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Periodic Table

Gist

The periodic table, also known as the periodic table of the elements, is an ordered arrangement of the chemical elements into rows ("periods") and columns ("groups"). An icon of chemistry, the periodic table is widely used in physics and other sciences.

The periodic table consists of 118 officially recognized elements, organized by atomic number, name, and symbol. Elements are ordered by increasing proton count, with symbols often matching the English name (e.g., Helium, He) or Latin roots (e.g., Gold, Au). Key groupings include metals, non-metals, halogens, and noble gases.

Summary

The periodic table of elements is widely used in the field of Chemistry to look up chemical elements as they are arranged in a manner that displays periodic trends in the chemical properties of the elements. However, the Periodic table generally displays only the symbol of the element and not its entire name.

Most of the symbols are similar to the name of the element but some symbols of elements have Latin roots. An example for this is silver which is denoted by Ag from its Latin name “Argentum”. Another such example would be the symbol ‘Fe’ which is used to denote Iron and can be traced to the Latin word for iron, “Ferrum”. It could prove difficult for a beginner in chemistry to learn the names of all the elements in the periodic table because these symbols do not always correspond to the English names of the elements.

Frequently Asked Questions – FAQs

Q1: What is the atomic number?
A1: The atomic number of an atom is equivalent to the total number of electrons present in a neutral atom or the total number of protons present in the nucleus of an atom.

Q2: What is an element?
A2. An element is a substance that can not be decomposed into simpler substances by ordinary chemical processes. It is the fundamental unit of the matter.

Q3: How many elements are there in the modern periodic table?
A3: There is a total of 118 elements present in the modern periodic table.

Q4: What is a chemical symbol?
A cA4: hemical symbol is a notation of one or two letters denoting a chemical element.
Example: The symbol of chlorine is Cl.

Q5: What are the rules for chemical symbols?
A5. The first letter is always capitalised for writing the chemical symbol of an element, while the second letter is small.

Q6: What is the significance of chemical symbols?
A6: Chemical symbols play a crucial role in easing the writing. It is universal, i.e. identical throughout the world.

Q7: What is the chemical symbol of a sodium metal?
A7: The chemical symbol of sodium metal is Na.

Q8: Name the smallest and the largest atom.
A8: Helium is the smallest atom with a radius of 31 pm, while the caesium is the largest atom with a radius of 298 pm.

Q9: Can atoms exist without neutrons?
A9: Yes, there is an isotope of the hydrogen atom, protium, which has no neutron.

Q10: What is the chemical symbol of a gold metal?
A10: The chemical symbol of gold metal is Au.

Details

The periodic table, also known as the periodic table of the elements, is an ordered arrangement of the chemical elements into rows ("periods") and columns ("groups"). An icon of chemistry, the periodic table is widely used in physics and other sciences. It is a depiction of the periodic law, which states that when the elements are arranged in order of their atomic numbers an approximate recurrence of their properties is evident. The table is divided into four roughly rectangular areas called blocks. Elements in the same group tend to show similar chemical characteristics.

Vertical, horizontal and diagonal trends characterize the periodic table. Metallic character increases going down a group and from right to left across a period. Nonmetallic character increases going from the bottom left of the periodic table to the top right.

The first periodic table to become generally accepted was that of the Russian chemist Dmitri Mendeleev in 1869; he formulated the periodic law as a dependence of chemical properties on atomic mass. As not all elements were then known, there were gaps in his periodic table, and Mendeleev successfully used the periodic law to predict some properties of some of the missing elements. The periodic law was recognized as a fundamental discovery in the late 19th century. It was explained early in the 20th century, with the discovery of atomic numbers and associated pioneering work in quantum mechanics, both ideas serving to illuminate the internal structure of the atom. A recognisably modern form of the table was reached in 1945 with Glenn T. Seaborg's discovery that the actinides were in fact f-block rather than d-block elements. The periodic table and law have become a central and indispensable part of modern chemistry.

The periodic table continues to evolve with the progress of science. In nature, only elements up to atomic number 94 exist; elements beyond that can only be synthesized in the laboratory. By 2010, the first 118 elements were known, thereby completing the first seven rows of the table; however, chemical characterization is still needed for the heaviest elements to confirm that their properties match their positions. New discoveries will extend the table beyond these seven rows, though it is not yet known how many more elements are possible; moreover, theoretical calculations suggest that this unknown region will not follow the patterns of the known part of the table. Some scientific discussion also continues regarding whether some elements are correctly positioned in the table. Many alternative representations of the periodic law exist, and there is some discussion as to whether there is an optimal form of the periodic table.

Each chemical element has a unique atomic number (Z— for "Zahl", German for "number") representing the number of protons in its nucleus. Each distinct atomic number therefore corresponds to a class of atom: these classes are called the chemical elements. The chemical elements are what the periodic table classifies and organizes. Hydrogen is the element with atomic number 1; helium, atomic number 2; lithium, atomic number 3; and so on. Each of these names can be further abbreviated by a one- or two-letter chemical symbol; those for hydrogen, helium, and lithium are respectively H, He, and Li. Neutrons do not affect the atom's chemical identity, but do affect its weight. Atoms with the same number of protons but different numbers of neutrons are called isotopes of the same chemical element. Naturally occurring elements usually occur as mixes of different isotopes; since each isotope usually occurs with a characteristic abundance, naturally occurring elements have well-defined atomic weights, defined as the average mass of a naturally occurring atom of that element. All elements have multiple isotopes, variants with the same number of protons but different numbers of neutrons. For example, carbon has three naturally occurring isotopes: all of its atoms have six protons and most have six neutrons as well, but about one per cent have seven neutrons, and a very small fraction have eight neutrons. Isotopes are never separated in the periodic table; they are always grouped together under a single element. When atomic mass is shown, it is usually the weighted average of naturally occurring isotopes; but if no isotopes occur naturally in significant quantities, the mass of the most stable isotope usually appears, often in parentheses.

In the standard periodic table, the elements are listed in order of increasing atomic number. A new row (period) is started when a new electron shell has its first electron. Columns (groups) are determined by the electron configuration of the atom; elements with the same number of electrons in a particular subshell fall into the same columns (e.g. oxygen, sulfur, and selenium are in the same column because they all have four electrons in the outermost p-subshell). Elements with similar chemical properties generally fall into the same group in the periodic table, although in the f-block, and to some respect in the d-block, the elements in the same period tend to have similar properties, as well. Thus, it is relatively easy to predict the chemical properties of an element if one knows the properties of the elements around it.

Today, 118 elements are known, the first 94 of which are known to occur naturally on Earth. The remaining 24, americium to oganesson (95–118), occur only when synthesized in laboratories. Of the 94 naturally occurring elements, 83 are primordial and 11 occur only in decay chains of primordial elements. A few of the latter are so rare that they were not discovered in nature, but were synthesized in the laboratory before it was determined that they exist in nature: technetium (element 43), promethium (element 61), astatine (element 85), neptunium (element 93), and plutonium (element 94). No element heavier than einsteinium (element 99) has ever been observed in macroscopic quantities in its pure form, nor has astatine; francium (element 87) has been only photographed in the form of light emitted from microscopic quantities. Of the 94 natural elements, eighty have a stable isotope and one more (bismuth) has an almost-stable isotope (with a half-life of 2.01×{10}^{19} years, over a billion times the age of the universe). Two more, thorium and uranium, have isotopes undergoing radioactive decay with a half-life comparable to the age of the Earth. The stable elements plus bismuth, thorium, and uranium make up the 83 primordial elements that survived from the Earth's formation. The remaining eleven natural elements decay quickly enough that their continued trace occurrence rests primarily on being constantly regenerated as intermediate products of the decay of thorium and uranium.[d] All 24 known artificial elements are radioactive.

Group names and numbers

Under an international naming convention, the groups are numbered numerically from 1 to 18 from the leftmost column (the alkali metals) to the rightmost column (the noble gases). The f-block groups are ignored in this numbering. Groups can also be named by their first element, e.g. the "scandium group" for group 3. Previously, groups were known by Roman numerals. In the United States, the Roman numerals were followed by either an "A" (if the group was in the s- or p-block) or a "B" (if the group was in the d-block). The Roman numerals used correspond to the last digit of today's naming convention (e.g., the group 4 elements were group IVB, and the group 14 elements were group IVA). In Europe, "A" was used for groups 1 through 7, and "B" was used for groups 11 through 17. In addition, groups 8, 9, and 10 used to be treated as one triple-sized group, known collectively in both notations as group VIII. In 1988, the new IUPAC (International Union of Pure and Applied Chemistry) naming system (1–18) was put into use, and the old group names (I–VIII) were deprecated.

Additional Information

Periodic table, in chemistry, is the organized array of all the chemical elements in order of increasing atomic number—i.e., the total number of protons in the atomic nucleus. When the chemical elements are thus arranged, there is a recurring pattern called the “periodic law” in their properties, in which elements in the same column (group) have similar properties. The initial discovery of this pattern by Dmitri I. Mendeleev in the mid-19th century has been of inestimable value in the development of chemistry.

It was not recognized until the 1910s that the order of elements in the periodic system is that of their atomic numbers, which are equal to the positive electrical charges of the atomic nuclei expressed in electronic units. In subsequent years great progress was made in explaining the periodic law in terms of the electronic structure of atoms and molecules. This clarification has increased the value of the law, which is used as much today as it was at the beginning of the 20th century, when it expressed the only known relationship among the elements.

The periodic table

The periodic table of the elements contains all of the chemical elements that have been discovered or made; they are arranged, in the order of their atomic numbers, in seven horizontal periods, with the lanthanoids (lanthanum, 57, to lutetium, 71) and the actinoids (actinium, 89, to lawrencium, 103) indicated separately below. The periods are of varying lengths. First there is the hydrogen period, consisting of the two elements hydrogen, 1, and helium, 2. Then there are two periods of eight elements each: the first short period, from lithium, 3, to neon, 10, and the second short period, from sodium, 11, to argon, 18. There follow two periods of 18 elements each: the first long period, from potassium, 19, to krypton, 36, and the second long period, from rubidium, 37, to xenon, 54. The first very long period of 32 elements, from cesium, 55, to radon, 86, is condensed into 18 columns by the omission of the lanthanoids (which are indicated separately below), permitting the remaining 18 elements, which are closely similar in their properties to corresponding elements of the first and second long periods, to be placed directly below these elements. The second very long period, from francium, 87, to oganesson, 118, is likewise condensed into 18 columns by the omission of the actinoids.

Groups

The six noble gases—helium, neon, argon, krypton, xenon, and radon—occur at the ends of the six completed periods and constitute the Group 18 (0) group of the periodic system. It is customary to refer to horizontal series of elements in the table as periods and vertical series as groups. The seven elements lithium to fluorine and the seven corresponding elements sodium to chlorine are placed in the seven groups, 1 (Ia), 2 (IIa), 13 (IIIa), 14 (IVa), 15 (Va), 16 (VIa), and 17 (VIIa), respectively. The 17 elements of the fourth period, from potassium, 19, to bromine, 35, are distinct in their properties and are considered to constitute Groups 1–17 (Ia–VIIa) of the periodic system.

The first group, the alkali metals, thereby includes, in addition to lithium and sodium, the metals from potassium down the table to francium but not the much less similar metals of Group 11 (Ib; copper, etc.). Also the second group, the alkaline-earth metals, is considered to include beryllium, magnesium, calcium, strontium, barium, and radium but not the elements of Group 12 (IIb). The boron group includes those elements in Group 13 (IIIa). The other four groups are as follows: The carbon group, 14 (IVa), consists of carbon, silicon, germanium, tin, lead, and flerovium; the nitrogen group, 15 (Va), includes nitrogen, phosphorus, math, antimony, bismuth, and moscovium; the oxygen group, 16 (VIa), includes oxygen, sulfur, selenium, tellurium, polonium, and livermorium; and the halogen group, 17 (VIIa), includes fluorine, chlorine, bromine, iodine, astatine, and tennessine.

Although hydrogen is included in Group 1 (Ia), it is not closely similar to either the alkali metals or the halogens in its chemical properties. It is, however, assigned the oxidation number +1 in compounds such as hydrogen fluoride, HF, and −1 in compounds such as lithium hydride, LiH; and it may hence be considered as being similar to a Group 1 (Ia) element and to a Group 17 (VIIa) element, respectively, in compounds of these two types, taking the place first of Li and then of F in lithium fluoride, LiF. Hydrogen is, in fact, the most individualistic of the elements: No other element resembles it in the way that sodium resembles lithium, chlorine resembles fluorine, and neon resembles helium. It is a unique element, the only element that cannot conveniently be considered a member of a group.

A number of the elements of each long period are called the transition metals. These are usually taken to be scandium, 21, to zinc, 30 (the iron-group transition metals); yttrium, 39, to cadmium, 48 (the palladium-group transition metals); and hafnium, 72, to mercury, 80 (the platinum-group transition metals). By this definition, the transition metals include Groups 3 to 12 (IIIb to VIIIb, and Ib and IIb).

Periodic trends in properties

The periodicity in properties of the elements arranged in order of atomic number is strikingly shown by the consideration of the physical state of the elementary substances and such related properties as the melting point, density, and hardness. The elements of Group 18 (0) are gases that are difficult to condense. The alkali metals, in Group 1 (Ia), are soft metallic solids with low melting points. The alkaline-earth metals, in Group 2 (IIa), are harder and have higher melting points than the adjacent alkali metals. The hardness and melting point continue to increase through Groups 13 (IIIa) and 14 (IVa) and then decrease through Groups 15 (Va), 16 (VIa), and 17 (VIIa). The elements of the long periods show a gradual increase in hardness and melting point from the beginning alkali metals to near the center of the period and then at Group 16 (VIa) an irregular decrease to the halogens and noble gases.

The valence of the elements (that is, the number of bonds formed with a standard element) is closely correlated with position in the periodic table, the elements in the main groups having maximum positive valence, or oxidation number, equal to the group number and maximum negative valence equal to the difference between eight and the group number.

Metallic elements in the periodic table

The general chemical properties described as metallic or base forming, metalloid or amphoteric, and nonmetallic or acid forming are correlated with the periodic table in a simple way: The most metallic elements are to the left and to the bottom of the periodic table and the most nonmetallic elements are to the right and to the top (ignoring the noble gases). The metalloids are adjacent to a diagonal line from boron to polonium.

A closely related property is electronegativity, the tendency of atoms to retain their electrons and to attract additional electrons. The degree of electronegativity of an element is shown by ionization potential, electron affinity, oxidation-reduction potential, the energy of formation of chemical bonds, and other properties. It is shown to depend upon the element’s position in the periodic table in the same way that nonmetallic character does, fluorine being the most electronegative element and cesium (or francium) the least electronegative (most electropositive) element.

The sizes of atoms of elements vary regularly throughout the periodic system. Thus, the effective bonding radius (or one-half the distance between adjacent atoms) in the elementary substances in their crystalline or molecular forms decreases through the first short period from 1.52 Å for lithium to 0.73 Å for fluorine; at the beginning of the second period, the bonding radius rises abruptly to 1.86 Å for sodium and gradually decreases to 0.99 Å for chlorine. The behavior through the long periods is more complex: The bonding radius decreases gradually from 2.31 Å for potassium to a minimum of 1.25 Å for cobalt and nickel, then rises slightly, and finally falls to 1.14 Å for bromine. The sizes of atoms are of importance in the determination of coordination number (that is, the number of groups attached to the central atom in a compound) and hence in the composition of compounds.

The increase in atomic size from the upper right corner of the periodic table to the lower left corner is reflected in the formulas of the oxygen acids of the elements in their highest states of oxidation. The smallest atoms group only three oxygen atoms about themselves; the next larger atoms, which coordinate a tetrahedron of four oxygen atoms, are in a diagonal belt; and the still larger atoms, which form octahedral oxygen complexes (stannic acid, antimonic acid, telluric acid, paraperiodic acid), lie below and to the left of this belt. Only the chemical and physical properties of the elements are determined by the extranuclear electronic structure; these properties show the periodicity described in the periodic law. The properties of the atomic nuclei themselves, such as the magnitude of the packing fraction and the power of entering into nuclear reactions, are, although dependent upon the atomic number, not dependent in the same periodic way.

The basis of the periodic system:

Electronic Structure

The noble gases—helium, neon, argon, krypton, xenon, radon, and oganesson—have the striking chemical property of forming few chemical compounds. This property would depend upon their possessing especially stable electronic structures (that is, structures so firmly knit that they would not yield to accommodate ordinary chemical bonds). During the development of modern atomic physics and the theory of quantum mechanics, a precise and detailed understanding was obtained of the electronic structure of the noble gases and other atoms that explains the periodic law in a thoroughly satisfactory manner.

The Pauli exclusion principle states that no more than two electrons can occupy the same orbit—or, in quantum-mechanical language, orbital—in an atom and that two electrons in the same orbital must be paired (that is, must have their spins opposed, with one spin up and one spin down). The orbitals in an atom may be described by a principal quantum number, n, which may assume the values 1, 2, 3,…, and by an azimuthal quantum number, l, which may assume the values 0, 1, 2,…, n − 1. There are 2l + 1 distinct orbitals for each set of values of n and l.

The most stable orbitals, which bring the electron closest to the nucleus, are those with the smallest values of n and l. The electrons that occupy the orbital with n = 1 (and l = 0) are said to be in the K shell of electrons; the L, M, N,… shells correspond respectively to n = 2, 3, 4,…. Each shell except the K shell is divided into subshells corresponding to the values 0, 1, 2, 3,… of the orbital quantum number l; these subshells are called the s, p, d, and f subshells, and they can accommodate a maximum of 2, 6, 10, and 14 electrons, respectively. (There is no special significance to the letter designations of the quantum numbers or of the shells and subshells.)

The approximate order of stability of the successive subshells in an atom is indicated in the chart below. The number of electrons in the atoms of the elements increases with increasing atomic number, and the added electrons go, of necessity, into successively less stable shells. The most stable shell, the K shell, is completed with helium, which has two electrons. The L shell is then completely filled at neon, with atomic number 10. The atoms of the heavier noble gases do not, however, have a completed outer shell but instead have s and p subshells only. The outer shell of eight electrons is called traditionally an octet. The d subshells and f subshells subsequently are also filled with electrons after the initially less stable orbitals are occupied, an inversion of stability having occurred with increasing atomic number.

The numbers 2, 8, 18, and 32 correspond to filling the s; s and p; s, p, and d; and s, p, d, and f subshells, respectively. The elements in groups 13 through 18 (with the exception of helium) are called p-block elements because in those elements, the p subshells are being filled across the periods.

The first period of the periodic table is complete at helium, when the K shell is filled with two electrons. The first and second short periods represent the filling of the 2s and 2p subshells (completing the L shell at neon) and the 3s and 3p subshells (at argon), leaving the M shell incomplete. The first long period begins with the introduction of electrons into the 4s orbital. Then, at scandium, the five 3d orbitals of the inner M shell begin to be occupied. It is the successive occupancy of these five 3d orbitals by their complement of ten electrons that characterizes the ten elements of the iron-group transition series. At krypton the M shell is complete and there is an octet in the N shell. The second long period, of 18 elements, similarly represents the completion of an outer octet and the next inner subshell of ten 4d electrons.

The very long period of 32 elements results from the completion of the 4f subshell of 14 electrons, the 5d subshell of 10 electrons, and the 6s, 6p octet. The filling of the 4f orbitals corresponds to the sequence of 14 lanthanoids and that of the 5d orbitals to the 10 platinum-group transition metals.

The next period involves the 5f subshell of 14 electrons, the 6d subshell of 10 electrons, and the 7s, 7p octet. The filling of the 5f orbitals corresponds to the actinoids, the elements beginning with thorium, atomic number 90.

There are advantages to replacing the K, L, M,… shells by a different grouping of the subshells, in which those with nearly the same energy are grouped together, in close correlation with the periodic system.

The periodicity of properties of the elements is caused by the periodicity in electronic structure. The noble gases are chemically unreactive, or nearly so, because their electronic structures are stable—their atoms hold their quota of electrons strongly, have no affinity for more electrons, and have little tendency to share electrons with other atoms. An element close to a noble gas in the periodic system, on the other hand, is reactive chemically because of the possibility of assuming the stable electronic configuration of the noble gas, by losing one or more electrons to another atom, by gaining one or more electrons from another atom, or by sharing electrons. The alkali metals, in Group 1 (Ia), can assume the noble-gas configuration by losing one electron, which is loosely held in the outermost (valence) shell, to another element with greater electron affinity, thus producing the stable singly charged positive ions. Similarly the alkaline-earth metals can form doubly charged positive ions with the noble-gas electronic configuration by losing the two loosely held electrons of the valence shell; the positive ionic valences of the elements of the first groups are hence equal to the group numbers. The elements just preceding the noble gases can form negative ions with the noble-gas configuration by gaining electrons; the negative ionic valences of these elements are equal to the difference between eight and their group numbers. The covalence (or number of shared electron pairs) of an atom is determined by its electron number and the stable orbitals available to it. An atom such as fluorine, with seven electrons in its outer shell, can combine with a similar atom by sharing a pair of electrons with it; each atom thus achieves the noble-gas configuration by having three unshared pairs and one shared electron pair in its valence shell.

The properties of elements in the same group of the periodic system are, although similar, not identical. The trend in properties from the lighter to the heavier elements may be attributed to changes in the strength of binding of the outer electrons and especially to the increasing size of the atoms.

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Duodenum

Gist

The duodenum is the first, shortest (approx. 25–30 cm), and most fixed "C"-shaped section of the small intestine, connecting the stomach to the jejunum. It neutralizes acidic chyme and breaks down fats, proteins, and carbohydrates using bile and pancreatic enzymes, playing a critical role in nutrient absorption.

What is the main function of the duodenum?

The first part of the small intestine. It connects to the stomach. The duodenum helps to further digest food coming from the stomach. It absorbs nutrients (vitamins, minerals, carbohydrates, fats, proteins) and water from food so they can be used by the body.

Summary

The duodenum is the first section of the small intestine in most vertebrates, including mammals, reptiles, and birds. In mammals, it may be the principal site for iron absorption. The duodenum precedes the jejunum and ileum and is the shortest part of the small intestine.

In humans, the duodenum is a hollow jointed tube about 25–38 centimetres (10–15 inches) long connecting the stomach to the jejunum, the middle part of the small intestine. It begins with the duodenal bulb, and ends at the duodenojejunal flexure marked by the suspensory muscle of duodenum. The duodenum can be divided into four parts: the first (superior), the second (descending), the third (transverse) and the fourth (ascending) parts.

Overview

The duodenum is the first section of the small intestine in most higher vertebrates, including mammals, reptiles, and birds. In fish, the divisions of the small intestine are not as clear, and the terms anterior intestine or proximal intestine may be used instead of duodenum. In mammals the duodenum may be the principal site for iron absorption.

In humans, the duodenum is a C-shaped hollow jointed tube, 25–38 centimetres (10–15 inches) in length, lying adjacent to the stomach (and connecting it to the small intestine). It is divided anatomically into four sections. The first part lies within the peritoneum but its other parts are retroperitoneal.

Details

The duodenum is the first part of your small intestine. Its main job is to transform the partially digested food it receives from your stomach into nutrients your body can use. Digestive juices from your liver, gallbladder and pancreas empty into your duodenum, helping with digestion and absorption.

Overview:

What is the duodenum?

The duodenum is the first part of your small intestine. Despite what the name suggests, your “small” intestine is the longest part of your digestive tract and plays a big role in your digestive system. Inside its many coils, digestive juices transform food into the nutrients (like proteins, fats, vitamins and water) that power your body.

The duodenum is a short, “C”-shaped chute. It’s the first stop food makes as it travels from your stomach to your small intestine. The other parts of your small intestine are your jejunum (the middle part) and ileum (the last part).

Function:

What is the function of the duodenum?

The duodenum continues the process of digestion (breakdown of food into nutrients) that starts in other parts of your gastrointestinal (GI) tract, like your mouth and stomach. It also begins the absorption process (moving the nutrients into your bloodstream). Think of it this way: Before reaching your duodenum, saliva and stomach acid have transformed food into food slush. Inside your duodenum, the slush becomes nutrients your body can use.

Your duodenum:

* Makes food traveling from your stomach less acidic. The partially digested food that travels from your stomach to your duodenum is called chyme. Chyme is highly acidic, thanks to stomach juices that break down food. Your duodenum releases a hormone (secretin) that triggers the release of an enzyme called bicarbonate that makes chyme less acidic. The breakdown of acid helps your digestive system absorb nutrients. It prevents the acid from damaging your small intestine.
* Transforms chyme into nutrients. Your duodenum releases a hormone (cholecystokinin) that triggers your pancreas, gallbladder and liver to release substances that help turn chyme into nutrients. Your liver and gallbladder release bile, which breaks down fats. Your pancreas releases lipase, which also breaks down fats, amylase to break down carbohydrates and protease to break down proteins. Your bloodstream absorbs these nutrients.
* Moves food molecules along. The duodenum pushes food molecules that don’t get absorbed into the next section of your small intestine, the jejunum. The duodenum squeezes and relaxes, creating a wave-like forward motion called peristalsis.

Anatomy:

How big is the duodenum?

It’s the shortest section of your small intestine, approximately 10 inches long — just 2 inches shy of a foot. “Duodenum,” translated from Latin, means “12 fingers,” a reference to its size. The length of your duodenum is approximately the width of 12 fingers placed side by side.

To put this in perspective, your entire small intestine is 22 feet long. If you stretched it out, it would be the length of a tennis court. Your duodenum wouldn’t be a single foot of the total length. Yet, important nutrient absorption happens in these 10 inches of your small intestine.

Where is the duodenum located?

Your duodenum starts just below your stomach. It curves to the right and back, down and then to the left in a “C” or horseshoe shape. It slants upward slightly before joining with the next part of your small intestine, your jejunum. The head of your pancreas (the widest part) sits inside the “C.”

What are the parts of the duodenum?

There are four basic parts. They get their name from their location and shape.

* Superior segment

The superior segment is the top part of the duodenum that connects with your stomach. It’s about 2 inches long. The part of the superior segment that connects directly with your pylorus (the stomach valve that opens to allow food to travel to your small intestine) is called the duodenal bulb. Most ulcers in your small intestine form here, where stomach acid is most likely to come into contact with your duodenum.

* Descending segment

As the name suggests, the descending segment is the part of the “C” shape that goes downward. It passes in front of your right kidney and is about 4 inches long.

This part of your small intestine connects to your pancreas (via the pancreatic duct) and your gallbladder and liver (via the common bile duct). “Ducts” are like tiny canals that allow substances to travel from one organ (like your liver) to another organ (like your small intestine). These organs produce substances that empty into the descending segment, breaking down fats, proteins and carbohydrates.

* Horizontal (inferior) segment

The horizontal segment is about 4 inches long. It extends from right to left and passes over essential blood vessels, including your aorta and inferior vena cava.

* Ascending segment

This is the smallest part of your duodenum, at just under an inch. It extends slightly upward and is located to the left of your aorta. It connects to your jejunum.

What is the duodenum made of?

The duodenum has four layers. Its cell makeup is the same as other organs in your GI tract. From the innermost layer to the outermost layer, the duodenum consists of the:

* Mucosa: It contains glands and fingerlike projections called microvilli. The microvilli increase the surface area of your duodenum, allowing it to absorb more nutrients than if it were flat.
* Submucosa: This layer consists of blood vessels and connective tissue. The submucosa contains Brunner’s glands. Brunner’s glands release a substance that makes chyme less acidic.
* Muscularis: This layer is mostly smooth muscle. Its job is mixing and moving. As it contracts, it blends the enzymes and bile that break down chyme. It also moves the chyme along the length of your duodenum, so it reaches your jejunum.
* Serosa: This layer consists of squamous epithelial cells that serve as your duodenum’s protective barrier.

Conditions and Disorders:

What problems can occur in the duodenum?

As the part of your small intestine closest to your stomach, your duodenum is especially susceptible to injury if you have excess stomach acid. The acid can lead to open stores in your stomach (peptic ulcers) and in your duodenum. The most common causes of these ulcers are H. pylori infection and overusing medicines called NSAIDs (nonsteroidal anti-inflammatory drugs). NSAIDs, like aspirin and ibuprofen, can ease symptoms like aches and pains but can cause ulcers if you use them too much.

If an untreated ulcer breaks down too much of your duodenum’s protective barrier, its contents can leak out and damage the gastroduodenal artery behind it. This can cause severe bleeding that requires emergency care.

Many of the same conditions that affect your small intestine, in general, can affect your duodenum specifically. Conditions that can affect your duodenum include:

* Brunner’s gland adenomas: Benign (noncancerous) growths that start in Brunner’s glands.
* Crohn’s disease: A type of irritable bowel disease (IBD) that causes irritation and inflammation.
* Celiac disease: A disorder that causes problems in your digestive system when you eat gluten.
* Duodenal atresia: A condition that causes a baby to be born with a closed duodenum.
* Duodenal stenosis: A condition that causes a baby to be born with a narrowed (but not completely closed) duodenum.
* Duodenal cancer: Cancer that starts in your duodenum.
* Duodenal diverticulum: A small, pouch-like structure that pushes outside the wall of your duodenum. Diverticula (plural of diverticulum) usually don’t cause issues or require treatment unless they become infected and inflamed (diverticulitis).
* Duodenitis: Inflammation in your duodenum.
* Small bowel obstruction: A medical emergency that happens when part of your small intestine (including your duodenum) is entirely or partially blocked.

Common signs or symptoms of issues with the duodenum

Symptoms depend on the specific condition. In general, symptoms of a condition affecting your duodenum are similar to problems with your GI tract. Signs and symptoms include:

* Abdominal pain.
* Bloating and gas.
* Constipation.
* Diarrhea.
* Nausea and vomiting.
* Indigestion (stomach discomfort after you eat).
* Bloody vomit or poop (a sign of a bleeding ulcer).

Common tests to check the health of the duodenum.

Common tests include:

* Breath test to check for H. pylori infections.
* Imaging procedures — like ultrasounds, X-rays, CT scans (computed tomography scans) and MRIs (magnetic resonance imaging) — that look for growths and inflammation inside your duodenum.
* Procedures that use a scope to see inside your duodenum, including enteroscopy and upper endoscopy.
* Biopsies to check abnormal growths, including cancer.

What are common treatments for conditions affecting the duodenum?

Common treatments include:

* Antibiotics to treat infections (like H. pylori).
* Corticosteroids to reduce severe inflammation.
* Medicines to reduce the amount or acidity level of stomach acid, like proton pump inhibitors (PPIs), histamine receptor blockers (H2 blockers) and antacids.
* Surgery to correct structural issues or treat cancer, including the Whipple procedure.

Care:

How can I keep my duodenum healthy?

Putting healthy habits into place to prevent irritating or overworking your digestive system is good for your entire GI tract, including your duodenum.

Choose a diet that keeps your digestive system running smoothly. Eating lots of fiber and drinking lots of water can help you have regular bowel movements so things don’t get backed up in your small intestine. Eating lots of vegetables and nonacidic foods can help you maintain a healthy acidity level in your gut.

Avoid substances that can irritate your gut. Smoking and drinking too much alcohol can irritate organs in your digestive system, including your small intestine. Taking too many NSAIDs (Nonsteroidal anti-inflammatory drugs) can lead to painful ulcers that require treatment.

Don’t ignore signs of digestive system issues. Changes in your bowel habits and unpleasant symptoms, like an upset stomach or indigestion, can be temporary. Or they can sound the alarm bells that you need to change your lifestyle or see a provider. Don’t delay getting help if you’ve got unpleasant digestive symptoms that aren’t improving.

Additional Information

Duodenum is the first part of the small intestine, which receives partially digested food from the stomach and begins the absorption of nutrients. The duodenum is the shortest segment of the intestine and is about 23 to 28 cm (9 to 11 inches) long. It is roughly horseshoe-shaped, with the open end up and to the left, and it lies behind the liver. On anatomic and functional grounds, the duodenum can be divided into four segments: the superior (duodenal bulb), descending, horizontal, and ascending duodenum.

A liquid mixture of food and gastric secretions enters the superior duodenum from the pylorus of the stomach, triggering the release of pancreas-stimulating hormones (e.g., secretin) from glands (crypts of Lieberkühn) in the duodenal wall. So-called Brunner glands in the superior segment provide additional secretions that help to lubricate and protect the mucosal layer of the small intestine. Ducts from the pancreas and gallbladder enter at the major duodenal papilla (papilla of Vater) in the descending duodenum, bringing bicarbonate to neutralize the acid in the gastric secretions, pancreatic enzymes to further digestion, and bile salts to emulsify fat. A separate minor duodenal papilla, also in the descending segment, may receive pancreatic secretions in small amounts. The mucous lining of the last two segments of the duodenum begins the absorption of nutrients, in particular iron and calcium, before the food contents enter the next part of the small intestine, the jejunum.

Inflammation of the duodenum is known as duodenitis, which has various causes, prominent among them infection by the bacterium Helicobacter pylori. H. pylori increases the susceptibility of the duodenal mucosa to damage from unneutralized digestive acids and is a major cause of peptic ulcers, the most common health problem affecting the duodenum. Other conditions that may be associated with duodenitis include celiac disease, Crohn disease, and Whipple disease. The horizontal duodenum, because of its location between the liver, pancreas, and major blood vessels, can become compressed by those structures in people who are severely thin, requiring surgical release to eliminate painful duodenal dilatation, nausea, and vomiting.

Potassium Iodide

Gist

Potassium iodide (KI) is an inorganic compound used to protect the thyroid gland from radiation, treat iodine deficiency, and manage specific skin conditions. Primarily taken as a tablet, it blocks the absorption of radioactive iodine during emergencies and serves as a supplement to combat hyperthyroidism and goiter.

Potassium iodide (KI) is a medication used to protect the thyroid gland from radiation during emergencies, treat hyperthyroidism and thyroid storm, and act as an expectorant to loosen mucus in the lungs. It is also used to treat certain fungal infections (sporotrichosis) and chronic skin conditions like erythema nodosum.

Summary

Potassium iodide (KI) is a chemical compound, medication, and dietary supplement. It is a medication used for treating hyperthyroidism, in radiation emergencies, and for protecting the thyroid gland when certain types of radiopharmaceuticals are used. It is also used for treating skin sporotrichosis and phycomycosis. It is a supplement used by people with low dietary intake of iodine. It is administered orally.

Common side effects include vomiting, diarrhea, abdominal pain, rash, and swelling of the salivary glands. Other side effects include allergic reactions, headache, goitre, and depression. While use during pregnancy may harm the baby, its use is still recommended in radiation emergencies. Potassium iodide has the chemical formula KI. Commercially it is made by mixing potassium hydroxide with iodine.

Potassium iodide has been used medically since at least 1820. It is on the World Health Organization's List of Essential Medicines. Potassium iodide is available as a generic medication and over the counter. Potassium iodide is also used for the iodization of salt.

Details

Potassium iodide (KI) is a medication that treats certain medical conditions — including some thyroid conditions — and protects your thyroid from radiation exposure. Never take KI without talking to a healthcare provider first. They’ll make sure it’s safe for you and explain proper dosing.

Overview:

What is potassium iodide?

Potassium iodide is a salt that healthcare providers sometimes use as a medication to treat certain thyroid conditions or protect your thyroid from radiation exposure.

Potassium iodide acts as a thyroid blocker, which means it stops your thyroid from releasing thyroid hormone. This can be useful in certain situations, like if your thyroid is producing high levels of thyroid hormone (hyperthyroidism). Potassium iodide can also help protect your thyroid from absorbing radioactive iodine that accidentally enters your body.

Healthcare providers intentionally use radioactive iodine — in controlled, safe amounts — for certain imaging tests and treatments. Nuclear weapon detonations and nuclear power plant accidents release unsafe amounts of radioactive iodine (radioiodine) into the air, water and soil. Potassium iodide can protect you from such unintended environmental exposure.

Potassium iodide comes in pill (tablet) and liquid forms. Some forms require a prescription, while others you can get over the counter (OTC). You should only take potassium iodide in any form if your healthcare provider or public health officials tell you to do so. Remember that just because you can buy something over the counter doesn’t mean it’s safe or appropriate for you to take.

What conditions are treated with potassium iodide?

Healthcare providers sometimes use potassium iodide to treat:

* Hyperthyroidism, particularly when associated with Graves’ disease.
* Thyroid storm.
* Some skin conditions, including cutaneous sporotrichosis (a fungal infection).
* Iodine deficiency.

Potassium iodide is also a prescription-strength expectorant. If you have a chronic lung disease, your healthcare provider may prescribe potassium iodide to loosen mucus and make it easier for you to cough.

Potassium iodide can also help protect your thyroid:

* During radiation emergencies (like a nuclear power plant meltdown).
* During medical testing (like MIBG scans) or treatments that expose your thyroid to radiation.

Potassium iodide for radiation

Potassium iodide is best known for protecting people during a radiation emergency. But it’s important to know there are limitations. Potassium iodide only protects your thyroid from radioactive iodine (one specific radioactive material). It doesn’t protect other parts of your body, and it doesn’t protect you from all the other radioactive materials you might be exposed to that could cause radiation sickness.

Healthcare providers and public health officials only recommend using potassium iodide in certain types of radiation emergencies. These typically include nuclear power plant accidents.

Potassium iodide won’t completely protect you if a nuclear bomb goes off because the greatest threat in that situation isn’t radioactive iodine. You’d be exposed to hundreds of other types of radioactive materials, and potassium iodide has no effect on those. If a bomb goes off, don’t worry about trying to find potassium iodide. Instead, seek shelter indoors and follow local officials’ guidance.

Thyroid protection after a nuclear power plant accident

Potassium iodide can help protect your thyroid from radioactive iodine released in a nuclear power plant accident. Here’s why. Your thyroid needs iodine to function normally and produce thyroid hormone. But it doesn’t know the difference between normal iodine (like what you get from your food) and radioactive iodine. This means your thyroid grabs iodine from wherever it can.

Nuclear power plant accidents may release radioactive iodine into the nearby environment. If you breathe in contaminated air or eat contaminated food, the radioactive iodine can enter your body. Your thyroid then absorbs it. Depending on the amount that gets into your body, radioactive iodine can damage your thyroid and potentially lead to thyroid cancer down the road.

The younger you are, the more vulnerable you are to the harmful effects of radioactive iodine. Babies and children face the greatest threat. If you’re pregnant, radioactive iodine is more dangerous for you compared to other adults because your thyroid is more active during pregnancy.

That’s where potassium iodide comes into play. It fills up your thyroid with enough iodine to keep it busy for a while. So, instead of absorbing the radioactive iodine, your thyroid ignores it, and the radioactive iodine passes out of your body in your pee.

Treatment Details:

How should I use potassium iodide?

Depending on your diagnosis, your healthcare provider may prescribe potassium iodide in tablet or liquid form. Your provider or local public health officials will tell you:

* How to take potassium iodide.
* When to take it.
* The appropriate dosage.

The dosage can vary widely according to the condition you’re treating. In the context of radiation emergencies, the recommended dosage varies according to a person’s age.

How long should I take potassium iodide?

It depends on the reason you’re taking it. Follow your healthcare provider’s guidance. In radiation emergencies, one dose typically protects you for about 24 hours. So, most people should take one dose per day until local officials say it’s safe to stop taking it.

Pregnant women and newborns should only take one dose (no repeat doses) unless told otherwise. That’s because potassium iodide may impact thyroid function in fetuses and newborns.

Risks / Benefits:

What are the potential benefits of potassium iodide?

When used during a radiation emergency, potassium iodide can lower a person’s risk of developing thyroid cancer down the road. This is especially important in children and adults under age 40, who face a greater risk of thyroid cancer from radioactive iodine exposure.

What are the side effects of potassium iodide?

Possible side effects of potassium iodide include:

* Skin rash.
* Swollen salivary glands.
* Metallic taste in your mouth.
* Burning of your mouth and throat.
* Sore teeth and gums.
* Upset stomach, nausea and diarrhea.
* Headache.
* Head cold symptoms, like a runny nose.

Newborns who are given more than a single dose of potassium iodide run the risk of developing hypothyroidism.

Can potassium iodide cause an allergic reaction?

Potassium iodide causes an allergic reaction in some people. Signs of an allergic reaction include:

* Fever.
* Joint pain.
* Swelling of your face, lips, tongue, throat, hands or feet.
* Wheezing and/or shortness of breath.
* Difficulty speaking or swallowing.

Call a healthcare provider right away if you develop signs of an allergic reaction. Call your local emergency number if you have trouble breathing, speaking or swallowing.

Taking more potassium iodide than healthcare providers or local officials recommend can make you very sick or even be fatal. That’s why it’s crucial to follow expert advice closely when taking potassium iodide or giving it to a child.

Is taking potassium iodide safe for me?

Potassium iodide isn’t safe for everyone. It’s important to check with your healthcare provider before taking potassium iodine to make sure it’s OK for you. In general, potassium iodine may not be safe to take if you:

* Have thyroid nodules as well as heart disease.
* Are taking certain medications, including those that affect how your thyroid works.
* Are sensitive or allergic to iodine.
* Have chronic kidney (renal) failure.
* Have tuberculosis or acute bronchitis.
* Have a history of adrenal insufficiency (Addison’s disease).
* Have a weakened immune system.
* Are pregnant or breastfeeding. In some situations, like radiation emergencies, the benefits of taking potassium iodide while pregnant or nursing may outweigh the risks. Follow your provider’s guidance closely.

Be sure to talk to your provider before starting potassium iodide or any other medicine. They’ll review your medical history and decide if it’s safe for you. They can tell you the benefits and risks of potassium iodide in your unique situation. They’ll also tell you if you need follow-ups or monitoring.

Recovery and Outlook:

Is there anything I can do to make this treatment easier on me?

Your provider may recommend taking potassium iodide along with milk or juice to limit stomach upset. Talk to your provider if you’re concerned about side effects or have a history of any medication allergies.

Additional Information

* In a radiation emergency, some people may be told to take potassium iodide (KI) to protect their thyroid.
* Do not take KI unless instructed by public health or emergency response officials or a healthcare provider.
* KI is recommended only for people under 40 and women who are pregnant or breastfeeding.
* KI can have harmful effects when used incorrectly. Only use KI products that are approved by the U.S. FDA.

Potassium iodide (KI) is a type of iodine that is not radioactive. It can be used to help block one type of radioactive material, radioactive iodine, from being absorbed by the thyroid.

In some radiation emergencies, radioactive iodine may be released into the environment and enter the body through breathing or eating. This is known as internal contamination.

The thyroid is a gland in the neck that plays an important role in many body functions. When the thyroid absorbs high levels of radioactive iodine, it can increase the risk of thyroid cancer many years after exposure in infants, children, and young adults.

How KI protects the thyroid

KI is the stable (non-radioactive) form of iodine. They are both absorbed by the thyroid.

The thyroid cannot distinguish between stable or radioactive iodine. To protect the thyroid from radioactive iodine, a person must take KI before or shortly after being exposed to radioactive iodine to saturate the thyroid and prevent the radioactive iodine from concentrating in the thyroid.

When a person takes the right amount of KI at the right time, it can help block the thyroid from absorbing radioactive iodine. This happens because the thyroid has already absorbed the KI, and there is no room to absorb the radioactive iodine. Think of filling a jar with blue marbles (KI). If you then pour green marbles (radioactive iodine) over the jar, there will not be room and they will just spill out.

Use KI only if instructed

Do not take KI unless you are instructed by public health or emergency response officials or a healthcare provider. KI can cause harmful health effects. KI is helpful only in specific situations for certain groups of people.

KI should be used only as directed.

* Do not use table salt or foods that contain iodine as a substitute for KI. They do not help prevent internal contamination, and eating large amounts could be harmful.
* Only use KI products that have been approved by the Food and Drug Administration (FDA). Dietary supplements that contain iodine may not work to protect the thyroid and can hurt you.

Important

KI can have harmful health effects and can cause allergic reactions. Only take KI if instructed by public health or emergency response officials or a healthcare provider.

Limits of KI use

KI is most effective if taken shortly before or right after internal contamination with radioactive iodine. The effectiveness of KI also depends on how much radioactive iodine gets into the body and how quickly it is absorbed in the body.

KI is only recommended for people under 40 and women who are pregnant or breastfeeding. People with certain medical conditions, including known iodine sensitivity, should not take KI or should talk to a healthcare provider about whether they can safely take KI.

KI only offers limited protection in specific situations:

* KI protects only against radioactive iodine and does not protect against other types of radioactive materials.
* KI protects only the thyroid. KI does not protect other parts of the body.
* KI must be taken within 24 hours before or 4 hours after exposure to be most effective.
* KI is not a treatment and cannot reverse damage already done to the thyroid.
* KI may not give a person 100% thyroid protection from radioactive iodine.

Most radiation emergencies will involve other types of radioactive materials and not radioactive iodine alone. Radioactive iodine is most common in nuclear power plant incidents.

How to take KI

KI is recommended as a medical countermeasure to protect the thyroid from radioactive iodine in people under 40 and women who are pregnant or breastfeeding. This is because younger people's cells are still growing and increasing in number more quickly. This puts them at risk for developing thyroid cancer after breathing in radioactive iodine.

Adults over 40 years old have a much lower risk of developing thyroid cancer. They are also more likely to have health conditions, like problems with their thyroids, that increase the risk for harmful health effects from KI. However, officials or healthcare providers may instruct adults over 40 to consume KI if the predicted exposure is high enough to cause hypothyroidism (when the thyroid does not make enough hormones).

Breastfeeding women should consider temporarily stopping breastfeeding until evacuated from the impacted area, if possible, and safely feed your baby other ways. Radioactive iodine can be passed to infants through breast milk.

There are two U.S. FDA-approved forms of KI:

* Tablets in two strengths, 130 milligram (mg) and 65 mg. The tablets may be cut into smaller pieces for lower doses.
* Oral liquid solution available in one concentration, each milliliter (mL) containing 65 mg of KI. The solution comes in a 1 oz (30 mL) bottle with a dropper marked for 1, 0.5, and 0.25 mL dosing. For reference, 5 mL of liquid is one teaspoon. One mL would be about the size of a large drop of water.

Q: Why did the orange fail his driving test?
A: He kept peeling out.
* * *
Q: How many marmalade sandwiches did Paddington bear eat?
A: None he was already stuffed.
* * *
Q: What do you call an orange that takes over the world?
A: Orange Julius Caesar.
* * *
Q: Do you now why a orange is smart?
A: Because it CONCERTRATES!
* * *
Q: What do you call the ruthless movie about building a fruit empire?
A: There Will Be Blood...Oranges.
* * *