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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 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]
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[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 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 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 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]
[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
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 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 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]
[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 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 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]
[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]
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]
[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]
[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
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 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 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 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]
[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 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]
[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 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 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.
[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) =
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
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
| ºF | ºC | |
|---|---|---|
| Lower Limit | 100.7 | 38.2 |
| Upper Limit | 102.5 | 39.2 |
Page 19
The Beat Goes On: Estimating the Total Number of Heartbeats Before Birth and Beyond
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 |