Osteology (Book) PDF

# Chapter 1: General Osteology ## Osteology It is the science which deals with the bones. ## Skeleton It is a framework of hard structures (bones and cartilages) which support and protect the soft tissues of animals. ## Classification of the Skeleton **A) According situation of the bones and th...

# Chapter 1: General Osteology ## Osteology It is the science which deals with the bones. ## Skeleton It is a framework of hard structures (bones and cartilages) which support and protect the soft tissues of animals. ## Classification of the Skeleton **A) According situation of the bones and their embryonic origin** 1. **Exo-skeleton** * Situated externally and derived from the ectoderm * **Examples:** shells of many invertebrates, scales of fishes, shields of turtles, feathers of birds, hair and hoofs of animals. 2. **Endo-skeleton** * Embedded in the soft tissues and mainly originate from the mesoderm. * **Examples:** Bones of higher vertebrates (scapula, femur, radius, ulna, etc.) **B) According to position of the bones** 1. **Axial skeleton** * It comprises the skull, vertebral column, ribs and sternum. 2. **Appendicular skeleton** * It includes the bones of thoracic and pelvic limbs. 3. **Splanchnic (visceral) skeleton** * It consists of bones developed in the some viscera, for examples: * Os penis of the dog * Os cordis in the heart of ruminants * Ossa diaphragmaticus in the diaphragm of the camel. **C) Phylogenic classification** 1. **Membranous skeleton** * Skeleton of invertebrates (no hard skeleton) * **The weakest** 2. **Cartilaginous skeleton** * Skeleton of cartilaginous fishes * **Moderate strength** 3. **Bony skeleton** * Skeleton of higher vertebrates * **The strongest** ## Functions of Bones 1. Give the body shape (through skeleton). 2. **Protection:** * Vertebral canal protects the spinal cord. * Skull protects the brain. * Thoracic cage protects the heart. * Pelvis protects the reproductive organs. 3. Leverage (force of motion). 4. Storage of minerals (calcium and phosphorus). 5. Storage of lipids (yellow bone marrow). 6. Blood cell formation (red bone marrow). ## Classification of the Bones **A. According to their situation** | Category | Description | Example | |---------------------|-----------------------------------------------------------------------|-----------------------------------------------------| | Axial bones | Unpaired bones present in median plane | Skull, vertebrae, sternum | | Appendicular bones | Paired bones present away from median plane | Bones of limbs | | Splanchnic (visceral) | Bones within soft tissues | Os cordis of ruminant, os penis of dog, and ossa diaphragmatic of camel | **B. According to their development** 1. **Endochondral bones** * Developed from hyaline cartilage and include all bones except those in 2. * Stages of Endochondral Ossification: * Formation of bone collar around cartilage * Cavitation of the hyaline cartilage * Invasion of internal cavities by the periosteal blood and spongy bone formation * Formation of the medullary cavity * Ossification of the epiphyseal cartilage 2. **Intramembranous bones** * Developed from fibrous membranes and include flat bones and some bones of the skull. * Intramembranous vs. Endochondral: * The skull needs to ossify fast! * Kids better bounce, not break! **C. According to the shape, position and function** 1. **Tubular bones (TB):** consist of compact and spongy substances forming a tube with cavity. They are divided into three types: * **Long TB:** * Long, cyindrical with medullary cavity. * Have shaft (body or corpus or diaphysis) and two extremities (epiphysis). * Extend in one direction. * Act as supporting column and levers. * **Examples:** Limbs long bones (femur, humerus) * **Short TB:** * Short but still tubular bones. * **Examples:** Phalanges * **Reduced long TB:** * Incompletely developed long bones with very small medullary cavity. * Usually fuse with long bones. * Extended in one direction (one extremity is well developed and the other is less developed) * **Examples:** Small metacarpal, metatarsal bones, fibula and ulna of horse. * **Epiphysial plate (physis or growth plate):** * A hyaline cartilage plate presents in metaphysis (a region connects between diaphysis and epiphysis) in immature bone. * It causes increase in length (growth) of the bone in one direction. * It is replaced by bone after growth is complete. 2. **Short bones:** * **Shape:** Short, with similar dimensions * **Structure:** Consist mainly of spongy substances and thin layer of cortical bone * **Function:** Diffuse and reduce concussion * **Examples:** Carpal and tarsal bones 3. **Flat bones:** * **Shape:** Plate like * **Structure:** 2 compact layers enclose a small amount of spongy substances. Extend in two dimensions * **Function:** Give large area for muscle attachment * **Examples:** Scapula, ilium and the bones of the skull 4. **Sesamoid bones:** * **Shape:** Small bones, resemble sesame seeds. * **Structure:** Presents between tendons and joints. * **Function:** Diminish friction between the tendon and bones and change the direction of tendons * **Examples:** Patella, the largest sesamoid bone, the navicular bone or distal sesamoid bone (the smallest sesamoid bone) and proximal sesamoid bones. 5. **Irregular bones:** * Small, irregular shape. * Mainly in midline of skeleton. * **Examples:** Vertebrae. 6. **Pneumatic bones:** * Containing air spaces (sinuses) instead of marrow. * **Examples:** Paranasal sinuses of the skull and some bones of the flying birds. ## Structure of the 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 longitudinal and concentric lamellae. The concentric lamellae (osteons) enclose the Haversian canal which contains Haversian blood vessels. * In long bones, it is thick at middle and thins at extremities and becomes denser at the joint to form the articular surface. ### 2- The Spongy Substance * It consists of delicate bony plates (trabeculae or spicules) which intercross forming spongy appearance. * The spaces (cellulae medullares) between the plates are occupied by bone marrow. * The spongy substance forms the bulk of short bones and of the extremities of long bones. * **Diploe:** A small amount of spongy bone located between the two compact layers of flat bone of the skull cranium. ### 3- The Periosteum * A thin but strong connective tissue membrane which covers the bone except at the articular cartilage. * It is attached to the bone with connective tissue fibers (called Sharpey’s fibers) penetrating the bone through special canaliculi. * It consists of outer fibrous and inner bone-forming (osteogenic) layer. * **Function:** * Growth and repair of bone. * Route for nerves and vessels. ### 4- The Endosteum * It is thin fibrous membrane which lines the medullary cavity and the larger Haversian canals and covers the trabeculae of spongy bone. ### 5- The Bone Marrow * The marrow occupies the spaces of the spongy bone and the medullary cavity of the long bones. * **Types of bone marrow:** * **Red marrow:** mainly in young and rich in blood forming cells (give it the red color). * **Yellow marrow:** mainly in adult, rich in fat cells (yellow color). * **Gelatinous marrow:** degenerated yellow marrow in senile animal or badly nourished animal. ## Blood Supply of the Bone There are many sets of blood vessels supply the bone: 1. **The periosteal arteries** ramify in the periosteum and gives 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 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. * Bones are innervated by special sensory nerve endings (vater pacini corpuscles) in the periosteum. ## Chemical Composition The bone consists of 5% water and 95% solid materials, that divided into: 1. **Organic matter (35%)** includes bone cells, ossein, and collagen fibers which gives the bone its toughness or elasticity. 2. **Inorganic matter (65%)** mostly calcium and phosphorus and gives hardness to the bone tissue. * Bones of young animals, which contain greater amount of ossein, are highly pliability, and so their fractures are rare. * In old animals, inorganic materials is more so the bones become less elastic, more fragile and so their fractures are common.