Иван Гайворонский - Anatomy of bone system. The manual for medical students / Анатомия костной системы. Учебное пособие для медицинских вузов

The bones, together with their joints, form the skeleton of the human body. It serves as a place for start and attachment of muscles, provides protection of visceral organs and also carries out the formbuilding and some other major functions.

Bone, os , is an organ, which is a component of the musculoskeletal system. It hаs a typical form and structure, specific architectonics of vessels and nerves, it is constructed mainly from osseous tissue covered with periosteum on the outside; periosteum containing inside bone marrow, medulla osseum .

Each bone has a certain shape, size and location in the human body. The conditions of bone development and functional loads which bones are subjected to in ontogenesis influence the morphogenesis of bones. Each bone has a certain number of blood supply sources (arteries), which have specific extra- and intraorganic architectonics. Nervous structures of bones also have such features.

The bone is coated with periosteum on the outside, except the surfaces and places where articular cartilages are locted, and where muscles, tendons and ligaments are attached to the bone. The periosteum separates the bone from its surrounding tissues. It is a thin sheath of dense connective tissue which contains blood and lymphatic vessels and nerves. The nerves penetrate into the bone tissue from the periosteum.

The periosteum, periosteum , plays a major role in bone growth at thickness and in its nutrition. The osseous tissue is formed in the inner osteogenic layer of the periosteum. A bone lacking periosteum becomes inviable and necrotizes. The periosteum has a rich nerve supply, therefore it is very sensitive. During surgical operations, doctors try to maximally preserve the periosteum because of its very important role in reparative processes.

Almost all bones (except for most of the skull bones) have articular surfaces for junction with other bones. The articular surfaces are covered not with periosteum, but with articular cartilage, cartilago articularis. The articular cartilage has a specific, nonuniform structure: its superficial layer resembles a hyaline cartilage, the deep layer is fibrous.

The majority of bones have bone marrow inside – in spaces between lamellae of the spongy bone or in the medullary cavity, cavitas medullaris . The medullary cavity is covered inside with a specific sheath which is termed endosteum – endosteum . The endosteum, as well as the periosteum, plays a great role in metabolic processes in bones.

Bones of fetuses and newborns contain only red (haematogenic) bone marrow, medulla ossea rubra . It is a homogenous red color mass, rich in reticulate tissue, blood corpuscles and blood vessels. The total amount of red bone marrow is about 1500 cm 3. In an adult, red bone marrow is partially substituted with yellow bone marrow , medulla osseum flava , which is mainly composed of adipose cells. Red bone marrow is substituted with yellow bone marrow only within medullar cavities.

It should be noted that there is no comprehensive classification of bones so far. For this purpose, various criteria are used in most of manuals on anatomy. At the same time, the principles of development and external structure features are often missed. Such feature as the structure of bones has an important clinical value. It determines the level of bone durability and specifications for treatment of injuries. In terms of phylogenesis, taking into consideration the existence of acranial and cranial organisms during the evolution, it is appropriate to divide bones into two groups: 1) bones of trunk and limbs; 2) skull bones. These bones differ from each other not only in their development but also in their structure.

According to the form and structure, four types of trunk and limb bones are distinguished: tubular, flat, volumetric and mixed bones.

Tubular bones have a cavity inside. They may be divided into long (humeral, forearm bones, femoral, leg bones, clavicle) and short (carpals, metatarsals, phalanges) bones.

In long tubular bones, one size prevails over other sizes. The middle part – diaphysis, diaphysis , (or body, corpus ) of such bone has a cylindrical or triangular shape and consists of compact tissue, substantia compacta . Within the diaphysis, the medullary cavity is located. The bone ends – epiphyses, epiphyses , – are somewhat thickened. Their surfaces intended for joining with adjacent bones are covered with articular cartilage. On the inside, the epiphysises consist of spongy bone – substantia spongiosa , and on the outside there is a thin layer of compact bone – substantia compacta . Long tubular bones form the proximal and middle parts of the limb skeleton and play the role of leverages actuated by muscles. Short tubular bones form the distal parts of the limb skeleton and also consist of the middle part – the corpus and two ends called basis and caput.

Flat bones mainly consist of homogenous mass of spongy bone covered outside with a thin layer of compact bone. In flat bones, two sizes (width and length) prevail over 1.3. thickness. Such bones form the walls of cavities enclosing important organs, or represent extensive surfaces for attachment of muscles. Here belong the pelvic bones, sternum, scapulae and ribs.

Volumetric bones have the same structure, as the flat bones, i.e. they consist of a thin layer of compact bone outside and spongy bone inside. By shape, they resemble a cube with all dimensions roughly the same. Such bones are the carpal and tarsal bones. These bones are situated on the border between the middle and distal parts of the limbs, where not only high durability, but also high mobility is necessary.

Mixed bones are specific and complicated in shape. In their composition there are structural elements of volumetric and flat bones (vertebrae, sacrum, coccyx). Spongy tissue is contained in the bodies of these bones, and their other parts are mainly formed of compact bone. Such bones possess specific durability at continious loads.

Skull bonesare classified by their location, development and structure.

According to location, they are divided into neurocranium bones and viscerocranium bones. According to development : into primary (endesmal), secondary (enchondral) and also mixed bones. The bones of the calvaria and viscerocranium are primary; the bones of the skull base are secondary; the occipital, sphenoidal and temporal bones are mixed; for example, the pyramid of the temporal bone and its mastoid part are secondary, but the squamous and tympanic parts of this bone are primary.

The skull bones have a very complicated external shape, thus it is appropriate to take their structure into consideration. According to the structure, it is possible to distinguish three types of the skull bones: 1) bones having diploё in their composition – diploic bones (parietal, occipital, frontal bones, mandible); 2) bones containing air cavities – pneumatized bones (temporal, sphenoid, ethmoid, frontal bones and maxilla); 3) bones built mainly from compact tissue – compact bones (lacrimal, zygomatic, palatine, nasal bones, inferior nasal concha, vomer, hyoid bone)The diploic substance is like spongy tissue, but its spaces between the osteal trabeculae are significantly smaller in diameter and have rounded shape.

The internal structure of bones essentially differs in a fetus and in a newborn child. Therefore two types of osseous tissue are distinguished – reticulofibrous and lamellar. The reticulofibrous bone tissue is the basis of the embrional human skeleton. Its bony matrix is not arranged structurally, the bundles of collagen fibers are located in different directions, and they are directly connected with connective tissue surrounding the bone.