Skeletal System Lecture Notes PDF

How strong are you?  Bone-a-fide Facts: The Truth About the Skeletal System  The Skeletal System The skeletal system consists of bones, associated connective tissues, whichinclude cartilage, tendons, and ligaments. The term skelet...

How strong are you?  Bone-a-fide Facts: The Truth About the Skeletal System  The Skeletal System The skeletal system consists of bones, associated connective tissues, whichinclude cartilage, tendons, and ligaments. The term skeleton is derived from a Greek word meaning dried. But the skeleton is far from being dry and nonliving. Rather, the skeletal system consists of dynamic, living tissues that are able to grow, detect pain stimuli, adapt to stress, and undergo repair after injury.  Functions of Skeletal System 1. Support Rigid strong bones – for bearing weight and is the major supporting tissue of the body. Cartilage – provides a firm yet flexible support within certain structures (ex. nose and external ears). Ligaments – are strong bands of fibrous connective tissue that attach to bone and hold them together. 2. Protection The hardness of the bone contributes to its ability to protect the vital organs of the body from injury (ex.cranial bones protect the brain).  Functions of Skeletal System 3. Movement Skeletal muscles attach to bones by tendons. When muscles contract, they pull on bones and together they produce movement. 4. Storage Fat is stored in the internal cavities of bones. Stores several minerals especially calcium and phosphorus. Important in maintaining homeostasis of minerals in the blood with minerals stored in the bone are released in response to body’s demand. 5. Blood cell production (hematopoiesis) Many bones contain cavities filled with bone marrow that gives rise to blood cells and platelets.  Skeletal System: A Group of Connective Tissue I. Connective Tissue Characteristics Determined by extracellular matrix composition Contains collagen, ground substance, organic molecules, water, and minerals Varying types and quantities in different connective tissues II. Key Components of the Extracellular Matrix Collagen: Tough, ropelike protein Proteoglycans: Large molecules with polysaccharides attached to core proteins o Form aggregates and attract water  Skeletal System: A Group of Connective Tissue III. Connective Tissues of the Skeletal System Tendons and Ligaments: o High collagen content for toughness o Rope-like structure Cartilage: o Contains collagen and proteoglycans o Tough and resilient due to water-filled proteoglycans o Excellent shock absorber Bone: o Contains collagen and minerals (calcium, phosphate) o Collagen provides flexible strength o Minerals provide compression strength o Hydroxyapatite crystals contribute to mineral component  Major Types of Bones Type Shape Examples Longer than Femur, tibia, Long they are wide humerus, ulna Approximately Short as wide as they Carpals, tarsals are long Skull bones, Relatively thin Flat ribs, sternum, and flattened scapulae Do not fit into Vertebrae, facial Irregular other categories bones  General Features and Histology of Bone Bones are composed of various tissues, including: Bone tissue: This is the primary tissue of bones and is divided into two types: Cortical bone (compact bone): This is dense, solid bone that forms the outer layer of most bones. It provides strength and rigidity. Trabecular bone (cancellous bone): This is porous bone that is found inside the cortical bone. It is lighter than cortical bone but still provides strength.  Structure of a Long Bone Part Function Shaft, contains medullary Diaphysis cavity Expanded ends, contains Epiphysis red bone marrow Region between diaphysis Metaphysis and epiphysis Outer membrane, Periosteum contains blood vessels and nerves, Inner membrane, involved Endosteum in bone remodeling  General Features and Histology of Bone Part Function Shaft, contains medullary Diaphysis cavity Expanded ends, contains Epiphysis red bone marrow Region between diaphysis Metaphysis and epiphysis Outer membrane, Periosteum contains blood vessels and nerves, Inner membrane, involved Endosteum in bone remodeling  Structure of a Long Bone Bones contain cavities, such as the large medullary cavity in the diaphysis, as well as smaller cavities in the epiphyses of long bones and in the interior of other bones. These spaces are filled with soft tissue called marrow. Yellow marrow consists mostly of adipose tissue. Red marrow consists of blood-forming cells and is the only site of blood formation in adults. Children’s bones have proportionately more red marrow than adult bones because, as a person ages, red marrow is mostly replaced by yellow marrow. In adults, red marrow is confined to the bones in the central axis of the body and in the most proximal epiphyses of the limbs.  Structure of a Long Bone Bone Cells Osteoblasts: Bone-forming cells; periosteum and endosteum contains this. Osteocytes: Mature bone cells - When osteoblasts become surrounded by matrix, they are referred to as Osteoclasts: Bone-resorbing cells Bone Matrix Lamellae: Thin sheets of extracellular matrix Lacunae: Spaces containing osteocytes Canaliculi: Tiny canals connecting osteocytes Types of Bone Tissue Compact bone: Dense, solid matrix Spongy bone (cancellous bone): Lacy network with marrow-filled spaces  General Features and Histology of Bone The histology of bone tissue is characterized by its matrix, which is composed of organic and inorganic components. Organic component – consists of collagen fibers, Inorganic component - composed of minerals, primarily calcium phosphate.  Surface Anatomy of the Bone Surface anatomy Refers to the visible structures of the body. When applied to bones, it involves identifying specific landmarks and features that can be seen or felt on the body's exterior. These features often provide clues about the underlying bone structure and its relationship to other anatomical structures.  Surface Anatomy of the Bone I. Projections: These are bony outgrowths that serve as attachment points for muscles, tendons, and ligaments. Process: A general term for any projection. Tuberosity: A large, rough projection, often for muscle attachment. Crest: A ridge-like projection. Spine: A sharp, pointed projection. Trochanter: A large, blunt projection, typically found on the femur. Epicondyle: A projection above a condyle (rounded articular surface).  Surface Anatomy of the Bone II. Depressions: These are hollows or indentations in the bone that often accommodate blood vessels, nerves, or muscles. Fossa: A shallow, dish-shaped depression. Notch: A deep, narrow groove. Sulcus: A groove or furrow. Foramen: An opening through a bone. Canal: A tube-like passageway  Surface Anatomy of the Bone III. Articulations: These are areas where two or more bones come together to form a joint. Condyle: A rounded articular surface. Head: A rounded, expanded end of a bone. Facet: A small, flat articular surface. The Bones The Bones  ACTIVITY 1: SKELETAL SYSTEM DISCUSSION PROPER The skeleton is subdivided into two major divisions— DIVISIONS OF THE SKELETAL SYSTEM the axial and appendicular. AXIAL SKELETON vs APPPENDICULAR SKELETON AXIAL SKELETON APPPENDICULAR SKELETON Part of the skeleton that consists of the bones of the head Portion of the skeleton of vertebrae consisting of the and trunk of a vertebrae bones that support the appendages Central axis of the skeleton Consists of appendages connected to the axial skeleton Composed of skull, ossicles of the ear, vertebral column, Composed of pectoral girdles, arms, foreams, hands, hyoid, rib cage and sternum pelvis, legs, feet, and ankles Made up of 80 bones Made up of 126 bones Supports the upright position and protects the internal Aid in the movement of the body organs  Ossification: How Bones are Formed Bone ossification is the process by which bone tissue is formed. It is a crucial developmental process that occurs throughout childhood and adolescence and continues to some extent into adulthood.  2 TYPES OF OSSIFICATION: Intramembranous Ossification Intramembranous Ossification Direct formation: Bone tissue develops directly from mesenchymal connective tissue. Flat bones: This method is primarily responsible for the formation of flat bones, such as the skull, clavicle, and sternum.  2 TYPES OF OSSIFICATION: Intramembranous Ossification STEP-BY-STEP MECHANISM: 1. Mesenchymal Condensation Formation of dense fibrous membrane: Mesenchymal cells, a type of embryonic connective tissue, gather and condense to form a dense, fibrous membrane. This membrane serves as the foundation for future bone formation. 2. Differentiation of Mesenchymal Cells Osteoblast development: Within this fibrous membrane, some mesenchymal cells differentiate into osteoblasts. Osteoblasts are specialized cells responsible for bone matrix production.  2 TYPES OF OSSIFICATION: Intramembranous Ossification 3. Osteoblast Activity and Matrix Secretion Bone matrix deposition: Osteoblasts secrete a matrix composed of collagen fibers and ground substance. This matrix forms the organic component of bone tissue. Calcification: Inorganic salts, primarily calcium phosphate, are deposited within the organic matrix, causing it to calcify and harden. 4. Formation of Trabecular Bone Interconnected network: As the matrix calcifies, it forms a network of interconnected trabeculae (spongy bone). These trabeculae provide a framework for the developing bone.  2 TYPES OF OSSIFICATION: Intramembranous Ossification 5. Blood Vessel Invasion Vascularization: Blood vessels invade the developing bone tissue, delivering nutrients and oxygen to support the growth and development of bone cells. 6. Remodeling and Haversian System Formation Osteoclast activity: Osteoclasts, specialized cells that break down bone tissue, begin to appear. They help to remodel the trabecular bone. Haversian system formation: The trabeculae are gradually remodeled into the mature lamellar bone structure, forming the characteristic Haversian canals that contain blood vessels and nerves.  2 TYPES OF OSSIFICATION: Intramembranous Ossification KEY DIFFERENTIATION: Mesenchymal cells → Osteoblasts  2 TYPES OF OSSIFICATION: Endochondral Ossification Indirect formation: Bone tissue replaces a preexisting cartilage model. Long bones: This method is primarily responsible for the formation of long bones, such as the femur, tibia, and humerus.  2 TYPES OF OSSIFICATION: Endochondral Ossification Steps-By-Step Mechanism 1. Formation of a Cartilage Model: o A hyaline cartilage model forms the shape of the future bone. o This model is composed of chondrocytes, specialized cells that secrete cartilage matrix. 2. Periosteal Bone Collar Formation: o A thin layer of bone, called the periosteal bone collar, forms around the diaphysis (shaft) of the cartilage model. o This collar is formed by osteoblasts, which differentiate from mesenchymal cells in the perichondrium (outer layer of cartilage).  2 TYPES OF OSSIFICATION: Endochondral Ossification 4. Formation of the Primary Ossification Center: o The cartilage within the diaphysis begins to break down and is replaced by bone tissue. o This process involves the invasion of blood vessels, which bring in osteoblasts and osteoclasts. o The region where bone replaces cartilage is called the primary ossification center. 5. Formation of the Secondary Ossification Centers: o As the primary ossification center grows, secondary ossification centers begin to form in the epiphyses (ends) of the long bone. o These centers also involve the breakdown of cartilage and its replacement by bone tissue.  2 TYPES OF OSSIFICATION: Endochondral Ossification 5. Growth of the Bone: o The epiphyseal plate, a layer of cartilage that remains between the diaphysis and epiphyses, continues to divide and produce new cartilage. o This growth leads to the lengthening of the long bone. 6. Epiphyseal Plate Closure: o As the individual reaches skeletal maturity, the epiphyseal plate closes. o The remaining cartilage is replaced by bone, and the bone reaches its full length.  2 TYPES OF OSSIFICATION: Endochondral Ossification 7. Remodeling and Maturation: o The bone continues to be remodeled throughout life, ensuring its strength and integrity. o The trabecular bone in the medullary cavity is replaced by compact bone, forming the mature structure of the long bone.  2 TYPES OF OSSIFICATION: Endochondral Ossification Key Cell Differentiations: Mesenchymal cells → Chondrocytes Perichondrial fibroblasts → Osteoblasts Chondrocytes → Osteocytes (in the epiphyseal plate) 2 TYPES OF OSSIFICATION: Endochondral Ossification  KEY DIFFERENCE Intramembranous Endochondral Feature Ossification Ossification Starting Material Mesenchymal tissue Hyaline cartilage Cartilage No Yes Involvement Growth Plate No Yes (epiphyseal plate)  The Bone Growth Bone growth occurs by the deposition of new bone lamellae onto existing bone or other connective tissue. APPOSITIONAL GROWTH Growth in the length of a bone The major source of increased height in an individual Occurs in the epiphyseal plate during endochondral ossification. HOW? ❖ As osteoblasts deposit new bone matrix on the surface of bones between the periosteum and the existing bone matrix, the bone increases in width, or diameter.  The Bone Growth: Step by Step Process 1. Chondrocytes increase in number on the epiphyseal side of the epiphyseal plate. 2. They line up in columns parallel to the long axis of the bone, causing the bone to elongate. 3. Then the chondrocytes enlarge and die. 4. The cartilage matrix becomes calcified. 5. Much of the cartilage that forms around the enlarged cells is removed by osteoclasts, and the dying chondrocytes are replaced by osteoblasts. 6. The osteoblasts start forming bone by depositing bone lamellae on the surface of the calcified cartilage. This process produces bone on the diaphyseal side of the epiphyseal plate.  The Bone Remodeling The removal of existing bone by osteoclasts and the deposition of new bone by osteoblasts. Occurs in all bone. Responsible for: changes in bone shape adjustment of bone to stress bone repair calcium ion regulation in the body fluids.  The Bone Repair Sometimes a bone is broken and needs to be repaired. 1. When this occurs, blood vessels in the bone are also damaged. The vessels bleed, and a clot (hematoma) forms in the damaged area. 2. Two to three days after the injury, blood vessels and cells from surrounding tissues begin to invade the clot. 3A. Some of these cells produce a fibrous network of connective tissue between the broken bones, which holds the bone fragments together and fills the gap between them.  The Bone Repair: Exploring the Callus Formation 3B. Other cells produce islets of cartilage in the fibrous network between the two bone fragments (called a callus ). 4. Osteoblasts enter the callus and begin forming spongy bone (complete 4–6 weeks after the injury). Immobilization of the bone is critical up to this time because movement can refracture the delicate new matrix. 5. Subsequently, the spongy bone is slowly remodeled to form compact and spongy bone, and the repair is complete. The Bone Repair Different Types of Bone Fractures