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76-539: However, although this was a major step forward in standardising radiation measurement, the roentgen has the disadvantage that it is only a measure of air ionisation, and not a direct measure of radiation absorption in other materials, such as different forms of human tissue . For instance, one roentgen deposits 0.00877 grays (0.877 rads ) of absorbed dose in dry air, or 0.0096 Gy (0.96 rad) in soft tissue. One roentgen of X-rays may deposit anywhere from 0.01 to 0.04 Gy (1.0 to 4.0 rad) in bone depending on

152-510: A degree of conductivity that 1 esu of charge is measured at saturation current." The stated 1 cc of air would have a mass of 1.293 mg at the conditions given, so in 1937 the ICR rewrote this definition in terms of this mass of air instead of volume, temperature and pressure. The 1937 definition was also extended to gamma rays, but later capped at 3 MeV in 1950. The USSR all-union committee of standards (GOST) had meanwhile adopted

228-743: A function is called cellular differentiation . Cells of meristematic tissue differentiate to form different types of permanent tissues. There are 2 types of permanent tissues: Simple permanent tissue is a group of cells which are similar in origin, structure, and function. They are of three types: Parenchyma (Greek, para – 'beside'; enchyma– infusion – 'tissue') is the bulk of a substance. In plants, it consists of relatively unspecialized living cells with thin cell walls that are usually loosely packed so that intercellular spaces are found between cells of this tissue. These are generally isodiametric, in shape. They contain small number of vacuoles or sometimes they even may not contain any vacuole. Even if they do so

304-604: A function of providing mechanical support. They do not have inter-cellular spaces between them. Lignin deposition is so thick that the cell walls become stronger, rigid and impermeable to water, which are also known as a stone cells or sclereids. These tissues are mainly of two types: sclerenchyma fiber and sclereids. Sclerenchyma fiber cells have a narrow lumen and are long, narrow and unicellular. Fibers are elongated cells that are strong and flexible, often used in ropes. Sclereids have extremely thick cell walls and are brittle, and are found in nutshells and legumes. The entire surface of

380-653: A recommendation that the definition be given in every document where the roentgen is used. The roentgen has its roots in the Villard unit defined in 1908 by the American Roentgen Ray Society as "the quantity of radiation which liberates by ionisation one esu of electricity per cm of air under normal conditions of temperature and pressure." Using 1 esu ≈ 3.33564 × 10 C and the air density of ~1.293 kg/m at 0 °C and 101 kPa, this converts to 2.58 × 10 C/kg, which

456-576: A sample of matter per unit mass. The unit was named after British physicist Louis Harold Gray , a pioneer in the measurement of X-ray and radium radiation and their effects on living tissue. The gray was adopted as part of the International System of Units in 1975. The corresponding cgs unit to the gray is the rad (equivalent to 0.01 Gy), which remains common largely in the United States, though "strongly discouraged" in

532-420: A significantly different definition of the roentgen in 1934. GOST standard 7623 defined it as "the physical dose of X-rays which produces charges each of one electrostatic unit in magnitude per cm of irradiated volume in air at 0 °C and normal atmospheric pressure when ionization is complete." The distinction of physical dose from dose caused confusion, some of which may have led Cantrill and Parker report that

608-535: A supporting tissue in stems of young plants. It provides mechanical support, elasticity, and tensile strength to the plant body. It helps in manufacturing sugar and storing it as starch. It is present in the margin of leaves and resists tearing effect of the wind. Sclerenchyma (Greek, Sclerous means hard and enchyma means infusion) consists of thick-walled, dead cells and protoplasm is negligible. These cells have hard and extremely thick secondary walls due to uniform distribution and high secretion of lignin and have

684-536: A thin and elastic primary cell wall made of cellulose . They are compactly arranged without inter-cellular spaces between them. Each cell contains a dense cytoplasm and a prominent cell nucleus . The dense protoplasm of meristematic cells contains very few vacuoles . Normally the meristematic cells are oval, polygonal , or rectangular in shape. Meristematic tissue cells have a large nucleus with small or no vacuoles because they have no need to store anything, as opposed to their function of multiplying and increasing

760-594: A wide range of stretch lengths. It is found in such organs as sea anemone tentacles and the body wall of sea cucumbers . Skeletal muscle contracts rapidly but has a limited range of extension. It is found in the movement of appendages and jaws. Obliquely striated muscle is intermediate between the other two. The filaments are staggered and this is the type of muscle found in earthworms that can extend slowly or make rapid contractions. In higher animals striated muscles occur in bundles attached to bone to provide movement and are often arranged in antagonistic sets. Smooth muscle

836-399: Is 0.7 millisieverts (0.0007 Sv), that from an abdominal CT scan is 8 mSv, that from a pelvic CT scan is 6 mGy, and that from a selective CT scan of the abdomen and the pelvis is 14 mGy. The absorbed dose also plays an important role in radiation protection , as it is the starting point for calculating the stochastic health risk of low levels of radiation, which is defined as

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912-445: Is 2.5 Gy, LD 50 is 5 Gy and LD 99 is 8 Gy. The LD 50 dose represents 375 joules for a 75 kg adult. The gray is used to measure absorbed dose rates in non-tissue materials for processes such as radiation hardening , food irradiation and electron irradiation . Measuring and controlling the value of absorbed dose is vital to ensuring correct operation of these processes. Kerma (" k inetic e nergy r eleased per unit ma ss")

988-435: Is a central element in human anatomy , and he considered organs as collections of often disparate tissues, rather than as entities in themselves". Although he worked without a microscope , Bichat distinguished 21 types of elementary tissues from which the organs of the human body are composed, a number later reduced by other authors. Gray (unit) The gray (symbol: Gy ) is the unit of ionizing radiation dose in

1064-466: Is a living tissue of primary body like Parenchyma . Cells are thin-walled but possess thickening of cellulose , water and pectin substances ( pectocellulose ) at the corners where a number of cells join. This tissue gives tensile strength to the plant and the cells are compactly arranged and have very little inter-cellular spaces. It occurs chiefly in hypodermis of stems and leaves. It is absent in monocots and in roots. Collenchymatous tissue acts as

1140-405: Is also known as conducting and vascular tissue. The common types of complex permanent tissue are: Xylem and phloem together form vascular bundles. Xylem (Greek, xylos = wood) serves as a chief conducting tissue of vascular plants. It is responsible for the conduction of water and inorganic solutes. Xylem consists of four kinds of cells: Xylem tissue is organised in a tube-like fashion along

1216-696: Is an equally important plant tissue as it also is part of the 'plumbing system' of a plant. Primarily, phloem carries dissolved food substances throughout the plant. This conduction system is composed of sieve-tube member and companion cells, that are without secondary walls. The parent cells of the vascular cambium produce both xylem and phloem. This usually also includes fibers, parenchyma and ray cells. Sieve tubes are formed from sieve-tube members laid end to end. The end walls, unlike vessel members in xylem, do not have openings. The end walls, however, are full of small pores where cytoplasm extends from cell to cell. These porous connections are called sieve plates. In spite of

1292-508: Is called an extracellular matrix . This matrix can be liquid or rigid. For example, blood contains plasma as its matrix and bone's matrix is rigid. Connective tissue gives shape to organs and holds them in place. Blood, bone, tendon, ligament, adipose, and areolar tissues are examples of connective tissues. One method of classifying connective tissues is to divide them into three types: fibrous connective tissue, skeletal connective tissue, and fluid connective tissue. Muscle cells (myocytes) form

1368-400: Is considered as the "Father of Histology". Plant histology is studied in both plant anatomy and physiology . The classical tools for studying tissues are the paraffin block in which tissue is embedded and then sectioned, the histological stain , and the optical microscope . Developments in electron microscopy , immunofluorescence , and the use of frozen tissue-sections have enhanced

1444-436: Is conventionally used to express the severity of what are known as "tissue effects" from doses received in acute exposure to high levels of ionizing radiation. These are effects that are certain to happen, as opposed to the uncertain effects of low levels of radiation that have a probability of causing damage. A whole-body acute exposure to 5 grays or more of high-energy radiation usually leads to death within 14 days. LD 1

1520-411: Is found in the walls of the uterus , bladder , intestines , stomach , oesophagus , respiratory airways , and blood vessels . Cardiac muscle is found only in the heart , allowing it to contract and pump blood through the body. Cells comprising the central nervous system and peripheral nervous system are classified as nervous (or neural) tissue. In the central nervous system, neural tissues form

1596-474: Is how the rad had been defined, but in MKS units it would be equivalent to the joule per kilogram. This was confirmed in 1975 by the 15th CGPM, and the unit was named the "gray" in honour of Louis Harold Gray, who had died in 1965. The gray was thus equal to 100 rad. Notably, the centigray (numerically equivalent to the rad) is still widely used to describe absolute absorbed doses in radiotherapy. The adoption of

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1672-450: Is important in predicting likely acute health effects, such as acute radiation syndrome and is used to calculate equivalent dose using the sievert , which is a measure of the stochastic health effect on the human body. The gray is also used in radiation metrology as a unit of the radiation quantity kerma ; defined as the sum of the initial kinetic energies of all the charged particles liberated by uncharged ionizing radiation in

1748-477: Is somewhat variable. Most classification schemes combine a description of the cell-shape in the upper layer of the epithelium with a word denoting the number of layers: either simple (one layer of cells) or stratified (multiple layers of cells). However, other cellular features such as cilia may also be described in the classification system. Some common kinds of epithelium are listed below: Connective tissues are made up of cells separated by non-living material, which

1824-400: Is the modern value given by NIST. 1  ⁠ esu / cm ⁠ × 3.33564 × 10  ⁠ C / esu ⁠ × 1,000,000  ⁠ cm / m ⁠ ÷ 1.293  ⁠ kg / m ⁠ = 2.58 × 10  ⁠ C / kg ⁠ This definition was used under different names ( e , R , and German unit of radiation ) for the next 20 years. In

1900-420: Is used in radiation metrology as a measure of the liberated energy of ionisation due to irradiation, and is expressed in grays. Importantly, kerma dose is different from absorbed dose, depending on the radiation energies involved, partially because ionization energy is not accounted for. Whilst roughly equal at low energies, kerma is much higher than absorbed dose at higher energies, because some energy escapes from

1976-483: The International System of Units (SI), defined as the absorption of one joule of radiation energy per kilogram of matter . It is used as a unit of the radiation quantity absorbed dose that measures the energy deposited by ionizing radiation in a unit mass of absorbing material, and is used for measuring the delivered dose in radiotherapy , food irradiation and radiation sterilization . It

2052-431: The brain and spinal cord . In the peripheral nervous system, neural tissues form the cranial nerves and spinal nerves , inclusive of the motor neurons . Mineralized tissues are biological tissues that incorporate minerals into soft matrices. Such tissues may be found in both plants and animals. Xavier Bichat introduced the word tissue into the study of anatomy by 1801. He was "the first to propose that tissue

2128-463: The ectoderm and endoderm (or their precursor in sponges ), with a small contribution from the mesoderm , forming the endothelium , a specialized type of epithelium that composes the vasculature . By contrast, a true epithelial tissue is present only in a single layer of cells held together via occluding junctions called tight junctions , to create a selectively permeable barrier. This tissue covers all organismal surfaces that come in contact with

2204-421: The probability of cancer induction and genetic damage. The gray measures the total absorbed energy of radiation, but the probability of stochastic damage also depends on the type and energy of the radiation and the types of tissues involved. This probability is related to the equivalent dose in sieverts (Sv), which has the same dimensions as the gray. It is related to the gray by weighting factors described in

2280-593: The rad , equal to 100 erg/g, as the new unit of measure of absorbed radiation. The rad was expressed in coherent cgs units. In the late 1950s, the CGPM invited the ICRU to join other scientific bodies to work on the development of the International System of Units , or SI. The CCU decided to define the SI unit of absorbed radiation as energy deposited by reabsorbed charged particles per unit mass of absorbent material, which

2356-460: The 1937 meeting of the ICRU, this definition was extended to apply to gamma radiation . This approach, although a great step forward in standardisation, had the disadvantage of not being a direct measure of the absorption of radiation, and thereby the ionisation effect, in various types of matter including human tissue, and was a measurement only of the effect of the X-rays in a specific circumstance;

Roentgen (unit) - Misplaced Pages Continue

2432-498: The ICRP reduced their recommended limit to 0.3 roentgen per week for whole-body exposure. The International Commission on Radiation Units and Measurements (ICRU) took over the definition of the roentgen in 1950, defining it as "the quantity of X or γ-radiation such that the associated corpuscular emission per 0.001293 gram of air produces, in air, ions carrying 1 electrostatic unit of quantity of electricity of either sign." The 3 MeV cap

2508-442: The SI unit sievert or the non-SI rem are used. The following table shows radiation quantities in SI and non-SI units: Human tissue In biology , tissue is an assembly of similar cells and their extracellular matrix from the same embryonic origin that together carry out a specific function. Tissues occupy a biological organizational level between cells and a complete organ . Accordingly, organs are formed by

2584-427: The absorbing volume in the form of bremsstrahlung (X-rays) or fast-moving electrons. Kerma, when applied to air, is equivalent to the legacy roentgen unit of radiation exposure, but there is a difference in the definition of these two units. The gray is defined independently of any target material, however, the roentgen was defined specifically by the ionisation effect in dry air, which did not necessarily represent

2660-420: The active contractile tissue of the body. Muscle tissue functions to produce force and cause motion, either locomotion or movement within internal organs. Muscle is formed of contractile filaments and is separated into three main types; smooth muscle , skeletal muscle and cardiac muscle . Smooth muscle has no striations when examined microscopically. It contracts slowly but maintains contractibility over

2736-429: The amount of radiation applied varies depending on the type and stage of cancer being treated. For curative cases, the typical dose for a solid epithelial tumor ranges from 60 to 80 Gy, while lymphomas are treated with 20 to 40 Gy. Preventive (adjuvant) doses are typically around 45–60 Gy in 1.8–2 Gy fractions (for breast, head, and neck cancers). The average radiation dose from an abdominal X-ray

2812-442: The articles on equivalent dose and effective dose . The International Committee for Weights and Measures states: "In order to avoid any risk of confusion between the absorbed dose D and the dose equivalent H , the special names for the respective units should be used, that is, the name gray should be used instead of joules per kilogram for the unit of absorbed dose D and the name sievert instead of joules per kilogram for

2888-475: The beam energy. As the science of radiation dosimetry developed, it was realised that the ionising effect, and hence tissue damage, was linked to the energy absorbed, not just radiation exposure. Consequently new radiometric units for radiation protection were defined which took this into account. In 1953 the International Commission on Radiation Units and Measurements (ICRU) recommended

2964-456: The colourless substance that covers the sieve plate. Callose stays in solution as long as the cell contents are under pressure. Phloem transports food and materials in plants upwards and downwards as required. Animal tissues are grouped into four basic types: connective , muscle , nervous , and epithelial . Collections of tissues joined in units to serve a common function compose organs. While most animals can generally be considered to contain

3040-531: The detail that can be observed in tissues. With these tools, the classical appearances of tissues can be examined in health and disease , enabling considerable refinement of medical diagnosis and prognosis . In plant anatomy , tissues are categorized broadly into three tissue systems: the epidermis , the ground tissue , and the vascular tissue . Plant tissues can also be divided differently into two types: Meristematic tissue consists of actively dividing cells and leads to increase in length and thickness of

3116-463: The development of a system of units that could be used consistently over many disciplines. This body, initially known as the "Commission for the System of Units", renamed in 1964 as the "Consultative Committee for Units" (CCU), was responsible for overseeing the development of the International System of Units (SI). At the same time it was becoming increasingly obvious that the definition of the roentgen

Roentgen (unit) - Misplaced Pages Continue

3192-414: The effect of neutron damage on human tissue, together with William Valentine Mayneord and the radiobiologist John Read, published a paper in which a unit of measure, dubbed the " gram roentgen " (symbol: gr) defined as "that amount of neutron radiation which produces an increment in energy in unit volume of tissue equal to the increment of energy produced in unit volume of water by one roentgen of radiation"

3268-583: The effect on other media. Wilhelm Röntgen discovered X-rays on November 8, 1895, and their use spread very quickly for medical diagnostics, particularly broken bones and embedded foreign objects where they were a revolutionary improvement over previous techniques. Due to the wide use of X-rays and the growing realisation of the dangers of ionizing radiation, measurement standards became necessary for radiation intensity and various countries developed their own, but using differing definitions and methods. Eventually, in order to promote international standardisation,

3344-433: The ends. They do not have end openings such as the vessels. The end overlap with each other, with pairs of pits present. The pit pairs allow water to pass from cell to cell. Though most conduction in xylem tissue is vertical, lateral conduction along the diameter of a stem is facilitated via rays. Rays are horizontal rows of long-living parenchyma cells that arise out of the vascular cambium. Phloem consists of: Phloem

3420-414: The external environment such as the skin , the airways, and the digestive tract. It serves functions of protection, secretion , and absorption, and is separated from other tissues below by a basal lamina . The connective tissue and the muscular are derived from the mesoderm. The nervous tissue is derived from the ectoderm. The epithelial tissues are formed by cells that cover the organ surfaces, such as

3496-399: The fact that their cytoplasm is actively involved in the conduction of food materials, sieve-tube members do not have nuclei at maturity. It is the companion cells that are nestled between sieve-tube members that function in some manner bringing about the conduction of food. Sieve-tube members that are alive contain a polymer called callose, a carbohydrate polymer, forming the callus pad/callus,

3572-573: The first International Congress of Radiology (ICR) meeting in London in 1925, proposed a separate body to consider units of measure. This was called the International Commission on Radiation Units and Measurements , or ICRU, and came into being at the Second ICR in Stockholm in 1928, under the chairmanship of Manne Siegbahn . One of the earliest techniques of measuring the intensity of X-rays

3648-400: The four tissue types, the manifestation of these tissues can differ depending on the type of organism. For example, the origin of the cells comprising a particular tissue type may differ developmentally for different classifications of animals. Tissue appeared for the first time in the diploblasts , but modern forms only appeared in triploblasts . The epithelium in all animals is derived from

3724-469: The functional grouping together of multiple tissues. Biological organisms follow this hierarchy : Cells < Tissue < Organ < Organ System < Organism The English word "tissue" derives from the French word " tissu ", the past participle of the verb tisser, "to weave". The study of tissues is known as histology or, in connection with disease, as histopathology . Xavier Bichat

3800-400: The girth and length of the plant, with no intercellular spaces. Permanent tissues may be defined as a group of living or dead cells formed by meristematic tissue and have lost their ability to divide and have permanently placed at fixed positions in the plant body. Meristematic tissues that take up a specific role lose the ability to divide. This process of taking up a permanent shape, size and

3876-464: The gray is independent of the primary ionizing radiation type, and can be used for both kerma and absorbed dose in a wide range of matter. When measuring absorbed dose in a human due to external exposure, the SI unit the gray , or the related non-SI rad are used. From these can be developed the dose equivalents to consider biological effects from differing radiation types and target materials. These are equivalent dose , and effective dose for which

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3952-407: The increment of energy produced in unit volume of water by one roentgen of radiation". This unit was found to be equivalent to 88 ergs in air, and made the absorbed dose, as it subsequently became known, dependent on the interaction of the radiation with the irradiated material, not just an expression of radiation exposure or intensity, which the roentgen represented. In 1953 the ICRU recommended

4028-434: The ionisation effect in dry air. In 1940, Louis Harold Gray, who had been studying the effect of neutron damage on human tissue, together with William Valentine Mayneord and the radiobiologist John Read, published a paper in which a new unit of measure, dubbed the gram roentgen (symbol: gr) was proposed, and defined as "that amount of neutron radiation which produces an increment in energy in unit volume of tissue equal to

4104-471: The main axes of stems and roots. It consists of a combination of parenchyma cells, fibers, vessels, tracheids, and ray cells. Longer tubes made up of individual cellssels tracheids, while vessel members are open at each end. Internally, there may be bars of wall material extending across the open space. These cells are joined end to end to form long tubes. Vessel members and tracheids are dead at maturity. Tracheids have thick secondary cell walls and are tapered at

4180-547: The meantime, the French Roentgen was given a different definition which amounted to 0.444 German R. In 1928, the International Congress of Radiology (ICR) defined the roentgen as "the quantity of X-radiation which, when the secondary electrons are fully utilised and the wall effect of the chamber is avoided, produce in 1 cc of atmospheric air at 0 °C and 76 cm of mercury pressure such

4256-526: The medium to be ionized. The CIPM's current SI brochure excludes the roentgen from the tables of non-SI units accepted for use with the SI. The US NIST clarified in 1998 that it was providing its own interpretations of the SI system, whereby it accepted the roentgen for use in the US with the SI, while recognizing that the CIPM did not. By then, the limitation to x and γ radiation had been dropped. NIST recommends defining

4332-461: The modern units, absorbed dose for energy absorption and the equivalent dose ( sievert ) for stochastic effect, are overwhelmingly used, and the roentgen is rarely used. The International Committee for Weights and Measures (CIPM) has never accepted the use of the roentgen. The roentgen has been redefined over the years. It was last defined by the U.S.'s National Institute of Standards and Technology (NIST) in 1998 as 2.58 × 10  C /kg , with

4408-411: The plant consists of a single layer of cells called epidermis or surface tissue. The entire surface of the plant has this outer layer of the epidermis. Hence it is also called surface tissue. Most of the epidermal cells are relatively flat. The outer and lateral walls of the cell are often thicker than the inner walls. The cells form a continuous sheet without intercellular spaces. It protects all parts of

4484-464: The plant. The outer epidermis is coated with a waxy thick layer called cutin which prevents loss of water. The epidermis also consists of stomata (singular:stoma) which helps in transpiration . The complex permanent tissue consists of more than one type of cells having a common origin which work together as a unit. Complex tissues are mainly concerned with the transportation of mineral nutrients, organic solutes (food materials), and water. That's why it

4560-689: The plant. The primary growth of a plant occurs only in certain specific regions, such as in the tips of stems or roots. It is in these regions that meristematic tissue is present. Cells of this type of tissue are roughly spherical or polyhedral to rectangular in shape, with thin cell walls . New cells produced by meristem are initially those of meristem itself, but as the new cells grow and mature, their characteristics slowly change and they become differentiated as components of meristematic tissue, being classified as: There are two types of meristematic Tissue 1.Primary meristem. 2.Secondary meristem. The cells of meristematic tissue are similar in structure and have

4636-511: The rad, equal to 100 erg/g, as the unit of measure of the new radiation quantity absorbed dose . The rad was expressed in coherent cgs units . In 1975 the unit gray was named as the SI unit of absorbed dose. One gray is equal to 1 J/kg (i.e. 100 rad). Additionally, a new quantity, kerma , was defined for air ionisation as the exposure for instrument calibration, and from this the absorbed dose can be calculated using known coefficients for specific target materials. Today, for radiation protection,

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4712-588: The roentgen as exactly 2.58 × 10 C/kg, as per the ICRU recommendation. Directive 80/181/EEC , published in December 1979, which replaced directive 71/354/EEC, explicitly catalogued the gray , becquerel , and sievert for this purpose and required that the curie, rad, rem and roentgen be phased out by 31 December 1985. Today the roentgen is rarely used, and the International Committee for Weights and Measures (CIPM) never accepted

4788-414: The roentgen had become shorthand for 83 ergs per gram (0.0083 Gy ) of tissue. They named this derivative quantity the roentgen equivalent physical (rep) to distinguish it from the ICR roentgen. The introduction of the roentgen measurement unit, which relied upon measuring the ionisation of air, replaced earlier less accurate practices that relied on timed exposure, film exposure, or fluorescence. This led

4864-464: The roentgen in every document where this unit is used. The continued use of the roentgen is strongly discouraged by the NIST. Although a convenient quantity to measure with an air ion chamber, the roentgen had the disadvantage that it was not a direct measure of either the intensity of X-rays or their absorption, but rather was a measurement of the ionising effect of X-rays in a specific circumstance; which

4940-590: The style guide for U.S. National Institute of Standards and Technology . The gray has a number of fields of application in measuring dose: The measurement of absorbed dose in tissue is of fundamental importance in radiobiology and radiation therapy as it is the measure of the amount of energy the incident radiation deposits in the target tissue. The measurement of absorbed dose is a complex problem due to scattering and absorption, and many specialist dosimeters are available for these measurements, and can cover applications in 1-D, 2-D and 3-D. In radiation therapy,

5016-639: The surface of skin , the airways , surfaces of soft organs, the reproductive tract , and the inner lining of the digestive tract . The cells comprising an epithelial layer are linked via semi-permeable, tight junctions ; hence, this tissue provides a barrier between the external environment and the organ it covers. In addition to this protective function, epithelial tissue may also be specialized to function in secretion , excretion and absorption . Epithelial tissue helps to protect organs from microorganisms, injury, and fluid loss. Functions of epithelial tissue: There are many kinds of epithelium, and nomenclature

5092-423: The unit of dose equivalent H ." The accompanying diagrams show how absorbed dose (in grays) is first obtained by computational techniques, and from this value the equivalent doses are derived. For X-rays and gamma rays the gray is numerically the same value when expressed in sieverts, but for alpha particles one gray is equivalent to 20 sieverts, and a radiation weighting factor is applied accordingly. The gray

5168-510: The use of the roentgen. From 1977 to 1998, the US NIST's translations of the SI brochure stated that the CIPM temporarily accepted the use of the roentgen (and other radiology units) with SI units since 1969. However, the only related CIPM decision shown in the appendix are with regards to the curie in 1964. The NIST brochures defined the roentgen as 2.58 × 10 C/kg, to be employed with exposures of x or γ radiation, but did not state

5244-654: The vacuole is of much smaller size than of normal animal cells. This tissue provides support to plants and also stores food. Chlorenchyma is a special type of parenchyma that contains chlorophyll and performs photosynthesis. In aquatic plants, aerenchyma tissues, or large air cavities, give support to float on water by making them buoyant. Parenchyma cells called idioblasts have metabolic waste. Spindle shaped fibers are also present in this cell to support them and known as prosenchyma, succulent parenchyma also noted. In xerophytes , parenchyma tissues store water. Collenchyma (Greek, 'Colla' means gum and 'enchyma' means infusion)

5320-533: The way to setting exposure limits, and the National Council on Radiation Protection and Measurements of the United States established the first formal dose limit in 1931 as 0.1 roentgen per day. The International X-ray and Radium Protection Committee , now known as the International Commission on Radiological Protection (ICRP) soon followed with a limit of 0.2 roentgen per day in 1934. In 1950,

5396-411: Was dry air at 0  °C and 1 standard atmosphere of pressure. Because of this the roentgen had a variable relationship to the amount of energy absorbed dose per unit mass in the target material, as different materials have different absorption characteristics. As the science of radiation dosimetry developed, this was seen as a serious shortcoming. In 1940, Louis Harold Gray , who had been studying

5472-489: Was no longer part of the definition, but the degraded usefulness of this unit at high beam energies was mentioned in the accompanying text. In the meantime, the new concept of roentgen equivalent man (rem) had been developed. Starting in 1957, the ICRP began to publish their recommendations in terms of rem, and the roentgen fell into disuse. The medical imaging community still has a need for ionization measurements, but they gradually converted to using C/kg as legacy equipment

5548-507: Was proposed. This unit was found to be equivalent to 88 ergs in air. In 1953 the ICRU recommended the rad , equal to 100 erg/g, as the new unit of measure of absorbed radiation. The rad was expressed in coherent cgs units. In the late 1950s the General Conference on Weights and Measures (CGPM) invited the ICRU to join other scientific bodies to work with the International Committee for Weights and Measures (CIPM) in

5624-607: Was replaced. The ICRU recommended redefining the roentgen to be exactly 2.58 × 10 C/kg in 1971. In 1971 the European Economic Community , in Directive 71/354/EEC , catalogued the units of measure that could be used "for ... public health ... purposes". The directive included the curie , rad , rem , and roentgen as permissible units, but required that the use of the rad, rem and roentgen be reviewed before 31 December 1977. This document defined

5700-456: Was to measure their ionising effect in air by means of an air-filled ion chamber . At the first ICRU meeting it was proposed that one unit of X-ray dose should be defined as the quantity of X-rays that would produce one esu of charge in one cubic centimetre of dry air at 0  °C and 1 standard atmosphere of pressure. This unit of radiation exposure was named the roentgen in honour of Wilhelm Röntgen, who had died five years previously. At

5776-493: Was unsound, and in 1962 it was redefined. The CCU decided to define the SI unit of absorbed radiation in terms of energy per unit mass, which in MKS units was J/kg. This was confirmed in 1975 by the 15th CGPM, and the unit was named the "gray" in honour of Louis Harold Gray, who had died in 1965. The gray was equal to 100 rad. The definition of the roentgen had had the attraction of being relatively simple to define for photons in air, but

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