Osteology PDF

General anatomy Osteology  GENERAL OSTEOLOGY Objectives 1. Classification of the skeleton 2. Classification of the bones 3. Structure of bone 4. Blood supply of the bone 5. Nerves of the bone 6. Chemical composition and physical properties of bone 7. Growth of bone 8. The func...

General anatomy Osteology  GENERAL OSTEOLOGY Objectives 1. Classification of the skeleton 2. Classification of the bones 3. Structure of bone 4. Blood supply of the bone 5. Nerves of the bone 6. Chemical composition and physical properties of bone 7. Growth of bone 8. The function of the skeleton: 9. Descriptive terms of the skeletal system:  Skeleton It is a term applied to the framework of hard structures (bones and cartilages) which support and protect the soft tissues of animals The term skeleton comes from a Greek word meaning “dried up”. NB: All the bones and articulations of the body make up the passive part of  1- Classification of the skeleton A) According situation of the bones: 1- The Exo-skeleton: The skeleton is situated externally and is derived from ectoderm e.g. shells of many invertebrates, scales of fishes, the shields of turtles and the feathers, hair and hoofs of the higher vertebrates. 2- The Endo-skeleton: The skeleton is embedded in the soft tissues. B) According to position of the bones: 1-The axial skeleton: It comprises the skull, vertebral column, ribs and sternum. 2-The appendicular skeleton: It includes the bones of the thoracic and pelvic limbs. 3-The splanchnic or visceral skeleton: it consists of certain bones developed in the substance of some soft organs, for examples: a. Os penis of the dog, b. Os cordis in the heart of ruminants and c. Ossa diaphragmaticus in the diaphragm of the camel. d. Entoglossal bone in the tongue of birds C) Phylogenic classification of the skeleton: 1- Membranous skeleton: as in invertebrates which have a membrane or connective tissue (no hard skeleton). 2- Cartilaginous skeleton: as in cartilaginous fishes. 3- Bony skeleton: s in the higher vertebrates which have a bony 2- Classification of the bones A- According to their situation: bones of the head, bones of the neck, bones of the trunk, bones of the limbs and bones of the tail B. According to the shape: 1. Tubular bones: Consist of compact and spongy substances forming a tube with cavity.  NB: Diaphysis is connected to epiphysis by metaphysis which contains the epiphysial plate (physis or growth plate). The epiphysial plate is a hyaline cartilage in immature bone and causes increase in length of the bone in one direction. A. Long tubular bones: Long, cylindrical, weight bearing, extend (grow) in one direction, have shaft (body or corpus or diaphysis) and two extremities (epiphysis) and have medullary cavity. e.g. femur, B. Short tubular bones: humerus. They are short (but still tubular) bones e.g. (phalanges). C. Reduced long tubular bones: They are incompletely developed long bones which extended in one direction but devoid of a medullary cavity, e.g. small metacarpal and metatarsal bones, fibula and ulna of the horse. 2. Short bones: Short, partially smooth surfaced, mainly found in joints, help in mobility, mainly spongy substances and thin layer of cortical bone. e.g. carpal bones. 3. Flat bones: Plate like, extend in two dimensions and composed of two compact layers which enclose a small amount of spongy substances. e.g. the scapula, ilium and the bones of the skull. 4. Irregular bones: Small, irregular surface mainly in midline of skeleton, have projections for muscular attachments. e.g. vertebrae. 5. Pneumatic bones: Bones containing air spaces (instead of spongy or marrow). These spaces are termed sinuses and lined with mucous membrane such as frontal and maxillary bones of the skull and some bones of the flying birds. 6. Sesamoid bones: Small bones, resemble sesame seeds, diminish friction between the tendon and bones and change the direction of tendons. the patella the navicular bone (distal sesamoid bone) and proximal sesamoid bones. 3- STRUCTURE OF BONE The bone consists of an external shell of dense compact substance (cortex) within which is the loosely arranged spongy substance. In long bone the shaft is hollowed to form the medullary cavity. 1- The compact substance Cortical substance consists of groups of lamellae (either longitudinal or concentric). The concentric lamellae (osteons) enclose the Haversian canal which contains Haversian blood vessels. This tissues type differs greatly in thickness in various situations in conformity with the stress and strains to which the bone is subjected.  Thickness of compact substance varies with the stress and strain beared by the bone. In long bones, it is thickest in or near the middle part or the shaft and thins out toward the extremities. On the latter the layer is very thin and is especially dense and smooth at the articular suffice.  2- The spongy substance: Cancellous tissue It consists of delicate bony plates and spicules which run in various directions and intercross forming a network of spongy appearance. The spaces between the plates are occupied by bone marrow. The spongy substance forms the bulk of short bones and of the extremities of long bones. In the latter it is not confined to the ends but extends a variable distance along the shaft.  The flat bone of the cranium of the skull are composed of an outer layer of ordinary compact bone substance (the lamina externa) and an inner layer of dense bone, (lamina interna) and between these a variable amount of spongy bone termed diploe.  The periosteum It is a thin strong, pale and pink connective tissue membrane which invests the outer surface of the bone except where it is covered with articular cartilage. The periosteum attached to the bone with connective tissue fibers (called Sharpey’s fibers) penetrating the bone through special canaliculi.  The periosteum consists of two layers, an outer fibrous layer and inner bone-forming (osteogenitic) layer. It is rich in nerves and vessels and therefore responsible for the nutrition and the growth of the bone thickness. Growth of the bone thickness occurs due to presence of osteoblasts, which are located in the inner periosteal layer and  4- The endosteum: It is thin fibrous membrane which lines the medullary cavity and the larger Haversian canals. 5- The bone marrow: The marrow occupies the spaces of the spongy bone and the medullary cavity of the long bones. In adult there are two types of marrow; red and yellow:  The red bone marrow is seen as fine red mass of reticular tissues in which lie cells directly concerned with haemopoiesis and bone formation. It is penetrated by nerves and blood vessels supplying nutrients to the marrow and the inner layers of the bone. The blood vessels and blood elements give the marrow its red colour. The colour of yellow bone marrow is due to the presence of fat cells.  During the development and growth of the organism the red bone marrow predominates (embryos and newborns have only the red marrow). With growth of the young subject the red marrow is gradually replaced by yellow marrow, which in adults fills the medullary cavities of the tubular bones entirely. There are three types of cells that contribute to bone homeostasis. a) osteoblasts are bone-forming cell b)osteoclasts resorb or break down the bone c) osteocytes are mature bone cells. An equilibrium between osteoblasts and osteoclasts  The morphofunctional unit of the bone is the osteon, or Haversian system. The osteon consists of a system of bony lamellae arranged concentrically around a canal, which is called Haversian canal and this canal contains nerves and vessels. - Blood Supply of the Bon There are many sets of blood vessels supply the bone: 1- The periosteal arteries ramify in the periosteum and gives off small branches which enter minute opening on the Haversian canals of the compact substance. Other branches enter the extremities of the long bones and supply the spongy bone. 2- The nutrient or medullary artery (in case of long bones) enters at the so called nutrient foramen, passes in a canal through the compact substance and ramifies in the marrow. Its branches anastomose with the central branches of the periosteal set. 3- Epiphysial arteries, enter the bone at the epiphysis. 4- Metaphysial arteries enter the bone at the metaphysis. * No lymphatic vessels are present within the bone. 5- Nerves of the bone Bones are innervated by special sensory nerve endings (vater pacini corpuscles) in the periosteum.  6- Chemical composition and physical properties of bone Bone (as a tissue) is a mineralized connective tissue which is mainly composed of inorganic mineral salts and organic matter with a ratio of 1:2. 1- Organic matter includes bone cells, ossein, collagen fibers and matrix or intercellular substance. It gives the bone its toughness or elasticity. 2- Inorganic matter is mainly calcium phosphate (85%), calcium carbonate (10%), magnesium phosphate, sodium carbonate and sodium  The colour of the bone is yellowish white in fresh state and when boiled and bleached it becomes white. When bone exposed to an acid solution (as HCL) the calcium phosphate salts dissolve (decalcification), while the organic material remains and preserves the shape of the bone , although it is soft and elastic.  If bone is subjected to burning however, the organic material burns away, while the inorganic material remains and also preserves the shape and hardness of the bone, although the bone is now fragile. Bones of young animals, which contain greater amount of ossein, are highly pliability, and so their fractures are rare. In old aged animals, the inorganic materials is more so the bones become less elastic and more fragile and so their fractures are common.  7- Growth of bone Flat bones of skull increase in size by continued ossification at margins of connective tissue. In long bone, epiphysial (growth) plate cartilage remains between the epiphysis and diaphysis. Epiphyseal cartilage is replaced by bone after growth is complete. Physeal closure times, i.e., when ossification of epiphyseal plate occurs, are important tools in aging animals. Most of these closure times are radiographically defined Width of bone increases by growth at subperiosteal membrane. The Function of the skeleton The bone system performs different functions, which are of either mechanical or biological significance. The mechanical functions of the skeleton A. The protection provided by The vertebral canal which protects the spinal cord, The bone of the cranium in the skull (brain cage) which protects the brain, The thoracic cage, which protects vitally important organs of the thoracic cavity (heart, lungs) and The pelvis which protects the reproductive organs which are important for the continuance of the species. B. Support (weight-bearing) is provided by attachment of the soft tissue and organs to the different parts of the skeleton. C. The bones have the structure of long and short levers connected by mobile articulations and set motion by muscles which are regulated by the nervous system.  The biological function of the skeleton: Mineral storage The skeleton is a reservoir of mineral salts, phosphorus, calcium, iron. This is important in understanding metabolic diseases (rickets, etc...) and in making diagnosis with x-rays. Haemopoiesis The skeleton also performs the function of in the bone marow. 9- Descriptive terms of the skeletal system: I -Terms of bony elevation (projections) A- Articular projections: Divide according to their shapes into: 1- Head: It is round e.g. head of the femur and humerus. 2- Condyle: It is more or less spherical e.g. condyles on distal extremity of femur. 3- Trochela : It is pully-like e.g. trochlea of femur on which the patella slides. 4- Capitulum: Looking like a small head. B-Non articular projection: 1- Process: An elongated projection e.g. spinous process, transverse process of the vertebrae. 2-Tuberosity: It is a relatively large (a bigger tubercle) e.g lateral tuberosity on the proximal extremity of the humerus. 3- Tubercle: It is a small round elevation e.g. psoas minor tubercle. 4-Crest: An elongated thick ridge with well defined borders e.g. crests of the tibia. 5- Spine: A small projection looking a thorn with pointed tip. e.g. spine of the tibia or thick tip as spine the scapula. 6-Neck: A constriction follows the head e.g. neck of humerus. 7- Line: A very low elevation demarcating the area, often caused by the pull of a muscle e.g. popliteal line of the tibia. 8- Styloid: A thick pin-like project e.g. styloid process of the ulna of some animals. 9- Hamulus: A curved process looking like a hook e.g. hamulus's of pterygoid bone of skull. 10- Epicondyle: It is a non- articular projection in connection with the condyle e.g. epicondyles of the femur. 11- Trochanter: It is a tuberosity related to running usually with square cut margins. 12- Cornu (coronoid): Look like the tip of a deer horn e.g. coronoid process of the mandible. 13- Ridge: A linear elevation with a sharp border. 14- Border: Separates between two surfaces e.g. borders of the tibia.  II- Bony depressions: A- Articular depressions: 1- Glenoid cavity: It is a shallow articular concavity as that of scapula. 2- Cotyloid: It is a deep articular concavity e.g. acetabulum. 3- Notch: An articular indentation e.g. semilunar notch of the ulna which articulates with the condyles of the humerus  B- Non-articular depressions: 1- Fossa: It is a large non articular depression e.g. atlantal fossa and sub scapular fossa. It may be shallow or deep. 2- Fovea: It is a small non articular depression e.g. fovea capitis on femur head. 3- Foramen: It is a perforation in bones and acts as a passage for the vessels, nerves etc. e.g. foramen magnum in the skull. 4- Fissure: An elongated deficiency in the bone appearing like a cleft, e.g. palatine fissure of the skull. 5- Canal: A passage with two openings through one or more bones, e.g. vertebral canal and canals of the skull. 6- Hiatus: A small narrow passage or gap, one opening of which is seen, the other opening is hidden. 7- Meatus: A shallow elongated passage. 8- Sulcus = groove: An elongated depression having edges or borders. 9- Sinus: It is air cavity within a bone. It is lined with the mucous membrane and connected with the exterior.