1.
Tight junction
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Tight junctions, also known as occluding junctions or zonulae occludentes, are the closely associated areas of two cells whose membranes join together forming a virtually impermeable barrier to fluid. It is a type of junctional complex present only in vertebrates, the corresponding junctions that occur in invertebrates are septate junctions. Tight junctions are composed of a network of sealing strands. Therefore, the efficiency of the junction in preventing ion passage increases exponentially with the number of strands, each strand is formed from a row of transmembrane proteins embedded in both plasma membranes, with extracellular domains joining one another directly. Although more proteins are present, the types are the claudins. These associate with different peripheral membrane proteins such as ZO-1 located on the side of plasma membrane. Thus, tight junctions join together the cytoskeletons of adjacent cells and they perform vital functions, They hold cells together. This aims to preserve the transcellular transport, tight Junctions prevent the passage of molecules and ions through the space between plasma membranes of adjacent cells, so materials must actually enter the cells in order to pass through the tissue. The constrained intracellular pathway exacted by the junction barrier system allows precise control over which substances can pass through a particular tissue. At the present time, it is unclear whether the control is active or passive. In human physiology there are two types of epithelia using distinct types of barrier mechanism. Dermal structures such as form a barrier from many layers of keratinised squamous cells. Internal epithelia on the other more often rely on tight junctions for their barrier function. This kind of barrier is formed by only one or two layers of cells. It was long unclear whether tight cell junctions also play any role in the function of the skin and similar external epithelia. Examples of tight epithelia include the distal convoluted tubule, the duct of the nephron in the kidney. Leaky epithelia do not have these tight junctions, or have less complex tight junctions, for instance, the tight junction in the kidney proximal tubule, a very leaky epithelium, has only two to three junctional strands, and these strands exhibit infrequent large slit breaks
2.
H&E stain
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Hematoxylin and eosin stain or haematoxylin and eosin stain is one of the principal stains in histology. A combination of hematoxylin and eosin, it produces blues, violets, the staining method involves application of hemalum, a complex formed from aluminum ions and hematein. Hemalum colors nuclei of cells blue, the nuclear staining is followed by counterstaining with an aqueous or alcoholic solution of eosin Y, which colors eosinophilic structures in various shades of red, pink and orange. The staining of nuclei by hemalum is ordinarily due to binding of the complex to DNA. The mechanism is different from that of nuclear staining by basic dyes such as thionine or toluidine blue, staining by basic dyes occurs only from solutions that are less acidic than hemalum, and it is prevented by prior chemical or enzymatic extraction of nucleic acids. The eosinophilic structures are composed of intracellular or extracellular protein. The Lewy bodies and Mallory bodies are examples of eosinophilic structures, most of the cytoplasm is eosinophilic. Red blood cells are stained intensely red, the structures do not have to be acidic or basic to be called basophilic and eosinophilic, the terminology is based on the affinity of cellular components for the dyes. Other colors, e. g. yellow and brown, can be present in the sample, they are caused by intrinsic pigments, some structures do not stain well. Basal laminae need to be stained by PAS stain or some silver stains, reticular fibers also require silver stain. Hydrophobic structures also tend to clear, these are usually rich in fats, e. g. adipocytes, myelin around neuron axons. Hematoxylin is a blue or violet stain that is basic/positive. DNA/RNA in the nucleus, and RNA in ribosomes in the endoplasmic reticulum are both acidic because the phosphate backbones of nucleic acids are negatively charged. The negatively charged backbones form salts with basic dyes containing positive charges, therefore, dyes like hematoxylin will bind to DNA and RNA and stain them violet. Eosin is a red or pink stain that is Acidic / Negative and it binds to acidophilic substances such as positively charged amino acid side chains. Most proteins in the cytoplasm of cells are basic because they are positively charged due to the arginine and lysine amino acid residues. These form salts with acid dyes containing negative charges, like eosin, therefore, eosin binds to these amino acids/proteins and stains them pink. This includes cytoplasmic filaments in muscle cells, intracellular membranes, kiernan JA Histological and Histochemical Methods, Theory and Practice
3.
Bone tissue
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Bone tissue, or osseous tissue, is the major structural and supportive connective tissue of the body. Bone tissue forms the part of the bones that make up the skeleton. Bones are organs that are made up of tissue as well as bone marrow, small blood vessels, epithelium. Bone tissue refers specifically to the mineral matrix that forms the rigid sections of the organ. The two types of tissue are cortical bone and cancellous bone. There is another kind of tissue called subchondral bone which underlies the epiphyseal cartilage at the ends of bones, the bone cells develop new bone tissue and continual bone remodeling – maintaining the bones and the regulation of minerals in the body. Types of bone cell include osteoclasts, which break down bone tissue, osteoblasts, which new bone tissue, osteocytes, which hold the bone together, and lining cells. There are two types of tissue, cortical bone and cancellous bone, The tissues are biologically identical. Cortical bone, synonymous with bone, is one of the two types of bone tissue that form bones. Cortical bone forms the extremely hard exterior of bones, cortical bone facilitates bones main functions, to support the whole body, protect organs, provide levers for movement, and store and release chemical elements, mainly calcium. As its name implies, cortical bone forms the cortex, or outer shell, cortical bone is much denser than cancellous bone. Furthermore, it is harder, stronger and stiffer than cancellous bone, cortical bone contributes about 80% of the weight of a human skeleton. The primary anatomical and functional unit of cortical bone is the osteon, cancellous bone is synonymous with trabecular or spongy bone. Cancellous bone has a surface area to mass ratio than cortical bone because it is less dense. This makes it softer, and weaker but more flexible, the greater surface area also makes it suitable for metabolic activities such as the exchange of calcium ions. Cancellous bone is found at the ends of long bones, near to joints. Cancellous bone is highly vascular and frequently contains red bone marrow where haematopoiesis, the primary anatomical and functional unit of cancellous bone is the trabecula. The trabeculae are aligned towards the load distribution that a bone experiences within long bones such as the femur
4.
Ancient Greek
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Ancient Greek includes the forms of Greek used in ancient Greece and the ancient world from around the 9th century BC to the 6th century AD. It is often divided into the Archaic period, Classical period. It is antedated in the second millennium BC by Mycenaean Greek, the language of the Hellenistic phase is known as Koine. Koine is regarded as a historical stage of its own, although in its earliest form it closely resembled Attic Greek. Prior to the Koine period, Greek of the classic and earlier periods included several regional dialects, Ancient Greek was the language of Homer and of fifth-century Athenian historians, playwrights, and philosophers. It has contributed many words to English vocabulary and has been a subject of study in educational institutions of the Western world since the Renaissance. This article primarily contains information about the Epic and Classical phases of the language, Ancient Greek was a pluricentric language, divided into many dialects. The main dialect groups are Attic and Ionic, Aeolic, Arcadocypriot, some dialects are found in standardized literary forms used in literature, while others are attested only in inscriptions. There are also several historical forms, homeric Greek is a literary form of Archaic Greek used in the epic poems, the Iliad and Odyssey, and in later poems by other authors. Homeric Greek had significant differences in grammar and pronunciation from Classical Attic, the origins, early form and development of the Hellenic language family are not well understood because of a lack of contemporaneous evidence. Several theories exist about what Hellenic dialect groups may have existed between the divergence of early Greek-like speech from the common Proto-Indo-European language and the Classical period and they have the same general outline, but differ in some of the detail. The invasion would not be Dorian unless the invaders had some relationship to the historical Dorians. The invasion is known to have displaced population to the later Attic-Ionic regions, the Greeks of this period believed there were three major divisions of all Greek people—Dorians, Aeolians, and Ionians, each with their own defining and distinctive dialects. Often non-west is called East Greek, Arcadocypriot apparently descended more closely from the Mycenaean Greek of the Bronze Age. Boeotian had come under a strong Northwest Greek influence, and can in some respects be considered a transitional dialect, thessalian likewise had come under Northwest Greek influence, though to a lesser degree. Most of the dialect sub-groups listed above had further subdivisions, generally equivalent to a city-state and its surrounding territory, Doric notably had several intermediate divisions as well, into Island Doric, Southern Peloponnesus Doric, and Northern Peloponnesus Doric. The Lesbian dialect was Aeolic Greek and this dialect slowly replaced most of the older dialects, although Doric dialect has survived in the Tsakonian language, which is spoken in the region of modern Sparta. Doric has also passed down its aorist terminations into most verbs of Demotic Greek, by about the 6th century AD, the Koine had slowly metamorphosized into Medieval Greek
5.
Terminologia Histologica
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The Terminologia Histologica is a controlled vocabulary for use in cytology and histology. In April 2011, Terminologia Histologica was published online by the Federative International Programme on Anatomical Terminologies and it was intended to replace Nomina Histologica. The Nomina Histologica was introduced in 1977, with the edition of Nomina Anatomica. It was developed by the Federative International Committee on Anatomical Terminology
6.
Greek language
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Greek is an independent branch of the Indo-European family of languages, native to Greece and other parts of the Eastern Mediterranean. It has the longest documented history of any living language, spanning 34 centuries of written records and its writing system has been the Greek alphabet for the major part of its history, other systems, such as Linear B and the Cypriot syllabary, were used previously. The alphabet arose from the Phoenician script and was in turn the basis of the Latin, Cyrillic, Armenian, Coptic, Gothic and many other writing systems. Together with the Latin texts and traditions of the Roman world, during antiquity, Greek was a widely spoken lingua franca in the Mediterranean world and many places beyond. It would eventually become the official parlance of the Byzantine Empire, the language is spoken by at least 13.2 million people today in Greece, Cyprus, Italy, Albania, Turkey, and the Greek diaspora. Greek roots are used to coin new words for other languages, Greek. Greek has been spoken in the Balkan peninsula since around the 3rd millennium BC, the earliest written evidence is a Linear B clay tablet found in Messenia that dates to between 1450 and 1350 BC, making Greek the worlds oldest recorded living language. Among the Indo-European languages, its date of earliest written attestation is matched only by the now extinct Anatolian languages, the Greek language is conventionally divided into the following periods, Proto-Greek, the unrecorded but assumed last ancestor of all known varieties of Greek. The unity of Proto-Greek would have ended as Hellenic migrants entered the Greek peninsula sometime in the Neolithic era or the Bronze Age, Mycenaean Greek, the language of the Mycenaean civilisation. It is recorded in the Linear B script on tablets dating from the 15th century BC onwards, Ancient Greek, in its various dialects, the language of the Archaic and Classical periods of the ancient Greek civilisation. It was widely known throughout the Roman Empire, after the Roman conquest of Greece, an unofficial bilingualism of Greek and Latin was established in the city of Rome and Koine Greek became a first or second language in the Roman Empire. The origin of Christianity can also be traced through Koine Greek, Medieval Greek, also known as Byzantine Greek, the continuation of Koine Greek in Byzantine Greece, up to the demise of the Byzantine Empire in the 15th century. Much of the written Greek that was used as the language of the Byzantine Empire was an eclectic middle-ground variety based on the tradition of written Koine. Modern Greek, Stemming from Medieval Greek, Modern Greek usages can be traced in the Byzantine period and it is the language used by the modern Greeks, and, apart from Standard Modern Greek, there are several dialects of it. In the modern era, the Greek language entered a state of diglossia, the historical unity and continuing identity between the various stages of the Greek language is often emphasised. Greek speakers today still tend to regard literary works of ancient Greek as part of their own rather than a foreign language and it is also often stated that the historical changes have been relatively slight compared with some other languages. According to one estimation, Homeric Greek is probably closer to demotic than 12-century Middle English is to modern spoken English, Greek is spoken by about 13 million people, mainly in Greece, Albania and Cyprus, but also worldwide by the large Greek diaspora. Greek is the language of Greece, where it is spoken by almost the entire population
7.
Cell (biology)
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The cell is the basic structural, functional, and biological unit of all known living organisms. A cell is the smallest unit of life that can replicate independently, the study of cells is called cell biology. Cells consist of cytoplasm enclosed within a membrane, which contains many such as proteins. Organisms can be classified as unicellular or multicellular, while the number of cells in plants and animals varies from species to species, humans contain more than 10 trillion cells. Most plant and animal cells are only under a microscope. The cell was discovered by Robert Hooke in 1665, who named the unit for its resemblance to cells inhabited by Christian monks in a monastery. Cells emerged on Earth at least 3.5 billion years ago, Cells are of two types, eukaryotic, which contain a nucleus, and prokaryotic, which do not. Prokaryotes are single-celled organisms, while eukaryotes can be either single-celled or multicellular, prokaryotic cells were the first form of life on Earth, characterised by having vital biological processes including cell signaling and being self-sustaining. They are simpler and smaller than eukaryotic cells, and lack membrane-bound organelles such as the nucleus, prokaryotes include two of the domains of life, bacteria and archaea. The DNA of a prokaryotic cell consists of a chromosome that is in direct contact with the cytoplasm. The nuclear region in the cytoplasm is called the nucleoid, most prokaryotes are the smallest of all organisms ranging from 0.5 to 2.0 µm in diameter. Though most prokaryotes have both a cell membrane and a wall, there are exceptions such as Mycoplasma and Thermoplasma which only possess the cell membrane layer. The envelope gives rigidity to the cell and separates the interior of the cell from its environment, the cell wall consists of peptidoglycan in bacteria, and acts as an additional barrier against exterior forces. It also prevents the cell from expanding and bursting from osmotic pressure due to a hypotonic environment, some eukaryotic cells also have a cell wall. Inside the cell is the region that contains the genome, ribosomes. The genetic material is found in the cytoplasm. Prokaryotes can carry extrachromosomal DNA elements called plasmids, which are usually circular, linear bacterial plasmids have been identified in several species of spirochete bacteria, including members of the genus Borrelia notably Borrelia burgdorferi, which causes Lyme disease. Though not forming a nucleus, the DNA is condensed in a nucleoid, plasmids encode additional genes, such as antibiotic resistance genes
8.
Cell nucleus
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In cell biology, the nucleus is a membrane-enclosed organelle found in eukaryotic cells. Eukaryotes usually have a nucleus, but a few cell types, such as mammalian red blood cells, have no nuclei. Cell nuclei contain most of the genetic material, organized as multiple long linear DNA molecules in complex with a large variety of proteins, such as histones. The genes within these chromosomes are the nuclear genome and are structured in such a way to promote cell function. The nucleus maintains the integrity of genes and controls the activities of the cell by regulating gene expression—the nucleus is, therefore, because the nuclear membrane is impermeable to large molecules, nuclear pores are required to regulate nuclear transport of molecules across the envelope. The pores cross both nuclear membranes, providing a channel through which larger molecules must be transported by carrier proteins while allowing free movement of small molecules. Movement of large molecules such as proteins and RNA through the pores is required for gene expression and the maintenance of chromosomes. The best-known of these is the nucleolus, which is involved in the assembly of ribosomes. After being produced in the nucleolus, ribosomes are exported to the cytoplasm where they translate mRNA, the nucleus was the first organelle to be discovered. What is most likely the oldest preserved drawing dates back to the early microscopist Antonie van Leeuwenhoek and he observed a lumen, the nucleus, in the red blood cells of salmon. Unlike mammalian red blood cells, those of other vertebrates still contain nuclei, the nucleus was also described by Franz Bauer in 1804 and in more detail in 1831 by Scottish botanist Robert Brown in a talk at the Linnean Society of London. Brown was studying orchids under microscope when he observed an opaque area and he did not suggest a potential function. In 1838, Matthias Schleiden proposed that the plays a role in generating cells. He believed that he had observed new cells assembling around cytoblasts, Franz Meyen was a strong opponent of this view, having already described cells multiplying by division and believing that many cells would have no nuclei. The function of the nucleus remained unclear, between 1877 and 1878, Oscar Hertwig published several studies on the fertilization of sea urchin eggs, showing that the nucleus of the sperm enters the oocyte and fuses with its nucleus. This was the first time it was suggested that an individual develops from a nucleated cell, therefore, the necessity of the sperm nucleus for fertilization was discussed for quite some time. However, Hertwig confirmed his observation in other groups, including amphibians. Eduard Strasburger produced the results for plants in 1884
9.
Ossification
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Ossification in bone remodeling is the process of laying down new bone material by cells called osteoblasts. It is synonymous with bone tissue formation, heterotopic ossification is a process resulting in the formation of bone tissue that is often atypical, at an extraskeletal location. Calcification is often confused with ossification, calcification is synonymous with the formation of calcium-based salts and crystals within cells and tissue. It is a process that occurs during ossification, but not vice versa, the exact mechanisms by which bone development is triggered remains unclear, but it involves growth factors and cytokines in some way. Intramembranous ossification forms the bones of the skull, clavicle and mandible. Endochondral ossification is the formation of bones and other bones. This requires a hyaline cartilage precursor, there are two centres of ossification for endochondral ossification. The primary centre In long bones, bone tissue first appears in the diaphysis, cartilage is progressively eroded and replaced by hardened bone, extending towards the epiphysis. The nutrient artery enters via the nutrient foramen from an opening in the diaphysis. It invades the primary centre of ossification, bringing osteogenic cells The canal of the nutrient foramen is directed away from more active end of bone when one end more than the other. When bone grows at same rate at both ends, the nutrient artery is perpendicular to the bone, most other bones also have primary ossification centres, and bone is laid down in a similar manner. Secondary centres The secondary centres generally appear at the epiphysis, secondary ossification mostly occurs after birth. The epiphyseal arteries and osteogenic cells invade the epiphysis, depositing osteoblasts and osteoclasts which erode the cartilage and this occurs at both ends of long bones but only one end of digits and ribs. Several hypotheses have proposed for how bone evolved as a structural element in vertebrates. One hypothesis is that developed from tissues that evolved to store minerals. Specifically, calcium-based minerals were stored in cartilage and bone was a development from this calcified cartilage. However, other possibilities include bony tissue evolving as an osmotic barrier, or as a protective structure
10.
Osteon
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The osteon or haversian system /həˈvɜːr. ʒən/ is the fundamental functional unit of much compact bone. Osteons are roughly cylindrical structures that are typically several millimeters long and they are present in many bones of most mammals and some bird, reptile, and amphibian species. Each osteon consists of layers, or lamellae, of compact bone tissue that surround a central canal. The haversian canal contains the bones blood supplies, the boundary of an osteon is the cement line. Each haversian canal is surrounding by varying number of concentrically arranged lamellae of bone martix, near the surface of the compact bone, the lamellae are arranged parallel to the surface, these are called circumferential lamellae. Some of the osteoblasts develop into osteocytes, each living within its own small space, osteocytes make contact with the cytoplasmic processes of their counterparts via a network of small transverse canals, or canaliculi. This network facilitates the exchange of nutrients and metabolic waste, collagen fibers in a particular lamella run parallel to each other, but the orientation of collagen fibers within other lamellae is oblique. The collagen fiber density is lowest at the seams between lamellae, accounting for the microscopic appearance of a transverse section of osteons. The space between osteons is occupied by interstitial lamellae, which are the remnants of osteons that were partially resorbed during the process of bone remodeling, osteons are connected to each other and the periosteum by oblique channels called Volkmanns canals or perforating canals. Drifting osteons are a phenomenon that is not fully understood, a drifting osteon is classified as one that runs both longitudinally as well as transversely through the cortex. An osteon can drift in one direction or change directions several times, osteons and their arrangement vary according to taxon, so that genus and sometimes species can be differentiated using a bone fragment not otherwise identifiable. More research is needed, but osteohistology has the potential to affect the studies in bioarchaeology, paleontology. Martiniaková, Monika 2006 Differences in bone microstructure of mammalian skeletons, faculty of Natural Sciences, Constantine the Philosopher University in Nita, Nitro, Slovakia. Netter, Frank H. Musculature system, anatomy, physiology, and metabolic disorders
11.
Mesenchymal stem cell
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Mesenchymal stem cells, or MSCs, are multipotent stromal cells that can differentiate into a variety of cell types, including, osteoblasts, chondrocytes, myocytes and adipocytes. This phenomenon has been documented in specific cells and tissues in living animals, stromal cells are connective tissue cells that form the supportive structure in which the functional cells of the tissue reside. While this is a description for one function of MSCs. The term multipotent stromal cell has been proposed as a replacement, scientists Ernest A. McCulloch and James E. Till first revealed the nature of marrow cells in the 1960s. An ex vivo assay for examining the potential of multipotent marrow cells was later reported in the 1970s by Friedenstein. In this assay system, stromal cells were referred to as colony-forming unit-fibroblasts, the first clinical trials of MSCs were completed in 1995 when a group of 15 patients were injected with cultured MSCs to test the safety of the treatment. Since then, over 200 clinical trials have been started, however, most are still in the safety stage of testing. Subsequent experimentation revealed the plasticity of marrow cells and how their fate could be determined by environmental cues, culturing marrow stromal cells in the presence of osteogenic stimuli such as ascorbic acid, inorganic phosphate and dexamethasone could promote their differentiation into osteoblasts. In contrast, the addition of transforming growth factor-beta could induce chondrogenic markers, bone marrow was the first source of MSCs ever used, and still is the most important source of them. The youngest, most primitive MSCs can be obtained from umbilical cord tissue, namely Whartons jelly, however MSCs are found in much higher concentration in the Wharton’s jelly compared to cord blood, which is a rich source of hematopoietic stem cells. The umbilical cord is easily obtained after a birth and it is normally thrown away and poses no risk for collection. The cord MSCs have more primitive properties than other adult MSCs obtained later in life, adipose tissue is a rich source of MSCs. A rich source for stem cells is the developing tooth bud of the mandibular third molar. While considered multipotent, they may prove to be pluripotent and they eventually form enamel, dentin, blood vessels, dental pulp and nervous tissues, a minimum of 24 other different unique end organs. Because of ease in collection at 8–10 years of age before calcification and minimal-to-no-morbidity, they constitute a major source for research. These stem cells have been capable of producing hepatocytes. Additionally, amniotic fluid has been shown to be a source of stem cells
12.
Collagen
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Collagen /ˈkɒlədʒᵻn/ is the main structural protein in the extracellular space in the various connective tissues in animal bodies. As the main component of tissue, it is the most abundant protein in mammals. Depending upon the degree of mineralization, collagen tissues may be rigid, compliant, Collagen, in the form of elongated fibrils, is mostly found in fibrous tissues such as tendons, ligaments and skin. It is also abundant in corneas, cartilage, bones, blood vessels, the gut, intervertebral discs, in muscle tissue, it serves as a major component of the endomysium. Collagen constitutes one to two percent of muscle tissue, and accounts for 6% of the weight of strong, tendinous muscles, the fibroblast is the most common cell that creates collagen. Gelatin, which is used in food and industry, is collagen that has been irreversibly hydrolyzed, Collagen also has many medical uses in treating complications of the bones and skin. The name collagen comes from the Greek κόλλα, meaning glue and this refers to the compounds early use in the process of boiling the skin and sinews of horses and other animals to obtain glue. Collagen occurs in places throughout the body. Over 90% of the collagen in the body, however, is type I. So far,28 types of collagen have been identified and described, type IV, forms basal lamina, the epithelium-secreted layer of the basement membrane. Type V, cell surfaces, hair and placenta The collagenous cardiac skeleton which includes the four valve rings, is histologically, elastically and uniquely bound to cardiac muscle. The cardiac skeleton also includes the separating septa of the heart chambers – the interventricular septum, Collagen contribution to the measure of cardiac performance summarily represents a continuous torsional force opposed to the fluid mechanics of blood pressure emitted from the heart. With support from collagen, atrial fibrillation should never deteriorate to ventricular fibrillation, Collagen is layered in variable densities with cardiac muscle mass. The mass, distribution, age and density of collagen all contribute to the required to move blood back. Individual cardiac valvular leaflets are folded into shape by specialized collagen under variable pressure, gradual calcium deposition within collagen occurs as a natural function of aging. Pathology of the underpinning of the heart is understood within the category of connective tissue disease. Collagen has been used in cosmetic surgery, as a healing aid for burn patients for reconstruction of bone and a wide variety of dental, orthopedic. Both human and bovine collagen is used as dermal fillers for treatment of wrinkles
13.
Osteocalcin
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Osteocalcin, also known as bone gamma-carboxyglutamic acid-containing protein, is a noncollagenous protein hormone found in bone and dentin. Because it has gla domains, its synthesis is vitamin K dependent, in humans, the osteocalcin is encoded by the BGLAP gene. Osteocalcin is secreted solely by osteoblasts and thought to play a role in the bodys metabolic regulation and is pro-osteoblastic, or bone-building and it is also implicated in bone mineralization and calcium ion homeostasis. Osteocalcin acts on Leydig cells of the testis to stimulate testosterone biosynthesis, osteocalcin also acts on myocytes to promote energy availability and utilization and in this manner favors exercise capacity. As osteocalcin is produced by osteoblasts, it is used as a marker for the bone formation process. In many studies, osteocalcin is used as a biomarker on the effectiveness of a given drug on bone formation. For instance, one study which aimed to study the effectiveness of a glycoprotein called lactoferrin on bone formation used osteocalcin as a measure of osteoblast activity, osteocalcin at the US National Library of Medicine Medical Subject Headings
14.
Osteopontin
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Not to be confused with Osteocalcin, Osteonectin or Osteoprotegerin. Osteopontin, also known as bone sialoprotein I, early T-lymphocyte activation, secreted phosphoprotein 1, 2ar, osteopontin is a SIBLING that was first identified in 1986 in osteoblasts. The prefix osteo- indicates that the protein is expressed in bone, the suffix -pontin is derived from pons, the Latin word for bridge, and signifies osteopontins role as a linking protein. Osteopontin is a structural protein and therefore an organic component of bone. Synonyms for this protein include sialoprotein I and 44K BPP, the gene has 7 exons, spans 5 kilobases in length and in humans it is located on the long arm of chromosome 4 region 22. The protein is rich in acidic residues, 30-36% are either aspartic or glutamic acid, OPN is a highly negatively charged, extracellular matrix protein that lacks an extensive secondary structure. It is composed of about 300 amino acids and is expressed as a 33-kDa nascent protein, OPN can go through posttranslational modifications, which increase its apparent molecular weight to about 44 kDa. The OPN gene is composed of 7 exons,6 of which containing coding sequence, the first two exons contain the 5 untranslated region. Exons 2,3,4,5,6, and 7 code for 17,13,27,14,108 and 134 amino acids, all intron-exon boundaries are of the phase 0 type, thus alternative exon splicing maintains the reading frame of the OPN gene. Full-length OPN can be modified by thrombin cleavage, which exposes a cryptic sequence and this thrombin-cleaved OPN exposes an epitope for integrin receptors of α4β1, α9β1, and α9β4. These integrin receptors are present on a number of cells such as mast cells, neutrophils. It is also expressed by monocytes and macrophages, upon binding these receptors, cells use several signal transduction pathways to elicit immune responses in these cells. OPN-R can be cleaved by Carboxypeptidase B by removal of C-terminal arginine. The function of OPN-L is largely unknown and it appears an intracellular variant of OPN is involved in a number of cellular processes including migration, fusion and motility. Intracellular OPN is generated using a translation start site on the same mRNA species used to generate the extracellular isoform. This alternative translation start site is downstream of the N-terminal endoplasmic reticulum-targeting signal sequence, various human cancers, including breast cancer, have been observed to express splice variants of OPN. The cancer-specific splice variants are osteopontin-a, osteopontin-b, and osteopontin-c, exon 5 is lacking from osteopontin-b, whereas osteopontin-c lacks exon 4. Osteopontin-c has been suggested to facilitate the anchorage-independent phenotype of human breast cancer cells due to its inability to associate with the extracellular matrix
15.
Hydroxylapatite
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Hydroxylapatite is the hydroxyl endmember of the complex apatite group. The OH− ion can be replaced by fluoride, chloride or carbonate and it crystallizes in the hexagonal crystal system. Naturally occurring apatites can, however, also have brown, yellow, or green colorations, up to 50% by volume and 70% by weight of human bone is a modified form of hydroxylapatite. Carbonated calcium-deficient hydroxylapatite is the mineral of which dental enamel. Hydroxylapatite crystals are found in the small calcifications known as corpora arenacea or brain sand. Hydroxyapatite can be synthesized via several methods such as wet chemical deposition, biomimetic deposition, the ultrasonically assisted synthesis of hydroxyapatite is a successful technique to produce nanostructured hydroxyapatite at high quality standards. The ultrasonic route allows to produce nano-crystalline hydroxyapatite as well as modified particles, e. g. core-shell nanospheres, Calcium deficient hydroxyapatite, Ca10−x6−xx2−x has a Ca/P ratio between 1.67 and 1.5. The Ca/P ratio is used in the discussion of calcium phosphate phases. Stoichiometric apatite Ca1062 has a Ca/P ratio of 10,6 normally expressed as 1.67, the non-stoichiometric phases have the hydroxyapatite structure with cation vacancies and anion vacancies. The sites occupied solely by phosphate anions in stochiometric hydroxyapatite, are occupied by phosphate or hydrogen phosphate, HPO42–, thus, it is commonly used as a filler to replace amputated bone or as a coating to promote bone ingrowth into prosthetic implants. Although many other phases exist with similar or even identical chemical makeup, coral skeletons can be transformed into hydroxylapatite by high temperatures, their porous structure allows relatively rapid ingrowth at the expense of initial mechanical strength. The high temperature also burns away any organic molecules such as proteins, preventing an immune response, many modern implants, e. g. hip replacements, dental implants and bone conduction implants, are coated with hydroxylapatite. It has been suggested that this may promote osseointegration, porous hydroxylapatite implants are used for local drug delivery in bone. It is also being used to repair early lesions in tooth enamel, a promising method of modification is the introduction of fluorine or silicon into the primary structure with the formation of fluorine- or silicon-substituted hydroxylapatite. The introduction of fluorine increases the resistance to biodegradation and improves the adsorption of proteins, hydroxylapatite deposits in tendons around joints resulting in the medical condition calcific tendinitis. Microcrystalline hydroxylapatite is marketed as a supplement with superior absorption in comparison to calcium. It is a calcium supplement derived from bovine bone. However, the limited tests seem to show positive results, a 1995 randomized placebo-controlled study of 40 people in Europe found that it was more effective than calcium carbonate in slowing bone loss
16.
Mineralized tissues
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Mineralized tissues are biological tissues that incorporate minerals into soft matrices. Typically these tissues form a shield or structural support. Bone, mollusc shells, deep sea sponge Euplectella species, radiolarians, diatoms, antler bone, tendon, cartilage, tooth enamel and these tissues have been finely tuned to enhance their mechanical capabilities over millions of years of evolution. Thus, mineralized tissues have been the subject of studies since there is a lot to learn from nature as seen from the growing field of biomimetics. The remarkable structural organization and engineering properties makes these tissues desirable candidates for duplication by artificial means, Mineralized tissues inspire miniaturization, adaptability and multifunctionality. While natural materials are made up of a number of components. Mineralized tissues combine stiffness, low weight, strength and toughness due to the presence of minerals in soft protein networks and tissues. Although one might think that the content of these tissues can make them fragile. The secret to this strength is in the organized layering of the tissue. Due to this layering, loads and stresses are transferred throughout several length-scales, from macro to micro to nano and these scales or hierarchical structures are therefore able to distribute damage and resist cracking. Two types of tissues have been the target of extensive investigation, namely nacre from mollusk shells and bone. Many mechanical and imaging such as nanoindentation and atomic force microscopy are used to characterize these tissues. Although the degree of efficiency of hard tissues are yet unmatched by any man-made ceramic composites. Not all mineralized tissues develop through normal physiologic processes and are beneficial to the organism, for example, kidney stones contain mineralized tissues that are developed through pathologic processes. Hence, biomineralization is an important process to understand how these diseases occur, the evolution of mineralized tissues has been puzzling for more than a century. It has been hypothesized that the first mechanism of mammalian tissue mineralization began either in the skeleton of conodont or the dermal skeleton of early agnathans. The dermal skeleton is just surface dentin and basal bone, which is overlaid by enameloid. It is thought that the dermal skeleton eventually became scales, which are homologous to teeth, teeth were first seen in chondrichthyans and were made from all three components of the dermal skeleton, namely dentin, basal bone and enameloid
17.
Vertebrate
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Vertebrates /ˈvɜːrtᵻbrᵻts/ comprise all species of animals within the subphylum Vertebrata /-ɑː/. Vertebrates represent the majority of the phylum Chordata, with currently about 66,000 species described. Vertebrates include the fish and the jawed vertebrates, which include the cartilaginous fish. A bony fish known as the lobe-finned fishes is included with tetrapods, which are further divided into amphibians, reptiles, mammals. Extant vertebrates range in size from the frog species Paedophryne amauensis, at as little as 7.7 mm, to the blue whale, vertebrates make up less than five percent of all described animal species, the rest are invertebrates, which lack vertebral columns. The vertebrates traditionally include the hagfish, which do not have proper vertebrae due to their loss in evolution, though their closest living relatives, hagfish do, however, possess a cranium. For this reason, the vertebrate subphylum is sometimes referred to as Craniata when discussing morphology, molecular analysis since 1992 has suggested that hagfish are most closely related to lampreys, and so also are vertebrates in a monophyletic sense. Others consider them a group of vertebrates in the common taxon of craniata. The word origin of vertebrate derives from the Latin word vertebratus, the Proto-Indo-European language origins are still unclear. Vertebrate is derived from the vertebra, which refers to any of the bones or segments of the spinal column. All vertebrates are built along the basic body plan, a stiff rod running through the length of the animal, with a hollow tube of nervous tissue above it. In all vertebrates, the mouth is found at, or right below, the remaining part of the body continuing after the anus forms a tail with vertebrae and spinal cord, but no gut. However, a few vertebrates have secondarily lost this anatomy, retaining the notochord into adulthood, such as the sturgeon, jawed vertebrates are typified by paired appendages, but this trait is not required in order for an animal to be a vertebrate. All basal vertebrates breathe with gills, the gills are carried right behind the head, bordering the posterior margins of a series of openings from the pharynx to the exterior. Each gill is supported by a cartilagenous or bony gill arch, the bony fish have three pairs of arches, cartilaginous fish have five to seven pairs, while the primitive jawless fish have seven. The vertebrate ancestor no doubt had more arches than this, as some of their relatives have more than 50 pairs of gills. In amphibians and some primitive fishes, the larvae bear external gills. These are reduced in adulthood, their function taken over by the gills proper in fishes, some amphibians retain the external larval gills in adulthood, the complex internal gill system as seen in fish apparently being irrevocably lost very early in the evolution of tetrapods
18.
Homeostasis
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Each of these variables is controlled by a separate “homeostat”, which, together, maintain life. The concept was described by French physiologist Claude Bernard in 1865, the term cybernetics is applied to technological control systems such as thermostats, which function as homeostats, but is often defined much more broadly than the biological term homeostasis. The word homeostasis uses combining forms of homeo- and -stasis, New Latin from Greek, ὅμοιος homoios, similar and στάσις stasis, standing still, yielding the idea of staying the same. The conceptual origins of homeostasis reach back to the ancient Greek concepts of balance, harmony, equilibrium, following these hypotheses, Hippocrates compared health to the harmonious balance of the elements, and illness and disease to the systematic disharmony of these elements. Cannon published an extrapolation from Bernards 1865 work naming his theory homeostasis, Cannon further posited that threats to homeostasis might originate from the external environment or the internal environment, and could be physical or psychological, as in emotional distress. Cannon identified these negative feedback systems and emphasized that, regardless of the nature of the threat to homeostasis, the metabolic processes of all living organisms can only take place in very specific physical and chemical environments. The conditions vary with each organism, and with whether the chemical processes take place inside the cell or in the bathing the cells in multicellular creatures. However, a great many other homeostats, encompassing many aspects of human physiology, if an entity is homeostatically controlled it does not imply that its value is necessarily absolutely steady in health. Core body temperature is, for instance, regulated by a homeostat with temperature sensors in, amongst others, however the set point of the regulator is regularly reset. For instance, core temperature in humans varies during the course of the day, with the lowest temperatures occurring at night. The temperature regulators set point is readjusted in adult women at the start of the phase of the menstrual cycle. The temperature regulators set point is reset during infections to produce a fever, Homeostasis does not govern every activity in the body. For instance the signal from the sensor to the effector is, of necessity, highly variable in order to information about the direction. Similarly the effector’s response needs to be adjustable to reverse the error – in fact it should be very nearly in proportion to the error that is threatening the internal environment. The sensors send messages via sensory nerves to the medulla oblongata of the brain indicating whether the pressure has fallen or risen. One of the effector organs is the heart rate is stimulated to rise when the arterial blood pressure falls. Thus the heart rate is not homeostatically controlled, but is one of effector responses to errors in the blood pressure. Another example is the rate of sweating, the blood urea concentration is an example
19.
Calcium
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Calcium is a chemical element with symbol Ca and atomic number 20. Calcium is a soft grayish-yellow alkaline earth metal, fifth-most-abundant element by mass in the Earths crust, the ion Ca2+ is also the fifth-most-abundant dissolved ion in seawater by both molarity and mass, after sodium, chloride, magnesium, and sulfate. Free calcium metal is too reactive to occur in nature, Calcium is produced in supernova nucleosynthesis. Calcium is a trace element in living organisms. It is the most abundant metal by mass in animals, and it is an important constituent of bone, teeth. In cell biology, the movement of the calcium ion into, Calcium carbonate and calcium citrate are often taken as dietary supplements. Calcium is on the World Health Organizations List of Essential Medicines, Calcium has a wide variety of applications, almost all of which are associated with calcium compounds and salts. Calcium metal is used as a deoxidizer, desulfurizer, and decarbonizer for production of ferrous and nonferrous alloys. In steelmaking and production of iron, Ca reacts with oxygen, Calcium carbonate is used in manufacturing cement and mortar, lime, limestone and aids in production in the glass industry. It also has chemical and optical uses as mineral specimens in toothpastes, Calcium hydroxide solution is used to detect the presence of carbon dioxide in a gas sample bubbled through a solution. The solution turns cloudy where CO2 is present, Calcium arsenate is used in insecticides. Calcium carbide is used to make acetylene gas and various plastics, Calcium chloride is used in ice removal and dust control on dirt roads, as a conditioner for concrete, as an additive in canned tomatoes, and to provide body for automobile tires. Calcium citrate is used as a food preservative, Calcium cyclamate is used as a sweetening agent in several countries. In the United States, it has been outlawed as a suspected carcinogen, Calcium gluconate is used as a food additive and in vitamin pills. Calcium hypochlorite is used as a swimming pool disinfectant, as an agent, as an ingredient in deodorant. Calcium permanganate is used in rocket propellant, textile production, as a water sterilizing agent. Calcium phosphate is used as a supplement for animal feed, fertilizer, in production for dough and yeast products, in the manufacture of glass. Calcium phosphide is used in fireworks, rodenticide, torpedoes, Calcium sulfate is used as common blackboard chalk, as well as, in its hemihydrate form, Plaster of Paris
20.
Bone remodeling
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Bone remodeling is a lifelong process where mature bone tissue is removed from the skeleton and new bone tissue is formed. These processes also control the reshaping or replacement of bone following injuries like fractures but also micro-damage, remodeling responds also to functional demands of the mechanical loading. In the first year of life, almost 100% of the skeleton is replaced, in adults, remodeling proceeds at about 10% per year. An imbalance in the regulation of bone remodelings two sub-processes, bone resorption and bone formation, results in many metabolic bone diseases, such as osteoporosis, bone homeostasis involves multiple but coordinated cellular and molecular events. Two main types of cells are responsible for metabolism, osteoblasts. The structure of bones as well as supply of calcium requires close cooperation between these two cell types and other cell populations present at the bone remodeling sites. Bone metabolism relies on complex signaling pathways and control mechanisms to achieve proper rates of growth and it is in this way that the body is able to maintain proper levels of calcium required for physiological processes. Subsequent to appropriate signaling, osteoclasts move to resorb the surface of the bone, together, the cells that are responsible for bone remodeling are known as the basic multicellular unit, and the temporal duration of the BMU is referred to as the bone remodeling period
21.
Protein
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Proteins are large biomolecules, or macromolecules, consisting of one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, responding to stimuli, a linear chain of amino acid residues is called a polypeptide. A protein contains at least one long polypeptide, short polypeptides, containing less than 20–30 residues, are rarely considered to be proteins and are commonly called peptides, or sometimes oligopeptides. The individual amino acid residues are bonded together by peptide bonds, the sequence of amino acid residues in a protein is defined by the sequence of a gene, which is encoded in the genetic code. In general, the code specifies 20 standard amino acids, however. Sometimes proteins have non-peptide groups attached, which can be called prosthetic groups or cofactors, proteins can also work together to achieve a particular function, and they often associate to form stable protein complexes. Once formed, proteins only exist for a period of time and are then degraded and recycled by the cells machinery through the process of protein turnover. A proteins lifespan is measured in terms of its half-life and covers a wide range and they can exist for minutes or years with an average lifespan of 1–2 days in mammalian cells. Abnormal and or misfolded proteins are degraded more rapidly due to being targeted for destruction or due to being unstable. Like other biological macromolecules such as polysaccharides and nucleic acids, proteins are essential parts of organisms, many proteins are enzymes that catalyse biochemical reactions and are vital to metabolism. Proteins also have structural or mechanical functions, such as actin and myosin in muscle and the proteins in the cytoskeleton, other proteins are important in cell signaling, immune responses, cell adhesion, and the cell cycle. In animals, proteins are needed in the diet to provide the essential amino acids that cannot be synthesized, digestion breaks the proteins down for use in the metabolism. Methods commonly used to study structure and function include immunohistochemistry, site-directed mutagenesis, X-ray crystallography, nuclear magnetic resonance. Most proteins consist of linear polymers built from series of up to 20 different L-α-amino acids, all proteinogenic amino acids possess common structural features, including an α-carbon to which an amino group, a carboxyl group, and a variable side chain are bonded. Only proline differs from this structure as it contains an unusual ring to the N-end amine group. The amino acids in a chain are linked by peptide bonds. Once linked in the chain, an individual amino acid is called a residue, and the linked series of carbon, nitrogen. The peptide bond has two forms that contribute some double-bond character and inhibit rotation around its axis, so that the alpha carbons are roughly coplanar
22.
Mineral
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A mineral is a naturally occurring chemical compound, usually of crystalline form and abiogenic in origin. A mineral has one specific chemical composition, whereas a rock can be an aggregate of different minerals or mineraloids, the study of minerals is called mineralogy. There are over 5,300 known mineral species, over 5,070 of these have been approved by the International Mineralogical Association, the silicate minerals compose over 90% of the Earths crust. The diversity and abundance of species is controlled by the Earths chemistry. Silicon and oxygen constitute approximately 75% of the Earths crust, which translates directly into the predominance of silicate minerals, minerals are distinguished by various chemical and physical properties. Differences in chemical composition and crystal structure distinguish the various species, changes in the temperature, pressure, or bulk composition of a rock mass cause changes in its minerals. Minerals can be described by their various properties, which are related to their chemical structure. Common distinguishing characteristics include crystal structure and habit, hardness, lustre, diaphaneity, colour, streak, tenacity, cleavage, fracture, parting, more specific tests for describing minerals include magnetism, taste or smell, radioactivity and reaction to acid. Minerals are classified by key chemical constituents, the two dominant systems are the Dana classification and the Strunz classification, the silicate class of minerals is subdivided into six subclasses by the degree of polymerization in the chemical structure. All silicate minerals have a unit of a 4− silica tetrahedron—that is, a silicon cation coordinated by four oxygen anions. These tetrahedra can be polymerized to give the subclasses, orthosilicates, disilicates, cyclosilicates, inosilicates, phyllosilicates, other important mineral groups include the native elements, sulfides, oxides, halides, carbonates, sulfates, and phosphates. The first criterion means that a mineral has to form by a natural process, stability at room temperature, in the simplest sense, is synonymous to the mineral being solid. More specifically, a compound has to be stable or metastable at 25 °C, modern advances have included extensive study of liquid crystals, which also extensively involve mineralogy. Minerals are chemical compounds, and as such they can be described by fixed or a variable formula, many mineral groups and species are composed of a solid solution, pure substances are not usually found because of contamination or chemical substitution. Finally, the requirement of an ordered atomic arrangement is usually synonymous with crystallinity, however, crystals are also periodic, an ordered atomic arrangement gives rise to a variety of macroscopic physical properties, such as crystal form, hardness, and cleavage. There have been recent proposals to amend the definition to consider biogenic or amorphous substances as minerals. The formal definition of an approved by the IMA in 1995, A mineral is an element or chemical compound that is normally crystalline. However, if geological processes were involved in the genesis of the compound, Mineral classification schemes and their definitions are evolving to match recent advances in mineral science
23.
Ultimate tensile strength
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In other words, tensile strength resists tension, whereas compressive strength resists compression. Ultimate tensile strength is measured by the stress that a material can withstand while being stretched or pulled before breaking. In the study of strength of materials, tensile strength, compressive strength, some materials break very sharply, without plastic deformation, in what is called a brittle failure. Others, which are more ductile, including most metals, experience some plastic deformation, the UTS is usually found by performing a tensile test and recording the engineering stress versus strain. The highest point of the curve is the UTS. It is a property, therefore its value does not depend on the size of the test specimen. However, it is dependent on other factors, such as the preparation of the specimen, the presence or otherwise of surface defects, Tensile strengths are rarely used in the design of ductile members, but they are important in brittle members. They are tabulated for common materials such as alloys, composite materials, ceramics, plastics, Tensile strength can be defined for liquids as well as solids under certain conditions. Tensile strength is defined as a stress, which is measured as force per unit area, for some non-homogeneous materials it can be reported just as a force or as a force per unit width. In the International System of Units, the unit is the pascal, or, equivalently to pascals, Many materials can display linear elastic behavior, defined by a linear stress–strain relationship, as shown in the left figure up to point 3. Beyond this elastic region, for materials, such as steel. A plastically deformed specimen does not completely return to its original size, for many applications, plastic deformation is unacceptable, and is used as the design limitation. The reversal point is the stress on the engineering stress–strain curve. The UTS is not used in the design of static members because design practices dictate the use of the yield stress. It is, however, used for quality control, because of the ease of testing and it is also used to roughly determine material types for unknown samples. The UTS is a common engineering parameter to design members made of material because such materials have no yield point. Typically, the testing involves taking a sample with a fixed cross-sectional area. When testing some metals, indentation hardness correlates linearly with tensile strength and this important relation permits economically important nondestructive testing of bulk metal deliveries with lightweight, even portable equipment, such as hand-held Rockwell hardness testers
24.
Compressive strength
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In other words, compressive strength resists compression, whereas tensile strength resists tension. In the study of strength of materials, tensile strength, compressive strength, some materials fracture at their compressive strength limit, others deform irreversibly, so a given amount of deformation may be considered as the limit for compressive load. Compressive strength is a key value for design of structures, Compressive strength is often measured on a universal testing machine, these range from very small table-top systems to ones with over 53 MN capacity. Measurements of compressive strength are affected by the specific test method, Compressive strengths are usually reported in relationship to a specific technical standard. When a specimen of material is loaded in such a way that it extends it is said to be in tension, on the other hand, if the material compresses and shortens it is said to be in compression. On an atomic level, the molecules or atoms are forced apart when in tension whereas in compression they are forced together. Since atoms in solids always try to find an equilibrium position, the phenomena prevailing on an atomic level are therefore similar. Tension tends to pull small sideways deflections back into alignment, while compression tends to amplify such deflection into buckling, Compressive strength is measured on materials, components, and structures. By definition, the compressive strength of a material is that value of uniaxial compressive stress reached when the material fails completely. The compressive strength is usually obtained experimentally by means of a compressive test, the apparatus used for this experiment is the same as that used in a tensile test. However, rather than applying a uniaxial tensile load, a uniaxial compressive load is applied, as can be imagined, the specimen is shortened as well as spread laterally. In a compression test, there is a region where the material follows Hookes Law. Hence for this region σ = E ϵ where this time E refers to the Youngs Modulus for compression, in this region, the material deforms elastically and returns to its original length when the stress is removed. This linear region terminates at what is known as the yield point, above this point the material behaves plastically and will not return to its original length once the load is removed. There is a difference between the stress and the true stress. By its basic definition the uniaxial stress is given by, σ = F A where, F = Load applied, A = Area As stated, in reality therefore the area is some function of the applied load i. e. Indeed, stress is defined as the force divided by the area at the start of the experiment, in engineering design practice, professionals mostly rely on the engineering stress. In reality, the stress is different from the engineering stress
25.
Composite material
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The individual components remain separate and distinct within the finished structure. The new material may be preferred for reasons, common examples include materials which are stronger, lighter. More recently, researchers have begun to actively include sensing, actuation, computation and communication into composites. The most advanced examples perform routinely on spacecraft and aircraft in demanding environments, the earliest man-made composite materials were straw and mud combined to form bricks for building construction. Ancient brick-making was documented by Egyptian tomb paintings, wattle and daub is one of the oldest man-made composite materials, at over 6000 years old. Concrete is also a material, and is used more than any other man-made material in the world. As of 2006, about 7.5 billion cubic metres of concrete are made each year—more than one metre for every person on Earth. 2181–2055 BC and was used for death masks Cob Mud Bricks, concrete was described by Vitruvius, writing around 25 BC in his Ten Books on Architecture, distinguished types of aggregate appropriate for the preparation of lime mortars. For structural mortars, he recommended pozzolana, which were volcanic sands from the beds of Pozzuoli brownish-yellow-gray in colour near Naples. Natural cement-stones, after burning, produced cements used in concretes from post-Roman times into the 20th century, the glass fiber is relatively strong and stiff, whereas the polymer is ductile. Thus the resulting fiberglass is relatively stiff, strong, flexible, concrete is the most common artificial composite material of all and typically consists of loose stones held with a matrix of cement. Concrete is a material, and will not compress or shatter even under quite a large compressive force. However, concrete cannot survive tensile loading, therefore, to give concrete the ability to resist being stretched, steel bars, which can resist high stretching forces, are often added to concrete to form reinforced concrete. Fibre-reinforced polymers or FRPs include carbon-fiber-reinforced polymer or CFRP, and glass-reinforced plastic or GRP, if classified by matrix then there are thermoplastic composites, short fiber thermoplastics, long fibre thermoplastics or long fibre-reinforced thermoplastics. There are numerous thermoset composites, including paper composite panels, many advanced thermoset polymer matrix systems usually incorporate aramid fibre and carbon fibre in an epoxy resin matrix. Shape memory polymer composites are high-performance composites, formulated using fibre or fabric reinforcement and they can also be reheated and reshaped repeatedly without losing their material properties. These composites are ideal for such as lightweight, rigid, deployable structures, rapid manufacturing. Although high strain composites exhibit many similarities to shape memory polymers, Composites can also use metal fibres reinforcing other metals, as in metal matrix composites or ceramic matrix composites, which includes bone, cermet and concrete
26.
Elastic deformation
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In materials science, deformation refers to any changes in the shape or size of an object due to- an applied force or a change in temperature. The first case can be a result of forces, compressive forces, shear. The movement or displacement of such mobile defects is thermally activated, deformation is often described as strain. As deformation occurs, internal inter-molecular forces arise that oppose the applied force, a larger applied force may lead to a permanent deformation of the object or even to its structural failure. In the figure it can be seen that the compressive loading has caused deformation in the cylinder so that the shape has changed into one with bulging sides. The sides bulge because the material, although enough to not crack or otherwise fail, is not strong enough to support the load without change. Internal forces resist the applied load, the concept of a rigid body can be applied if the deformation is negligible. Depending on the type of material, size and geometry of the object, the image to the right shows the engineering stress vs. strain diagram for a typical ductile material such as steel. Different deformation modes may occur under different conditions, as can be depicted using a deformation mechanism map and this type of deformation is reversible. Once the forces are no longer applied, the returns to its original shape. Elastomers and shape memory metals such as Nitinol exhibit large elastic deformation ranges, however elasticity is nonlinear in these materials. Normal metals, ceramics and most crystals show linear elasticity and an elastic range. This relationship only applies in the range and indicates that the slope of the stress vs. strain curve can be used to find Youngs modulus. Engineers often use this calculation in tensile tests, the elastic range ends when the material reaches its yield strength. At this point plastic deformation begins, note that not all elastic materials undergo linear elastic deformation, some, such as concrete, gray cast iron, and many polymers, respond in a nonlinear fashion. For these materials Hookes law is inapplicable and this type of deformation is irreversible. However, an object in the plastic deformation range will first have undergone elastic deformation, soft thermoplastics have a rather large plastic deformation range as do ductile metals such as copper, silver, and gold. Steel does, too, but not cast iron, hard thermosetting plastics, rubber, crystals, and ceramics have minimal plastic deformation ranges
27.
Osteoclast
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An osteoclast is a type of bone cell that breaks down bone tissue. This function is critical in the maintenance, repair, and remodelling of bones of the vertebral skeleton, the osteoclast disassembles and digests the composite of hydrated protein and mineral at a molecular level by secreting acid and a collagenase, a process known as bone resorption. This process also helps regulate the level of blood calcium, an odontoclast is an osteoclast associated with absorption of the roots of deciduous teeth. An osteoclast is a multinucleated cell and human osteoclasts on bone typically have five nuclei and are about 150-200 µm in diameter. When osteoclast-inducing cytokines are used to convert macrophages to osteoclasts, very large cells that may reach 100 µm in diameter occur and these may have dozens of nuclei, and typically express major osteoclast proteins but have significant differences from cells in living bone because of the not-natural substrate. The size of the multinucleated assembled osteoclast allows it to focus the ion transport, protein secretory, in bone, osteoclasts are found in pits in the bone surface which are called resorption bays, or Howships lacunae. Osteoclasts are characterized by a cytoplasm with a homogeneous, foamy appearance and this appearance is due to a high concentration of vesicles and vacuoles. These vacuoles include lysosomes filled with acid phosphatase, at a site of active bone resorption, the osteoclast forms a specialized cell membrane, the ruffled border, that opposes the surface of the bone tissue. Since their discovery in 1873 there has been debate about their origin. After years of controversy it is now clear that these cells develop from the fusion of macrophages. It was in the beginning of 1980 that the monocyte phagocytic system was recognized as precursor of osteoclasts, osteoclast formation requires the presence of RANKL and M-CSF. These membrane-bound proteins are produced by neighbouring cells and osteoblasts. M-CSF acts through its receptor on the osteoclast, c-fms, a transmembrane tyrosine kinase-receptor, both of these molecules are necessary for osteoclastogenesis and are widely involved in the differentiation of monocyte/macrophage derived cells. RANKL is a member of the tumour necrosis family, and is essential in osteoclastogenesis, RANKL knockout mice exhibit a phenotype of osteopetrosis and defects of tooth eruption, along with an absence or deficiency of osteoclasts. RANKL activates NF-κβ and NFATc1 through RANK, NF-κβ activation is stimulated almost immediately after RANKL-RANK interaction occurs and is not upregulated. NFATc1 stimulation, however, begins ~24–48 hours after binding occurs, osteoclast differentiation is inhibited by osteoprotegerin, which is produced by osteoblasts and binds to RANKL thereby preventing interaction with RANK. It may be important to note that while osteoclasts are derived from the hematopoietic lineage, once activated, osteoclasts move to areas of microfracture in the bone by chemotaxis. Osteoclasts lie in a cavity called Howships lacunae, formed from the digestion of the underlying bone
28.
Adipocyte
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Adipocytes, also known as lipocytes and fat cells, are the cells that primarily compose adipose tissue, specialized in storing energy as fat. There are two types of tissue, white adipose tissue and brown adipose tissue, which are also known as white fat and brown fat, respectively. Most recently, the presence of beige adipocytes with an expression pattern distinct from either white or brown adipocytes has been described. White fat cells or monovacuolar cells contain a lipid droplet surrounded by a layer of cytoplasm. The nucleus is flattened and located on the periphery, a typical fat cell is 0.1 mm in diameter with some being twice that size and others half that size. The fat stored is in a state, and is composed primarily of triglycerides. White fat cells secrete many proteins acting as such as resistin, adiponectin, leptin and apelin. An average human adult has 30 billion fat cells with a weight of 30 lbs or 13.5 kg, if excess weight is gained as an adult, fat cells increase in size about fourfold before dividing and increasing the absolute number of fat cells present. Brown fat cells or plurivacuolar cells are polygonal in shape, unlike white fat cells, these cells have considerable cytoplasm, with lipid droplets scattered throughout. The nucleus is round, and, although eccentrically located, it is not in the periphery of the cell, the brown color comes from the large quantity of mitochondria. Brown fat, also known as fat, is used to generate heat. Pre-adipocytes are undifferentiated fibroblasts that can be stimulated to form adipocytes, recent studies shed light into potential molecular mechanisms in the fate determination of pre-adipocytes although the exact lineage of adipocyte is still unclear. The variation of body fat distribution resulting from normal growth is influenced by nutritional and hormonal status in dependence on intrinsic differences in cells found in each adipose depot, mesenchymal stem cells can differentiate into adipocytes, connective tissue, muscle or bone. The term lipoblast is used to describe the precursor of the adult cell, the term lipoblastoma is used to describe a tumor of this cell type. Even after marked weight loss, the body never loses adipocytes. As a rule, to changes in weight. However, if the adipocytes in the body reach their capacity of fat. Adult rats of various strains became obese when they were fed a highly palatable diet for several months, analysis of their adipose tissue morphology revealed increases in both adipocyte size and number in most depots. Reintroduction of an ordinary chow diet to such animals precipitated a period of loss during which only mean adipocyte size returned to normal
29.
Myocyte
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Skeletal muscle is one of three major muscle types, the others being cardiac muscle and smooth muscle. It is a form of striated muscle tissue which is under the control of the somatic nervous system. Most skeletal muscles are attached to bones by bundles of collagen fibers known as tendons, a skeletal muscle refers to multiple bundles of cells called muscle fibers. The fibres and muscles are surrounded by connective tissue layers called fasciae, Muscle fibres, or muscle cells, are formed from the fusion of developmental myoblasts in a process known as myogenesis. Muscle fibres are cylindrical, and have more than one nucleus, Muscle fibers are in turn composed of myofibrils. The myofibrils are composed of actin and myosin filaments, repeated in units called sarcomeres, the sarcomere is responsible for the striated appearance of skeletal muscle, and forms the basic machinery necessary for muscle contraction. Connective tissue is present in all muscles as fascia, Muscle fibres are the individual contractile units within muscle. A single muscle such as the biceps contains many muscle fibres, another group of cells, the myosatellite cells are found between the basement membrane and the sarcolemma of muscle fibers. These cells are normally quiescent but can be activated by exercise or pathology to provide additional myonuclei for muscle growth or repair, development Individual muscle fibers are formed during development from the fusion of several undifferentiated immature cells known as myoblasts into long, cylindrical, multi-nucleated cells. Differentiation into this state is completed before birth with the cells continuing to grow in size thereafter. Microanatomy Skeletal muscle exhibits a distinctive banding pattern when viewed under the due to the arrangement of cytoskeletal elements in the cytoplasm of the muscle fibers. The principal cytoplasmic proteins are myosin and actin which are arranged in a unit called a sarcomere. The interaction of myosin and actin is responsible for muscle contraction, every single organelle and macromolecule of a muscle fiber is arranged to ensure form meets function. The cell membrane is called the sarcolemma with the known as the sarcoplasm. In the sarcoplasm are the myofibrils, the myofibrils are long protein bundles about 1 micrometer in diameter each containing myofilaments. Pressed against the inside of the sarcolemma are the unusual flattened myonuclei, between the myofibrils are the mitochondria. While the muscle fiber does not have a smooth endoplasmic reticulum, the sarcoplasmic reticulum surrounds the myofibrils and holds a reserve of the calcium ions needed to cause a muscle contraction. Periodically, it has dilated end sacs known as terminal cisternae and these cross the muscle fiber from one side to the other
30.
Periosteum
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The periosteum is a membrane that covers the outer surface of all bones, except at the joints of long bones. Endosteum lines the surface of all bones. The periosteum consists of irregular connective tissue. It is divided into a fibrous layer and inner cambium layer. The fibrous layer contains fibroblasts, while the layer contains progenitor cells that develop into osteoblasts. These osteoblasts are responsible for increasing the width of a long bone, after a bone fracture the progenitor cells develop into osteoblasts and chondroblasts, which are essential to the healing process. As opposed to osseous tissue, the periosteum has nociceptive nerve endings and it also provides nourishment by providing the blood supply to the body from the marrow. The periosteum is attached to the bone by strong collagenous fibers called Sharpeys fibres and it also provides an attachment for muscles and tendons. The periosteum that covers the surface of the bones of the skull is known as the pericranium. The word Periosteum is derived from the Greek Peri-, meaning surrounding, the Peri refers to the fact that the Periosteum is the outermost layer of long bones, surrounding other inner layers
31.
Endosteum
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In anatomy the endosteum is a thin vascular membrane of connective tissue that lines the inner surface of the bony tissue that forms the medullary cavity of long bones. This endosteal surface is usually resorbed during long periods of malnutrition, the outer surface of a bone is lined by a thin layer of connective tissue that is very similar in morphology and function to endosteum. It is called the periosteum, or the periosteal surface, during bone growth, the width of the bone increases as osteoblasts lay new bone tissue at the periosteum. To prevent the bone from becoming unnecessarily thick, osteoclasts resorb the bone from the endosteal side, anatomy photo, Musculoskeletal/bone/structure1/structure2 - Comparative Organology at University of California, Davis - Bone, structure Image at dal. ca
32.
Osteoid
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In histology, osteoid is the unmineralized, organic portion of the bone matrix that forms prior to the maturation of bone tissue. Osteoblasts begin the process of forming bone tissue by secreting the osteoid as several specific proteins, when the osteoid becomes mineralized, it and the adjacent bone cells have developed into new bone tissue. Osteoid makes up about fifty percent of volume and forty percent of bone weight. It is composed of fibers and ground substance, the predominant fiber-type is Type I collagen and comprises ninety percent of the osteoid. The ground substance is made up of chondroitin sulfate and osteocalcin. When there is insufficient nutrient minerals or osteoblast dysfunction, the osteoid does not mineralize properly, the resultant disorder is termed rickets in children and osteomalacia in adults. In some cases, secondary hyperparathyroidism can cause disturbance in mineralisation of calcium, another condition is a disturbance in primitive transformed cells of mesenchymal origin which exhibit osteoblastic differentiation and produce malignant osteoid. This results in the formation of a malignant primary bone tumor known as osteosarcoma or osteogenic sarcoma and this malignancy most often develops in adolescence during periods of rapid osteoid formation. Netter, Frank H. Musculoskeletal system, anatomy, physiology, histology image, 69_03 at the University of Oklahoma Health Sciences Center - Bone, femur Dr. Susan Otts website on osteomalacia
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Osteocyte
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An osteocyte, a star-shaped type of bone cell, is the most commonly found cell in mature bone tissue, and can live as long as the organism itself. The adult human body has about 42 billion osteocytes, osteocytes have an average half life of 25 years, they do not divide, and they are derived from osteoprogenitors, some of which differentiate into active osteoblasts. In mature bone, osteocytes and their processes reside inside spaces called lacunae and canaliculi, when osteoblasts become trapped in the matrix that they secrete, they become osteocytes. Osteocytes are networked to each other via long cytoplasmic extensions that occupy tiny canals called canaliculi and they destroy bone through a rapid, transient mechanism called osteocytic osteolysis. Hydroxyapatite, calcium carbonate and calcium phosphate is deposited around the cell, osteocytes have a stellate shape, approximately 7 micrometers deep and wide by 15 micrometers in length. The cell body varies in size from 5-20 micrometers in diameter and contain 40-60 cell processes per cell, a mature osteocyte contains a single nucleus that is located toward the vascular side and has one or two nucleoli and a membrane. The cell also exhibits a reduced size endoplasmic reticulum, Golgi apparatus and mitochondria, osteocytes form an extensive connecting syncitial network via small cytoplasmic/dendritic processes in canaliculi. During bone formation, an osteoblast is left behind and buried in the matrix as an osteoid osteocyte. 10-20% of osteoblasts differentiate into osteocytes and those osteoblasts on the bone surface that are destined for burial as osteocytes slow down matrix production, and are buried by neighboring osteoblasts that continue to produce matrix actively. Palumbo et al. distinguish three types from osteoblast to mature osteocyte, type I preosteocyte, type II preosteocyte. The embedded osteoid-osteocyte must do two functions simultaneously, regulate mineralization and form connective dendritic processes, which requires cleavage of collagen, as the osteoblast transitions to an osteocyte, alkaline phosphatase is reduced, and casein kinase II is elevated, as is osteocalcin. Osteocytes appear to be enriched in proteins that are resistant to hypoxia, oxygen tension may regulate the differentiation of osteoblasts into osteocytes, and osteocyte hypoxia may play a role in disuse-mediated bone resorption. They are the most common type in bone. Most of the activities that play an important role in bone function are present in the mature osteocyte. Osteocytes contain glutamate transporters that produce growth factors after bone fracture. When osteocytes were experimentally destroyed, the bones showed a significant increase in bone resorption, decreased bone formation, trabecular bone loss, osteocytes generate an inhibitory signal that is passed through their cell processes to osteoblasts for recruitment to enable bone formation. The osteocyte is an important regulator of bone mass and a key regulator of phosphate metabolism. Osteocytes synthesize sclerostin, a protein that inhibits bone formation by binding to LRP5/LRP6 coreceptors
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Blood vessel
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The blood vessels are the part of the circulatory system that transports blood throughout the human body. The word vascular, meaning relating to the vessels, is derived from the Latin vas. A few structures do not contain blood vessels and are labeled, tunica media, circularly arranged elastic fiber, connective tissue, polysaccharide substances, the second and third layer are separated by another thick elastic band called external elastic lamina. The tunica media may be rich in smooth muscle, which controls the caliber of the vessel. Veins dont have the external elastic lamina, but only an internal one, tunica adventitia, entirely made of connective tissue. It also contains nerves that supply the vessel as well as nutrient capillaries in the blood vessels. Capillaries consist of more than a layer of endothelium and occasional connective tissue. When blood vessels connect to form a region of diffuse vascular supply it is called an anastomosis, anastomoses provide critical alternative routes for blood to flow in case of blockages. There is a layer of muscle surrounding the arteries and the veins which help contract and this creates enough pressure for blood to be pumped around the body. Blood vessels are part of the system, together with the heart. They are roughly grouped as arterial and venous, determined by whether the blood in it is flowing away from or toward the heart. The term arterial blood is used to indicate blood high in oxygen. This is because they are carrying the blood to and from the lungs, respectively, blood vessels do not actively engage in the transport of blood, but arteries—and veins to a degree—can regulate their inner diameter by contraction of the muscular layer. This changes the flow to downstream organs, and is determined by the autonomic nervous system. Vasodilation and vasoconstriction are also used antagonistically as methods of thermoregulation, oxygen is the most critical nutrient carried by the blood. In all arteries apart from the artery, hemoglobin is highly saturated with oxygen. In all veins apart from the vein, the hemoglobin is desaturated at about 75%. The blood pressure in blood vessels is traditionally expressed in millimetres of mercury, in the arterial system, this is usually around 120 mmHg systolic and 80 mmHg diastolic
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Endochondral ossification
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Endochondral ossification is one of the two essential processes during fetal development of the mammalian skeletal system by which bone tissue is created. Unlike intramembranous ossification, which is the process by which bone tissue is created. Endochondral ossification is also a process during the rudimentary formation of long bones, the growth of the length of long bones. The cartilage model will grow in length by continuous cell division of chondrocytes, the first site of ossification occurs in the primary center of ossification, which is in the middle of diaphysis. Then, Formation of periosteum The perichondrium becomes the periosteum, the periosteum contains a layer of undifferentiated cells which later become osteoblasts. Formation of bone collar The osteoblasts secrete osteoid against the shaft of the cartilage model and this serves as support for the new bone. Calcification of matrix Chondrocytes in the center of ossification begin to grow. They stop secreting collagen and other proteoglycans and begin secreting alkaline phosphatase, osteoclasts, formed from macrophages, break down spongy bone to form the medullary cavity. About the time of birth in mammals, an ossification center appears in each end of long bones. Periosteal buds carry mesenchyme and blood vessels in and the process is similar to that occurring in a primary ossification center, growth continues until the individual is about 20 years old or until the cartilage in the plate is replaced by bone. The point of union of the primary and secondary ossification centers is called the epiphyseal line, the growth in diameter of bones around the diaphysis occurs by deposition of bone beneath the periosteum. Osteoclasts in the interior cavity continue to resorb bone until its thickness is achieved, at which point the rate of formation on the outside. During endochondral ossification, five distinct zones can be seen at the light-microscope level, during fracture healing, cartilage is often formed and is called callus. This cartilage ultimately develops into new bone tissue through the process of endochondral ossification
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Intramembranous ossification
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Intramembranous ossification is one of the two essential processes during fetal development of the gnathostome skeletal system by which rudimentary bone tissue is created. Intramembranous ossification is also a process during the natural healing of bone fractures. Unlike endochondral ossification, which is the process by which bone tissue is created during fetal development. Mesenchymal stem cells within mesenchyme or the medullary cavity of a bone fracture initiate the process of intramembranous ossification, a mesenchymal stem cell, or MSC, is an unspecialized cell which can develop into an osteoblast. Furthermore, the stem cells are widely dispersed within an extracellular matrix that is devoid of every type of collagen. The process of intramembranous ossification starts when a group of adjacent MSCs begin to replicate and form a small, dense cluster of cells. Once a nidus has been formed the MSCs within it stop replicating, eventually, all of the cells within the nidus develop into, and display the morphologic characteristics of, an osteoprogenitor cell. Eventually, all of the cells within the nidus develop into, and display the characteristics of. Then the osteoblasts create a matrix containing Type-I collagen fibrils. The osteoblasts, while lining the periphery of the nodule, continue to form osteoid in the center of the nidus, some of the osteoblasts become incorporated within the osteoid to become osteocytes. At this point, the osteoid becomes mineralized resulting in a nidus consisting of mineralized osteoid that contains osteocytes and is lined by active osteoblasts, the nidus, that began as a diffuse collection of MSCs, has become rudimentary bone tissue. The first step in the process is the formation of bone spicules which eventually fuse with each other, the periosteum is formed and bone growth continues at the surface of trabeculae. Much like spicules, the growth of trabeculae result in interconnection. Eventually, woven bone is replaced by lamellar bone, embryologic mesenchymal cells condense into layers of vascularized primitive connective tissue. Certain mesenchymal cells group together, usually near or around blood vessels and these aggregates of bony matrix are called bone spicules. Separate mesenchymal cells differentiate into osteoblasts, which line up along the surface of the spicule and secrete more osteoid, as the spicules continue to grow, they fuse with adjacent spicules and this results in the formation of trabeculae. When osteoblasts become trapped in the matrix they secrete, they differentiate into osteocytes, osteoblasts continue to line up on the surface which increases the size. As growth continues, trabeculae become interconnected and woven bone is formed, the term primary spongiosa is also used to refer to the initial trabecular network
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Cartilage
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It is not as hard and rigid as bone, but it is stiffer and less flexible than muscle. Because of its rigidity, cartilage often serves the purpose of holding tubes open in the body, cartilage is classified in three types, elastic cartilage, hyaline cartilage and fibrocartilage, which differ in relative amounts of collagen and proteoglycan. Cartilage does not contain blood vessels or nerves, nutrition is supplied to the chondrocytes by diffusion. The compression of the cartilage or flexion of the elastic cartilage generates fluid flow. Compared to other tissues, cartilage has a very slow turnover of its extracellular matrix. In embryogenesis, the system is derived from the mesoderm germ layer. Following the initial chondrification that occurs during embryogenesis, cartilage growth consists mostly of the maturing of immature cartilage to a mature state. The division of cells within cartilage occurs very slowly, and thus growth in cartilage is not based on an increase in size or mass of the cartilage itself. The articular cartilage function is dependent on the composition of the extracellular matrix. The ECM consists mainly of proteoglycan and collagens, the main proteoglycan in cartilage is aggrecan, which, as its name suggests, forms large aggregates with hyaluronan. These aggregates are negatively charged and hold water in the tissue, the collagen, mostly collagen type II, constrains the proteoglycans. The ECM responds to tensile and compressive forces that are experienced by the cartilage, cartilage growth thus refers to the matrix deposition, but can also refer to both the growth and remodeling of the extracellular matrix. Due to the stress on the patellofemoral joint during resisted knee flexion. The mechanical properties of articular cartilage in load bearing joints such as knee and hip have been studied extensively at macro, micro and these mechanical properties include the response of cartilage in frictional, compressive, shear and tensile loading. Cartilage is resilient and displays viscoelastic properties, lubricin, a glycoprotein abundant in cartilage and synovial fluid, plays a major role in bio-lubrication and wear protection of cartilage. Cartilage has limited capabilities, Because chondrocytes are bound in lacunae. Therefore, cartilage damage is difficult to heal, also, because hyaline cartilage does not have a blood supply, the deposition of new matrix is slow. Damaged hyaline cartilage is replaced by fibrocartilage scar tissue
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Chondrocyte
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Chondrocytes are the only cells found in healthy cartilage. They produce and maintain the cartilaginous matrix, which consists mainly of collagen and these chondrogenic cells differentiate into so-called chondroblasts, which then synthesize the cartilage extra cellular matrix, consisting of a ground substance and fibers. The chondroblast is now a mature chondrocyte that is inactive but can still secrete and degrade the matrix. BMP4 and FGF2 have been shown to increase chondrocyte differentiation. Chondrocytes undergo terminal differentiation when they become hypertrophic, which happens during endochondral ossification and this last stage is characterized by major phenotypic changes in the cell. Endochondral ossification Intramembranous ossification Dominici M, Hofmann T, Horwitz E. Bone marrow mesenchymal cells, biological properties, bianco P, Riminucci M, Gronthos S, Robey P. Bone marrow stromal cells, nature, biology, and potential applications. Histology image, 03317loa – Histology Learning System at Boston University Chondrocytes at the US National Library of Medicine Medical Subject Headings Stem cell information
