Articles

Articles are a collaborative effort to provide a single canonical page on all topics relevant to the practice of radiology. As such, articles are written and edited by countless contributing members over a period of time. A global group of dedicated editors oversee accuracy, consulting with expert advisers, and constantly reviewing additions.

273 results found
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Pathology curriculum

The pathology curriculum is one of our curriculum modules and aims to be a collection of articles that represent the core pathology knowledge for radiologists and other imaging professionals: general pathology cellular pathology ​pathologic classification systemic pathology pathology of the...
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Perivascular pseudorosettes (ependymoma)

Perivascular pseudorosettes are a common histologic feature of central nervous system ependymomas. They represent sections through papillary structures composed of tumor cells arranged radially around a central vessel. Between the central vessel and the tumor cells is a relatively microscopicall...
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Phlegmon

Phlegmon (plural: phlegmons) refers to unbounded, non-specific inflammation of soft tissue, usually in the context of infectious disease. It is distinct from an abscess which is walled-off by peripheral granulation tissue. Terminology Both historically and contemporaneously, phlegmon is used i...
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Pick bodies

Pick bodies are intracytoplasmic spherical inclusions found in Pick disease. They are composed of tau fibrils (thus Pick disease is a tauopathy) arranged in a disorderly array 1. Although tau protein is a major component a number of other protein products are present, including ubiquitin and tub...
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Picornaviruses

Picornaviruses (pico-RNA-viruses) are non-enveloped, positive-stranded RNA viruses with an icosahedral capsule. Their positive, single stranded RNA architecture places them in Baltimore group IV. The name derives from the fact that they are small (pico) RNA viruses. The picornavirus family cont...
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Placode

Placode (or neural placode) refers in terms of radiology to a segment of non-neurulated neural tissue, which has had development frozen in the neural plate stage. A placode can be found in all open spinal dysraphisms and in some closed spinal dysraphisms. In the former, the placode is exposed to...
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Poliovirus

Poliovirus is the causative agent involved in poliomyelitis. It is a single-stranded RNA virus and one of the smallest significantly described viruses: group: group IV family: picornaviruses genus: enterovirus species: enterovirus C subtype: poliovirus Related pathology poliomyelitis pol...
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Polyostotic

Polyostotic is term used to describe a condition involving multiple bones. Examples of conditions that can be polyostotic include fibrous dysplasia and melorheostosis. See also monostotic monomelic
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Prefemoral fat pad impingement syndrome

The prefemoral fat pad, also known as the posterior suprapatellar fat pad or the supratrochlear fat pad is located anterior to the distal femur and superior to the trochlea, separated from the quadriceps fat pad by the suprapatellar recess. It is one of the three main anterior fat pads of the kn...
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Pregnancy-associated plasma protein-A

Pregnancy-associated plasma protein-A (PAPP-A) is a protein found in the maternal circulation and is produced by the placenta. The PAPP-A gene has been assigned to human chromosome 9q33.1 and contains 22 exons 5. PAPP-A values tend to rise exponentially during pregnancy and the reference range d...
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Primary lung tumors in children

Pediatric primary lung tumors are rare in children however they must be distinguished from locally aggressive inflammatory conditions and benign disease. 1 Primary lung tumors in the neonates and infants include: pleuropulmonary blastoma (PPB) infantile fibrosarcoma of the lung fetal lung in...
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Primary pulmonary enteric adenocarcinoma

Pulmonary enteric adenocarcinoma (PEAC) or pulmonary adenocarcinoma with enteric differentiation (PAED) is an extremely rare variant of primary invasive adenocarcinoma of the lung. It has morphological and immunohistochemical profiles overlapping with that of colorectal carcinoma. Due to this, i...
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Probabilistic atlas

Probabilistic atlases, also known as probability maps, are anatomical or anatomopathological atlases based on statistically-weighted composites of many specimens. Traditional anatomy atlases were based on one or a few specimens sometimes with common variations indicated or shown. Probabilistic a...
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Programmed death-ligand 1 (PD-L1)-targeted monoclonal antibodies

Programmed death-ligand 1 (PD-L1)-targeted monoclonal antibodies interact with a protein called PD-1 on T-cells and can be useful in determining if certain immunomodulation therapies can be used in treatment of certain types of cancers. PD-L1 is a major immune checkpoint protein that mediates an...
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Prostate specific antigen

Prostate specific antigen (PSA) is currently used as a tumor marker for prostate adenocarcinoma. PSA is a 33 kilodalton glycoprotein produced in prostate epithelial cells. Its normal physiologic role is as a liquefying agent for seminal fluid; only a tiny amount leaks into the blood, therefore ...
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Prostate-specific membrane antigen

Prostate-specific membrane antigen (PSMA) (also known as glutamate carboxypeptidase II) is a type II transmembrane glycoprotein that has become an increasingly prominent imaging biomarker 1. PSMA has emerged as a useful target in PET imaging of prostate cancer, especially in the evaluation of sm...
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Prostatic acid phosphatase

Prostatic acid phosphatase (PAP) also known as prostatic specific acid phosphatase (PSAP) is an enzyme generated by prostatic glandular tissue. Usage It can be used in immunohistochemistry to identify prostatic tissue including prostatic epithelium and prostatic ducts and is usually expressed ...
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Proteins

Proteins comprise long chains of amino acids joined together by peptide bonds. Structure A peptide bond is formed by the carboxyl group of one amino acid linking to the amino group of the next one.  Arbitrarily proteins are categorized according to length of the amino acid chain: peptides (2-...
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PSA density

The PSA density (PSAD), is a calculation performed at diagnosis and is the serum prostate specific antigen (PSA) level (ng/mL) divided by the volume of the prostate gland (mL), resulting in a value with the units, ng/mL2 1. Prostate volume is calculated from TRUS measurements 2,3.  Alternativel...
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Psammoma bodies

Psammoma bodies are round microscopic calcific collections. It is a form of dystrophic calcification. Necrotic cells form the focus for surrounding calcific deposition. They have a lamellated concentric calcified structure, sometimes large enough to be seen on CT.  Psammoma bodies are found in ...
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PSA velocity

The PSA velocity (PSAV) is a statistically-derived measure of how the prostate specific antigen (PSA) changes over time, and has been used as a marker of how prostate malignancy progresses or regresses.  Any cancer grows over time and relative changes of tumor markers, such as PSA, would seem t...
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Pseudocyst

A pseudocyst is an abnormal fluid-filled cavity which is not lined by epithelium.  It is this fact that distinguishes it pathologically from a cyst, which is lined by epithelium. Examples of pseudocysts include: adrenal pseudocyst auricular pseudocyst intraspinal epidural gas pseudocysts me...
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Pulmonary Acinetobacter infection

Pulmonary Acinetobacter infection refers to pulmonary infection with Acinetobacter species of which Acinetobacter calcoaceticus-A baumannii complex accounts for a considerable proportion. Pulmonary infection with this organism can cause hospital-acquired pneumonia (especially the late onset typ...
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Pulmonary blastoma

Pulmonary blastomas (PBs) comprise a rare group of lung tumors principally consisting of immature mesenchymal and epithelial structures that structurally mimic the embryonic lung. Traditionally they were classified as well-differentiated fetal adenocarcinoma (WDFA) of lung - now considered rem...
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Red blood cell

Red blood cells (RBCs), also known as erythrocytes (or haematids), are "cells" that carry oxygen by means of hemoglobin, and form part of the cellular component of blood as it circulates throughout the body. These extremely common cells are typically made in the bone marrow in a process called e...
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Reed-Sternberg cells

Reed-Sternberg cells are a classical finding diagnostic of Hodgkin lymphoma. They are giant, multinucleated cells with abundant pale cytoplasm. Reed-Sternberg cells are rare, making up <1% of lymphoid tissue, with the background consisting of lymphocytes, plasma cells, eosinophils and macrophages.
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Rheumatoid factor

Rheumatoid factor (RF) is an immunoglobulin initially described in association with rheumatoid arthritis. It is an IgM antibody against the FC portion of the IgG antibodies. Ongoing research has identified a group of related immunoglobulins, classed as rheumatoid factors (RFs) and despite extens...
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ROS1 mutation

The ROS1 mutation is a mutation occurring in the ROS1 oncogene on chromosome 6 resulting in a defective receptor tyrosine kinase which has structural similarity to the anaplastic lymphoma kinase (ALK) protein. It is thought to be present in several cancers of the subtype non-small cell lung can...
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Rosenthal fibers

Rosenthal fibers are astrocytic cytoplasmic inclusions, typically found in areas of longstanding gliosis. These elongated or "corkscrew" structures occur within astrocytic processes and are brightly eosinophilic (stain bright pink on the H&E stain) 1-3. They represent astrocytic processes swolle...
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S100

S100 is a family of cytoplasmic calcium-binding proteins expressed in numerous cell lines which can be targeted by immunohistochemistry. Staining for S100 is helpful in characterizing a number of tumors, including malignant melanoma, glial tumors, neurogenic tumors (e.g. schwannomas and neurofib...
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Schiller-Duval body (histology)

Schiller-Duval body is a perivascular structure that can be found in 50% of testicular yolk sac tumors also known as endodermal sinus tumors. If present it is considered pathognomonic.  Pathology A central vessel is surrounded by tumor cells, and the cell-vessel complex is contained in a cysti...
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Scientific notation

In general, the Radiopaedia style guide adheres to internationally-agreed standards for scientific notation. The main exception is isotope notation, for which we have decided to drop the use of superscripted mass numbers. anatomic nomenclature chemical element notation genes and proteins nam...
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Sclerodema of Buschke

Scleredema of Buschke also known as scleredema diabetorum is a dermal complication of chronic type 1 and type 2 diabetes mellitus, streptococcus infections and monoclonal gammopathies 1-3. Pathology Scleredema diabetorum is characterized by non-pitting swelling and thickening of skin secondary...
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Selenium

Selenium (chemical symbol Se) is one of the trace elements. It has a vital role in the metabolism of the thyroid hormones and for the functioning of several important enzymes. Chemistry Basic chemistry Selenium has the atomic number 34 with an atomic weight of 78.96 g/mol. It is a non-metal a...
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Sentinel lymph node

The sentinel lymph nodes (SLNs) are defined as those lymph nodes that directly drain a malignancy, or alternatively can be considered as the first node(s) that a tumor metastasizes to. History and etymology "Sentinel node" as the initial draining node of a malignancy was first used in a paper ...
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Septum (general)

Septa (singular: septum) are anatomical or pathological sheet-like structures that subdivide a component of normal anatomy or a lesion. Terminology Septa is the plural of the Latin word septum. Septae and septi are erroneous forms and are not words in English, nor correct plurals in Latin 2. S...
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Serum ascites albumin gradient

The serum–ascites albumin gradient (SAAG) is the difference between the concurrently obtained serum albumin concentration and the albumin concentration of the ascitic fluid obtained during paracentesis.  Pathology A difference ≥1.1 grams/deciliter (g/dL) indicates portal hypertension as the li...
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Smooth muscle actin

Smooth muscle actin (SMA) is a target in immunohistochemistry which is positive in cell lines which expresses actin. It is generally used to identify cells of myoepithelial origin 1. Related pathology leiomyoma perivascular epithelioid cell tumors (PEComas)
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Spontaneous rupture of the urinary bladder

Spontaneous ruptures of the urinary bladder (SRUB) are usually secondary to pathological conditions and are less commonly idiopathic and constitute a rare urological emergency. For a general discussion, please refer to the article on urinary bladder rupture. Epidemiology Intraperitoneal bladd...
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Staghorn pattern of vascularity

The staghorn pattern of vascularity is a pathological term describing a pattern of vascularity seen on low-power light microscopy. It is defined by multiple thin-walled, sharply-branched and jagged vessels having an "antler-like" or "staghorn-like" appearance 1. It is classically described with...
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Starling forces

Starling forces describe the movement of fluids between the vasculature and interstitial spaces. Fluid movement is determined by the balance of hydrostatic and osmotic pressure gradients 1. Starling forces Net pressure = [ (Pc - Pi) - (pc - pi) ] where: Pc = hydrostatic pressure of the capil...
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Streptococcus anginosus group

The Streptococcus anginosus group (also part of the Streptococcus milleri group) comprise a subgroup of viridans streptococci which are gram-positive, catalase-negative bacteria. There are three distinct main streptococcal species and several subspecies: S. anginosus: has two subspecies S. an...
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Sulfur

Sulfur (chemical symbol S) is one of the essential trace elements. It has an important biological role as part of sulfur-containing amino acids and other important biochemical species such as glutathione, hydrogen sulfide, and coenzyme A. Terminology Sulfur has been the preferred spelling of t...
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Synaptophysin

Synaptophysin is a membrane glycoprotein found in presynaptic vesicles and is commonly used as an immunohistochemical marker for cells of neuronal (e.g. gangliogliomas) and neuroendocrine lineage (e.g. pheochromocytomas and paragangliomas) 1,2.  In the brain, it has been suggested that perisoma...
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Synchronous (pathology)

The term synchronous is used in oncology to refer to two (or more) independent primary malignancies, when the second (or third, etc.) malignancy arose within six months of the diagnosis of the first malignancy 1,2. These may be in the same, or in different, organs. See also metachronous multi...
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Syndemic

A syndemic is a relatively novel concept in epidemiology, referring to the simultaneous occurrence and synergy of two or more diseases or conditions in a large population in a social context that aggravates them. A syndemic is usually confined to a certain geographical area at a certain time an...
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Synechiae

Synechiae (singular: synechia, alternative plural: synechias) are another term for adhesions, which in radiological contexts usually relates to bands of scar tissue between structures, e.g. within the abdominal cavity or pleural cavity or within the uterus. In a more narrow sense, synechia refe...
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Systemic pathology

The systemic pathology article aims to outline knowledge of systemic pathological conditions important for medical imaging specialists. Systemic pathology pathology of the vascular system cardiac pathology pathology of the hematological and lymphatic systems pathology of the lung and pleura...
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Tanycytes

Tanycytes are one of the three types of ependymal cells, themselves a type of glial cell. They are found lining the floor of the third ventricle overlying the median eminence of the hypothalamus 1.   It is believed that these specialized cells are involved in the feedback mechanisms on the ante...
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Thyroid nodules in pediatric patients

Thyroid nodules in pediatric patients is much less common in terms occurrence (with an estimated prevalence of around 1-2% 4) compared with that of adults but raise greater concern due to higher rates of malignancy (20-26%) verses in (5-15%) adults 4.  Pathology  They can represent a vast rang...
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Thyroid transcription factor 1

Thyroid transcription factor 1 (TTF1) refers to a homeodomain-containing nuclear transcription factor which belongs to the Nkx2 gene family encoded by a gene located on chromosome 14q13. It is expressed in the forebrain, thyroid and lung tissues. The presence of TTF-1 protein on a tissue sample...
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Thyroseq

Thyroseq® is an expanded gene classifier test designed for further evaluation of indeterminate thyroid nodules on fine needle aspiration (FNA). In particular, it is designed to further evaluate nodules that show atypia of undetermined significance/follicular lesion of undetermined significance (...
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Tissue tropism

Tissue tropism is a phenomenon by which certain host tissues preferentially support the growth and proliferation of pathogens. This concept is central to the radiological evaluation of infectious disease.  Pathology As infections that display tissue tropism will thrive in certain tissue locati...
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TP53 (gene)

The TP53 gene, located on chromosome 17, is a tumor suppressor gene, responsible for the production of the p53 protein, a transcription regulatory protein which works in concert with a number of other proteins, together forming the p53 pathway 1,2. Inherited mutations in this gene result in the...
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Trace elements

The trace elements are chemical elements which are essential - but only in tiny quantities - for optimal physical and mental well being. The elements are: cobalt copper iodine iron manganese molybdenum selenium sulfur zinc It is now contentious whether chromium is a truly essential tra...
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Transitional meningioma

Transitional meningiomas are also known as mixed meningiomas because they have components of meningothelial and fibrous subtypes of meningiomas. Their epidemiology, clinical aspects, radiographic characteristics, treatment, prognosis, and differential diagnosis are in the main article (see meni...
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Trigeminal autonomic cephalgia

Trigeminal autonomic cephalgia is a relatively rare group of condition consisting of cluster headaches, paroxysmal hemicrania, hemicrania continua, and short-lasting unilateral neuralgiform headache attacks with conjunctival injection and tearing (short lasting unilateral neuralgiform headache a...
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Tumor markers

Tumor markers are a group of molecules in serum that are elevated in various malignancies and are often used to monitor treatment response as well as alert for potential progressive disease when in remission. Commonly used markers include: AFP (alpha fetoprotein) beta-hCG CA 15-3 CA 19-9 C...
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Tumor spread through air spaces

Tumor spread through air spaces (STAS) is a relatively recently recognized pattern of invasion in lung adenocarcinoma. According to the 2015 WHO classification, STAS is defined as “micropapillary clusters, solid nests, or single cells spreading within air spaces beyond the edge of the main tumor...
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Tungsten

Tungsten (chemical symbol, W) is a hard refractory metallic element with remarkable resilience which forms the basis for its industrial uses. It is the metal of choice in the filaments and targets of x-ray tubes. There is no evidence that tungsten is required by the human body, although some mic...
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Urine

Urine represents the biofluid end-product of the renal filtration process. Normally it is a transparent, sterile, pale-yellow liquid (although clearly color varies with the person's hydration status).  Urine is one of the most easily-accessible biofluids in the human body and has been intensive...
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Vascular invasion in lung cancer

Vascular invasion in lung cancer is one of the invasive patterns that can occur in lung cancer. Dependent on the publication, this could mean: intratumoral vascular invasion (IVI)  microscopic vascular invasion (MVI) lymphovascular invasion (LVI) lymphatic permeation arterial invasion veno...
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Vector (infectious disease)

A vector, (also known as a biological vector) in the context of infectious diseases, is a carrier, in particular an animal, and most commonly an arthropod, that transmits the infective entity from one host to another 1. Often the infective agent undergoes some change as part of its normal life c...
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Verocay bodies

Verocay bodies are a histological feature of schwannomas and represent a particular growth pattern of Antoni type A pattern in which tumor cells form alternating parallel rows of nuclear palisades separated by regions of acellularity 1. 
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Vimentin

Vimentin is a fairly widespread cytoskeletal component encoding for intermediate filaments. It can be used as a target for immunohistochemistry to help characterize numerous tissues and tumors. 
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Vitamin A

Vitamin A are a group of fat-soluble vitamers (the retinoids) required for many physiological functions, mainly vision, reproduction and epithelial maintenance. In the retina, a specific retinoid, 11-cis-retinal, is formed by photoisomerisation within the rods and cones. Related pathology Path...
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Vitamin B1

Vitamin B1 (thiamine) is a water-soluble vitamin, that is part of the vitamin B complex, and is an important coenzyme for two reactions in the citric acid cycle (Kreb cycle). It therefore is vital for cellular ATP production, particularly in the central nervous system. Terminology Thiamine is ...
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Vitamin B12

Vitamin B12 (hydroxocobalamin, hydroxycobalamin or B12a) is a water-soluble vitamin, part of the vitamin B complex, and synthesized by intestinal flora that forms a cobalt-based coenzyme that is required for two vital cellular reactions, namely the production of methionine (an amino acid) and th...
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Vitamin B2

Vitamin B2 (riboflavin) is a water-soluble vitamin, part of the vitamin B complex, that is an important component of the cofactors flavin adenine dinucleotide (FAD) and flavin mononucleotide (FMN). The flavoproteins contribute to many cellular reactions, including the metabolism of several other...
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Vitamin B3

Vitamin B3 (niacin or nicotinic acid) is a water-soluble vitamin, part of the vitamin B complex, that is an important part of the coenzyme nicotinamide adenine dinucleotide (NAD+) which is involved in many reactions of cellular metabolism. Related pathology pellagra is the clinical syndrome of...
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Vitamin B5

Vitamin B5 (pantothenic acid) is a water-soluble vitamin, part of the vitamin B complex, that is required to synthesize coenzyme A, a very important coenzyme in many cellular metabolic reactions.Vitamin B5 deficiency (hypovitaminosis B5) is extremely rare. There is no evidence of any deleteriou...
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Vitamin B6

Vitamin B6 is a group of water-soluble vitamins, part of the vitamin B complex, and that are derivatives of pyridine, the main vitamers are known as pyridoxine, pyridoxal and pyridoxamine. All three form part of the coenzyme pyridoxal 5'-phosphate (PLP) which is involved in many cellular reactio...
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Vitamin B9

Vitamin B9 (folate or folic acid) is a water-soluble vitamin, part of the vitamin B complex, vital for the synthesis of several amino acids, the purines adenosine and guanine and the pyrimidine thymine (three of the four nucleotide bases and hence critical for the synthesis of nucleic acids). T...
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Vitamin B complex

Historically, the vitamin B complex was the collective name given to a specific subset of the vitamins, known as the B vitamins. However the chemical structures of these compounds are structurally heterogeneous and they do not constitute a distinct biochemical group. They are all water soluble v...
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Vitamin C

Vitamin C (ascorbic acid) is a water soluble vitamin that is a coenzyme for the formation of the structure protein collagen, particularly creating cross-linking of collagen fibers which greatly increases its tensile strength. It also acts as an antioxidant. History and etymology Vitamin C was ...
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Vitamin D

Vitamin D (calciferol) is used to describe a group of five fat-soluble secosteroid vitamins required for the homeostasis of serum calcium and phosphorus. Vitamin D exists in two main forms (vitamers) in humans: ergocalciferol (vitamin D2) and cholecalciferol (vitamin D3).  Vitamin D3 acts by re...
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Vitamin D deficiency (overview)

Vitamin D deficiency (also known as hypovitaminosis D) is common, and untreated, may result in serious sequelae. Traditionally its pathological manifestations have been regarded through the lens of skeletal maturity: rickets in children osteomalacia in adults However it has become increasingl...
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Vitamin E

Vitamin E (the tocopherols) are a group of fat-soluble vitamins that act as antioxidants. hypovitaminosis E is rarely seen outside premature infants hypervitaminosis E is extremely rare as the toxicity of vitamin E is low except in chronic (usually >1 year) high doses. The commonest sequela is...
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Vitamin K

Vitamin K is not a single compound but a family of fat-soluble vitamins essential for normal blood-clotting function and comprises two vitamers that are found naturally: phytomenadione (also known as phylloquinone or K1) and menaquinone (or K2). Menaquinone (K2) is synthesized by normal flora i...
Article

Vitamins

Vitamins are a group of organic compounds used in biochemical pathways. Many are components of coenzymes in particular metabolic reactions. Vitamins are generally not synthesized by the human body and hence must be acquired through the diet. Vitamer is the name given to the different forms of a ...
Article

Well differentiated fetal adenocarcinoma of lung

A well-differentiated fetal adenocarcinoma (WDFA) of lung is a rare low grade lung tumor. Some consider this as a variant of adenocarcinoma with others considering this under the group of pulmonary blastomas 5.  According to classification by the World Health Organization in 1999, it was remove...
Article

White blood cell

White blood cells or leukocytes are one of the main cell types found in normal human blood. They are actually colourless (but appear white on light microscopy) and are divided into granular and non-granular types. Types of white blood cell: granular neutrophils eosinophils basophils non-gr...
Article

WHO classification of eye tumors

The World Health Organization (WHO) classification of eye tumors is a widely used pathologic classification system of neoplasms of the orbit. The current revision, part of the 4th edition of the WHO series, was published in 2018 and is reflected in the article below 1. Classification Tumors of...
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WHO classification of odontogenic and maxillofacial bone tumors

The WHO classification of odontogenic and maxillofacial bone tumors, last published in 2017, is a subset of the WHO classification of head and neck tumors (4th edition), that lays out a histological classification system for neoplasms and other tumors related to the odontogenic apparatus. Class...
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WHO histological classification of tumors of the uterine cervix

The WHO histological classification is a detailed classification of tumors of the uterine cervix. epithelial tumors squamous tumors and precursors squamous cell carcinoma, not otherwise specified - 8070/3 keratinizing - 8071/3 non-keratinizing - 8072/3 basaloid - 8083/3 verrucous - 8051/3...
Article

Zinc

Zinc (chemical symbol Zn) is a trace element with a key role as a constituent of enzymes, e.g. carbonic anhydrase, and as part of zinc finger proteins, vital for the correct folding of macromolecules, such as DNA. More recently zinc has been found to act as an important cellular messenger 3. Ch...
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Zoonosis

A zoonosis (plural: zoonoses), also known as a zoonotic disease, is an infectious disease in humans (the host) for which another vertebrate animal can be the vector. Some zoonoses have an additional vector besides the vertebrate e.g. R. rickettsii is carried by ticks on mammals. Viruses, bacteri...

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