Haversian canals

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... 

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... 

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. 

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... 

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). 

The Haversian canals will still be visible on a hollow or concave piece of bone. 

Swirls of colour, or the complete lack of structure or Haversian canals, indicate plastic or reconstituted material. 

Under magnification the polished surface of ander shows a more mottled appearance with lots of tiny, dark spots, and it lacks the strai t, dark lines of the Haversian canals in bone. In cross-secdon ander lacks the small, black dots of these canals. 

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. 

Figure 3.2 Schematics of the hierarchical architecture of cortical bone. (A) Longitudinal section of femur. (B) Enlarged cross section of cortical bone showing cylindrical osteons. (C) Enlargement of an osteon showing the central Haversian canal with a blood vessel, the concentric lamellae and the radial canaliculi (see also J). A more detailed view of an osteon is shown in the inset in the bottom right. (D) Collagen fibre composed of hundreds of fibrils. The evenly spaced dark spirals are...

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. 

The outer compact bone is formed as concentric layers (lamellae) that surround small holes ( Haversian canals) see illustration. The inner spongy bone is chemically similar but forms a network of bony bars. The spaces between the bars may contain bone marrow or (in birds) air for lightness. See also CARTILAGE BONE MEMBRANE BONE periosteum. 

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). 

FIGURE 15.1 Scanning acoustic microscopy image of conical bone from a human femur. Note the circular arrangement of the lamellae around the central Haversian canal. 

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