生後における 健康の促進も また可能と なることでしょう

 

 


[169] Glover and Fisk, 1999, 882; Hepper and Shahidullah, 1994, F81.
[170] Connors et al., 1989, 932; de Vries et al., 1985, 117; Patrick et al., 1980, 26 & 28; Visser et al., 1992, 178.
[171] DiPietro et al., 2002, 2: “One of the hallmarks of development before birth is the coalescence of patterns of fetal and behavioral and cardiac function into behavioral states, which is widely viewed as reflective of the developing integration of the central nervous system.“
[172] Lauria et al., 1995, 467.
[173] Moore and Persaud, 2003, 108.
[174] Schaal et al., 2000, 729.
[175] Liley, 1972, 100.
[176] Moore and Persaud, 2003, 131.
[177] Cunningham et al., 2001, 252.

Page 16


Appendix A − Calculations

To the Sun and Back: Determining the Length of DNA in an Adult

Given:

1.      The DNA molecule measures 3.4×10-9 meters per 10 base pairs.[178]

2.      There are 3 billion (3×109) base pairs per cell.

3.      There are an estimated 100 trillion (1014) cells per adult.

4.      The distance from the earth to the sun is approximately 93 million miles.

5.      There are 2.54 centimeters (cm) per inch.

Step 1   Compute the length of DNA in a single cell:

3.4×10-9 meters/10 base pairs ×  3×109 base pairs/cell = 1.02 meters of DNA per cell

Step 2   Compute the total length of DNA in an adult’s 100 trillion cells:

1.02 meters of DNA/cell × 1014 cells  =  1.02×1014 meters of DNA per adult*

Step 3   Convert 1.02×1014 meters to miles:

1.02×1014 meters × 100 cm/meter × 1inch/2.54 cm × 1 foot/12 inches × 1 mile/5,280 feet
 = 6.3379×1010miles of DNA

Step 4   Compute how many round trips from the earth to the sun:

6.3379×1010 miles of DNA ÷ (93,000,000 miles/trip × 2 trips/round trip)  =

340 round trips between earth and sun

Therefore, the DNA in a single adult, if oriented in linear fashion, would exceed 63 billion miles in length. This is long enough to extend from the earth to the sun and back––340 times.

* Approximately 25 trillion red blood cells are present in the adult.[179] It should be noted that red blood cells contain DNA early in their maturation phase but this DNA degenerates and is not present in the mature form. This calculation includes the DNA from red blood cells.

 

 


[178] Lodish et al., 2000, 104.
[179] Guyton and Hall, 2000, 2.

Page 17

A Tight Squeeze: Appreciating the Number of Bases Contained in the DNA of a Single Cell

The following page contains a list of 3,808 capital letters each of which represents a single base.

Given:

1.      A, G, T, and C each represent a base within the DNA of a single cell.

2.      Each line contains 68 letters without spaces representing 68 bases.

3.      Each page contains 56 lines. (Page size: 8½ × 11 inches, font: Times New Roman, font size: 10, spaces between letters: none, lines: single spaced, margins: as shown)

4.      Each cell contains 3 billion base pairs equaling 6 billion bases.

The calculation of the number of pages required to list all DNA bases in a single cell is as follows:

68 bases/line × 56 lines/page  =  3,808 bases/page

6,000,000,000 bases/cell ÷ 3,808 bases/page  =  1,575,630 pages/cell



ATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCG
ATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCG
ATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCG
ATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCG
ATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCG
ATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCG
ATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCG
ATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCG
ATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCG
ATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCG
ATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCG
ATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCG
ATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCG
ATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCG
ATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCG
ATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCG
ATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCG
ATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCG
ATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCG
ATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCG
ATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCG
ATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCG
ATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCG
ATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCG
ATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCG
ATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCG
ATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCG
ATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCG
ATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCG
ATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCG
ATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCG
ATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCG
ATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCG
ATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCG
ATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCG
ATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCG
ATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCG
ATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCG
ATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCG
ATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCG
ATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCG
ATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCG
ATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCG
ATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCG
ATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCG
ATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCG
ATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCG
ATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCG
ATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCG
ATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCG
ATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCG
ATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCG
ATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCG
ATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCG
ATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCG
ATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCG

Page 18

Climate Control: Approximating the Normal Range of Embryonic and Fetal Body Temperature

Given:

1.      The placenta maintains embryonic and fetal temperature between 0.5 ºC and 1.5 ºC above maternal core temperature.[180]

2.      Maternal core temperature is approximately 99.6º Fahrenheit.

3.      The formula to convert temperature from Fahrenheit (ºF) to Celsius (ºC) is:

ºC = 5/9 (ºF - 32)

The calculation to compute the range of embryonic and fetal body temperature is as follows:

Step 1             Convert maternal core temperature to Celsius:

Maternal core temperature in ºC: ºC = 5/9 (99.6 - 32) = 37.56 ºC

Step 2             Compute lower and upper ranges of fetal body temperature in Celsius:

Lower range (Celsius) = maternal core temperature + 0.5 ºC = 37.56 + 0.5 = 38.2 ºC

Upper range (Celsius) = maternal core temperature + 1.5 ºC = 37.56 + 1.5 = 39.2 ºC

Step 3             Convert results to Fahrenheit:

ºC = 5/9 (ºF - 32)                     9/5 ºC = (ºF - 32)                     ºF = 9/5 ºC + 32

Substituting to find the lower limit of fetal body temperature

ºF = 9/5 ºC + 32                      ºF = 9/5 (38.16) + 32   ºF = 100.7º

Substituting to find the upper limit of fetal body temperature

ºF = 9/5 ºC + 32                      ºF = 9/5 (39.16) + 32   ºF = 102.5º

Summary of Normal Embryonic and Fetal Body Temperature Range

  °F °C
Lower Limit 100.7 38.2
Upper Limit 102.5 39.2

 

 


[180] Liley, 1972, 101.

Page 19

The Beat Goes On: Estimating the Total Number of Heartbeats Before Birth and Beyond

The Embryonic Period

Week # Average Heart Rate
(Beats per Minute)
Beats per Week Running Total
4 113.00 1,139,040 1,139,040
5 132.00 1,330,560 2,469,600
6 151.00 1,522,080 3,991,680
7 170.00 1,713,600 5,705,280
8 169.03 1,703,845 7,409,125
(Approximately 7.41 million beats during the embryonic period)

Various authors agree the heart rate peaks at 7 weeks. Reported heart rates vary however. Van Heeswijk et al. report a peak heart rate of 167 ± 8 beats per minute (bpm)[181] while Leeuwen et al. report a peak rate of 175 bpm.[182] Van Lith et al. report the median fetal heart rate peaks at 177 bpm at 7 weeks.[183] One hundred seventy (170) bpm has been chosen as the peak heart rate for illustration purposes in this calculation. The heart rate for the various weeks from 7 through 38 have been calculated via linear interpolations[184] assuming heart rates of 170 bpm at 7 weeks and 140 bpm at term or 38 weeks.[185]

(Note: Heart rates are estimated. Living conditions and individual experience can and will vary.)

The Fetal Period

Week # Average Heart Rate
(Beats per Minute)
Beats per Week Running Total
9 168.06 1,694,090 9,103,216
10 167.10 1,684,336 10,787,551
11 166.13 1,674,581 12,462,132
12 165.16 1,664,826 14,126,958
13 164.19 1,655,071 15,782,029
14 163.23 1,645,316 17,427,346
15 162.26 1,635,562 19,062,907
16 161.29 1,625,807 20,688,714
17 160.32 1,616,052 22,304,766
18 159.35 1,606,297 23,911,063
19 158.39 1,596,542 25,507,605
20 157.42 1,586,787 27,094,393
21 156.45 1,577,033 28,671,425
22 155.48 1,567,278 30,238,703
23 154.52 1,557,523 31,796,226
24 153.55 1,547,768 33,343,994
25 152.58 1,538,013 34,882,008
26 151.61 1,528,259 36,410,266
27 150.65 1,518,504 37,928,770
28 149.68 1,508,749 39,437,519
29 148.71 1,498,994 40,936,513
30 147.74 1,489,239 42,425,752
31 146.77 1,479,484 43,905,237
32 145.81 1,469,730 45,374,966
33 144.84 1,459,975 46,834,941
34 143.87 1,450,220 48,285,161
35 142.90 1,440,465 49,725,626
36 141.94 1,430,710 51,156,337
37 140.97 1,420,956 52,577,292
38 140.00 1,411,201 53,988,493
(Approximately 54 million beats before birth)

Counting the Beats of a Lifetime

The Postnatal Period from Birth to 80 Years

Year # Average Heart Rate
(Beats per Minute)*[186]
Beats per Year Running Total
1 120 63,115,200 63,115,200
2 110 57,855,600 120,970,800
3 103 54,173,880 175,144,680
4 103 54,173,880 229,318,560
5 103 54,173,880 283,492,440
6 103 54,173,880 337,666,320
7 95 49,966,200 387,632,520
8 95 49,966,200 437,598,720
9 95 49,966,200 487,564,920
10 95 49,966,200 537,531,120
11 85 44,706,600 582,237,720
12 85 44,706,600 626,944,320
13 85 44,706,600 671,650,920
14 85 44,706,600 716,357,520
15 80 42,076,800 758,434,320
16 80 42,076,800 800,511,120
17 75 39,447,000 839,958,120
18 75 39,447,000 879,405,120
19 70 36,817,200 916,222,320
20 70 36,817,200 953,039,520
21-80 70 2,209,032,000 3,162,071,520
(Approximately 3.16 billion beats from birth to age 80 years)
Estimated Total Heart Beats From the
3-Week Embryo to Age 80 Years
3,216,060,000
(Approximately 3.2 Billion Beats Per Lifetime)

 

 


[181] van Heeswijk et al., 1990, 153.
[182] Leeuwen et al., 1999, 265.
[183] van Lith et al., 1992, 741.
[184] See Appendix A.
[185] DiPietro et al., 1996, 2559.
[186] Age appropriate pediatric heart rates adapted from Bates, 1987, 541.

Page 20


Appendix B − Relating Embryonic Age & Stage

O’Rahilly and Müller’s Age Assignments vs. Carnegie Stages, 1987 to 2001

 

Carnegie
Stage
Number
of Somites
Greatest
Length (mm)
1987 Age [187]
Convention
(in PF Days*)
1999 Age [188]
Convention
(in PF Days*)
2001 Age [189]
Convention
(in PF Days*)
1   0.1 - 0.15 1 - 1
2   0.1 - 0.2 1½ - 3 2 - 3 2 - 3
3   0.1 - 0.2 4 4 - 5 4 - 5
4   0.1 - 0.2 5 - 6 6 6
5   0.1 - 0.2 7 - 12 7 - 12 -
5a   0.1 7 - 8 - 7 - 8
5b   0.1 9 - 9
5c   0.15 - 0.2 11 - 12 - 11 - 12
6   0.2 13 17 17
6a   - - - -
6b   - - - -
7   0.4 16 19 19
8   1.0 - 1.5 18 23 -
8a   - - - 23
8b   - - - 23
9 1-3 1.5 - 2.5 20 26 25
10 4-12 2 - 3.5 22 29 28
11 13-20 2.5 - 4.5 24 30 29
12 21-29 3 - 5 26 31 30
13 30+ 4 - 6 28 32 32
14   5 - 7 32 33 33
15   7 - 9 33 35 36
16   8 - 11 37 37 38
17   11 - 14 41 40 41
18   13 - 17 44 42 44
19   16 - 18 47½  44 46
20   18 - 22 50½  47 49
21   22 - 24 52 50 51
22   23 - 28 54 52 53
23   27 - 31 56½  56 56

* PF Days = Postfertilization Days

 

There is international agreement among embryologists that human development during the embryonic period be divided into 23 stages (which were initially proposed by Mall, described by Streeter, and amended by O’Rahilly and Müller in 1987).[190] These have come to be known as Carnegie Stages. Particular internal and external features are required for inclusion in any given embryonic stage. These stages are independent of age and length and the use of the term ‘stage’ should be reserved for reference to this system per O’Rahilly and Müller in multiple publications.

Along with nearly-universal acceptance of the human embryonic staging system, a variety of age assignments have been proposed for each embryonic stage. Streeter believed the embryonic period spanned a 47- to 48-day period instead of the 56-day period accepted today. The Endowment for Human Development adopts the convention set forth by O’Rahilly and Müller in 1987 which has received widespread, but not universal, acceptance. O’Rahilly and Müller have since proposed amending this convention in light of transvaginal ultrasound data through a personal communication with Dr. Josef Wisser in 1992.[191] These alternate proposals are provided for the interested reader.

For instance, the onset of embryonic cardiac contraction (onset of the heartbeat) has long been described as a Carnegie Stage 10 or possibly a late Stage 9 event.[192] We report this event occurring at an age of 3 weeks, 1 day (22 days) postfertilization using the 1987 convention. Others may report this occurrence at 28 or 29 days as shown above. Of interest is a paper by Wisser and Dirschedl who reported using transvaginal ultrasound to visualize the embryonic heartbeat 23 days postfertilization in two embryos fertilized in vitro “with exactly known … age“ and “in embryos from 2 mm of greatest length onwards.“[193] This finding most closely coincides with the 1987 age convention. Schats et al. reported the earliest cardiac activity at 25 days after follicle aspiration in embryos conceived in vitro.[194] Tezuka et al. reported the earliest cardiac activity at 23 days postfertilization in embryos conceived naturally.[195]

There is considerable variation in normal human development during the postnatal period. The prenatal period is no different with variations in the size, rate of growth, and order of appearance of some structures or functions. No one knows the exact age range for each stage with absolute certainty. These approximations may change in the future as additional knowledge is gained through careful, published research.

 

 


[187] O’Rahilly and Müller, 1987, 3. Greatest length data is essentially uniform throughout the various texts.
[188] O’Rahilly and Müller, 1999a. Various pages.
[189] O’Rahilly and Müller, 2001, 490. Table A-1 – essentially unchanged from the 1996 edition. The 2001 convention differs only slightly from the 1999 convention as shown.
[190] O’Rahilly and Müller, 2001, 3.
[191] O’Rahilly and Müller, 1999a, 13.
[192] See footnote #51.
[193] Quotes from Wisser and Dirschedl, 1994, 108.
[194] Schats et al., 1990, 989.
[195] Tezuka, 1991, 211.

Page 21


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Full Names of Journals Cited

Journal Abbreviation Journal Name
Acta Anat Acta Anatomica
Acta Opthalmol Acta Ophthalmologica
Adv Contracept Advances in Contraception
Alcohol Res Health Alcohol Research & Health
Am J Anat The American Journal of Anatomy
Am J Cardiol The American Journal of Cardiology
Am J Kidney Dis American Journal of Kidney Diseases
Am J Obstet Gynecol American Journal of Obstetrics and Gynecology
Am J Reprod Immunol American Journal of Reproductive Immunology and Microbiology
Am J Respir Cell Mol Biol American Journal of Respiratory Cell and Molecular Biology
Am J Roentgenol American Journal of Roentgenology
Anat Embryol Anatomy and Embryology
Ann Otol Rhinol Laryngol The Annals of Otology, Rhinology, and Laryngology
Ann R Coll Surg Eng Annals of the Royal College of Surgeons of England
Arch Dis Child Archives of Disease in Childhood
Arch Ophthalmol Archives of Ophthalmology
Aust N Z J Psychiatry The Australian and New Zealand Journal of Psychiatry
Biol Neonate Biology of the Neonate
Birth Defects Orig Artic Ser Birth Defects Original Article Series
Br J Obstet Gynaecol British Journal of Obstetrics and Gynaecology
Br Med Bull British Medical Bulletin
Br Med J British Medical Journal
Chem Senses Chemical Senses
Child Dev Child Development
Clin Obstet Gynecol Clinical Obstetrics and Gynecology
Contrib Embryol Contributions to Embryology
Dev Med Child Neurol Developmental Medicine and Child Neurology
Dev Pharmacol Ther Developmental Pharmacology and Therapeutics
Early Hum Dev Early Human Development
Eur J Obstet Gynecol Reprod Biol European Journal of Obstetrics, Gynecology, and Reproductive Biology
Eye Eye
Facial Plast Surg Facial Plastic Surgery
Fertil Steril Fertility and Sterility
Fetal Ther Fetal Therapy
Gastroenterology Gastroenterology
Gynecol Invest Gynecologic Investigation
Gynecol Obstet Invest Gynecologic and Obstetric Investigation
Int J Psychoanal The International Journal of Psycho-Analysis
Ir J Med Sci Irish Journal of Medical Science
J Clin Ultrasound Journal of Clinical Ultrasound
J Comp Neurol The Journal of Comparative Neurology
J Med Genet Journal of Medical Genetics
J Comp Neurol Journal of Neuroradiology
J Pathol Bacteriol The Journal of Pathology and Bacteriology
J Pediatr Surg Journal of Pediatric Surgery
J Perinat Med Journal of Perinatal Medicine
J Anat Journal of Anatomy
JAMA JAMA : The Journal of the American Medical Association
Lancet Lancet
N Engl J Med The New England Journal of Medicine
N Z Med J New Zealand Medical Journal
Nature Nature
Neurology Neurology
Neuropsychologia Neuropsychologia
Nutr Rev Nutrition Reviews
Obstet Gynecol Obstetrics & Gynecology
Pediatr Pathol Lab Med Pediatric Pathology & Laboratory Medicine
Pediatr Res Pediatric Research
Pediatrics Pediatrics
Physiol Rev Physiological Reviews
Science Science
Semin Pediatr Surg Seminars in Pediatric Surgery
Semin Perinatol Seminars in Perinatology
Semin Reprod Endocrinol Seminars in Reproductive Endocrinology
Semin Roentgenol Seminars in Roentgenology
Teratology Teratology
Trans Am Neurol Assoc Transactions of the American Neurological Association
Ultrasound Obstet Gynecol Ultrasound in Obstetrics & Gynecology
Z Anat Entwicklungsgesch Zeitschrift fur Anatomie und Entwicklungsgeschichte

Page 28


Program Index

A

Page Links

abdomen 8, 9, 14
abdominal 6, 12
activity 10, 14, 16
adenine 4
adult(s) 3, 4, 10, 11, 14
age 14
age of viability 14
air 11, 14, 16
alveoli 16
amnion 6, 7
amniotic fluid 7, 11, 12, 14, 15
anise 16
articular 11

B

base pairs 17
base(s) 4, 18
behavior(al) 11, 15, 16
billion 4, 7, 11
birth 3, 6, 7, 11, 12, 13, 15, 16
blastocyst 5
blink-startle 15
blood 4, 5, 6, 7, 9, 11, 13
blood cells 6
blood vessels 6, 11
blueprint 4
body 3, 4, 5, 6, 11, 12, 13, 15
body plan 6
bone(s) 6, 10, 11, 12, 13
bowel 13
brain 6, 7, 9, 11, 15
breastfeeding 13
breathing 9, 11, 16
bronchi 8
bronchial tree 14
buds 7, 13

C

cardiac 16, 21
cardiovascular 6
Carnegie Stage(s) 3, 4, 5, 6, 7, 8, 9, 10, 21
cartilage 6, 8
cell(s) 3, 4, 5, 6, 7, 8, 9, 11, 12, 13, 16
central nervous system 16
cerebral hemispheres 7, 9
chambers 6, 7
cheeks 13
chest 6, 10
childbirth 16
chromosomes 4
circulatory 5, 6
clavicle 10
close 12
cochlea 14
collar bone 10
conception 3
contraction 16
cytosine 4

D

day(s) 5, 6, 8, 10
development(al) 3, 4, 6, 7, 9, 12, 13, 16
diaphragm 9
digestive 6, 13
distinguish(ed) 12, 16
DNA 4, 17, 18

E

ear 9, 14
early pregnancy factor (EPF) 4
earth 4, 17
ectoderm 6
egg 4
elbows 10
electrocardiogram 10
electrodes 9
embryo 3, 4, 5, 6, 7, 8, 9, 11, 13
embryology 4
embryonic 3, 4, 5, 7, 9, 11, 19, 20
embryonic period 11, 20
encephalography 9
endoderm 6
energy 15
enzymes 13
epiblast 6
epidermis 11
estrogen 16
extension 11
eye(s) 10, 11, 12, 15
eyelids 10, 11, 12, 15

Page 29

F

Page Links

face 11, 12, 13
Fallopian tubes 4
fat 13, 15
female 10, 12, 13, 15
fertilization 3, 4, 5, 6, 12, 14, 15, 16
fetal 3, 5, 12, 13, 14, 15, 16
fetal period 3, 12, 17
fetus 3, 5, 6, 12, 13, 14, 15, 16
fingerprints 12
fingers 10
flattening 9
fluid 7, 11, 12, 14, 15
folding 6
follicles 14
forebrain 6, 7
formation 3, 8, 11, 12
function(s) 3, 7, 21
fuse 11

G

genitalia 12
germ cells 8
germ layers 6
gestational age 3, 14
glands 14
glucose 12
grasp 12, 16
grasping 11
gravity 11
grow(ing)(s) 3, 5, 6, 9, 11, 14
growth 6, 7, 10, 11, 12, 15
guanine 4

H

hair 6, 11, 14
hand(s) 8, 9, 10, 11, 12, 16
head 5, 7, 9, 11, 12, 13
health 15, 16
hearing 7, 14, 15
hearing loss 15
heart 6, 7, 8, 10, 14, 15
heart rate 14, 15, 20
heartbeat(s) 20
helix 4
hindbrain 6, 7
hormone(s) 5
hours 4, 14
human 3, 4, 5, 6, 11, 12, 16
human chorionic gonadotropin (hCG) 5
hypoblast 6

I

implantation 5
inner cell mass 5, 6
intestine 9, 12

J

jaw 10, 11, 12, 13
jaw movement 11, 13
joints 10, 11

Page 30

K

Page Links

kidneys 6, 8, 11
knee 10

L

labor 16
larynx 12
learning 7
left-handed 11
leg 15
licorice 16
life cycle 12
lifespan 7
light 12, 13, 15
limb(s) 7, 11, 13
lips 12
liver 6, 8, 9
lungs 8, 14, 16
lymphocytes 9

M

male 11, 12, 13
man 4
marrow 13
maternal 4, 5, 19
meconium 13
medications 5
memory 7
menstrual cycle 5
mesoderm 6
metaphase 4
meters 17
midbrain 6, 7
miles 4, 17
million 4, 7, 17
mitosis 4
molecule(s) 4, 17
morula 5
mouth 9, 11, 12, 13
move 12
movement(s) 7, 9, 10, 11, 13, 14, 16
mulberry 5
muscle(s) 6, 11
muscular 11

N

nails 6
nerve(s) 6, 11
neural 11
neuromuscular 9
newborn(s) 11, 13, 14, 16
nipple(s) 10, 13
noise 15
noradrenaline 14
norepinephrine 14
nose 12

O

odors 15
oocyte 4
oogonia 12
open(s) 12, 13, 15
ossification 10
ovaries 4, 10
ovary 4, 12
ovulation 4
oxygen 5

Page 31

P

Page Links

palms 12
pancreas 6
percent 11, 12, 13, 15, 16
physiologic herniation 9
placenta 5, 19
postfertilization age 9, 10, 13, 14, 15, 20
postmenstrual age 3, 9, 13, 14
postnatal 20
preference(s) 11, 16
pregnancy 3, 4, 5, 13, 15, 16
premature(ly) 14, 15
prenatal 21
problem-solving 7
proportion 13
protection 7
pupils 15

Q

quickening 13

R

reflex 13
reflexive(ly) 9, 11
reopen 15
reproductive 4, 8, 12
respiratory 6, 8, 14, 15
respond(s) 13, 14, 15
response 10, 12, 13, 14, 15
retina 10, 15
right-hand 11
rolling over 11
roof 13
rooting reflex 13
rotation 11

S

sac 6, 7
scalp 14
sense(s) 12, 13, 15
sex 12
sigh 12
skeletal 11
skin 6, 7, 11, 14, 15
skin layers 14
sole(s) 12
somersaults 15
sounds 14, 16
speech 7
sperm 4
spermatozoon 4
spinal cord 6
spontaneous 9, 11
squinting 11
startle 10, 15
stem cells 5, 13
stimulation 12, 13
stress response 14
stretch 12
structure(s) 3, 5, 6, 11, 14, 21
survival 3, 14
swallow(ed)(ing) 12, 15
system(s) 3, 5, 6, 8, 9, 14, 16, 21

T

taste 13, 16
taste buds 13
tears 15
temperature 5, 15, 19
testes 11
testosterone 11
thought 7
thumb sucking 12
thymine 4
toes 10, 12
tongue 12, 13
tooth 13
touch(ing) 9, 11, 12, 13
trachea 8
transparency 7, 11
trillion 3, 4, 17
trimester 13, 15
trunk 10

U

umbilical cord 5, 9, 12
umbilical vesicle 6
urine 11
uterine tube(s) 4, 5
uterus 4, 5, 11, 12, 16

V

vascular 11
vernix caseosa 14
viability 14
vocal cord development 12
vocal ligaments 12

W

walking 15
water 12
weight 11, 12, 13, 15
white blood cell 9
windpipe 8
woman 4, 13
womb 4, 14
wrinkled 15
wrist 8

Y

yawns 12
yolk sac 6, 8

Z

zygote 3, 4