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Isosceles triangle
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"Isosceles" redirects here. For other uses, see Isosceles (disambiguation).
Isosceles triangle
Isosceles triangle with vertical axis of symmetry
Type
triangle
Edges and vertices
3
Schläfli symbol
( ) ∨ { }
Symmetry group
Dih2, [ ], (*), order 2
Dual polygon
Self-dual
Properties
convex, cyclic
In geometry, an isosceles triangle is a triangle that has two sides of equal length. Sometimes it is specified as having two and only two sides of equal length, and sometimes as having at least two sides of equal length, the latter version thus including the equilateral triangle as a special case. Examples of isosceles triangles include the isosceles right triangle, the golden triangle, and the faces of bipyramids and certain Catalan solids.
The mathematical study of isosceles triangles dates back to ancient Egyptian mathematics and Babylonian mathematics. Isosceles triangles have been used as decoration from even earlier times, and appear frequently in architecture and design, for instance in the pediments and gables of buildings.
The two equal sides are called the legs and the third side is called the base of the triangle. The other dimensions of the triangle, such as its height, area, and perimeter, can be calculated by simple formulas from the lengths of the legs and base. Every isosceles triangle has an axis of symmetry along the perpendicular bisector of its base. The two angles opposite the legs are equal and are always acute, so the classification of the triangle as acute, right, or obtuse depends only on the angle between its two legs.
Contents
[hide]
1 Terminology, classification, and examples
2 Formulas
2.1 Height
2.2 Area
2.3 Perimeter
2.4 Angle bisector length
2.5 Radii
2.6 Inscribed square
3 Isosceles subdivision of other shapes
4 Applications
4.1 In architecture and design
4.2 In other areas of mathematics
5 History and fallacies
6 Notes
7 References
8 External links
Terminology, classification, and examples[edit]
Euclid defined an isosceles triangle as one having exactly two equal sides,[1] but modern treatments prefer to define them as having at least two equal sides, making equilateral triangles (with three equal sides) a special case of isosceles triangles.[2] A triangle that is not isosceles (having three unequal sides) is called a scalene triangle.[3] "Isosceles" is a compound word, made from the Greek roots "isos" (equal) and "skelos" (leg). The same word is used, for instance, for isosceles trapezoids, trapezoids with two equal sides,[4] and for sets of more than three points that have only two distinct distances between pairs of points.[5]
In an isosceles triangle that has exactly two equal sides, the equal sides are called legs and the third side is called the base. The angle included by the legs is called the vertex angle and the angles that have the base as one of their sides are called the base angles.[6] The vertex opposite the base is called the apex.[7] In the equilateral triangle case, since all sides are equal, any side can be called the base.[8]
Special isosceles triangles
Isosceles right triangle
Three congruent inscribed squares in the Calabi triangle
A golden triangle subdivided into a smaller golden triangle and golden gnomon
The triakis triangular tiling
Catalan solids with isosceles triangle faces
Triakis tetrahedron
Triakis octahedron
Tetrakis hexahedron
Pentakis dodecahedron
Triakis icosahedron
Whether an isosceles triangle is acute, right or obtuse depends only on the angle at its apex. In Euclidean geometry, the base angles cannot be obtuse (greater than 90°) or right (equal to 90°) because their measures would sum to at least 180°, the total of all angles in any Euclidean triangle.[8] Since a triangle is obtuse or right if and only if one of its angles is obtuse or right, respectively, an isosceles triangle is obtuse, right or acute if and only if its apex angle is respectively obtuse, right or acute.[7] In Edwin Abbott's book Flatland, this classification of shapes was used as a satire of social hierarchy: isosceles triangles represented the working class, with acute isosceles triangles lower in the hierarchy than right or acute isosceles triangles.[9]
As well as the isosceles right triangle, several other specific shapes of isosceles triangles have been studied. These include the Calabi triangle (a triangle with three congruent inscribed squares),[10] the golden triangle and golden gnomon (two isosceles triangles whose sides and base are in the golden ratio),[11] the 80-80-20 triangle appearing in the Langley’s Adventitious Angles puzzle,[12] and the 30-30-120 triangle of the triakis triangular tiling. Five Catalan solids, the triakis tetrahedron, triakis octahedron, tetrakis hexahedron, pentakis dodecahedron, and triakis icosahedron, each have isosceles-triangle faces, as do the infinitely-many pyramids[8] and bipyramids.[13]
Formulas[edit]
Height[edit]
For any isosceles triangle, the following six line segments coincide:
the altitude, a line segment from the apex perpendicular to the base,[14]
the angle bisector from the apex to the base,[14]
the median from the apex to the midpoint of the base,[14]
the perpendicular bisector of the base within the triangle,[14]
the segment within the triangle of the unique axis of symmetry of the triangle, and[14]
the segment within the triangle of the Euler line of the triangle.[15]
Their common length is the height of the triangle.
If the triangle has equal sides of length a {\displaystyle a} and base of length b {\displaystyle b} , the general triangle formulas for these quantities all simplify to[16]
h = 1 2 4 a 2 − b 2 . {\displaystyle h={\frac {1}{2}}{\sqrt {4a^{2}-b^{2}}}.}
This formula can also be derived from the Pythagorean theorem using the fact that the altitude bisects the base and partitions the isosceles triangle into two congruent right triangles.[17]
The Euler line of any triangle goes through the triangle's orthocenter (the intersection of its three altitudes), its centroid (the intersection of its three medians), and its circumcenter (the intersection of the perpendicular bisectors of its three sides, which is also the center of the circumcircle that passes through the three vertices). In an isosceles triangle with exactly two equal sides, these three points are distinct, and (by symmetry) all lie on the symmetry axis of the triangle, from which it follows that the Euler line coincides with the axis of symmetry. The incenter of the triangle also lies on the Euler line, something that is not true for other triangles.[15] If any two of an angle bisector, median, or altitude coincide in a given triangle, that triangle must be isosceles.[18]
Area[edit]
The area T {\displaystyle T} of an isosceles triangle can be derived from the formula for its height, and the general formula for the area of a triangle as half the product of base and height:[16]
T = b 4 4 a 2 − b 2 . {\displaystyle T={\frac {b}{4}}{\sqrt {4a^{2}-b^{2}}}.}
The same area formula can also be derived from Heron's formula for the area of a triangle from its three sides. However, applying Heron's formula directly can be numerically unstable for isosceles triangles with very sharp angles, because of the near-cancellation between the semiperimeter and side length in those triangles.[19]
If the apex angle ( θ ) {\displaystyle (\theta )} and leg lengths ( a ) {\displaystyle (a)} of an isosceles triangle are known, then the area of that triangle is:[20]
T = 1 2 a 2 sin  θ . {\displaystyle T={\frac {1}{2}}a^{2}\sin \theta .}
This is a special case of the general formula for the area of a triangle as half the product of two sides times the sine of the included angle.[21]
Perimeter[edit]
The perimeter p {\displaystyle p} of an isosceles triangle with equal sides a {\displaystyle a} and base b {\displaystyle b} is just[16]
p = 2 a + b . {\displaystyle p=2a+b.}
As in any triangle, the area T {\displaystyle T} and perimeter p {\displaystyle p} are related by the isoperimetric inequality[22]
p 2 > 12 3 T . {\displaystyle p^{2}>12{\sqrt {3}}T.}
This is a strict inequality for isosceles triangles with sides unequal to the base, and becomes an equality for the equilateral triangle. The area, perimeter, and base can also be related to each other by the equation[23]
2 p b 3 − p 2 b 2 + 16 T 2 = 0. {\displaystyle 2pb^{3}-p^{2}b^{2}+16T^{2}=0.}
If the base and perimeter are fixed, then this formula determines the area of the resulting isosceles triangle, which is the maximum possible among all triangles with the same base and perimeter.[24] On the other hand, if the area and perimeter are fixed, this formula can be used to recover the base length, but not uniquely: there are in general two distinct isosceles triangles with given area T {\displaystyle T} and perimeter p {\displaystyle p} . In the equilateral case (when the isoperimeteric inequality becomes an equality) there is only one such triangle, which is equilateral.[25]
Angle bisector length[edit]
If the two equal sides have length a {\displaystyle a} and the other side has length b {\displaystyle b} , then the internal angle bisector t {\displaystyle t} from one of the two equal-angled vertices satisfies[26]
2 a b a + b > t > a b 2 a + b {\displaystyle {\frac {2ab}{a+b}}>t>{\frac {ab{\sqrt {2}}}{a+b}}}
as well as
t < 4 a 3 ; {\displaystyle t<{\frac {4a}{3}};}
and conversely, if the latter condition holds, an isosceles triangle parametrized by a {\displaystyle a} and t {\displaystyle t} exists.[27]
The Steiner–Lehmus theorem states that every triangle with two angle bisectors of equal lengths is isosceles. It was formulated in 1840 by C. L. Lehmus. Its other namesake, Jakob Steiner, was one of the first to provide a solution.[28] Although originally formulated only for internal angle bisectors, it works for many (but not all) cases when, instead, two external angle bisectors are equal. The 30-30-120 isosceles triangle makes an interesting test case for this variation of the theorem, as it has four equal angle bisectors (two internal, two external).[29]
Radii[edit]
Isosceles triangle showing its circumcenter (blue), centroid (red), and incenter (green)
The inradius and circumradius formulas for an isosceles triangle may be derived from their formulas for arbitrary triangles.[30] The radius of the inscribed circle of an isosceles triangle with side length a {\displaystyle a} , base b {\displaystyle b} , and height h {\displaystyle h} is:[16]
2 a b − b 2 4 h . {\displaystyle {\frac {2ab-b^{2}}{4h}}.}
The center of the circle lies on the symmetry axis of the triangle, this distance above the base. Any isosceles triangle has the largest possible inscribed circle among the triangles with the same base and apex angle, as well as also having the largest area and perimeter among the same class of triangles.[31]
The radius of the circumscribed circle is:[16]
a 2 2 h . {\displaystyle {\frac {a^{2}}{2h}}.}
The center of the circle lies on the symmetry axis of the triangle, this distance below the apex.
Inscribed square[edit]
For any isosceles triangle there is a unique square with one side collinear with the base of the triangle and the opposite two corners on its sides. The Calabi triangle is a special isosceles triangle with the property that the other two inscribed squares, with sides collinear with the sides of the triangle, are of the same size as the base square.[10] A much older theorem, preserved in the works of Hero of Alexandria, states that, for an isosceles triangle with base b {\displaystyle b} and height h {\displaystyle h} , the side length of the inscribed square on the base of the triangle is[32]
b h b + h . {\displaystyle {\frac {bh}{b+h}}.}
Isosceles subdivision of other shapes[edit]
Partition of a cyclic pentagon into isosceles triangles by radii of its circumcircle
For any integer n ≥ 4 {\displaystyle n\geq 4} , any triangle can be partitioned into n {\displaystyle n} isosceles triangles.[33] In a right triangle, the median from the hypotenuse (that is, the line segment from the midpoint of the hypotenuse to the right-angled vertex) divides the right triangle into two isosceles triangles. This is because the midpoint of the hypotenuse is the center of the circumcircle of the right triangle, and each of the two triangles created by the partition has two equal radii as two of its sides.[34] Similarly, an acute triangle can be partitioned into three isosceles triangles by segments from its circumcenter,[35] but this method does not work for obtuse triangles, because the circumcenter lies outside the triangle.[30]
Generalizing the partition of an acute triangle, any cyclic polygon that contains the center of its circumscribed circle can be partitioned into isosceles triangles by the radii of this circle through its vertices. The fact that all radii of a circle have equal length implies that all of these triangles are isosceles. This partition can be used to derive a formula for the area of the polygon as a function of its side lengths, even for cyclic polygons that do not contain their circumcenters. This formula generalizes Heron's formula for triangles and Brahmagupta's formula for cyclic quadrilaterals.[36]
Either diagonal of a rhombus divides it into two congruent isosceles triangles. Similarly, one of the two diagonals of a kite divides it into two isosceles triangles, which are not congruent except when the kite is a rhombus.[37]
Applications[edit]
In architecture and design[edit]
Obtuse isosceles pediment of the Pantheon, Rome
Acute isosceles gable over the Saint-Etienne portal, Notre-Dame de Paris
Isosceles triangles commonly appear in architecture as the shapes of gables and pediments. In Ancient Greek architecture and its later imitations, the obtuse isosceles triangle was used; in Gothic architecture this was replaced by the acute isosceles triangle.[8] In the architecture of the Middle Ages, another isosceles triangle shape became popular: the so-called Egyptian isosceles triangle. This is an isosceles triangle that is acute, but less so than the equilateral triangle; its height is proportional to 5/8 of its base.[38] The Egyptian isosceles triangle was brought back into use in modern architecture by Dutch architect Hendrik Petrus Berlage.[39]
Detailed view of a modified Warren truss with verticals
Warren truss structures, such as bridges, are commonly arranged in isosceles triangles, although sometimes vertical beams are also included for additional strength.[40] Surfaces tessellated by obtuse isosceles triangles can be used to form deployable structures that have two stable states: an unfolded state in which the surface expands to a cylindrical column, and a folded state in which it folds into a more compact prism shape that can be more easily transported.[41]
Flag of Guyana
Flag of Saint Lucia
In graphic design and the decorative arts, isosceles triangles have been a frequent design element in cultures around the world from the Early Neolithic[42] to modern times.[43] They are a common design element in flags and heraldry, appearing prominently with a vertical base, for instance, in the Flag of Guyana, or with a horizontal base in the Flag of Saint Lucia, where they form a stylized image of a mountain island.[44] They also have been used in designs with religious or mystic significance, for instance in the Sri Yantra of Hindu meditational practice.[45]
In other areas of mathematics[edit]
If a cubic equation with real coefficients has three roots that are not all real numbers, then when these roots are plotted in the complex plane as an Argand diagram they form vertices of an isosceles triangle whose axis of symmetry coincides with the horizontal (real) axis. This is because the complex roots are complex conjugates and hence are symmetric about the real axis.[46]
In celestial mechanics, the three-body problem has been studied in the special case that the three bodies form an isosceles triangle, because assuming that the bodies are arranged in this way reduces the number of degrees of freedom of the system without reducing it to the solved Lagrangian point case when the bodies form an equilateral triangle. The first solutions of the problem with unbounded oscillations were found in the isosceles three-body problem.[47]
History and fallacies[edit]
Long before they were studied by the ancient Greek mathematicians, the practitioners of Ancient Egyptian mathematics and Babylonian mathematics knew how to calculate the area of isosceles triangles. Problems of this type are included in the Rhind Mathematical Papyrus, for instance.[48]
The theorem that the base angles of an isosceles triangle are equal appears as Proposition I.5 in Euclid.[49] This result has been called the pons asinorum (the bridge of asses) or the isosceles triangle theorem. Some say that its name as the bridge of asses is because the diagram used by Euclid in his demonstration of the result resembles a bridge. Others claim that the name stems from the fact that this is the first difficult result in Euclid, and acts to separate those who can understand Euclid's geometry from those who can't.[50]
A well known fallacy is the false proof of the statement that all triangles are isosceles. This argument has been attributed to Lewis Carroll,[51] but W.W. Rouse Ball claims priority in this matter.[52] The fallacy is rooted in Euclid's lack of recognition of the concept of betweenness and the resulting ambiguity of inside versus outside of figures.[53]
Notes[edit]
Jump up ^ Heath (1956), p. 187, Definition 20.
Jump up ^ Stahl (2003), p. 37.
Jump up ^ Usiskin & Griffin (2008), p. 4.
Jump up ^ Usiskin & Griffin (2008), p. 41.
Jump up ^ Ionin (2009).
Jump up ^ Jacobs (1974), p. 144.
^ Jump up to: a b Gottschau, Haverkort & Matzke (2017).
^ Jump up to: a b c d Lardner (1840), p. 46.
Jump up ^ Barnes (2012).
^ Jump up to: a b Conway & Guy (1996).
Jump up ^ Loeb (1992).
Jump up ^ Langley (1922).
Jump up ^ Montroll (2009).
^ Jump up to: a b c d e Hadamard (2008), p. 23.
^ Jump up to: a b Guinand (1984).
^ Jump up to: a b c d e Harris & Stöcker (1998), p. 78.
Jump up ^ Salvadori & Wright (1998).
Jump up ^ Hadamard (2008), Exercise 5, p. 29.
Jump up ^ Kahan (2014).
Jump up ^ Young (2011), p. 298.
Jump up ^ Young (2011), p. 398.
Jump up ^ Alsina & Nelsen (2009), p. 71.
Jump up ^ Baloglou & Helfgott (2008), Equation (1).
Jump up ^ Wickelgren (2012).
Jump up ^ Baloglou & Helfgott (2008), Theorem 2.
Jump up ^ Arslanagić.
Jump up ^ Oxman (2005).
Jump up ^ Gilbert & MacDonnell (1963).
Jump up ^ Conway & Ryba (2014).
^ Jump up to: a b Harris & Stöcker (1998), p. 75.
Jump up ^ Alsina & Nelsen (2009), p. 67.
Jump up ^ Gandz (1940).
Jump up ^ Lord (1982). See also Hadamard (2008, Exercise 340, p. 270).
Jump up ^ Posamentier & Lehmann (2012), p. 24.
Jump up ^ Bezdek & Bisztriczky (2015).
Jump up ^ Robbins (1995).
Jump up ^ Usiskin & Griffin (2008), p. 51.
Jump up ^ Lavedan (1947).
Jump up ^ Padovan (2002).
Jump up ^ Ketchum (1920).
Jump up ^ Pellegrino (2002).
Jump up ^ Washburn (1984).
Jump up ^ Jakway (1922).
Jump up ^ Smith (2014).
Jump up ^ Bolton, Nicol & Macleod (1977).
Jump up ^ Bardell (2016).
Jump up ^ Diacu & Holmes (1999).
Jump up ^ Høyrup. Some other sources claim that the Rhind area formula is incorrect, using the side length of the triangle where it should use the height, but this interpretation rests on the translation of one of the words in the Rhind papyrus, and with this word translated as height (or more precisely as the ratio of height to base) the formula is correct (Gunn & Peet 1929, pp. 173–174).
Jump up ^ Heath (1956), p. 251.
Jump up ^ Venema (2006), p. 89.
Jump up ^ Wilson (2008).
Jump up ^ Ball & Coxeter (1987).
Jump up ^ Specht et al. (2015).
References[edit]
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External links[edit]
Weisstein, Eric W. "Isosceles triangle". MathWorld.
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text:
Prenatal development
From Wikipedia, the free encyclopedia
Jump to: navigation, search
For maternal changes in the prenatal period, see Maternal physiological changes in pregnancy.
Prenatal development is the process in which an embryo and later fetus develops during gestation. Prenatal development starts with fertilization the first stage in embryogenesis which continues in fetal development until birth.
In human pregnancy, prenatal development, also known as antenatal development, is the development of the embryo following fertilization, and continued as fetal development. By the end of the tenth week of gestational age the embryo has acquired its basic form and is referred to as a fetus. The next period is that of fetal development where many organs become fully developed. This fetal period is described both topically (by organ) and chronologically (by time) with major occurrences being listed by gestational age.
In other animals the very early stages of embryogenesis are the same as those in humans. In later stages, development across all taxa of animals and the length of gestation vary.
Contents
[hide]
1 Definitions of periods
2 Fertilization
3 Embryonic period
3.1 Changes by weeks of gestation
3.1.1 Gestational age vs. embryonic age
3.1.2 Week 3
3.1.3 Week 4
3.1.4 Week 5
3.1.5 Week 6
3.1.6 Week 7
3.1.7 Week 8
3.1.8 Week 9
4 Fetal period
4.1 Changes by organ
4.2 Changes by weeks of gestation
4.2.1 Weeks 10 to 12
4.2.2 Weeks 13 to 16
4.2.3 Week 21
4.2.4 Week 23
4.2.5 Week 26
4.2.6 Week 31
4.2.7 Week 35
4.2.8 Weeks 36 to 40
5 Nutrition
6 Growth rate
6.1 Factors influencing growth rate
7 Fetal hematology
7.1 Erythrocytes
7.2 Leukocytes
8 Fetal endocrinology
9 See also
10 References
11 Further reading
12 External links
Definitions of periods[edit]
Stages during pregnancy. Embryogenesis is marked in green. Weeks and months are numbered by gestation.
The perinatal period (from Greek peri, "about, around" and Latin nasci "to be born") is "around the time of birth".
In developed countries and at facilities where expert neonatal care is available, it is considered from 22 completed weeks (usually about 154 days) of gestation (the time when birth weight is normally 500 g) to 7 completed days after birth.[1]
In many of the developing countries the starting point of this period is considered 28 completed weeks of gestation (or weight more than 1000 g).[2]
In ICD-10, a medical classification list by the WHO, there is a particular chapter relating to certain conditions originating in the perinatal period.
The antepartum period (from Latin ante "before" and parere "to give birth") is literally equivalent to prenatal (from Latin pre- "before" and nasci "to be born"). Practically, however, antepartum usually refers to the period between the 24th/26th week of gestational age until birth, for example in antepartum hemorrhage.[3][4]
Fertilization[edit]
Main article: Human fertilization
A sperm fertilizing an ovum.
When semen is released into the vagina, the spermatozoa travel through the cervix and body of the uterus and into the Fallopian tubes. Fertilization of the egg cell (ovum), usually takes place in one of the Fallopian tubes. Many sperm are released with the possibility of just one sperm cell managing to adhere to and enter the thick protective shell-like layer surrounding the ovum. The first sperm that penetrates fully into the egg donates its genetic material (DNA). The egg then polarizes, repelling any additional sperm. The resulting combination is called a zygote, a new and genetically unique organism. The term "conception" refers variably to either fertilization or to formation of the conceptus after its implantation in the uterus, and this terminology is controversial.
Prior to fertilization, each ovum, as a gamete, contains half of the genetic material that will fuse with the male gamete, which carries the other half of the genetic material (DNA). The ovum only carries the X female sex chromosome whilst the sperm carries a single sex chromosome of either an X or a male Y chromosome. The resulting human zygote is similar to the majority of somatic cells because it contains two copies of the genome in a diploid set of chromosomes. One set of chromosomes came from the nucleus of the ovum and the second set from the nucleus of the sperm.
The zygote is male if the egg is fertilized by a sperm that carries a Y chromosome, and it is female if the egg is fertilized by a sperm that carries an X chromosome.[5] The Y chromosome contains a gene, SRY, which will switch on androgen production at a later stage, leading to the development of a male body type. In contrast, the mitochondrial genetic information of the zygote comes entirely from the mother via the ovum.
Embryonic period[edit]
Main article: Human embryogenesis
The initial stages of human embryogenesis.
The embryonic period in humans begins at fertilization (penetration of the egg by the sperm) and continues until the end of the 10th week of gestation (8th week by embryonic age). The period of two weeks from fertilization is also referred to as the germinal stage.
The embryo spends the next few days traveling down the Fallopian tube. It starts out as a single cell zygote and then divides several times to form a ball of cells called a morula. Further cellular division is accompanied by the formation of a small cavity between the cells. This stage is called a blastocyst. Up to this point there is no growth in the overall size of the embryo, as it is confined within a glycoprotein shell, known as the zona pellucida. Instead, each division produces successively smaller cells.
The blastocyst reaches the uterus at roughly the fifth day after fertilization. It is here that lysis of the zona pellucida occurs. This process is analogous to zona hatching, a term that refers to the emergence of the blastocyst from the zona pellucida, when incubated in vitro. This allows the trophectoderm cells of the blastocyst to come into contact with, and adhere to, the endometrial cells of the uterus. The trophectoderm will eventually give rise to extra-embryonic structures, such as the placenta and the membranes. The embryo becomes embedded in the endometrium in a process called implantation. In most successful pregnancies, the embryo implants 8 to 10 days after ovulation.[6] The embryo, the extra-embryonic membranes, and the placenta are collectively referred to as a conceptus, or the "products of conception".
Rapid growth occurs and the embryo's main features begin to take form. This process is called differentiation, which produces the varied cell types (such as blood cells, kidney cells, and nerve cells). A spontaneous abortion, or miscarriage, in the first trimester of pregnancy is usually[7] due to major genetic mistakes or abnormalities in the developing embryo. During this critical period (most of the first trimester), the developing embryo is also susceptible to toxic exposures, such as:
Alcohol, certain drugs, and other toxins that cause birth defects, such as fetal alcohol syndrome
Infection (such as rubella or cytomegalovirus)
Radiation from x-rays or radiation therapy
Nutritional deficiencies such as lack of folate which contributes to spina bifida
Changes by weeks of gestation[edit]
See also: Embryo and Human embryogenesis
Gestational age vs. embryonic age[edit]
Gestational age is the time that has passed since the onset of the last menstruation, which generally or as standard occurs 2 weeks before the actual fertilization. Embryonic age, in contrast measures the actual age of the embryo or fetus from the time of fertilization. Nevertheless, menstruation has historically been the only means of estimating embryonal/fetal age, and is still the presumed measure if not else specified. However, the actual duration between last menstruation and fertilization may in fact differ from the standard 2 weeks by several days.
Thus, the first week of embryonic age is already week three counting with gestational age.
Furthermore, the number of the week is one more than the actual age of the embryo/fetus. For example, the embryo is 0 whole weeks old during the 1st week after fertilization.
The following table summarizes the various expression systems during week number x of gestation.
Week
number Initial age
(whole weeks)
Gestational x x-1
Embryonic x-2 x-3
Week 3[edit]
Gestational age: 2 weeks and 0 days until 2 weeks and 6 days old. 15–21 days from last menstruation.
Embryonic age: Week nr 1. 0 (whole) weeks old. 1–7 days from fertilization.
Fertilization of the ovum to form a new human organism, the human zygote. (day 1 of fertilization[8])
The zygote undergoes mitotic cellular divisions, but does not increase in size. This mitosis is also known as cleavage. A hollow cavity forms marking the blastocyst stage. (day 1.5–3 of fertilization.[8])
The blastocyst contains only a thin rim of trophoblast cells and a clump of cells at one end known as the "embryonic pole" which include embryonic stem cells.
The embryo hatches from its protein shell (zona pellucida) and performs implantation onto the endometrial lining of the mother's uterus. (day 5–6 of fertilization.[8])
If separation into identical twins occurs, 1/3 of the time it will happen before day 5.[9]
Week 4[edit]
Gestational age: 3 weeks and 0 days until 3 weeks and 6 days old. 22–28 days from last menstruation.
Embryonic age: Week nr 2. 1 week old. 8–14 days from fertilization.
Trophoblast cells surrounding the embryonic cells proliferate and invade deeper into the uterine lining. They will eventually form the placenta and embryonic membranes. The blastocyst is fully implanted day 7–12 of fertilization.[8]
Formation of the yolk sac.
The embryonic cells flatten into a disk, two cells thick.
If separation into identical twins occurs, 2/3 of the time it will happen between days 5 and 9. If it happens after day 9, there is a significant risk of the twins being conjoined.
Primitive streak develops. (day 13 of fertilization).[8]
Primary stem villi appear. (day 13 of fertilization).[8]
Week 5[edit]
Gestational age: 4 weeks and 0 days until 4 weeks and 6 days old. 29–35 days from last menstruation.
Embryonic age: Week nr 3. 2 weeks old. 15–21 days from fertilization.
A notochord forms in the center of the embryonic disk. (day 16 of fertilization.[8])
Gastrulation commences. (day 16 of fertilization.[8])
A neural groove (future spinal cord) forms over the notochord with a brain bulge at one end. Neuromeres appear. (day 18 of fertilization.[8])
Somites, the divisions of the future vertebra, form. (day 20 of fertilization.[8])
Primitive heart tube is forming. Vasculature begins to develop in embryonic disc. (day 20 of fertilization.[8])
Embryo at 4 weeks after fertilization.[10]
A 10mm embryo from an ectopic pregnancy, still in the oviduct. This embryo is about five weeks old (or from the seventh week of menstrual age).
Week 6[edit]
Gestational age: 5 weeks and 0 days until 5 weeks and 6 days old. 36–42 days from last menstruation.
Embryonic age: Week nr 4. 3 weeks old. 22–28 days from fertilization.
The embryo measures 4 mm (1/8 inch) in length and begins to curve into a C shape.
The heart bulges, further develops, and begins to beat in a regular rhythm. Septum primum appears.[8]
Pharyngeal arches, grooves which will form structures of the face and neck, form.
The neural tube closes.
The ears begin to form as otic pits.
Arm buds and a tail are visible.
Lung bud, the first traits of the lung appear.[8]
Hepatic plate, the first traits of the liver appear.[8]
Buccopharyngeal membrane ruptures. This is the future mouth.[8]
Cystic diverticulum, which will become the gallbladder, and dorsal pancreatic bud, which will become the pancreas appear.[8]
Urorectal septum begins to form. Thus, the rectal and urinary passageways become separated.[8]
Anterior and posterior horns differentiate in the spinal cord.[8]
Spleen appears.[8]
Ureteric buds appear.[8]
A six-week embryonic age or eight-week gestational age intact human embryo.
Week 7[edit]
Gestational age: 6 weeks and 0 days until 6 weeks and 6 days old. 43–49 days from last menstruation.
Embryonic age: Week nr 5. 4 weeks old. 29–35 days from fertilization.
The embryo measures 8mm (0.315 inch) in length and weighs about 1 gram.[11]
Optic vesicles and optic cups form the start of the developing eye.
Nasal pits form.
The brain divides into 5 vesicles, including the early telencephalon.
Leg buds form and hands form as flat paddles on the arms.
Rudimentary blood moves through primitive vessels connecting to the yolk sac and chorionic membranes.
The metanephros, precursor of the definitive kidney, starts to develop.
The initial stomach differentiation begins.
[12]
This embryo is also from an ectopic pregnancy, this one in the cornu (the part of the uterus to which the Fallopian tube is attached). The features are consistent with a developmental age of seven weeks (reckoned as the ninth week of pregnancy).
Week 8[edit]
Gestational age: 7 weeks and 0 days until 7 weeks and 6 days old. 50–56 days from last menstruation.
Embryonic age: Week nr 6. 5 weeks old. 36–42 days from fertilization.
The embryo measures 13 mm (1/2 inch) in length.
Lungs begin to form.
The brain continues to develop.
Arms and legs have lengthened with foot and hand areas distinguishable.
The hands and feet have digits, but may still be webbed.
The gonadal ridge begins to be perceptible.
The lymphatic system begins to develop.
Main development of sex organs starts.
Week 9[edit]
Gestational age: 8 weeks and 0 days until 8 weeks and 6 days old. 57–63 days from last menstruation.
Embryonic age: Week nr 7. 6 weeks old. 43–49 days from fertilization.
The embryo measures 18 mm (3/4 inch) in length.
Fetal heart tone (the sound of the heart beat) can be heard using doppler.
Nipples and hair follicles begin to form.
Location of the elbows and toes are visible.
Spontaneous limb movements may be detected by ultrasound.
All essential organs have at least begun.
The vitelline duct normally closes.
Fetal period[edit]
From the 10th week of gestation (8th week of development), the developing organism is called a fetus.
All major structures are already formed in the fetus, but they continue to grow and develop.
Since the precursors of all the major organs are created by this time, the fetal period is described both by organ and by a list of changes by weeks of gestational age.
Because the precursors of the organs are now formed, the fetus is not as sensitive to damage from environmental exposure as the embryo was. Instead, toxic exposure often causes physiological abnormalities or minor congenital malformation.
Changes by organ[edit]
Each organ has its own development.
Development of circulatory system
Heart development
Development of digestive system
Tooth development
Development of the endocrine system
Development of integumentary system
Development of lymphatic system
Development of muscular system
Development of nervous system
Development of the urinary and reproductive system
Development of the reproductive system
Development of the gonads
Development of respiratory system
Changes by weeks of gestation[edit]
Fetus at 8 weeks after fertilization.[13]
Weeks 10 to 12[edit]
Gestational age: 9 weeks and 0 days until 11 weeks and 6 days old.
Embryonic age: 7 weeks and 0 days until 9 weeks and 6 days old.
Fetus at 10 weeks
Embryo measures 30–80 mm (1.2–3.2 inches) in length.
Ventral and dorsal pancreatic buds fuse during the 8th week
Intestines rotate.
Facial features continue to develop.
The eyelids are more developed.
The external features of the ear begin to take their final shape.
The head comprises nearly half of the fetus' size.
The face is well formed.
The eyelids close and will not reopen until about the 28th week.
Tooth buds, which will form the baby teeth, appear.
The limbs are long and thin.
The fetus can make a fist with its fingers.
Genitals appear well differentiated.
Red blood cells are produced in the liver.
Heartbeat can be detected by ultrasound.[14]
Weeks 13 to 16[edit]
Gestational age: 12 weeks and 0 days until 15 weeks and 6 days old.
Embryonic age: 10 weeks and 0 days until 13 weeks and 6 days old.
The fetus reaches a length of about 15 cm (6 inches).
A fine hair called lanugo develops on the head.
Fetal skin is almost transparent.
More muscle tissue and bones have developed, and the bones become harder.
The fetus makes active movements.
Sucking motions are made with the mouth.
Meconium is made in the intestinal tract.
The liver and pancreas produce fluid secretions.
From week 13, sex prediction by obstetric ultrasonography is almost 100% accurate.[15]
At week 15, main development of external genitalia is finished.
Fetus at 18 weeks after fertilization.[16]
Week 21[edit]
Gestational age: 20 weeks old.
Embryonic age: 18 weeks old.
The fetus reaches a length of 20 cm (8 inches).
Lanugo covers the entire body.
Eyebrows and eyelashes appear.
Nails appear on fingers and toes.
The fetus is more active with increased muscle development.
"Quickening" usually occurs (the mother and others can feel the fetus moving).
The fetal heartbeat can be heard with a stethoscope.
Week 23[edit]
Gestational age: 22 weeks old.
Embryonic age: 20 weeks old.
The fetus reaches a length of 28 cm (11.2 inches).
The fetus weighs about 500g.
Eyebrows and eyelashes are well formed.
All of the eye components are developed.
The fetus has a hand and startle reflex.
Footprints and fingerprints continue forming.
Alveoli (air sacs) are forming in lungs.
Week 26[edit]
Gestational age: 24 weeks old.
Embryonic age: Week nr 25. 24 weeks old.
The fetus reaches a length of 38 cm (15 inches).
The fetus weighs about 1.2 kg (2 lb 11 oz).
The brain develops rapidly.
The nervous system develops enough to control some body functions.
The eyelids open and close.
The cochleae are now developed, though the myelin sheaths in neural portion of the auditory system will continue to develop until 18 months after birth.
The respiratory system, while immature, has developed to the point where gas exchange is possible.
Week 31[edit]
Gestational age: 30 weeks old.
Embryonic age: Week nr 29. 28 weeks old.
The fetus reaches a length of about 38–43 cm (15–17 inches).
The fetus weighs about 1.5 kg (3 lb 0 oz).
The amount of body fat rapidly increases.
Rhythmic breathing movements occur, but lungs are not fully mature.
Thalamic brain connections, which mediate sensory input, form.
Bones are fully developed, but are still soft and pliable.
The fetus begins storing a lot of iron, calcium and phosphorus.
Week 35[edit]
Gestational age: 34 weeks old.
Embryonic age: Week nr 33. 32 weeks old.
The fetus reaches a length of about 40–48 cm (16–19 inches).
The fetus weighs about 2.5 to 3 kg (5 lb 12 oz to 6 lb 12 oz).
Lanugo begins to disappear.
Body fat increases.
Fingernails reach the end of the fingertips.
A baby born at 36 weeks has a high chance of survival, but may require medical interventions.
Fetus at 38 weeks after fertilization.[17]
Weeks 36 to 40[edit]
Gestational age: 35 and 0 days until 39 weeks and 6 days old.
Embryonic age: Weeks nr 34–38. 33–37 weeks old.
The fetus is considered full-term at the end of the 39th week of gestational age.
It may be 48 to 53 cm (19 to 21 inches) in length.
The lanugo is gone except on the upper arms and shoulders.
Fingernails extend beyond fingertips.
Small breast buds are present on both sexes.
Head hair is now coarse and thickest.
The development is continued postnatally with adaptation to extrauterine life and child development stages.
Nutrition[edit]
The fetus passes through 3 phases of acquisition of nutrition from mother:[18]
Absorption phase: Zygote is nourished by cellular cytoplasm and secretions in fallopian tubes and uterine cavity.
Histoplasmic transfer: After nidation and before establishment of uteroplacental circulation, fetal nutrition is derived from decidual cells and maternal blood pools that open up as a result of eroding activity of trophoblasts.
Hematotrophic phase: After third week of gestation, substances are transported passively via intervillous space.
Growth rate[edit]
Growth rate of fetus is linear up to 37 weeks of gestation, after which it plateaus.[18] The growth rate of an embryo and infant can be reflected as the weight per gestational age, and is often given as the weight put in relation to what would be expected by the gestational age. A baby born within the normal range of weight for that gestational age is known as appropriate for gestational age (AGA). An abnormally slow growth rate results in the infant being small for gestational age, and, on the other hand, an abnormally large growth rate results in the infant being large for gestational age. A slow growth rate and preterm birth are the two factors that can cause a low birth weight. Low birth weight (below 2000 grams) can ultimately increase the likelihood of schizophrenia by almost four times. [19]
The growth rate can be roughly correlated with the fundal height which can be estimated by abdominal palpation. More exact measurements can be performed with obstetric ultrasonography.
Factors influencing growth rate[edit]
This section does not cite any sources. Please help improve this section by adding citations to reliable sources. Unsourced material may be challenged and removed. (November 2012) (Learn how and when to remove this template message)
Intrauterine growth restriction is one of the causes of low birth weight associated with over half of neonatal deaths.[20]
Poverty
Poverty has been linked to poor prenatal care and has been an influence on prenatal development. Women in poverty are more likely to have children at a younger age, which results in low birth weight. Many of these expecting mothers have little education and are therefore less aware of the risks of smoking, drinking alcohol, and drug use – other factors that influence the growth rate of a fetus. Women in poverty are more likely to have diseases that are harmful to the fetus.
Mother's age
Women between the ages of 16 and 35 have a healthier environment for a fetus than women under 16 or over 35.[citation needed] Women between this age gap are more likely to have fewer complications. Women over 35 are more inclined to have a longer labor period, which could potentially result in death of the mother or fetus. Women under 16 and over 35 have a higher risk of preterm labor (premature baby), and this risk increases for women in poverty, African Americans, and women who smoke. Young mothers are more likely to engage in high risk behaviors, such as using alcohol, drugs, or smoking, resulting in negative consequences for the fetus.[citation needed] Premature babies from young mothers are more likely to have neurological defects that will influence their coping capabilities – irritability, trouble sleeping, constant crying for example. There is a risk of Down syndrome for infants born to those aged over 40 years. Young teenaged mothers (younger than 16) and mothers over 35 are more exposed to the risks of miscarriages, premature births, and birth defects.
Drug use
Eleven percent of fetuses are exposed to illicit drug use during pregnancy.[citation needed] Maternal drug use occurs when drugs ingested by the pregnant woman are metabolized in the placenta and then transmitted to the fetus. When using drugs (narcotics), there is a greater risk of birth defects, low birth weight, and a higher rate of death in infants or stillbirths. Drug use will influence extreme irritability, crying, and risk for SIDS once the fetus is born. The chemicals in drugs can cause an addiction in the babies once they are born. Marijuana will slow the fetal growth rate and can result in premature delivery. It can also lead to low birth weight, a shortened gestational period and complications in delivery. Heroin will cause interrupted fetal development, stillbirths, and can lead to numerous birth defects. Heroin can also result in premature delivery, creates a higher risk of miscarriages, result in facial abnormalities and head size, and create gastrointestinal abnormalities in the fetus. There is an increased risk for SIDS, dysfunction in the central nervous system, and neurological dysfunctions including tremors, sleep problems, and seizures. The fetus is also put at a great risk for low birth weight and respiratory problems. Cocaine use results in a smaller brain, which results in learning disabilities for the fetus. Cocaine puts the fetus at a higher risk of being stillborn or premature. Cocaine use also results in low birthweight, damage to the central nervous system, and motor dysfunction.
Alcohol
Alcohol use leads to disruptions of the fetus's brain development, interferes with the fetus's cell development and organization, and affects the maturation of the central nervous system. Alcohol use can lead to heart and other major organ defects, such as small brain, which will affect the fetus's learning behaviors. Alcohol use during pregnancy can cause behavioral problems in a child, mental problems or retardation and facial abnormalities – meaning smaller eyes, thin upper lip, and little groove between the nose and lips. Use can also increase the risk of miscarriages and stillbirths, or low birth weight. Fetal alcohol syndrome (FAS) is a developmental disorder that is a consequence of too much alcohol intake by the mother during pregnancy. Children with FAS have a variety of distinctive facial features, brain abnormalities, and cognitive deficits.[5]
Smoking and nicotine
When a mother smokes during pregnancy the fetus is exposed to nicotine, tar, and carbon monoxide. Nicotine results in less blood flow to the fetus because it constricts the blood vessels. Carbon monoxide reduces the oxygen flow to the fetus. The reduction of blood and oxygen flow results in stillbirth, low birth weight, and ectopic pregnancy. There is an increase of risk of sudden death syndrome (SIDS) in infants. Nicotine also increases the risk for miscarriages and premature births or infant mortality. There has been a link from smoking during pregnancy that led to asthma in childhood. Low birth weight and premature births can also increase the risk of asthma if a mother smoked during pregnancy because of the effects on the respiratory system of the fetus.
Diseases
If a mother is infected with a disease, the placenta cannot always filter out pathogens. Babies can be born with venereal diseases transmitted by the mother.
Mother's diet and physical health
An adequate nutrition is needed for a healthy fetus. A lack of iron results in anemia in the fetus, the lack of calcium can result in poor bone and teeth formation, and the lack of protein can lead to a smaller fetus and mental retardation. Generally prenatal care gives an improved result in the newborn.[21]
Mother's prenatal depression
A study found that mother's prenatal depression was associated with adverse perinatal outcomes such as slower fetal growth rates. It appears that prenatal maternal cortisol levels play a role in mediating these outcomes.[22]
Environmental toxins
Exposure to environmental toxins in pregnancy lead to higher rates of miscarriage, sterility, and birth defects. Toxins include fetal exposure to lead, mercury, and ethanol or hazardous environments.
Low birth weight
Low birth weight increases an infants risk of long-term growth and cognitive and language deficits. It also results in a shortened gestational period and can lead to prenatal complications.
Fetal hematology[edit]
Fetal hematopoiesis first takes place in the yolk sac. The function is transferred to liver by 10th week of gestation and to spleen and bone marrow beyond that. The total blood volume is about 125 ml/kg fetal body weight near term.
Erythrocytes[edit]
Fetus produces megaloblastic red blood cells early in development, which become normoblastic near term. Life span of fetal RBCs is 80 days. Rh antigen appears at about 40 days of gestation.
Leukocytes[edit]
Fetus starts producing leukocytes at 2 months gestation mainly from thymus and spleen. Lymphocytes derived from thymus are called T lymphocytes, whereas the ones derived from bone marrow are called B lymphocytes. Both these populations of lymphocytes have short-lived and long-lived groups. Short-lived T lymphocytes usually reside in thymus, bone marrow and spleen; whereas long-lived T lymphocytes reside in blood stream. Plasma cells are derived from B lymphocytes and their life in fetal blood is 0.5 to 2 days.
Fetal endocrinology[edit]
Main article: Development of the endocrine system
Thyroid gland is the first to develop in fetus at 4th week of gestation. Insulin secretion in fetus starts around 12th week of gestation.
See also[edit]
Fetal pig
References[edit]
Jump up ^ Definitions and Indicators in Family Planning. Maternal & Child Health and Reproductive Health. By European Regional Office, World Health Organization. Revised March 1999 & January 2001. In turn citing: WHO Geneva, WHA20.19, WHA43.27, Article 23
Jump up ^ Singh, Meharban (2010). Care of the Newborn. p. 7. Edition 7. ISBN 9788170820536
Jump up ^ patient.info » PatientPlus » Antepartum Haemorrhage Last Updated: 5 May 2009
Jump up ^ The Royal Women’s Hospital > antepartum haemorrhage Archived 8 January 2010 at the Wayback Machine. Retrieved on Jan 13, 2009
^ Jump up to: a b Schacter, Daniel (2009). "11-Development". Psychology Second Edition. United States of America: Worth Publishers. ISBN 978-1-4292-3719-2.
Jump up ^ Wilcox AJ, Baird DD, Weinberg CR (1999). "Time of implantation of the conceptus and loss of pregnancy". N. Engl. J. Med. 340 (23): 1796–9. doi:10.1056/NEJM199906103402304. PMID 10362823.
Jump up ^ Moore L. Keith. (2008). Before We Are Born: Essentials of Embryology and Birth Defects. Philadelphia, PA: Saunders/Elsevier. ISBN 978-1-4160-3705-7.
^ Jump up to: a b c d e f g h i j k l m n o p q r s t William J. Larsen (2001). Human embryology. Edinburgh: Churchill Livingstone. ISBN 0-443-06583-7. [page needed]
Jump up ^ Scott F. Gilbert; with a chapter on plant development by Susan R. Singer (2000). Developmental biology. Sunderland, Mass: Sinauer Associates. ISBN 0-87893-243-7.
Jump up ^ 3D Pregnancy Archived 27 September 2007 at the Wayback Machine. (large image of fetus at 4 weeks after fertilization). Retrieved 2007-08-28. A rotatable 3D version of this photo is available here Archived 14 September 2007 at the Wayback Machine., and a sketch is available here Archived 27 September 2007 at the Wayback Machine..
Jump up ^ "7 Weeks Pregnant – Symptoms, Fetal Development, Tips". Retrieved 2016-07-18.
Jump up ^ Wagner F, Erdösová B, Kylarová D (December 2004). "Degradation phase of apoptosis during the early stages of human metanephros development". Biomed Pap Med Fac Univ Palacky Olomouc Czech Repub. 148 (2): 255–6. doi:10.5507/bp.2004.054. PMID 15744391.
Jump up ^ 3D Pregnancy Archived 27 September 2007 at the Wayback Machine. (large image of fetus at 10 weeks after fertilization). Retrieved 2007-08-28. A rotatable 3D version of this photo is available here Archived 16 September 2007 at the Wayback Machine., and a sketch is available here Archived 27 September 2007 at the Wayback Machine..
Jump up ^ Jeve, Y (13 October 2011). "Accuracy of first-trimester ultrasound in the diagnosis of early embryonic demise: a systematic review". Ultrasound in Obstetrics and Gynecology. 38 (5): 489–496. doi:10.1002/uog.10108. Retrieved 26 October 2015.
Jump up ^ Mazza V, Falcinelli C, Paganelli S, et al. (June 2001). "Sonographic early fetal gender assignment: a longitudinal study in pregnancies after in vitro fertilization". Ultrasound Obstet Gynecol. 17 (6): 513–6. doi:10.1046/j.1469-0705.2001.00421.x. PMID 11422974.
Jump up ^ 3D Pregnancy Archived 27 September 2007 at the Wayback Machine. (large image of fetus at 18 weeks after fertilization). Retrieved 2007-08-28. A rotatable 3D version of this photo is available here Archived 16 September 2007 at the Wayback Machine., and a sketch is available here Archived 27 September 2007 at the Wayback Machine..
Jump up ^ 3D Pregnancy Archived 27 September 2007 at the Wayback Machine. (large image of fetus at 38 weeks after fertilization). Retrieved 2007-08-28. A rotatable 3D version of this photo is available here Archived 16 September 2007 at the Wayback Machine., and a sketch is available here Archived 27 September 2007 at the Wayback Machine..
^ Jump up to: a b Daftary, Shirish; Chakravarti, Sudip (2011). Manual of Obstetrics, 3rd Edition. Elsevier. pp. 1-16. ISBN 9788131225561.
Jump up ^ [1], "Prenatal Factors in Schizophrenia", 2012-07-10
Jump up ^ Lawn JE, Cousens S, Zupan J (2005). "4 million neonatal deaths: when? Where? Why?". The Lancet. 365: 891–900. doi:10.1016/s0140-6736(05)71048-5. PMID 15752534.
Jump up ^ "What is prenatal care and why is it important?". www.nichd.nih.gov.
Jump up ^ Diego M. A.; Field T.; Hernandez-Reif M.; Schanberg S.; Kuhn C.; Gonzalez-Quintero V. H. (2009). "Prenatal depression restricts fetal growth". Early human development. 85 (1): 65–70. doi:10.1016/j.earlhumdev.2008.07.002. PMC 2651570  . PMID 18723301.
Further reading[edit]
MedlinePlus Encyclopedia Fetal development
Moore, Keith L. The Developing Human (3rd ed.). Philadelphia PA: W.B. Saunders Company.
Wilcox AJ, Baird DD, Weinberg CR (June 1999). "Time of implantation of the conceptus and loss of pregnancy". N. Engl. J. Med. 340 (23): 1796–9. doi:10.1056/NEJM199906103402304. PMID 10362823.
Ljunger E, Cnattingius S, Lundin C, Annerén G (November 2005). "Chromosomal anomalies in first-trimester miscarriages". Acta Obstet Gynecol Scand. 84 (11): 1103–7. doi:10.1111/j.0001-6349.2005.00882.x. PMID 16232180.
Newman, Barbara; Newman, Philip (10 March 2008). "The Period of Pregnancy and Prenatal Development". Development Through Life: A Psychosocial Approach. Cengage Learning. ISBN 0-495-55341-7.
"Prenatal Development - Prenatal Environmental Influences - Mother, Birth, Fetus, and Pregnancy." Social Issues Reference. Version Child Development Vol. 6. N.p., n.d. Web. 19 Nov. 2012. <http://social.jrank.org/pages/515/Prenatal-Development-Prenatal-Environmental-Influences.html>.
Niedziocha, Laura. "The Effects Of Drugs And Alcohol On Fetal Development | LIVESTRONG.COM." LIVESTRONG.COM - Lose Weight & Get Fit with Diet, Nutrition & Fitness Tools | LIVESTRONG.COM. N.p., 4 Sept. 2011. Web. 19 Nov. 2012. <http://www.livestrong.com/article/535499-the-effects-of-drugs-and-alcohol-on-fetal-development/>.
Jaakkola, JJ; Gissler, M (January 2004). "Maternal smoking in pregnancy, fetal development, and childhood asthma". American Journal of Public Health. 94 (1): 136–40. doi:10.2105/ajph.94.1.136. PMC 1449839  . PMID 14713711.
Gutbrod, T (1 May 2000). "Effects of gestation and birth weight on the growth and development of very low birthweight small for gestational age infants: a matched group comparison". Archives of Disease in Childhood: Fetal and Neonatal Edition. 82 (3): 208F–214. doi:10.1136/fn.82.3.F208. PMC 1721075  . PMID 10794788.
Brady, Joanne P., Marc Posner, and Cynthia Lang. "Risk and Reality: The Implications of Prenatal Exposure to Alcohol and Other Drugs ." ASPE. N.p., n.d. Web. 19 Nov. 2012. <http://aspe.hhs.gov/hsp/cyp/drugkids.htm>.
Pregnancy Approach (eBook ed.). Lauren Lee. 2013.
External links[edit]
Wikimedia Commons has media related to Embryology.
Chart of human fetal development, U.S. National Library of Medicine (NLM)
U.K. Human Fertilisation and Embryology Authority (HFEA), regulatory agency overseeing the use of gametes and embryos in fertility treatment and research
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King (playing card)
From Wikipedia, the free encyclopedia
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"King of clubs" redirects here. For other uses, see King of clubs (disambiguation).
"King of spades" redirects here. For the Frederick Manfred novel, see King of Spades (novel).
"King of diamonds" redirects here. For the 1936 film, see King of Diamonds (film).
King cards of all four suits in the Rouennais pattern
The king is a playing card with a picture of a king on it. The king is usually the highest-ranking face card. In French playing cards and tarot decks, the king immediately outranks the queen. In Italian and Spanish playing cards, the king immediately outranks the knight. In German and Swiss playing cards, the king immediately outranks the Ober. In some games, the king is the highest-ranked card; in others, the ace is higher. Aces began outranking kings around 1500 with Trappola being the earliest known game in which the aces were highest in all four suits.[1] In the Ace-Ten family of games such as pinochle and schnapsen, both the ace and the 10 rank higher than the king.[2]
Contents
1 History
2 Example cards
3 See also
4 References
History[edit]
French Rouen pattern on the left, Spanish Toledo pattern on the right
The king card is the oldest and most universal court card. It most likely originated in Persian Ganjifeh where kings are depicted as seated on thrones and outranking the viceroy cards which are mounted on horses. Playing cards were transmitted to Italy and Spain via the Mamluks and Moors.[3][4] The best preserved and most complete deck of Mamluk cards, the Topkapı pack, did not display human figures but just listed their rank most likely due to religious prohibition. It is not entirely secure if the Topkapı pack was representative of all Mamluk decks as it was a custom-made luxury item used for display. A fragment of what may be a seated king card was recovered in Egypt which may explain why the poses of court cards in Europe resemble those in Persia and India.[5]
Evolution of the King of Hearts in the Rouennais pattern
Seated kings were generally common throughout Europe. During the 15th century, the Spanish started producing standing kings. The French originally used Spanish cards before developing their regional deck patterns. Many Spanish court designs were simply reused when the French invented their own suit-system around 1480.[5] The English imported their cards from Rouen until the early 17th century when foreign card imports were banned.[6] The king of hearts is sometimes called the "suicide king" because he appears to be sticking his sword into his head. This is a result of centuries of bad copying by English card makers where the king's axe head has disappeared.[7][8]
Starting in the 15th century, French manufacturers assigned to each of the court cards names taken from history or mythology.[9] This practice survives only in the Paris pattern which ousted all its rivals, including the Rouen pattern around 1780.[10][11] The names for the kings in the Paris pattern (portrait officiel) are:[12]
David Charles Cesar Alexandre
Most French-suited continental European patterns are descended from the Paris pattern but they have dropped the names associated with each card.[10]
Example cards[edit]
Kings from French playing cards:
King of Clubs (Russian pattern)
King of Diamonds (Russian pattern)
King of Hearts (Russian pattern)
King of Spades (Russian pattern)
Industrie und Glück pattern
Kings from Italian playing cards:
King of Clubs (Bergamo pattern)
King of Coins (Bergamo pattern)
King of Cups (Bergamo pattern)
King of Swords (Bergamo pattern)
Kings from Spanish playing cards:
King of Clubs (Aluette)
King of Coins (Aluette)
King of Cups (Aluette)
King of Swords (Aluette)
Catalan pattern
Castilian pattern
Kings from German playing cards:
King of Acorns (Saxon pattern)
King of Bells (Saxon pattern)
King of Hearts (Saxon pattern)
King of Leaves (Saxon pattern)
See also[edit]
List of poker hand nicknames
References[edit]
Wikimedia Commons has media related to Kings (playing cards).
Jump up ^ Parlett, David (1990). The Oxford Guide to Card Games. Oxford: Oxford University Press. p. 252.
Jump up ^ McLeod, John. Ace-Ten Games at pagat.com. Retrieved 25 February 2016.
Jump up ^ Tor, Gjerde. "Mamluk cards, ca. 1500". old.no.
Jump up ^ Wintle, Simon. Moorish playing cards at World of Playing Cards. Retrieved 25 February 2017.
^ Jump up to: a b Dummett, Michael (1980). The Game of Tarot. London: Duckworth. pp. 10–64.
Jump up ^ English pattern at the International Playing-Card Society. Retrieved 25 February 2017.
Jump up ^ "The Rouen Pattern". whiteknucklecards.com.
Jump up ^ Wintle, Simon. Suicide King at the World of Playing Cards. Retrieved 25 February 2017.
Jump up ^ "The Four King Truth" at the Urban Legends Reference Pages. Retrieved 25 February 2017.
^ Jump up to: a b Mann, Sylvia (1990). All Cards on the Table. Leinfelden: Jonas Verlag. pp. 115–124.
Jump up ^ Pollett, Andy. France and Belgium at Andy's Playing Cards. Retrieved 25 February 2017.
Jump up ^ Paris and Rouen pattern figures at the International Playing-Card Society. Retrieved 25 February 2017.
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Playing cards
Standard
52-card deck
Suit/rank
Ace
King
Queen
Jack
10
9
8
7
6
5
4
3
2
Spades♠
Ace King Queen Jack 10 9 8 7 6 5 4 3 2
Hearts♥
Ace King Queen Jack 10 9 8 7 6 5 4 3 2
Diamonds♦
Ace King Queen Jack 10 9 8 7 6 5 4 3 2
Clubs♣
Ace King Queen Jack 10 9 8 7 6 5 4 3 2
Other cards
Blank
Face card/Court card (Knight, Ober, Unter)
Pip card (Deuce, Weli)
Joker
Card nicknames
Stripped deck
Talon
Unicode
Other suits
German deck: Acorns
Leaves
Hearts
Bells
Swiss deck: Acorns
Shields
Roses
Bells
Latin deck: Cups
Coins
Batons
Swords
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