DIE BIOLOGIE DER PRÄNATALEN ENTWICKLUNG
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
Der dynamische Prozess, durch den die einzellige menschliche Zygote zu einem Erwachsenen aus 100 Billionen Zellen wird, ist wohl das bemerkenswerteste Phänomen in der Natur insgesamt.
Forscher wissen nun, dass viele der gewöhnlichen Funktionen des erwachsenen Körpers bereits während der Schwangerschaft bestimmt werden -- häufig lange vor der Geburt.
Die Entwicklungsphase vor der Geburt wird zunehmend verstanden als eine Zeit der Vorbereitung, während der der sich entwickelnde Mensch die vielen Strukturen und Praktiken, die vielen Fertigkeiten erwirbt, die zum Überleben nach der Geburt notwendig sind.
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
Die Schwangerschaft dauert beim Menschen etwa 38 Wochen, gemessen vom Zeitpunkt der Befruchtung oder der Empfängnis bis zur Geburt.
Während der ersten 8 Wochen nach der Befruchtung nennt man den sich entwickelnden Menschen ein Embryo, was soviel heißt wie: "innen wachsend". Diese Periode, die embryonale Phase, ist gekennzeichnet durch die Bildung der meisten körperlichen Systeme.
Nach 8 Wochen bis zum Ende der Schwangerschaft "wird der sich entwickelnde Mensch Fötus genannt", was soviel heißt wie: "ungeborener Nachwuchs". Während dieser Zeit, der fötalen Phase, wächst der Körper heran, und seine Systeme beginnen zu funktionieren.
Alle embryonalen und fötalen Altersstufen in diesem Programm beziehen sich auf die Zeit seit der Befruchtung.
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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
Biologisch ausgedrückt, "beginnt die menschliche Entwicklung mit der Befruchtung", wenn eine Frau und ein Mann jeweils 23 ihrer eigenen Chromosomen verbinden durch die Vereinigung ihrer reproduktiven Zellen.
Die reproduktiven Zellen der Frau werden gewöhnlich "Eizellen" genannt, doch der korrekte Begriff ist Oozyten.
Entsprechend sind die reproduktiven Zellen des Mannes allgemein als "Spermien" bekannt, doch der bevorzugte Begriff ist Spermatozoen.
Auf die Abstoßung einer Oozyte vom Eierstock der Frau in dem Prozess, den man Ovulation nennt, vereinigen sich die Oozyte und das Spermatozoon in einem der Eileiter, auch als Tuben oder Muttertrompeten bezeichnet.
Die Eileiter verbinden die Eierstöcke einer Frau mit ihrem Uterus oder ihrer Gebärmutter.
Das entstandene einzellige Embryo wird eine Zygote genannt, was soviel heißt wie "zusammengefügt" oder "verbunden".
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
Die 46 Chromosomen der Zygote stellen die einzigartige Erstausgabe des kompletten genetischen Fingerabdrucks des neuen Individuums dar. Dieser Bauplan wohnt in den eng gedrehten Molekülen, die man DNS nennt. Sie enthalten die Instruktionen für die Entwicklung des gesamten Körpers.
DNS Moleküle ähneln einer verdrehten Leiter, auch als Doppelhelix bekannt. Die Sprossen der Leiter bestehen aus gepaarten Molekülen oder Basen mit den Namen Guanin, Cytosin, Adenin und Thymin.
Guanin paart sich nur mit Cytosin und Adenin mit Thymin. Jede menschliche Zelle enthält annähernd 3 Milliarden dieser Basenpaare.
Die DNS einer einzelnen Zelle enthält so viele Informationen, dass sie, wenn sie in Worten aufschreiben würde, die einfach den ersten Buchstaben jeder Base auflisten, über 1,5 Millionen Seiten Text ergebenwürden!
Nacheinander aufgereiht, misst die DNS einer einzelnen menschlichen Zelle 3 1/3 Fuß oder 1 Meter.
Wenn wir die gesamte DNS in den 100 Billionen Zellen eines Erwachsenen aufrollen würden, würde dieses sich über 63 Milliarden Meilen erstrecken. Diese Distanz reicht von der Erde zur Sonne und zurück, 340 mal.
Cell Division
Etwa 24 bis 30 Stunden nach der Befruchtung, vollendet die Zygote ihre erste Zellteilung. Durch den Prozess der Zellkernteilung, teilt sich eine Zelle in zwei Teile, dann zwei in vier und so weiter.
Early Pregnancy Factor (EPF)
Bereits 24 bis 48 Stunden nach der Befruchtung kann eine Schwangerschaft durch Nachweis eines Hormons, des "Frühschwangerschaftsfaktors" im Blut der Mutter nachgewiesen werden.
[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
Bis 3 bis 4 Tage nach Befruchtung, nehmen die sich teilenden Zellen des Embryos eine Kugelform an, und man nennt den Embryo eine Morula.
Bis 4 bis 5 Tagen bildet sich ein Hohlraum in dieser Zellkugel, und der Embryo wird Keimblase genannt.
Die Zellen innerhalb der Keimblase werden als innere Zellmasse bezeichnet, aus der Kopf, Körper und andere Strukturen entstehen, die für den sich entwickelnden Menschen wichtig sind.
Zellen in der inneren Zellmasse werden embryonale Stammzellen genannt, weil sie jeden der mehr als 200 Zelltypen bilden können, die im menschlichen Körper enthalten sind.
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)
Nach dem Abgang durch den Eileiter bettet sich der frühe Embryo in die innere Wand der Gebärmutter der Mutter ein. Dieser Prozess, die Einpflanzung, beginnt 6 Tage und endet 10 bis 12 Tage nach der Befruchtung.
Zellen des wachsenden Embryos beginnen, ein Hormon zu produzieren, das humane Choriongonadotropin oder HCG, die Substanz, die von den meisten Schwangerschaftstest nachgewiesen wird.
HCG bringt die mütterlichen Hormone dazu, den normalen Menstrualzyklus zu unterbrechen und den Fortlauf der Schwangerschaft zu ermöglichen.
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
In Folge der Einpflanzung lassen die Zellen im Umfeld der Keimblase eine Struktur entstehen, die Plazenta, welche als Verbindungsstück zwischen dem mütterlichen und dem embryonalen Kreislaufsystem dient.
Die Plazenta liefert den Sauerstoff und die Nährstoffe, die Hormone und die Medikamente der Mutter an den sich entwickelnden Menschen, beseitigt alle Ausscheidungen, und verhindert, dass das Blut der Mutter sich mit dem Blut von Embryo und Fötus vermischt.
Die Plazenta produziert auch Hormone und hält die Temperatur von Embryo und Fötus etwas über der der Mutter.
Die Plazenta kommuniziert mit dem sich entwickelnden Menschen durch die Gefäße der Nabelschnur.
Die Lebenserhaltungsmaßnahmen der Plazenta sind denen einer Intensivstation eines modernen Krankenhauses ebenbürtig.
[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
Bis 1 Woche, bilden die Zellen der inneren Zellmasse zwei Schichten, Hypoblast und Epiblast.
Der Hypoblast lässt den Dottersack entstehen, eine der Strukturen, durch welche die Mutter den Embryo in seinem frühen Stadium mit Nährstoffen versorgt.
Zellen vom Epiblast formen eine Membrane, die Embryonalhülle, in der sich der Embryo und später der Fötus bis zur Geburt entwickelt.
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
Nach etwa 2 1/2 Wochen, hat der Epiblast 3 spezialisierte Gewebe oder Keimblätter gebildet, das Ektoderm, das Endoderm, und das Mesoderm.
Das Ektoderm bildet zahlreiche Strukturen einschließlich des Gehirns, des Rückenmarks, der Nerven, der Haut, der Fingernägel, und der Haare.
Das Endoderm bildet die Hülle des Atmungstraktes sowie des Verdauungstraktes, und erzeugt Teile der wichtigen Organe wie der Leber und der Bauchspeicheldrüse.
Das Mesoderm bildet das Herz, die Nieren, Knochen, Knorpel, Muskeln, Blutkörperchen, und andere Strukturen.
Nach 3 Wochen teilt sich das Gehirn in 3 Hauptregionen, Vorderhirn, Mittelhirn, und Nachhirn.
Die Entwicklung des Atem- und Verdauungstraktes läuft ebenfalls.
Wenn die ersten Blutkörperchen im Dottersack erscheinen, bilden sich Blutgefäße innerhalb des Embryos, und das tubulusförmige Herz entsteht.
Beinahe sofort, faltet sich das wachsende Herz in sich selbst, während sich die getrennten Herzkammern zu entwickeln beginnen.
Das Herz beginnt zu schlagen 3 Wochen und 1 Tag nach der Befruchtung.
Das Kreislaufsystem ist das erste Körpersystem, die erste Gruppe verwandter Organe, die ein funktionstüchtiges Stadium erreicht.
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
Zwischen 3 und 4 Wochen zeigt sich der Körperplan, und Gehirn, Rückenmark, und Herz des Embryos sind leicht zu erkennen neben dem Dottersack.
Schnelles Wachstum führt zu einer Faltung des relativ flachen Embryos. Dieser Prozess schließt einen Teil des Dottersacks in die Hülle des Verdauungssystems ein und bildet die Brust- und Bauchhöhlen des sich entwickelnden Menschen.
[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 12 The Heart in Action
Das Herz schlägt gewöhnlich etwa 113 Mal pro Minute.
Achten Sie auf die Farbwechsel des Herzens, wenn das Blut mit jedem Herzschlag in die Kammern ein- und austritt.
Das Herz schlägt etwa 54 Million Mal vor der Geburt und über 3,2 Milliarden Mal im Verlauf eines 80-jährigen Lebens.
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
Die Entwicklung der unteren Extremitäten beginnt mit dem Entstehender Extremitätenknospen bis 4 Wochen.
Die Haut ist an diesem Punkt durchsichtig, weil sie nur eine Zelle dick ist.
Wenn die Haut dicker wird, verliert sie ihre Transparenz. D.h. wir können die Entwicklung der inneren Organe nur noch etwa einen Monat lang verfolgen.
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
Zwischen 4 und 5 Wochen setzt das Gehirn sein schnelles Wachstum fort und teilt sich in 5 verschiedene Sektoren.
Der Kopf umfasst etwa 1/3 der Gesamtgröße des Embryos.
Die beiden Hirnhälften erscheinen und bilden schließlich die größten Teile des Gehirns.
Funktionen werden irgendwann von den Hirnhälften kontrolliert, darunter Denken, Lernen, Gedächtnis, Sprache, Sehen, Hören, absichtliche Bewegungen und Problemlösung.
[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]
Embryonic Development: 6 to 8 Weeks
Chapter 20 6 Weeks: Motion and Sensation
Bis 6 Wochen wachsen die Gehirnhälften unverhältnismäßig schneller als andere Teile des Gehirns.
Der Embryo beginnt mit spontanen und reflexartigen Bewegungen. Solche Bewegungen sind notwendig, um eine normale neuromuskuläre Entwicklung zu ermöglichen.
Eine Berührung in der Mundgegend bewirkt, dass der Embryo als Reflex den Kopf einzieht.
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
Das Zwerchfell, der Hauptmuskel, der zur Atmung verwendet wird, ist bis 6 Wochen größtenteils ausgebildet.
Ein Teil des Darms erstreckt sich nun vorübergehend in die Nabelschnur. Dieser normale Prozess, die physiologische Herniation, macht Platz für die Entwicklung anderer Organe im Bauch.
[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
Nach pädiatrischen Lehrbüchern beginnt die Fähigkeit, sich zu drehen, 10 bis 20 Wochen nach der Geburt. Diese eindrucksvolle Koordination zeigt sich jedoch viel früher in der geringen Schwerkraft der flüssigkeitsgefüllten Fruchtblase. Nur der Mangel an Kraft, die erforderlich ist, um die höhere Schwerkraft außerhalb der Gebärmutter zu überwinden, hält Neugeborene ab, sich zu drehen.
Der Embryo wird physisch viel aktiver während dieser Zeit.
Bewegungen können langsam oder schnell sein, einzeln oder wiederholt, spontan oder reflexhaft.
Kopfdrehung, Strecken des Halses und Hand-Gesichts-Kontakt treten häufiger auf.
Die Berührung des Embryos führt zu Blinzeln, Kieferbewegung, Greifbewegungen, und Strecken der Zehenspitzen.
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 34 "Breathing" Motion and Urination
Obwohl keine Luft in der Gebärmutter ist, zeigt der Embryo gelegentliche Atembewegungen bis 8 Wochen.
Bis zu diesem Zeitpunkt produzieren die Nieren Urin, der in die Fruchtblase entlassen wird.
In männlichen Embryos beginnen die sich entwickelnden Hoden Testosteron zu produzieren und abzugeben.
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
Die Knochen, Gelenke, Muskeln, Nerven und Blutgefäße der Extremitäten ähneln stark denen von Erwachsenen.
Bis 8 Wochen wird die Epidermis, die Außenhaut, zu einer mehrschichtigen Membran und verliert viel von seiner Transparenz.
Augenbrauen wachsen, und Haare erscheinen um den Mund.
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
Acht Wochen markieren das Ende der embryonalen Phase.
Während dieser Zeit ist der menschliche Embryo aus einer einzelnen Zelle zu annähernd 1 Milliarde Zellen herangewachsen, die über 4000 anatomische Strukturen bilden.
Der Embryo besitzt nun mehr als 90% der Strukturen, die man bei Erwachsenen findet.
[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
Die Fötale Phase erstreckt sich bis zur Geburt.
Bis 9 Wochen beginnt das Daumensaugen, und der Fötus kann Fruchtwasser schlucken.
Der Fötus kann auch einen Gegenstand greifen und den Kopf vorwärts und rückwärts bewegen, den Kiefer öffnen und schließen, die Zunge bewegen, seufzen und strecken.
Nervenrezeptoren im Gesicht, den Handflächen und den Fußsohlen können leichte Bewegungen spüren.
"Als Reaktion auf eine leichte Bewegung an der Fußsohle" beugt der Fötus Hüfte und Knie und kann die Zehen krümmen.
Die Augenlider sind jetzt vollständig geschlossen.
Im Kehlkopf weist das Erscheinen von Stimmbändern auf den Beginn der Entwicklung von Stimmbändern hin.
Bei weiblichen Föten ist der Uterus identifizierbar undunreife reproduktive Zellen, die Ovoginien, vervielfältigen sich in den Ovarien.
Die äußeren Genitalien beginnen sich entweder in männliche oder weibliche weiterzuentwickeln.
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
Ein Wachstumssprung zwischen 9 und 10 Wochen erhöht das Körpergewicht um über 75%.
Bis 10 Wochen bewirkt eine Anregung des oberen Augenlids ein Abwärtsrollen des Auges.
Der Fötus gähnt und öffnet und schließt häufig den Mund.
Die meisten Föten lutschen den rechten Daumen.
Darmabschnitte in der Nabelschnur ziehen sich in die Bauchhöhle zurück.
Ossifikation findet in den meisten Knochen statt.
Fingernägel und Zehennägel beginnen sich zu entwickeln.
Unverwechselbare Fingerabdrücke erscheinen 10 Wochen nach Befruchtung. Diese Muster können ein Leben lang als Identifikation verwendet werden.
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
Bis 11 Wochen sind Nase und Lippen vollständig geformt. Wie alle anderen Körperteile wird sich ihre Erscheinung auf jeder Stufe des menschlichen Lebenszyklus verändern.
Der Darm beginnt Glukose und Wasser zu absorbieren, die vom Fötus verschluckt werden.
Obwohl das Geschlecht bei der Befruchtung festgelegt wird, können die äußeren Geschlechtsteile nun unterschieden werden als männlich oder weiblich.
[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
Zwischen 11 und 12 Wochen erhöht sich das Gewicht des Fötus um fast 60%.
Zwölf Wochen markieren das Ende des ersten Drittels oder Trimesters der Schwangerschaft.
Deutliche Geschmacksknospen bedecken nun das Innere des Mundes. Bis zur Geburt bleiben Geschmacksknospen nur auf der Zunge und am Gaumen.
Darmbewegungen beginnen bereits bis 12 Wochen und fahren etwa 6 Wochen weiter fort.
Das Material, das zuerst aus dem Darm des Neugeborenen ausgeschieden wird, heißt Mekonium. Es besteht aus Verdauungsenzymen, Eiweißen und abgestorbenen Zellen, ausgeschieden vom Verdauungstrakt.
Bis 12 Wochen hat die Länge der oberen Extremitäten fast die endgültige Proportion zur Körpergröße erreicht. Die unteren Extremitäten brauchen länger, um ihre endgültigen Proportionen zu erhalten.
Mit Ausnahme des Rückens und des Scheitels des Kopfes reagiert der gesamte Körper des Fötus nun auf leichte Berührungen.
Geschlechtsspezifische Entwicklungsunterschiede erscheinen erstmals. Zum Beispiel weisen weibliche Föten Kieferbewegungen häufiger auf als männliche.
Im Gegensatz zu dem Rückzugsreflex, den man vorher sah, regt eine Berührung in Mundnähe nun eine Zuwendung in Reizrichtung und Öffnung des Mundes an. Diesen Reflex nennt man den "Wurzelreflex". Er besteht nach der Geburt fort, und hilft dem Neugeborenen die Brust der Mutter zu finden, um zu stillen.
Das Gesicht entwickelt sich weiter, Fettgewebe beginnt die Wangen zu füllen, und die Zahnentwicklung beginnt.
Bis 15 Wochen erscheinen Blut bildende Stammzellen und vermehren sich im Knochenmark. Die Blutbildung findet überwiegend hier statt.
Obwohl die Bewegungen im 6-wöchigen Embryo beginnen, spürt die schwangere Frau die Fötusbewegungen erstmals zwischen 14 und 18 Wochen. Dies gilt traditionell als erste Kindsbewegung.
[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
Bis 16 Wochen lösen Eingriffe, die mit dem Einstich einer Nadel in die Bauchdecke des Fötus verbunden sind, eine hormonelle Stressreaktion aus, entlassen Noradrenalin oder Norepinephrin in die Blutbahn.
Im Atemtrakt ist der Bronchialbaum nun fast vollständig ausgebildet.
Eine schützende weiße Substanz, die Käseschmiere, bedeckt nun den Fötus. Sie schützt die Haut vor einer Reizung durch das Fruchtwasser.
Von 19 Wochen an beginnen Bewegungen, Atmungsaktivität und Herzrhythmus Tageszyklen zu folgen, dem Tag-Nacht-Rhythmus.
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
Bis 20 Wochen hat die Kochlea, das Hörorgan, die Größe von Erwachsenen erreicht, innerhalb des voll entwickelten inneren Ohres. Von jetzt an reagiert der Fötus auf eine zunehmende Anzahl von Geräuschen.
Haare beginnen auf der Kopfhaut zu wachsen.
Alle Hautschichten und -strukturen sind ausgebildet, einschließlich Haarfollikel und Drüsen.
21 bis 22 Wochen nach der Befruchtung haben die Lungen bereits eine begrenzte Fähigkeit, Luft zu atmen. Dies gilt als das lebensfähige Alter, da das Überleben außerhalb der Gebärmutter für einige Föten möglich wird.
[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
Bis 24 Wochen öffnen sich die Augenlider wieder, und der Fötus zeigt einen Blinzel-Schreckreflex. Diese Reaktion auf plötzliche laute Geräusche entwickelt sich normalerweise früher im weiblichen Fötus.
Mehrere Forschungen weisen darauf hin, dass laute Geräusche der Gesundheit des Fötus schaden können. Sofortfolgen sind langfristig erhöhte Herzfrequenz, exzessives Schlucken und plötzliche Verhaltensänderungen. Langfristige Folgen beinhalten Gehörverlust.
Die Atemfrequenz des Fötus kann sich bis zu 44 Ein- und Ausatemzyklen pro Minute steigern.
Während des dritten Trimesters der Schwangerschaft verbraucht das schnelle Gehirnwachstum mehr als 50% der Energie, die von dem Fötus verbrauchtwird. Das Gewicht des Gehirns erhöht sich um 400 bis 500%.
Bis 26 Wochen tränen die Augen.
Die Pupillen reagieren bereits bis 27 Wochen auf Licht. Diese Reaktion regelt die Lichtmenge, die im Leben die Retina erreicht.
Alle Komponenten, die für einen funktionierenden Geruchssinn notwendig sind, funktionieren. Studien an Frühgeborenen zeigen die Fähigkeit, Gerüche wahrzunehmen bereits 26 Wochen nach der Befruchtung.
Das Einbringen einer süßen Substanz in das Fruchtwasser erhöht die Schluckfrequenz des Fötus. Im Gegensatz dazu verringert sich die Schluckfrequenz des Fötus nach dem Einbringen einer bitteren Substanz. Häufig folgt ein veränderter Gesichtsausdruck.
Durch eine Serie trittähnlicher Beinbewegungen ähnlich denen beim Laufen schlägt der Fötus Saltos.
Der Fötus erscheint weniger faltig, während sich zusätzliches Fett unter der Haut ablagert. Fett spielt eine wichtige Rolle beim Beibehalten der Körpertemperatur und Speichern von Energie nach der Geburt.
[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
Bis 28 Wochen kann der Fötus zwischen hohen und niedrigen Tönen unterscheiden.
Bis 30 Wochen sind Atembewegungen häufiger und treten 30% bis 40% der Zeit beim durchschnittlichen Fötus auf.
Während der letzten 4 Monate der Schwangerschaft hat der Fötus Phasen koordinierter Aktivität im Wechsel mit Ruhephasen. Dieses Verhalten zeigt die zunehmende Komplexität des Zentralnervensystems.
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
Bis etwa 32 Wochen beginnen sich echte Alveolen oder Luft-"Taschen"-Zellen in der Lunge zu entwickeln. Die Bildung geht bis 8 Jahre nach der Geburt weiter.
Nach 35 Wochen kann der Fötus fest zugreifen.
Die Berührung mit verschiedenen Substanzen beeinflusst offenbar Geschmacksvorlieben nach der Geburt. Zum Beispiel hatten Föten, deren Mütter Anis einnahmen, eine Substanz, die Lakritze den Geschmack gibt, eine Vorliebe für Anis nach der Geburt. Neugeborene ohne diese Berührung verabscheuten Anis.
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)
Der Fötus stimuliert die Wehen durch Freisetzen großer Mengen des Hormons Östrogen, und beginnt so den Übergang vom Fötus zum Neugeborenen.
Die Wehen werden markiert durch kräftige Kontraktionen des Uterus, die zur Geburt führen.
Von der Befruchtung zur Geburt und danach ist die menschliche Entwicklung dynamisch, stetig und komplex. Neue Entdeckungen über diesen faszinierenden Prozess zeigen zunehmend die Bedeutung der Entwicklung des Fötus für die lebenslange Gesundheit.
Mit zunehmendem Verständnis der Frühstufen menschlicher Entwicklung wird auch unsere Fähigkeit, die Gesundheit zu verbessern, vor und nach der Geburt, zunehmen.
[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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Page 27
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 |