Skeletal System Anatomy and Physiology PDF

THE SKELETAL SYSTEM ANATOMY AND PHYSIOLOGY BY: Ms. Nicolle Dajang  What will we learn today? Identify and describe the main functions of the skeletal system. Classify different types of bones based on shape and function. Explain the structure of a typical long bone and the roles of differen...

THE SKELETAL SYSTEM ANATOMY AND PHYSIOLOGY BY: Ms. Nicolle Dajang  What will we learn today? Identify and describe the main functions of the skeletal system. Classify different types of bones based on shape and function. Explain the structure of a typical long bone and the roles of different bone cells. Differentiate compact and spongy bones. Identify the division of the skeletal system.  COMPONENTS, STRUCTURE, AND FUNCTIONS OF THE SKELETAL SYSTEM FUNCTION Support: Framework for the body, stabilizing tissues. Protection: Safeguards vital organs (brain, heart, lungs). Movement: Serves as levers for muscular action. Blood Cell Production: Hemopoiesis in red bone marrow. Storage: Reservoir for minerals (calcium, phosphorus) and fats. COMPOSITION Bones Cartilage Ligaments Tendons Joints EXTRACELLULAR MATRIX The extracellular matrix is a network of proteins and minerals that provide bones with strength and flexibility. Components: Collagen, Hydroxyapatite, Proteoglycans Collagen: Tough, rope-like protein for tensile strength. Reinforces bones like steel bars in concrete. Hydroxyapatite: Calcium phosphate crystals giving bones weight-bearing capacity. Acts as the mineralized "concrete" for compression strength. Ca10(PO4)6(OH)2 (CALCIUM PHOSPHATE AND CALCIUM HYDROXIDE) Proteoglycans: Molecules retaining water and providing resilience Polysaccharides attached to core proteins (like pine tree needles). Retain water to ensure flexibility and resilience in connective tissues. EXTRACELLULAR MATRIX BONE MARKINGS Bone markings are NOT smooth but shows a lot. Bone markings reveal: where the muscles, tendons, and ligaments attatched nerves and blood vessels passes Three general bone markings: articulation (bones meet) projection (projects above the surface) hole (opening or groove) CLASSIFICATION OF BONES LONG BONES Typically longer than wide Have a shaft with heads at both ends. Contain mostly compact bone Examples: Femur, humerus SHORT BONES Generally cube-shape Contain mostly spongy bone Examples: Carpals, tarsals CLASSIFICATION OF BONES FLAT BONES Thin and flattened Usually curved thin layers of compact bone around a layer of spongy bone Examples: Skull, ribs, sternum IRREGULAR BONES Irregular shape Do not fit into other bone classification categories Example: Vertebrae and hip CLASSIFICATION OF BONES SESAMOID BONES sesame seeds (pea - shaped) oval shaped bones located within tendons Examples: patella SUTURAL BONES Small bones located between flat bones of the skull at the suture Example: wormian bones of skull (small irregular bones embedded in a cranial suture) STRUCTURE OF BONE DIAPHYSIS Shaft Composed of compact bone EPIPHYSIS Ends of the bone Composed mostly of spongy bone METAPHYSIS regions between the diaphysis and the epiphyses. contains an epiphyseal (growth) plate STRUCTURE OF BONE ARTICULAR CARTILAGE Covers the external surface of the epiphyses Made of hyaline cartilage Decreases friction at joint surfaces PERIOSTEUM Outside covering of the diaphysis Fibrous connective tissue membrane PERFORATING FIBERS Sharpey’s Fibers Secure periosteum and underlying bone STRUCTURE OF BONE MEDULLARY CAVITY Cavity of the shaft Contains yellow marrow (mostly fat) in adults Contains red marrow (for blood cell formation) ENDOSTEUM a thin membrane that lines the medullary cavity and the internal spaces of spongy bone.  BONE HISTOLOGY CARTILAGE HYALINE CARTILAGE Chondroblasts: Immature cells producing cartilage matrix. Chondrocytes: Mature cells residing in lacunae. Matrix Composition: Collagen: Provides tensile strength. Proteoglycans: Trap water, giving resilience. Protective Sheath: Perichondrium: Double-layered sheath covering cartilage except at joints. Appositional Growth: New cartilage added to the outer edge. Chondroblasts lay down matrix and differentiate into chondrocytes. Interstitial Growth: Growth from within the tissue.Chondrocytes divide and produce new matrix between existing cells. BONE HISTOLOGY Osteoblasts: Bone-forming cells. Osteocytes: Mature bone cells, located in lacunae. Osteoclasts: Bone-resorbing cells. Tissue Types: Compact Bone: Dense; forms osteons with Haversian canals. Spongy Bone: Trabecular structure; houses red bone marrow. BONE HISTOLOGY OSTEOPROGENITOR CELLS all connective tissues are formed only bone cells to undergo cell division; the resulting cells develop into osteoblasts. develops into an osteoblast OSTEOBLASTS bone-building cells. forms bone extracellular matrix synthesize and secrete collagen fibers and other organic components needed to build the extracellular matrix of bone tissue BONE HISTOLOGY OSTEOCYTES mature bone cells, are the main cells in bone tissue and maintain its daily metabolism, such as the exchange of nutrients and wastes with the blood OSTEOCLASTS huge cells derived from the fusion of as many as 50 monocytes and are concentrated in the endosteum. COMPACT BONE TISSUE Definition: Compact bone is the strongest type of bone tissue, with minimal spaces. Location: Found beneath the periosteum and in the diaphysis of long bones. Function: Provides protection and support. Resists stresses from weight and movement. Main Component: Osteons (Haversian systems). Parts of an Osteon: Concentric Lamellae: Circular plates of mineralized matrix. Central (Haversian) Canal: Contains blood vessels and nerves. Lacunae: Small spaces containing osteocytes. Canaliculi: Tiny channels connecting lacunae to the central canal. COMPACT BONE TISSUE COMPACT BONE TISSUE Interstitial Lamellae : Found between osteons. Fragments of older osteons, formed during bone rebuilding or growth. Circumferential Lamellae: Found around the entire inner and outer surface of the bone. Types: External Circumferential Lamellae: Just beneath the periosteum. Internal Circumferential Lamellae: Line the medullary cavity. Connected to the periosteum by Sharpey’s fibers. Interosteonic (Volkmann’s) Canals: Transverse canals connecting blood vessels and nerves in the periosteum to the medullary cavity and central canals. Nutrient and waste exchange happens through the interconnected system of lacunae and canaliculi. COMPACT BONE TISSUE SPONGY BONE TISSUE Definition: Spongy bone, also known as trabecular or cancellous bone, lacks osteons. Location: Found in the interior of bones, protected by compact bone. Key Features: Contains trabeculae (thin columns of lamellae). Spaces between trabeculae are filled with red or yellow bone marrow. Trabeculae: Irregular patterns of lamellae. Contain osteocytes in lacunae connected by canaliculi. Bone Marrow: Red Bone Marrow: Produces blood cells. Yellow Bone Marrow: Stores adipose tissue. Nourished by small blood vessels. SPONGY BONE TISSUE Weight Reduction: Light structure reduces overall bone weight for easier movement. Stress Adaptation: Trabeculae align along lines of stress. Helps resist stresses and transfer forces efficiently. Protection of Bone Marrow: Supports and protects red bone marrow, essential for blood cell production (hemopoiesis). Found in: Hip bones, Ribs, Sternum (breastbone), vertebrae, Proximal ends of the humerus and femur. COMPACT BONE TISSUE  BONE OSSIFICATION INITIAL BONE FORMATION Embryonic skeleton starts as mesenchyme. Two patterns of formation: Intramembranous Ossification: Bone forms directly within mesenchyme. Endochondral Ossification: Bone forms within hyaline cartilage. INTRAMEMBRANOUS OSSIFICATION Process Overview: Development of ossification center: At the site where the bone will develop, specific chemical messages cause the cells of the mesenchyme to cluster together and differentiate, first into osteoprogenitor cells and then into osteoblasts. The site of such a cluster is called an ossification center. Osteoblasts secrete the organic extracellular matrix of bone until they are surrounded by it. Calcification of the extracellular matrix: Next, the secretion of extracellular matrix stops, and the cells, now called osteocytes, lie in lacunae and extend their narrow cytoplasmic processes into canaliculi that radiate in all directions. Within a few days, calcium and other mineral salts are deposited and the extracellular matrix hardens or calcifies (calcification) INTRAMEMBRANOUS OSSIFICATION Process Overview: Formation of trabeculae (spongy bone): As the bone extracellular matrix forms, it develops into trabeculae that fuse with one another to form spongy bone around the network of blood vessels in the tissue. Connective tissue associated with the blood vessels in the trabeculae differentiates into red bone marrow. Development of periosteum and compact bone layers: In conjunction with the formation of trabeculae, the mesenchyme condenses at the periphery of the bone and develops into the periosteum. Eventually, a thin layer of compact bone replaces the surface layers of the spongy bone, but spongy bone remains in the center. Much of the newly formed bone is remodeled (destroyed and reformed) as the bone is transformed into its adult size and shape Examples: Flat bones of the skull, mandible, and clavicle. INTRAMEMBRANOUS OSSIFICATION ENDOCHONDRAL OSSIFICATION Replacement of cartilage by bone. Most bones, especially long bones, develop this way. Key Steps: Development of cartilage model: At the site where the bone is going to form, specific chemical messages cause the cells in mesenchyme to crowd together in the general shape of the future bone, and then develop into chondroblasts. The chondroblasts secrete cartilage extracellular matrix, producing a cartilage model (future diaphysis) consisting of hyaline cartilage. A covering called the perichondrium (per′-i-KON-drē-um) develops around the cartilage model. ENDOCHONDRAL OSSIFICATION Growth of cartilage (interstitial and appositional): Once chondroblasts become deeply buried in the cartilage extracellular matrix, they are called chondrocytes The cartilage model grows. Interstitial Growth: Length increases from within. Appositional Growth: Thickness increases at the outer surface. Midregion: Chondrocytes hypertrophy, matrix calcifies, creating lacunae. Primary ossification center formation: Initiated by nutrient artery penetration. Formation of spongy bone trabeculae. Spreads outward along the diaphysis. Medullary cavity development: Osteoclasts break down spongy bone. Forms the hollow medullary cavity in the diaphysis. Wall of the diaphysis replaced by compact bone. ENDOCHONDRAL OSSIFICATION Secondary ossification centers formation: Appear in the epiphyses around birth. Spongy bone forms without medullary cavities. Proceeds outward from the center of the epiphysis. Formation of articular cartilage and epiphyseal plate: Hyaline cartilage at epiphyses → Articular cartilage. Epiphyseal (growth) plate: Site of lengthwise bone growth during development. ENDOCHONDRAL OSSIFICATION BONE GROWTH GROWTH IN LENGTH Bone growth in length involves two main processes: Interstitial growth: Cartilage growth on the epiphyseal side. Endochondral ossification: Cartilage replacement by bone on the diaphyseal side. Central structure: Epiphyseal (growth) plate. GROWTH IN LENGTH Structure of Epiphyseal Plate Made up of hyaline cartilage. Located in the metaphysis of growing bones. Divided into four zones: Resting cartilage. Proliferating cartilage. Hypertrophic cartilage. Calcified cartilage. GROWTH IN LENGTH Zone of Resting Cartilage Location: Nearest the epiphysis. Contains small, scattered chondrocytes. Function: Anchors the epiphyseal plate to the epiphysis. Zone of Proliferating Cartilage Larger chondrocytes arranged in stacks. Chondrocytes divide and secrete extracellular matrix. Function: Replace dying chondrocytes on the diaphyseal side. GROWTH IN LENGTH Zone of Hypertrophic Cartilage Consists of large, maturing chondrocytes. Chondrocytes are arranged in columns. Function: Contribute to bone elongation Zone of Calcified Cartilage Contains dead chondrocytes in a calcified matrix. Processes: Osteoclasts dissolve calcified cartilage. Osteoblasts lay down bone matrix via endochondral ossification. Outcome: Forms the "new diaphysis." GROWTH IN LENGTH Epiphyseal Plate Closure Around age 18 in females. Around age 21 in males. Results in the formation of the epiphyseal line. Implication: Bone growth in length ceases. Importance Closure timing provides critical information: Bone age. Predicted adult height. Age at death in skeletal remains. Gender Difference: Closure occurs 1–2 years earlier in females. GROWTH IN LENGTH GROWTH IN THICKNESS Bone thickness growth occurs via appositional growth. Key processes: Formation of bone ridges. Enclosure of blood vessels. Formation of new osteons. Deposition of circumferential lamellae. GROWTH IN THICKNESS Formation of Bone Ridges At the bone surface: Periosteal cells differentiate into osteoblasts. Osteoblasts secrete collagen fibers and organic matrix. Matrix surrounds osteoblasts, forming osteocytes. Result: Bone ridges form around periosteal blood vessels, creating grooves. Formation of Tunnels Bone ridges enlarge and fold together, fusing to form a tunnel. The tunnel encloses the periosteal blood vessel. The former periosteum becomes the endosteum lining the tunnel. GROWTH IN THICKNESS Creation of New Osteons Osteoblasts in the endosteum: Deposit bone extracellular matrix. Form new concentric lamellae inward toward the periosteal blood vessel. Outcome: Tunnel fills in, creating a new osteon. Increasing Bone Thickness Under the periosteum: Osteoblasts deposit new circumferential lamellae. Bone thickness increases as periosteal blood vessels become enclosed. Process repeats: Additional periosteal blood vessels are enclosed. GROWTH IN THICKNESS Role of the Medullary Cavity Simultaneous processes: New bone tissue deposited on the outer surface. Osteoclasts destroy bone tissue lining the medullary cavity. Result: Medullary cavity enlarges as bone thickness increases. GROWTH IN THICKNESS GROWTH IN THICKNESS  BONE REMODELING BONE REMODELLING Bone remodeling is the continuous process of replacing old bone tissue with new. Key processes: Bone resorption (by osteoclasts) Bone deposition (by osteoblasts) Key Points: About 5% of the bone mass is remodeled at any given time. Remodeling occurs at different rates in various regions of the body. BONE RESORPTION Osteoclasts play a key role in bone resorption. The process involves: Osteoclasts attach to the bone surface. Formation of a leakproof seal around the osteoclasts. Release of lysosomal enzymes and acids. Digestion of collagen fibers and minerals (e.g., calcium and phosphorus). Outcome: Bone proteins and minerals are resorbed into the bloodstream. BONE DEPOSITION Osteoblasts are responsible for bone deposition. Key steps in deposition: Osteoblasts secrete collagen fibers and bone extracellular matrix. Minerals (calcium and phosphate) are deposited into the matrix. Osteoblasts eventually become osteocytes when encased in the matrix. REMODELLING IN DIFFERENT BONES Bone remodeling occurs at different rates depending on the bone region: Distal femur: Replaced about every 4 months. Femoral shaft: Some areas are never completely replaced in a person’s lifetime. Factors affecting remodeling rate: Exercise, sedentary lifestyle, changes in diet. BENEFITS Strength Enhancement: Bone becomes stronger and thicker when subjected to heavy loads. Shape Adjustment: Bone shape alters for better support based on stress patterns. Fracture Resistance: Newly formed bone is more resistant to fractures than old bone. FACTORS (MINERALS) Calcium and Phosphorus: Large amounts are required during growth and remodeling. Magnesium, Fluoride, Manganese: Smaller amounts are also necessary for healthy bones. Role: These minerals are crucial for the structure and function of bones. FACTORS (VITAMINS) Vitamin A: Stimulates osteoblast activity. Vitamin C: Needed for collagen synthesis, the primary protein in bone. Vitamin D: Helps absorb calcium from the gastrointestinal tract into the blood. Vitamin K and B12: Important for synthesizing bone proteins. FACTORS (HORMONES) Insulin-Like Growth Factors (IGFs): Stimulate osteoblasts and promote cell division. Produced in response to Growth Hormone (GH) from the pituitary gland. Thyroid Hormones (T3 and T4): Promote bone growth by stimulating osteoblasts. Insulin: Promotes bone growth by enhancing bone protein synthesis. SEX HORMONES AND BONE GROWTH At Puberty: Estrogens (Females) and Androgens (Males) cause rapid bone growth. Both hormones increase osteoblast activity and extracellular matrix synthesis. Result in the "growth spurt" and the development of secondary sexual characteristics. Females: Estrogens promote pelvic widening and other skeletal changes typical of females. Higher estrogen levels cause earlier cessation of bone elongation (epiphyseal plate closure). Males: Higher androgen levels result in delayed epiphyseal closure. HORMONAL CONTROL Sex hormones in adulthood: Help regulate bone remodeling by slowing down resorption and promoting new bone deposition. Estrogens: Promote apoptosis (programmed death) of osteoclasts, slowing resorption. Other Hormones: Parathyroid Hormone (PTH), Calcitriol (Active Vitamin D), Calcitonin also influence bone remodeling. EXERCISE Moderate Weight-Bearing Exercise: Essential for maintaining bone density. Provides sufficient strain to stimulate bone growth and strengthening. Outcome: Exercise helps maintain healthy bones throughout life FRACTURE Definition: A fracture is any break in a bone. Fractures are categorized by: Severity Shape or position of the fracture line Physician who first described them. Stress Fracture: Microscopic fissures without visible bone breakage. Often caused by repetitive activities such as running or dancing. Can also result from conditions like osteoporosis. STRESS FRACTURES Cause: Repetitive, strenuous activities like running, jumping, or dancing. Risk Factor: Diseases like osteoporosis. Common Location: 25% of stress fractures occur in the tibia. Detection: Often not visible in x-rays, but visible in bone scans. PHASES OF BONE FRACTURE REPAIR Reactive Phase Timeframe: 6-8 hours after injury Events: Blood vessels across the fracture line break, causing blood to leak and form a fracture hematoma (blood clot around fracture). Lack of circulation leads to cell death near the fracture site. Inflammation and swelling occur as a result. Phagocytes (neutrophils & macrophages) and osteoclasts begin cleaning up dead tissue. Duration: Several weeks PHASES OF BONE FRACTURE REPAIR Reparative Phase: Fibrocartilaginous Callus Formation Key Events: Blood vessels grow into the fracture hematoma. Fibroblasts from periosteum produce collagen fibers. Chondroblasts develop and produce fibrocartilage. The result is a fibrocartilaginous (soft) callus bridging the broken bone ends. Timeframe: About 3 weeks PHASES OF BONE FRACTURE REPAIR Reparative Phase: Bony Callus Formation Key Events: Osteoprogenitor cells turn into osteoblasts near healthy bone tissue. Osteoblasts produce spongy bone trabeculae to connect living and dead bone fragments. Fibrocartilage gradually turns into spongy bone forming a bony (hard) callus. Timeframe: 3 to 4 months PHASES OF BONE FRACTURE REPAIR Bone Remodeling Phase Key Events: Osteoclasts resorb dead bone fragments. Compact bone replaces spongy bone around the fracture site. Healing: The fracture line may be undetectable in radiographs. A thickened area remains on the bone surface as evidence of healed fracture. Timeframe: Months, depending on the severity. HEALING TIME Healing Time: Bone healing may take months depending on the fracture severity and bone location. Factors Affecting Healing: Blood supply to the bone Age and overall health of the individual Nutritional intake (calcium, phosphorus) COMMON FRACTURES COMMON FRACTURES COMMON FRACTURES COMMON FRACTURES