Types of Bones in the Human Body

Classification of Bones

• Flat bones are thin, flattened, and curved, with two parallel layers of compact bone surrounding a layer of spongy bone; examples include most skull bones, scapula, sternum, and sacrum
• Irregular bones do not fit into any other category, contain foramina for soft tissue and neurovascular structures, and include vertebrae, hip bone, and some skull bones
• Sesamoid bones are small, rounded, and embedded in muscle tendons near joints; examples include patella and pisiform

Method of Formation

• Ossification (osteogenesis) is the process of bone tissue development, beginning in utero and completing around 21 years of age
• During fetal development, three germ layers (endoderm, mesoderm, and ectoderm) are present
• Mesenchyme develops from mesoderm and forms the embryonic skeleton, which undergoes either intramembranous or endochondral ossification
• Osteoblasts converge on the mesenchymal/cartilaginous models to initiate ossification

Bone Structure

• Bones are covered in dense connective tissue called periosteum (outer) and endosteum (inner)
• Spongy (cancellous) bone is a deep, airy layer of bone that is highly vascularized
• Central canal contains nerves, lymphatics, and blood vessels
• Lamellae are cylindrical plates of bone surrounding the central canal
• Lacunae are small cavities between lamellae that house osteocytes

Classification by Shape

• Long bones are tubular in shape, composed mostly of compact bone, and include femur, humerus, ulna, tibia, and clavicle
• Short bones are roughly cuboid or round in shape, contain a thin layer of compact bone surrounding spongy bone, and include tarsal and carpal bones
• Flat bones are thin, flattened, and curved, with two parallel layers of compact bone surrounding a layer of spongy bone
• Irregular bones do not fit into any other category, contain foramina for soft tissue and neurovascular structures, and include vertebrae, hip bone, and some skull bones
• Sesamoid bones are small, rounded, and embedded in muscle tendons near joints; examples include patella and pisiform

Clinical: Fracture of Bone

• A fracture is a breakage in bone due to injury, stress, or disease
• Types of fractures include simple, compound, comminute, and incomplete

Cartilage and Joints

• Cartilage is a flexible connective tissue found in multiple organ systems, composed of chondrocytes, collagen fibers, and ground substance rich in proteoglycan and elastin fibers
• Types of cartilage include hyaline, elastic, and fibrocartilage
• Joints are connections or unions of two or more bones or cartilages
• Joints can be classified into fibrous, cartilaginous, and synovial joints

Musculo-Skeletal System

• The musculo-skeletal system includes skeletal muscle, tendons, ligaments, bones, joints, and articulating cartilages
• The skeletal system can be divided into axial skeleton (skull, vertebral column, and thoracic cage) and appendicular skeleton (upper and lower limb bones)

Bone Functions

• Bones provide support for the body and its cavities, protect vital organs, and serve as a mechanical basis for movement
• Bones store salts, supply new blood cells, and are highly specialized living tissue
• Bone tissue is composed of cells and fibers (organic component) and calcium salts (inorganic component)

This quiz covers the characteristics and examples of different bone types, including flat bones, irregular bones, and sesamoid bones.