Skeletal System Structure and Function PDF

# Skeletal System Structure and Function ## Classification of Bones ### Long Bones * **Definition:** Longer than they are wide. * **Examples:** Femur, Humerus. * **Structures:** * **Diaphysis:** * Shaft made of compact bone. * **Epiphysis:** * Ends made of spongy bone....

# Skeletal System Structure and Function ## Classification of Bones ### Long Bones * **Definition:** Longer than they are wide. * **Examples:** Femur, Humerus. * **Structures:** * **Diaphysis:** * Shaft made of compact bone. * **Epiphysis:** * Ends made of spongy bone. * **Articular Cartilage:** * Covers epiphyses to reduce friction. * **Epiphyseal Plate:** * Growth region in juveniles. * **Medullary Cavity:** * Contains red marrow in juveniles and yellow marrow in adults. ### Short Bones * **Definition:** Generally cube-shaped. * **Characteristics:** * Mostly spongy bone. * **Examples:** Carpals (wrist bones), Tarsals (ankle bones). * **Sesamoid Bones:** * A type of short bone that forms within tendons (e.g., Patella). ### Flat Bones * **Definition:** Thin, flattened, and usually curved. * **Structure:** * Two thin layers of compact bone surrounding a layer of spongy bone. * **Examples:** Skull, Ribs, Sternum. ### Irregular Bones * **Definition:** Irregular shape and do not fit into other categories. * **Examples:** Vertebrae, Hip bones. ## Anatomy of a Long Bone 1. **Diaphysis:** * Shaft of the bone. * Contains compact bone. 2. **Epiphysis:** * Ends of the bone. * Contains spongy bone. 3. **Articular Cartilage:** * Covers the epiphyses. * Reduces friction in joints. 4. **Epiphyseal Plate:** * Growth region in young bones. 5. **Epiphyseal Line:** * Remnant of the epiphyseal plate in adults. 6. **Medullary Cavity:** * Center of the diaphysis. * Contains yellow marrow in adults and red marrow in infants. 7. **Periosteum:** * Membrane around the outer surface of the bone. * Contains perforating (Sharpey's) fibers that secure it to the bone. ## Key Points * **Growth:** * The epiphyseal plate allows for lengthwise growth during childhood. * In adulthood, the plate becomes ossified, and growth stops. * **Marrow:** * Red marrow is responsible for blood cell formation, primarily found in infants. * In adults, red marrow is located in the cavities of spongy bone and epiphyses of some long bones. ## Skeletal System Study Notes ### Overview * The skeletal system is the framework of the body. * It consists of bones, cartilage, tendons, and ligaments. ### Functions of the Skeletal System 1. **Support the Body** * Provides structure and shape. 2. **Protect Internal Organs** * Skull and vertebrae protect the brain and spinal cord. * Rib cage protects thoracic cavity organs. 3. **Movement** * Facilitates movement through attached skeletal muscles. 4. **Storage** * Stores calcium and phosphorus. * Stores fat in the internal marrow cavity. 5. **Blood Cell Formation (Hematopoiesis)** * Produces blood cells within the bone marrow. ### Components of the Skeletal System * **Bone (Skeleton)** * **Cartilage** * Reduces friction and serves as a model for bone formation. * **Tendons** * Attach bone to muscle. * **Ligaments** * Attach bone to bone. ## Background Information * Bones, cartilage, tendons, and ligaments are types of connective tissues. * **Proteoglycans:** * Large polysaccharides attached to proteins. * Part of the ground substance, helping cartilage to be smooth and resilient. * Store water. ## Extracellular Matrix * **Bone** * Composed of collagen and minerals (flexible and weight-bearing). * **Cartilage** * Composed of collagen and proteoglycans (good shock absorber). * **Tendons and Ligaments** * Composed of collagen (very tough). ## Skeleton Structure * The adult skeleton has 206 bones. * Two subdivisions: 1. **Axial Skeleton** 2. **Appendicular Skeleton** ## Appendicular Skeleton * Composed of 126 bones. * Includes: * Limbs (appendages) * Pectoral girdle * Pelvic girdle ## Classification of Bones * **Based on Shape:** 1. Long 2. Short 3. Flat 4. Irregular * **Type of Bone Tissue:** * Compact * Spongy (cancellous) ## Long Bones * Typically longer than they are wide. * Shaft with heads at both ends. * Contain mostly compact bone. ## Summary The skeletal system is essential for support, protection, movement, storage, and blood cell formation. Understanding its components and classifications helps in grasping its functions and importance in the human body. ## Bone Formation ### Ossification * **Definition:** The process of bone formation. * **Occurs:** Primarily in utero. * **Osteoblast's Role:** * Build bone. * After secreting enough bone matrix, it transforms into an osteocyte. ### Ossification Centers 1. **Ossification Center:** The starting point of bone formation. 2. **Primary Ossification Center:** * First area where bone appears. * Forms the diaphyses (shaft of long bones). 3. **Secondary Ossification Center:** * Forms the epiphyses (ends of long bones). ### Processes of Bone Formation Bone formation in the fetus follows two main processes: 1. **Intramembranous Ossification** 2. **Endochondral Ossification** ### Intramembranous Ossification * **Definition:** Bone formation within connective tissue membranes. * **Process:** * Osteoblasts build bone. * **Examples:** * Skull bones. * Lower jaw. * Diaphysis of clavicles. * **Note:** Fontanels (soft spots) are membrane-covered spaces between developing skull bones that have not yet ossified. ### Endochondral Ossification * **Definition:** Bone formation inside cartilage. * **Process:** * Cartilage models are replaced by bone. * **Examples:** All bones except the skull. ### Steps in Endochondral Ossification 1. Chondroblasts create a cartilage model, which then becomes chondrocytes. 2. The cartilage model calcifies (hardens). 3. Osteoblasts invade the calcified cartilage, forming the primary ossification center in the diaphysis. 4. Secondary ossification centers form in the epiphysis. 5. The original cartilage model is nearly completely ossified, with remaining cartilage becoming articular cartilage. ### Bone Growth * **Infancy and Youth:** * Long bones lengthen at the epiphyseal plate. * Long bones widen by adding more lamella. * **End of Bone Growth:** * The epiphyseal plate is replaced by an epiphyseal line. * Occurs approximately between 12 to 25 years of age. ### Formation of the Human Skeleton * In embryos, the skeleton is primarily made of hyaline cartilage. ## Bone Structure and Function ### Bone Tissue Types * **Compact Bone** * **Location:** Outer part of diaphysis (long bones) and thinner surfaces of other bones. * **Osteon:** * Structural unit of compact bone. * **Components:** * **Lamella:** Rings of bone matrix. * **Lacunae:** Spaces between lamellae containing osteocytes. * **Canaliculus:** Tiny canals for nutrient transport and waste removal. * **Central Canal:** Center of osteon containing blood vessels. * **Spongy Bone (Cancellous Bone)** * **Location:** Epiphyses of long bones and center of other bones. * **Trabeculae:** Interconnecting rods; spaces contain marrow. * No osteons present. ### Bone Cell Types 1. **Osteocytes** * Maintain bone matrix. * Account for 90-95% of bone cells. * Produce components needed for matrix maintenance. 2. **Osteoblasts** * Build bone (bone-building cells). 3. **Osteoclasts** * Carve bone (bone-destroying cells). * The suffix "-blast" indicates an immature cell. ### Microscopic Anatomy of Bone * **Canaliculi:** * Tiny canals radiating from the central canal to lacunae. * Form a transport system connecting all bone cells to a nutrient supply. * **Lacunae:** * Cavities containing bone cells (osteocytes). * Arranged in concentric rings called lamellae. ### Bone Membranes * **Endosteum:** * Membrane lining the medullary cavity. * **Periosteum:** * Outer layer of bone. ### Medullary Cavity * Contains red marrow in juveniles and yellow marrow in adults. ### Summary * Compact bone consists of osteons, while spongy bone consists of marrow-filled spaces surrounded by trabeculae. * Bone cells play crucial roles in maintaining, building, and breaking down bone tissue. ## Bone Development and Growth ### Cartilage and Bone Replacement * **During development:** * Much of the cartilage is replaced by bone. * Cartilage remains in isolated areas such as: * Bridge of the nose * Parts of ribs * Joints ### Bone Growth (Ossification) * **Epiphyseal Plates:** * Allow for lengthwise growth of long bones during childhood. * New cartilage is continuously formed. * Older cartilage becomes ossified (turned into bone). * **Process of Ossification:** 1. Cartilage is broken down. 2. Enclosed cartilage is digested away, creating a medullary cavity. 3. Bone replaces cartilage through the action of osteoblasts. * **Remodeling and Lengthening:** * Bones are remodeled and lengthened until growth stops. * **Factors influencing remodeling:** * Blood calcium levels * Pull of gravity and muscles on the skeleton * Bones grow in width, known as appositional growth. ### Stages of Bone Growth 1. **In an Embryo:** * Bone collar forms around a hyaline cartilage model. * Bone starts to replace cartilage. 2. **In a Fetus:** * Medullary cavity develops. * New centers of bone growth appear. 3. **In a Child:** * Epiphyseal plate cartilage allows for growth in bone length. * New bone forms, and blood vessels invade. ### Bone Remodeling * **Definition:** Removal of existing bone by osteoclasts and deposition of new bone by osteoblasts. * **Occurs in all bones and is responsible for:** * Changes in bone shape * Bone repair * Adjustment of bone to stress * Regulation of calcium ions ### Bone Fractures * **Definition:** A fracture is a break in a bone. * **Types of Bone Fractures:** 1. **Closed (Simple) Fracture:** * Break that does not penetrate the skin. 2. **Open (Compound) Fracture:** * Broken bone penetrates through the skin. * **Common Types of Fractures:** * **Comminuted:** Bone breaks into many fragments. * **Compression:** Bone is crushed. * **Depressed:** Broken bone portion is pressed inward. * **Impacted:** Broken bone ends are forced into each other. * **Spiral:** Ragged break due to twisting forces. * **Treatment:** * Fractures are treated by reduction (realigning the bone) and immobilization (keeping the bone still).