The skeletal system is a complex network of bones, cartilage, ligaments, and tendons that provide structural support and protection for the human body. Comprising 206 bones in adults, it is the foundation for movement and plays essential roles in various physiological processes.
Bone Structure
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Compact Bone:
- Osteons: The structural units of compact bone, consisting of concentric layers of mineralized matrix (lamellae) surrounding a central Haversian canal containing blood vessels and nerves. Osteocytes are found in small cavities called lacunae between the lamellae.
- Canaliculi: Tiny canals that connect lacunae, allowing for nutrient and waste exchange between osteocytes and blood vessels.
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Spongy Bone:
- Trabeculae: Lattice-like structures that provide strength without the weight of compact bone. The spaces between trabeculae contain red or yellow marrow.
- Bone Marrow:
- Red Bone Marrow: Hematopoietic tissue responsible for blood cell production. It is found in the flat bones (e.g., sternum, pelvis) and the epiphyses of long bones.
- Yellow Bone Marrow: Composed mainly of adipose tissue, it serves as a fat reserve and can convert back to red marrow in cases of severe blood loss.
Types of Bones and Locations
- Long Bones:
- Examples: Femur, tibia, fibula, humerus, radius, and ulna.
- Structure: Longer than wide; consists of a diaphysis (shaft), two epiphyses (ends), and a medullary cavity filled with marrow.
- Short Bones:
- Examples: Carpals (wrist) and tarsals (ankle).
- Structure: Approximately equal in length and width, providing support and stability.
- Flat Bones:
- Examples: Cranial bones (frontal, parietal), sternum, ribs, and scapulae.
- Structure: Thin and flat, often curved; contains two layers of compact bone with a layer of spongy bone in between (diploë).
- Irregular Bones:
- Examples: Vertebrae, facial bones, and the pelvis.
- Structure: Complex shapes that do not fit into other categories provide various functions, including support and protection.
- Sesamoid Bones:
- Examples: Patella, bones within the flexor hallucis brevis tendons in the foot.
- Structure: Small and round; develop within tendons to protect them and improve mechanical advantage.
Functions of the Skeletal System
- Support: The skeleton provides a rigid framework for the body, allowing it to maintain its shape and posture.
- Protection: Bone structures shield vital organs from physical damage. For instance, the rib cage protects the lungs and heart, while the skull protects the brain.
- Movement: Bones are levers that muscles pull on to move. The arrangement of muscles and bones around joints allows for a wide range of motion.
- Mineral Storage: Bones serve as reservoirs for essential minerals, especially calcium and phosphorus. Approximately 99% of the body’s calcium is stored in bones.
- Blood Cell Production: Hematopoiesis occurs in the red bone marrow. This process is crucial for maintaining adequate levels of red blood cells, white blood cells, and platelets in the bloodstream.
Bone Composition and Development
- Bone Matrix: Composed of:
- Organic Component: Primarily, collagen fibers provide tensile strength and flexibility.
- Inorganic Component: Mineral salts, mainly hydroxyapatite (calcium phosphate), giving bones their hardness.
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Bone Cells:
- Osteoblasts: Responsible for bone formation; secrete osteoid (the unmineralized organic matrix).
- Osteocytes: Mature bone cells that maintain bone tissue. They communicate with each other through canaliculi and are involved in the regulation of bone remodeling.
- Osteoclasts: Large multinucleated cells responsible for bone resorption; they break down bone tissue and release minerals into the bloodstream.
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Bone Development:
- Ossification: The process of bone formation. There are two primary types:
- Intramembranous Ossification: Bone develops directly from mesenchymal tissue (e.g., flat skull bones).
- Endochondral Ossification: Bone develops by replacing hyaline cartilage (e.g., long bones).
- Ossification: The process of bone formation. There are two primary types:
Joint Types and Functions
Joint Classification
- Fibrous Joints:
- Structure: Connected by dense connective tissue with no joint cavity.
- Examples: Sutures of the skull (immovable) and syndesmoses (slightly movable, such as the connection between the tibia and fibula).
- Cartilaginous Joints:
- Structure: Connected by cartilage; no joint cavity.
- Examples: Symphysis pubis (slightly movable) and intervertebral discs (allow limited movement).
- Synovial Joints:
- Structure: The most movable type of joint, featuring a synovial cavity filled with synovial fluid, articular cartilage covering the ends of bones, and a joint capsule.
- Types:
- Hinge Joints: Allow movement in one plane (e.g., elbow, knee).
- Ball-and-Socket Joints: Allow movement in multiple planes (e.g., shoulder, hip).
- Pivot Joints: Allow rotational movement (e.g., atlas and axis of the cervical spine).
- Condyloid Joints: Allow movement but no rotation (e.g., wrist).
- Saddle Joints: Allow for grasping and rotation (e.g., thumb).
- Plane Joints: Allow gliding movements (e.g., intercarpal joints).
Synovial Fluid and Joint Function
- Synovial Fluid: A viscous fluid secreted by the synovial membrane, providing lubrication, reducing friction, and supplying nutrients to the articular cartilage.
Clinical Relevance
Common Disorders
- Osteoporosis:
- Etiology: Age, hormonal changes, inadequate calcium and vitamin D intake, and sedentary lifestyle.
- Assessment: Bone density testing (DEXA scans), patient history, and risk factors.
- Nursing Management: Promote lifestyle changes, nutritional education, and medications (e.g., bisphosphonates).
- Arthritis:
- Types: Osteoarthritis (degenerative) and rheumatoid arthritis (autoimmune).
- Symptoms: Pain, stiffness, swelling, and decreased range of motion.
- Nursing Management: Pain management, physical therapy, patient education on joint protection strategies.
- Fractures:
- Types: Simple, compound, comminated, and greenstick fractures.
- Nursing Management: Assess for circulation, sensation, and movement (CSM), immobilization techniques, and education on healing processes.
- Scoliosis:
- Description: An abnormal lateral curvature of the spine. It can be idiopathic or secondary to other conditions.
- Assessment: Physical examination, X-rays, and monitoring of progression.
- Nursing Management: Education on brace use, physical therapy, and, in severe cases, surgical intervention.
Assessment Techniques
- Physical Examination: Inspect and palpate bones and joints for abnormalities. Assess range of motion, strength, and stability.
- Imaging Studies: X-rays identify fractures, while MRIs provide detailed images of soft tissues around joints.
- Bone Density Tests: DEXA scans measure bone mineral density to assess osteoporosis risk.