Hyaline cartilage
Hyaline cartilage is the glass-like but translucent cartilage found on many joint surfaces. It is most found in the ribs, nose and trachea. Hyaline cartilage is pearl-grey in color, with a firm consistency and has a considerable amount of collagen, it contains no nerves or blood vessels, its structure is simple. Hyaline cartilage is covered externally by a fibrous membrane known as the perichondrium or, when it's along articulating surfaces, the synovial membrane; this membrane contains vessels. Hyaline cartilage matrix is made of type II collagen and chondroitin sulphate, both of which are found in elastic cartilage. Hyaline cartilage exists on the ventral ends of ribs, in the larynx and bronchi, on the articulating surfaces of bones, it gives the structures a pliable form. The presence of collagen fibres makes such structures and joints strong, but with limited mobility and flexibility. Hyaline cartilage is the most prevalent type of cartilage, it forms the temporary embryonic skeleton, replaced by bone, the skeleton of elasmobranch fish.
When a thin slice of hyaline cartilage is examined under the microscope, it is shown to consist of cells of a rounded or bluntly angular form, lying in groups of two or more in a granular, or homogeneous matrix. When arranged in groups of two or more, the chondrocytes have rounded, but straight outlines, they consist of translucent protoplasm with fine interlacing filaments and minute granules are sometimes present. Embedded in this are one or two round nuclei, having the usual intranuclear network; the cells are contained in cavities in the matrix, called cartilage lacunæ. These cavities are artificial gaps formed from the shrinking of the cells during the staining and setting of the tissue for examination; the inter-territorial space between the isogenous cell groups contains more collagen fibres, allowing it to maintain its shape while the actual cells shrink, creating the lacunae. This constitutes the so-called'capsule' of the space; each lacuna is occupied by a single cell, but during mitosis, it may contain two, four, or eight cells.
Articular cartilage is hyaline cartilage on the articular surfaces of bones, lies inside the joint cavity of synovial joints, bathed in synovial fluid produced by the synovial membrane, which lines the walls of the cavity. Though it is found in close contact with menisci and articular disks, articular cartilage is not considered a part of either of these structures, which are made of fibrocartilage; the biochemical breakdown of the articular cartilage results in osteoarthritis - the most common type of joint disease. Osteoarthritis affects over 30 million individuals in the United States alone, is the leading cause of chronic disability amongst the elderly. Cartilage Hyaline Articular cartilage injuries Articular cartilage damage Articular cartilage repair UIUC Histology Subject 331 Histology image: 03301lba – Histology Learning System at Boston University
Cell nucleus
In cell biology, the nucleus is a membrane-bound organelle found in eukaryotic cells. Eukaryotes have a single nucleus, but a few cell types, such as mammalian red blood cells, have no nuclei, a few others including osteoclasts have many; the cell nucleus contains all of the cell's genome, except for a small fraction of mitochondrial DNA, organized as multiple long linear DNA molecules in a complex with a large variety of proteins, such as histones, to form chromosomes. The genes within these chromosomes 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, the control center of the cell. The main structures making up the nucleus are the nuclear envelope, a double membrane that encloses the entire organelle and isolates its contents from the cellular cytoplasm, the nuclear matrix, a network within the nucleus that adds mechanical support, much like the cytoskeleton, which supports the cell as a whole.
Because the nuclear envelope 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 and ions. Movement of large molecules such as proteins and RNA through the pores is required for both gene expression and the maintenance of chromosomes. Although the interior of the nucleus does not contain any membrane-bound subcompartments, its contents are not uniform, a number of nuclear bodies exist, made up of unique proteins, RNA molecules, particular parts of the chromosomes; the best-known of these is the nucleolus, 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 the oldest preserved drawing dates back to the early microscopist Antonie van Leeuwenhoek.
He observed the nucleus, in the red blood cells of salmon. Unlike mammalian red blood cells, those of other vertebrates still contain nuclei; the nucleus was 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 the microscope when he observed an opaque area, which he called the "areola" or "nucleus", in the cells of the flower's outer layer, he did not suggest a potential function. In 1838, Matthias Schleiden proposed that the nucleus plays a role in generating cells, thus he introduced the name "cytoblast", he believed that he had observed new cells assembling around "cytoblasts". Franz Meyen was a strong opponent of this view, having described cells multiplying by division and believing that many cells would have no nuclei; the idea that cells can be generated de novo, by the "cytoblast" or otherwise, contradicted work by Robert Remak and Rudolf Virchow who decisively propagated the new paradigm that cells are generated by cells.
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. This was in contradiction to Ernst Haeckel's theory that the complete phylogeny of a species would be repeated during embryonic development, including generation of the first nucleated cell from a "monerula", a structureless mass of primordial mucus. Therefore, the necessity of the sperm nucleus for fertilization was discussed for quite some time. However, Hertwig confirmed his observation in other animal groups, including amphibians and molluscs. Eduard Strasburger produced the same results for plants in 1884; this paved the way to assign the nucleus an important role in heredity. In 1873, August Weismann postulated the equivalence of the maternal and paternal germ cells for heredity; the function of the nucleus as carrier of genetic information became clear only after mitosis was discovered and the Mendelian rules were rediscovered at the beginning of the 20th century.
The nucleus is the largest organelle in animal cells. In mammalian cells, the average diameter of the nucleus is 6 micrometres, which occupies about 10% of the total cell volume; the contents of the nucleus are held in the nucleoplasm similar to the cytoplasm in the rest of the cell. The fluid component of this is termed the nucleosol, similar to the cytosol in the cytoplasm. In most types of granulocyte, a white blood cell, the nucleus is lobated and can be bi-lobed, tri-lobed or multi-lobed; the nuclear envelope, otherwise known as nuclear membrane, consists of two cellular membranes, an inner and an outer membrane, arranged parallel to one another and separated by 10 to 50 nanometres. The nuclear envelope encloses the nucleus and separates the cell's genetic material from the surrounding cytoplasm, serving as a barrier to prevent macromolecules from diffusing between the nucleoplasm and the cytoplasm; the outer nuclear membrane is continuous with the membrane of the rough endoplasmic reticulum, is studded with ribosomes.
The space between the membranes is called the perinuclear space and is continuous with the RER lumen. Nuclear pores, which provide aqueous cha
Anatomical terms of microanatomy
Anatomical terminology is used to describe microanatomical structures. This helps describe the structure and position of an object, minimises ambiguity. An internationally accepted lexicon is Terminologia Histologica. Epithelial cells line body surfaces, are described according to their shape, with three principal shapes: squamous and cuboidal. Squamous epithelium has cells. Cuboidal epithelium has cells whose height and width are the same. Columnar epithelium has cells taller. Endothelium refers to cells that line the interior surface of blood vessels and lymphatic vessels, forming an interface between circulating blood or lymph in the lumen and the rest of the vessel wall, it is a thin layer of single-layered, squamous cells called endothelial cells. Endothelial cells in direct contact with blood are called vascular endothelial cells, whereas those in direct contact with lymph are known as lymphatic endothelial cells. Epithelium can be arranged in a single layer of cells described as "simple", or more than one layer, described as "stratified".
By layer, epithelium is classed as either simple epithelium, only one cell thick or stratified epithelium as stratified squamous epithelium, stratified cuboidal epithelium, stratified columnar epithelium that are two or more cells thick, both types of layering can be made up of any of the cell shapes. However, when taller simple columnar epithelial cells are viewed in cross section showing several nuclei appearing at different heights, they can be confused with stratified epithelia; this kind of epithelium is therefore described as pseudostratified columnar epithelium. Transitional epithelium has cells that can change from squamous to cuboidal, depending on the amount of tension on the epithelium. A mucous membrane or mucosa is a membrane that lines various cavities in the body and covers the surface of internal organs, it consists of one or more layers of epithelial cells overlying a layer of loose connective tissue. It is of endodermal origin and is continuous with the skin at various body openings such as the eyes, inside the nose, inside the mouth, the urethral opening and the anus.
Some mucous membranes a thick protective fluid. The function of the membrane is to stop pathogens and dirt from entering the body and to prevent bodily tissues from becoming dehydrated; the submucosa consists of a dense and irregular layer of connective tissue with blood vessels and nerves branching into the mucosa and muscular layer. It contains the submucous plexus, enteric nervous plexus, situated on the inner surface of the muscular layer; the muscular layer consists of two layers of the inner and outer layer. The muscle of the inner layer is arranged in circular rings around the tract, whereas the muscle of the outer layer is arranged longitudinally; the stomach has an inner oblique muscular layer. Between the two muscle layers are the myenteric or Auerbach's plexus; this controls peristalsis. Activity is initiated by the pacemaker cells; the gut has intrinsic peristaltic activity due to its self-contained enteric nervous system. The rate can of course be modulated by the rest of the autonomic nervous system.
The layers are not longitudinal or circular, rather the layers of muscle are helical with different pitches. The inner circular is helical with a steep pitch and the outer longitudinal is helical with a much shallower pitch. Serosa / Adventitia -- these last two tissue types differ in form and function according to the part of the gastrointestinal tract they belong to; the hollow inner part of a body organ or tube is called the lumen. The side of a cell facing the lumen is called the apical surface.
Fibrocartilage callus
A fibrocartilage callus is a temporary formation of fibroblasts and chondroblasts which forms at the area of a bone fracture as the bone attempts to heal itself. The cells dissipate and become dormant, lying in the resulting extracellular matrix, the new bone; the callus is the first sign of union visible on x-rays 3 weeks after the fracture. Callus formation is slower in adults than in children, in cortical bones than in cancellous bones. Bone healing Bony+callus at the US National Library of Medicine Medical Subject Headings
Cell potency
Cell potency is a cell's ability to differentiate into other cell types. The more cell types. Potency is described as the gene activation potential within a cell, which like a continuum, begins with totipotency to designate a cell with the most differentiation potential, multipotency and unipotency. Totipotency is the ability of a single cell to divide and produce all of the differentiated cells in an organism. Spores and zygotes are examples of totipotent cells. In the spectrum of cell potency, totipotency represents the cell with the greatest differentiation potential, being able to differentiate into any embryonic cell, as well as extraembryonic cells. In contrast, pluripotent cells can only differentiate into embryonic cells, it is possible for a differentiated cell to return to a state of totipotency. This conversion to totipotency is complex, not understood and the subject of recent research. Research in 2011 has shown that cells may differentiate not into a totipotent cell, but instead into a "complex cellular variation" of totipotency.
Stem cells resembling totipotent blastomeres from 2-cell stage embryos can arise spontaneously in mouse embryonic stem cell cultures and can be induced to arise more in vitro through down-regulation of the chromatin assembly activity of CAF-1. The human development model is one. Human development begins when a sperm fertilizes an egg and the resulting fertilized egg creates a single totipotent cell, a zygote. In the first hours after fertilization, this zygote divides into identical totipotent cells, which can develop into any of the three germ layers of a human, or into cells of the placenta. After reaching a 16-cell stage, the totipotent cells of the morula differentiate into cells that will become either the blastocyst's Inner cell mass or the outer trophoblasts. Four days after fertilization and after several cycles of cell division, these totipotent cells begin to specialize; the inner cell mass, the source of embryonic stem cells, becomes pluripotent. Research on Caenorhabditis elegans suggests that multiple mechanisms including RNA regulation may play a role in maintaining totipotency at different stages of development in some species.
Work with zebrafish and mammals suggest a further interplay between miRNA and RNA-binding proteins in determining development differences. In mouse primordial germ cells, genome-wide reprogramming leading to totipotency involves erasure of epigenetic imprints. Reprogramming is facilitated by active DNA demethylation involving the DNA base excision repair enzymatic pathway; this pathway entails erasure of CpG methylation in primordial germ cells via the initial conversion of 5mC to 5-hydroxymethylcytosine, a reaction driven by high levels of the ten-eleven dioxygenase enzymes TET-1 and TET-2. In cell biology, pluripotency refers to a stem cell that has the potential to differentiate into any of the three germ layers: endoderm, mesoderm, or ectoderm. However, cell pluripotency is a continuum, ranging from the pluripotent cell that can form every cell of the embryo proper, e.g. embryonic stem cells and iPSCs, to the incompletely or pluripotent cell that can form cells of all three germ layers but that may not exhibit all the characteristics of pluripotent cells.
Induced pluripotent stem cells abbreviated as iPS cells or iPSCs, are a type of pluripotent stem cell artificially derived from a non-pluripotent cell an adult somatic cell, by inducing a "forced" expression of certain genes and transcription factors. These transcription factors play a key role in determining the state of these cells and highlights the fact that these somatic cells do preserve the same genetic information as early embryonic cells; the ability to induce cells into a pluripotent state was pioneered in 2006 using mouse fibroblasts and four transcription factors, Oct4, Sox2, Klf4 and c-Myc. This was followed in 2007 by the successful induction of human iPSCs derived from human dermal fibroblasts using methods similar to those used for the induction of mouse cells; these induced cells exhibit similar traits to those of embryonic stem cells but do not require the use of embryos. Some of the similarities between ESCs and iPSCs include pluripotency, self-renewal ability, a trait that implies that they can divide and replicate indefinitely, gene expression.
Epigenetic factors are thought to be involved in the actual reprogramming of somatic cells in order to induce pluripotency. It has been theorized that certain epigenetic factors might work to clear the original somatic epigenetic marks in order to acquire the new epigenetic marks that are part of achieving a pluripotent state. Chromatin is reorganized in iPSCs and becomes like that found in ESCs in that it is less condensed and therefore more accessible. Euchromatin modifications are common, consistent with the state of euchromatin found in ESCs. Due to their great similarity to ESCs, iPSCs have been of great interest to the medical and research community. IPSCs could have the same therapeutic implications and applications as ESCs but without the controversial use of embryos
Collagen
Collagen is the main structural protein in the extracellular space in the various connective tissues in the body. As the main component of connective tissue, it is the most abundant protein in mammals, making 25% to 35% of the whole-body protein content. Collagen consists of amino acids wound together to form triple-helices of elongated fibrils, it is found in fibrous tissues such as tendons and skin. Depending upon the degree of mineralization, collagen tissues may be rigid, compliant, or have a gradient from rigid to compliant, it is abundant in corneas, blood vessels, the gut, intervertebral discs, the dentin in teeth. 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, muscles; the fibroblast is the most common cell. Gelatin, used in food and industry, is collagen that has been, hydrolyzed. Collagen has many medical uses in treating complications of skin; the name collagen comes from the Greek κόλλα, meaning "glue", suffix -γέν, -gen, denoting "producing".
This refers to the compound's early use in the process of boiling the skin and tendons of horses and other animals to obtain glue. Over 90% of the collagen in the human body is type I. However, as of 2011, 28 types of collagen have been identified and divided into several groups according to the structure they form: Fibrillar Non-fibrillar FACIT Short chain Basement membrane Multiplexin MACIT Other The five most common types are: Type I: skin, vasculature, bone Type II: cartilage Type III: reticulate found alongside type I Type IV: forms basal lamina, the epithelium-secreted layer of the basement membrane Type V: cell surfaces and placenta The collagenous cardiac skeleton which includes the four heart valve rings, is histologically and uniquely bound to cardiac muscle; the cardiac skeleton includes the separating septa of the heart chambers – the interventricular septum and the atrioventricular 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.
The collagenous structure that divides the upper chambers of the heart from the lower chambers is an impermeable membrane that excludes both blood and electrical impulses through typical physiological means. With support from collagen, atrial fibrillation never deteriorates to ventricular fibrillation. Collagen is layered in variable densities with cardiac muscle mass; the mass, distribution and density of collagen all contribute to the compliance required to move blood back and forth. 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. Calcified points within collagen matrices show contrast in a moving display of blood and muscle, enabling methods of cardiac imaging technology to arrive at ratios stating blood in and blood out. Pathology of the collagen 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 and surgical purposes.
Both human and bovine collagen is used as dermal fillers for treatment of wrinkles and skin aging. Some points of interest are: When used cosmetically, there is a chance of allergic reactions causing prolonged redness. Most medical collagen is derived from young beef cattle from certified BSE-free animals. Most manufacturers use donor animals from either "closed herds", or from countries which have never had a reported case of BSE such as Australia and New Zealand; as the skeleton forms the structure of the body, it is vital that it maintains its strength after breaks and injuries. Collagen is used in bone grafting as it has a triple helical structure, making it a strong molecule, it is ideal for use in bones. The triple helical structure of collagen prevents it from being broken down by enzymes, it enables adhesiveness of cells and it is important for the proper assembly of the extracellular matrix. Collagen scaffolds are used in tissue regeneration, whether in thin sheets, or gels. Collagen has the correct properties for tissue regeneration such as pore structure, permeability and being stable in vivo.
Collagen scaffolds are ideal for the deposition of cells such as osteoblasts and fibroblasts, once inserted, growth is able to continue as normal in the tissue. Collagens are employed in the construction of the artificial skin substitutes used in the management of severe burns and wounds; these collagens may be derived from bovine, porcine, or human sources. Collagen is one of the body’s key natural resources and a component of skin tissu
Micrograph
A micrograph or photomicrograph is a photograph or digital image taken through a microscope or similar device to show a magnified image of an object. This is opposed to a macrograph or photomacrograph, an image, taken on a microscope but is only magnified less than 10 times. Micrography is the art of using microscopes to make photographs. A micrograph contains extensive details of microstructure. A wealth of information can be obtained from a simple micrograph like behavior of the material under different conditions, the phases found in the system, failure analysis, grain size estimation, elemental analysis and so on. Micrographs are used in all fields of microscopy. A light micrograph or photomicrograph is a micrograph prepared using an optical microscope, a process referred to as photomicroscopy. At a basic level, photomicroscopy may be performed by connecting a camera to a microscope, thereby enabling the user to take photographs at reasonably high magnification. Scientific use began in England in 1850 by Prof Richard Hill Norris FRSE for his studies of blood cells.
Roman Vishniac was a pioneer in the field of photomicroscopy, specializing in the photography of living creatures in full motion. He made major developments in light-interruption photography and color photomicroscopy. Photomicrographs may be obtained using a USB microscope attached directly to a home computer or laptop. An electron micrograph is a micrograph prepared using an electron microscope. Micrographs have micron bars, or magnification ratios, or both. Magnification is a ratio between the size of an object on its real size. Magnification can be a misleading parameter as it depends on the final size of a printed picture and therefore varies with picture size. A scale bar, or micron bar, is a line of known length displayed on a picture; the bar can be used for measurements on a picture. When the picture is resized the bar is resized making it possible to recalculate the magnification. Ideally, all pictures destined for publication/presentation should be supplied with a scale bar. All but one of the micrographs presented on this page do not have a micron bar.
The microscope has been used for scientific discovery. It has been linked to the arts since its invention in the 17th century. Early adopters of the microscope, such as Robert Hooke and Antonie van Leeuwenhoek, were excellent illustrators. After the invention of photography in the 1820s the microscope was combined with the camera to take pictures instead of relying on an artistic rendering. Since the early 1970s individuals have been using the microscope as an artistic instrument. Websites and traveling art exhibits such as the Nikon Small World and Olympus Bioscapes have featured a range of images for the sole purpose of artistic enjoyment; some collaborative groups, such as the Paper Project have incorporated microscopic imagery into tactile art pieces as well as 3D immersive rooms and dance performances. Close-up Digital microscope Macro photography Microphotograph Microscopy USB microscope Make a Micrograph – This presentation by the research department of Children's Hospital Boston shows how researchers create a three-color micrograph.
Shots with a Microscope – a basic, comprehensive guide to photomicrography Scientific photomicrographs – free scientific quality photomicrographs by Doc. RNDr. Josef Reischig, CSc. Micrographs of 18 natural fibres by the International Year of Natural Fibres 2009 Seeing Beyond the Human Eye Video produced by Off Book - Solomon C. Fuller bio Charles Krebs Microscopic Images Dennis Kunkel Microscopy Andrew Paul Leonard, APL Microscopic Cell Centered Database - Montage Nikon Small World Olympus Bioscapes Other examples
