Haversian systems

Single Haversian systems differ significantly in calcium-phosphorus ratio. 

Most bones of the human skeleton are composed of two structurally distinct types of tissue compact (dense) and trabecular (cancellous, spongy) bone. Both types contain the same elements cells ( osteocytes) embedded in a mineralised matrix and connected by small canals ( canaliculi ). In compact bone, which makes up 85% of the skeleton, these components form elongated cylinders of concentric lamellae surrounding a central blood vessel (called osteon or Haversian system). Cancellous bone, in contrast, forms thin,... 

There are two types of bone (a) compact or cortical bone and (b) trabecular or cancellous bone. Cortical bone is found principally in the shafts (diaphyses) of long bones. It consists of a number of irregularly spaced overlapping cylindrical units termed Haversian systems. Each consists of a central Haversian canal surrounded by concentric lamellae of bony tissue. Trabecular bone is found principally at the ends of long bones and flat bones. It is composed of a meshwork of trabeculae within which... 

A section through a human toe bone (fifth metatarsal, amputated by Roger Gundle who took the pictures in 1.3) is shown in Fig. 9.18. The circular patterns relate to the Haversian system responsible for blood flow in the bone. The regions around the holes are osteons. The osteons appear with different contrast in this picture. As always this relates to different mechanical properties. In this case it enables you to distinguish the different ages of osteons, because the variation in contrast is related to different degrees of mineralization. 

The reason to extend the experiments to tooth material was the idea that the matrix would have a less porous structure compared to human haversian bone and be less exposed to diagenetic alteration. While the porosity in human bone is mainly determined by a complicated network between the Haversian system and the Volk-mann canals that are perpendicular to it, especially enamel is a far denser material than human bone and its organic content is significantly less (2% of organic material only). But in contrast to the enamel, dentine has a similar composition of the organic and the inorganic matrix compared to bone, and it has a high microporosity due to nerve canals that start from the pulpa and stop close to the enamel-dentine junction (edj). However, these nerve canals have a smaller diameter than a haversian pore (70 pm) and the canals are orientated parallel and are not connected with each other. So a fluorine ion cannot percolate from one pore to another, as it is the case in a human bone, but it has to overcome the distance from one canal to the next one by diffusion. So the permeability is low and this results in a smaller diffusion rate D. 

Compact bone like long bones, most abundant among archaeological bone remains, shows basically two different parts a central one called diaphysis, mainly composed of compact bone, and two extremities called epiphysis which are more porous. It contains a fundamental substance - a mixture of the organic and mineral phase - and cells that remodel continuously the bone material as well as the so-called Haversian systems containing channels that provide the nutrition to the bone cells as they accommodate blood vessels and nerves. The Haversian channels exhibit diameters between 10 and 70 pm [26], The periosteum closes the bone at its outside and the medullar cavity at the inside accommodating the bone marrow [40],... 

Osteoclasts are multinucleated cells found on the endosteal surface of bone, in Haversian systems and periosteal surfaces. PTH activates osteoclasts (indirectly via osteoblasts that possess PTH receptors). Calcitonin is a potent inhibitor of osteoclast activity. Local cytokine factors, including interleukin-1 (IL-1), tumour-necrosis factor (TNF), TGF- 0 and interferon-y (INF-y), are important regulators. Osteoclast resorption of bone releases collagen peptides, pyridinoline cross-links and calcium from the bone matrix, through the action of lysosomal enzymes (collagenases and cathepsins). The collagen breakdown products in serum and urine (e.g. hydroxyproline) can be used as biochemical markers. 

Cortical bone, also called compact or lamellar bone, is remodelled from woven bone by means of vascular channels that invade the embryonic bone from its periosteal and endosteal surfaces. It forms the internal and external tables of flat bones and the external surfaces of long bones. The primary structural unit is an osteon, also known as a Haversian system, a cylindrical shaped lamellar bone surrounding longitudinally oriented vascular channels (the Haversian canals). Horizontally oriented canals (Volkmann canals) connect adjacent osteons. The mechanical strength of cortical bone results from the tight packing of the osteons. 

Figure 3 Structures of mammal bone (a) Haversian systems and osteons, (b) Pl)rwood-like structure with twisted lamella, (c) Lamellar bone showing the different orientations of fibers in successive lamella, (d) Minerahzed collagen fibers...

Figure 23 Mammalian bone at different levels of resolution (a) Collagen fibril with associated mineral, (b) Woven bone (random collagen distribution), (c) Lamellar bone showing separate lamellae with collagen organized in domains with preferred orientation alternating in adjacent lamellae, (d) Woven bone with blood channels shown as dark spots, woven bone stippled, (e) Primary lamellar bone orientation indicated by dashes, (f) Haversian bone, a collection of haversian systems are shown as a longitudinal structure. Each system has concentric lamellae around a central blood channel. Darkened area represents an empty (eroded) portion of the section which will be reconstituted with new bone, (g) Alternation of woven and lamellar bone, (h) Various orientations of heavily mineralized (cortical, or compact) bone, (i) Trabecular, or cancellous, bone (Wainwright et aL, 1976) (reproduced by permission of Hodder Arnold from Mechanical Design in Organisms, 1976).

Haversian system, 530 HDl-s [high-density lipoproteins), 312,332 altaied by diel, 363 apo A-1,336,339-340 apo A-ll, 336 apo C-U, 337 apo E, 337-33S in bloodstream, 343-344 cardiovascular disease and, 370 cyding of cholestErol and, 339 343 Maditeiranean diet 364-365 Heart attack, 360 Heat stroke. 699 Hedgehog (protein), 326 Helicobacter pylori, 87 Helper phage, 951 Heme... 

Osteoblastic activity initiates the process of mineralization. Unmineralized bone is known as osteoid. Minerals are deposited in specific holes that are located between collagen fibrils produced by the osteoblast. The architecture of the fibrils is designed to withstand external stress. Mineralization begins shortly after the formation of the secreted matrix. This process occurs in osteons, also referred to as Haversian systems, and is completed in several weeks. Blood vessels penetrate bond through channels known as Haversian canals. 

Haversian bone Also called osteonic. The form of bone found in adult humans and mature mammals, consisting mainly of concentric lamellar structures, surrounding a central canal called the haversian canal, plus lamellar remnants of older haversian systems (osteons) called interstitial lamellae. 

Bones offer a classical example of hierarchically organized architecture from nano-scale, where the collagen/hydroxyapatite nanocomposite is organized in fibrils, and fibrils are then laid in different textures, to the microscopic one where a regular organization of cells (osteocytes) and matrix around blood vessels constitutes the basic structure of compact bone (the so-called Haversian system or osteon). 

Compact bone is found in the cylindrical shells of most long bones in vertebrates. It often contains osteons which consist of lamellae that are cylindrically wrapped around a central blood vessel (Haversian system or secondary osteon). These secondary osteons form during bone remodeling. Studies have shown that the orientation of the collagen fibrils within individual lamellas is a function of external stresses on the bone and adapted to the specific function." " ... 

Haversian canals Narrow tubes within compact bone containing blood vessels and nerves. They generally run parallel to the bone surface. Each canal surrounded by a series of rings of bone (lamellae) is known as a Haversian system. Haversian systems are joined to each other by bone material. They are named after Clopton Havers (1650-1702). 

The cement line round Haversian systems (secondary osteons) contains less calcium and phosphorus, and more sulphur than nearby parts of bone. This may indicate the presence of more sulphated mucosubstances, making the cement line viscous [9]. 

Microstructure 10-500 mm Haversian system, osteons, single trabeculae... 

At the microstructural level, the Haversian system or osteon is the repeated structural unit of compact bone, which acts as a weight-bearing pillar. In contrast, spongy bones are made of an interconnecting framework of trabeculae. There are three types of cellular structures in the trabeculae, (1) plate/platelike, (2) plate/ barlike, and (3) bar/barlike. The bone tissue primarily consists of collagen nanofibers and bone minerals crystals (particularly HAp) at the nanostructural level. 

In adult humans, these lamellae form tube-shaped structures, called osteons or Haversian systems. A single osteon has a diameter of about 200 pm and a length of a few millimetres or centimetres. In long bones, like limb bones, they are parallel to the bone axis. In the centre of each osteon, there is a blood vessel that supplies the cells within the bone with nutrients. 

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