Haversian

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,... 

The properties described above have important consequences for the way in which these skeletal tissues are subsequently preserved, and hence their usefulness or otherwise as recorders of dietary signals. Several points from the discussion above are relevant here. It is useful to ask what are the most important mechanisms or routes for change in buried bones and teeth One could divide these processes into those with simple addition of new non-apatitic material (various minerals such as pyrites, silicates and simple carbonates) in pores and spaces (Hassan and Ortner 1977), and those related to change within the apatite crystals, usually in the form of recrystallization and crystal growth. The first kind of process has severe implications for alteration of bone and dentine, partly because they are porous materials with high surface area initially and because the approximately 20-30% by volume occupied by collagen is subsequently lost by hydrolysis and/or consumption by bacteria and the void filled by new minerals. Enamel is much denser and contains no pores or Haversian canals and there is very, little organic material to lose and replace with extraneous material. Cracks are the only interstices available for deposition of material. 

Figure 7.2. Microradiograpli of Burial 30, periosteal surface at top. Snake Hill bone microradiographs show radiolucent cavities around Haversian canals surrounded by hypermineralized rims, which Baud and Lacotte (1984) argue are characteristic of bacterial colonization.

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... 

In attempting to reconcile these findings, it should be pointed out that rats may not be appropriate models for the study of calcium metabolism in humans. Unlike humans, the rat does not undergo epiphyseal plate closure and does not have a significant haversian remodeling sequence (21) Furthermore, rats excrete only l-270 of their calcium intake in their urine whereas humans excrete approximately 20-30% or more. This fact is especially significant, since most of the known effects of phosphates on calcium retention in humans are effected by alterations in urinary calcium. 

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. 

Of the many structural types of bone, only the lamellar , plexiform bone in the diaphysis compacta of long bones is of importance for fluorine dating, because only this material is homogeneous enough for the development of a dominant profile that starts from the periosteal surface. Especially in haversian bone (e.g. human bone), profiles may be forming at a number of points in the bone and in a number of different directions, stemming from surfaces within the bone (e.g. Haversian canals) or from the medullary cavity. These profiles often hide the true... 

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. 

Structure of living bone plexiform, haversian, osteoporotic ... 

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],... 

Endothelium Connective tissue (haversian canal) Blood supply... 

Figure 3.19. Structure of compact bone. Compact bone consists of an outer layer of mineralized lamellae that are wrapped around the shaft of the bone. Beneath the outer layer are concentric rings of mineralized collagenous lamellae. Each concentric unit is termed an osteon and has a vessel running through its center (haversian canal).

Haversian canal The central opening of compact bone contains nerves and blood vessels. 

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. 

As we move from the periphery of the bone to the center, the stmcture becomes anisotropic and tubular. This structure, called osteons , consists of tubes of approximately 200-/rm diameter with a central canal called the Haversian canal to house blood vessels. Lamellae are arranged concentric to this canal and parallel to the... 

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...

Bone is the most common simulant of ivory. In smaU items or as inlay it can be difBcult to tell which material has been used as both bone and ivory appear much the same colour and have many similar properties. However, bone contains none of the structural patterns of ivories, for example the engine turned pattern of elephant and mammoth ivory or the tapioca pattern of the secondary dentine in walrus ivory. Instead it has the black dots or lines of the Haversian canals (nutrient bearing canals) (Figs 4.2 and 4.3). 

Bone is the hard material that forms the skeleton of most vertebrate animals. It consists of a network of collagen fibres impregnated with mineral salts, mostly calcium phosphate. Bone varies in strength and can be as tough as reinforced concrete. Most bones are hollow, the cavity being filled with soft, spongy material. The solid part is interspersed by Haversian canals, which are tiny canals carrying blood, nerves and lymphatics. 

F ure 4.1 Small box, showing insened base and Haversian canals. 

F ure 4.2 Longitudmal section of bone bracelet, showing Haversian canals (magnified). 

Figure 4.3 Detail of cross ection of bone bracelet, diowing Haversian canals.

On a polished, smooth surface of bone, the Haversian canals ccm be seen. In cross-section these appear as tiny dark dots, while in longitudinal section they show up as straight, thin, dark lines. These ate unique to bone (Figs 4.2 and 4.3). 

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