Skeletal System- Introduction

Introduction

The skeletal system comprises bones, joints, cartilage, and connective tissues that support body structure, protect vital organs, enable movement, produce blood cells, and store essential minerals—forming the foundation of the musculoskeletal system.

Role of the Skeletal System

The skeletal system serves as the structural framework of the human body. It not only provides support and shape but also protects vital organs, facilitates movement in conjunction with the muscular system, stores essential minerals, and houses bone marrow for blood cell production (haematopoiesis). For nurses, a working knowledge of the skeletal system is vital for patient assessment, injury management, and rehabilitation, as well as for understanding various pathological conditions affecting bones and joints.

Overview of the Skeletal System

Definition

The skeletal system refers to the collective framework of bones, cartilage, ligaments, and joints that provide structural support and leverage for movement. In adults, the human skeleton typically consists of 206 bones, though this number can vary slightly due to anatomical variations.

Major Functions

• Support: Maintains body shape and posture.
• Protection: Shields vital organs (e.g., the skull protects the brain, the rib cage protects the heart and lungs).
• Movement: Works with muscles to enable bodily movement.
• Mineral Storage: Stores calcium and phosphorus, essential for various physiological processes.
• Blood Cell Production: Bone marrow produces red and white blood cells and platelets.
• Fat Storage: Yellow bone marrow acts as a reservoir for adipose tissue.

Components

• Bones: Rigid organs forming the skeleton’s main structure.
• Cartilage: Flexible connective tissue providing cushioning and structure at joints.
• Ligaments: Bands of connective tissue linking bones together at joints.
• Joints: Articulations where two or more bones meet, enabling movement and flexibility.

Classification of Bones

Bones are classified based on their shape and structure, which relates to their specific functions within the body. Understanding these categories aids nurses in identifying skeletal landmarks during assessment and in recognising the implications of different types of fractures.

Long Bones

Long bones are characterised by a greater length than width and are primarily found in the limbs. Examples include the femur, tibia, fibula, humerus, ulna, and radius. These bones act as levers, facilitating movement and bearing the body’s weight.

Short Bones

Short bones are roughly cube-shaped and provide stability with limited movement. They are predominantly found in the wrists (carpals) and ankles (tarsals).

Flat Bones

Flat bones are thin, flattened, and often slightly curved. They serve as points of attachment for muscles and protect internal organs. Examples include the sternum, ribs, scapulae, and most bones of the skull.

Irregular Bones

Irregular bones have complex shapes that do not fit into the previous categories. They include the vertebrae, sacrum, and certain facial bones, each serving specialised functions such as protecting nervous tissue or providing multiple points of articulation.

Sesamoid Bones

Sesamoid bones are small, round bones embedded within tendons. The patella (kneecap) is the largest and most notable example. These bones protect tendons from stress and wear.

Structure of Bones

Gross Anatomy

A bone consists of several distinct regions:

• Diaphysis: The shaft or central part of a long bone, composed mainly of compact bone providing strength.
• Epiphyses: The expanded ends of long bones, filled with spongy bone and red marrow.
• Metaphysis: The area between diaphysis and epiphysis, containing the growth plate in children and adolescents.
• Periosteum: A dense, fibrous membrane covering the outer surface of bones, housing nerves and blood vessels.
• Endosteum: A thin membrane lining the medullary cavity within the bone.
• Medullary Cavity: The central cavity within the diaphysis, containing yellow marrow in adults.

Microscopic Anatomy

Bone tissue is classified into two main types:

• Compact (Cortical) Bone: Dense and strong, forming the outer layer of bones.
• Spongy (Cancellous) Bone: Light and porous, found mainly at the ends of long bones and within flat bones, housing red marrow.

The basic structural unit of compact bone is the osteon or Haversian system, consisting of concentric rings (lamellae) around a central canal containing blood vessels and nerves.

Bone Cells

• Osteoblasts: Cells responsible for bone formation by synthesising new bone matrix.
• Osteocytes: Mature bone cells that maintain bone tissue; they reside in small spaces called lacunae.
• Osteoclasts: Large cells that break down bone tissue, aiding in bone remodelling and calcium homeostasis.

Bone Development and Growth

Ossification

Ossification is the process by which bone tissue forms. It occurs in two primary ways:

• Intramembranous Ossification: Direct formation of bone from connective tissue, seen mainly in flat bones like the skull.
• Endochondral Ossification: Replacement of cartilage by bone, typical in long bones and most of the skeleton.

Growth Plates (Epiphyseal Plates)

Growth plates are regions of cartilage located at the ends of long bones in children and adolescents. They are responsible for longitudinal bone growth. Once growth ceases, these plates ossify and become the epiphyseal line, marking skeletal maturity.

Bone Remodelling

Bone remodelling is a continuous process involving the resorption of old bone by osteoclasts and formation of new bone by osteoblasts. This process allows bones to adapt to stress, repair minor damage, and regulate calcium levels. Hormones such as parathyroid hormone, calcitonin, and vitamin D play key roles in these processes.

Axial Skeleton

The axial skeleton forms the central axis of the body and consists of the skull, vertebral column, and rib cage. These structures provide support and protection for the brain, spinal cord, and thoracic organs.

Skull

The skull is composed of 22 bones, divided into:

• Cranial Bones (8): Enclose and protect the brain (e.g., frontal, parietal, temporal, occipital bones).
• Facial Bones (14): Form the framework of the face and house the upper and lower teeth (e.g., maxilla, mandible, zygomatic, nasal bones).

The skull also contains several foramina (openings) for nerves and blood vessels, and sinuses that lighten the skull and enhance voice resonance.

Vertebral Column

The vertebral column, or spine, consists of 33 vertebrae in five regions:

1. Cervical (7): Supporting the head and allowing for its movement.
2. Thoracic (12): Articulating with the ribs.
3. Lumbar (5): Bearing the weight of the upper body.
4. Sacral (5, fused): Forming the sacrum, part of the pelvis.
5. Coccygeal (4, fused): Forming the coccyx or tailbone.

Intervertebral discs between vertebrae act as shock absorbers and allow flexibility.

Rib Cage

The rib cage consists of 12 pairs of ribs, the sternum, and thoracic vertebrae. It protects the heart and lungs and assists in breathing. Ribs are classified as:

• True Ribs (1-7): Attach directly to the sternum via costal cartilage.
• False Ribs (8-10): Attach indirectly to the sternum.
• Floating Ribs (11-12): Do not attach to the sternum.

Appendicular Skeleton

The appendicular skeleton comprises the limbs and the girdles that attach them to the axial skeleton, enabling movement and manipulation of the environment.

Upper Limbs

• Shoulder Girdle: Clavicle (collarbone) and scapula (shoulder blade) provide attachment points for muscles and support arm movement.
• Arm: Humerus in the upper arm.
• Forearm: Radius and ulna.
• Hand: Carpals (wrist bones), metacarpals (palm bones), and phalanges (finger bones).

Lower Limbs

• Pelvic Girdle: Formed by the hip bones (ilium, ischium, pubis), supports the weight of the upper body and protects pelvic organs.
• Thigh: Femur, the longest and strongest bone in the body.
• Leg: Tibia (shinbone) and fibula.
• Foot: Tarsals (ankle bones), metatarsals (foot bones), and phalanges (toe bones).

Joints

Classification of Joints

Joints, or articulations, are classified based on their structure and the type of movement they permit:

1. Fibrous Joints: Bones joined by dense connective tissue; immovable or only slightly movable (e.g., sutures of the skull).
2. Cartilaginous Joints: Bones connected by cartilage; allow limited movement (e.g., intervertebral discs, pubic symphysis).
3. Synovial Joints: Most common and freely movable joints; characterised by a synovial cavity filled with fluid (e.g., knee, shoulder, hip).

Structure of Synovial Joints

• Articular Cartilage: Covers bone surfaces, reducing friction and absorbing shock.
• Joint (Synovial) Cavity: Space containing synovial fluid for lubrication.
• Articular Capsule: Encloses the joint, composed of an outer fibrous layer and an inner synovial membrane.
• Ligaments: Strengthen and stabilise joints.
• Bursae and Tendon Sheaths: Fluid-filled sacs reducing friction where tendons or skin rub over bone.

Types of Synovial Joints

• Plane (Gliding) Joints: Allow sliding movements (e.g., intercarpal joints).
• Hinge Joints: Permit flexion and extension (e.g., elbow, knee).
• Pivot Joints: Allow rotation (e.g., atlantoaxial joint in the neck).
• Permit movement in two planes (e.g., wrist).
• Saddle Joints: Allow movement back and forth and side to side (e.g., thumb joint).
• Ball-and-Socket Joints: Allow movement in all directions (e.g., shoulder, hip).

Clinical Relevance

Common Disorders of the Skeletal System

• Fractures: Breaks in the continuity of bone, classified as simple (closed) or compound (open), among others.
• Osteoporosis: A condition characterised by reduced bone density and increased fracture risk, common in the elderly, especially post-menopausal women.
• Arthritis: Inflammation of joints, leading to pain and reduced mobility. Common types include osteoarthritis and rheumatoid arthritis.
• Osteomalacia/Rickets: Softening of bones due to vitamin D deficiency; rickets refers to the condition in children.
• Scoliosis, Kyphosis, Lordosis: Abnormal curvatures of the spine, potentially leading to pain and functional impairment.

Fractures: Types and Nursing Care

Nurses play a critical role in the management of fractures. Types of fractures include:

• Transverse: Straight across the bone.
• Oblique: Diagonal to the bone’s axis.
• Spiral: Twisting injury.
• Comminuted: Bone breaks into several pieces.
• Greenstick: Incomplete fracture, common in children.

Nursing care includes immobilisation, monitoring for complications (e.g., infection, compartment syndrome), pain management, patient education, and supporting rehabilitation.

Osteoporosis: Prevention and Management

Osteoporosis is a major concern in the ageing population. Nurses should focus on patient education regarding nutrition (adequate calcium and vitamin D), weight-bearing exercise, fall prevention, and medication adherence. Early identification and intervention can prevent debilitating fractures.

Nursing Care for Skeletal Disorders

• Assessment of pain, swelling, deformity, and functional impairment.
• Monitoring neurovascular status (circulation, sensation, movement).
• Providing assistive devices (e.g., splints, crutches).
• Educating patients and families about the condition, treatment options, and rehabilitation.
• Encouraging adherence to therapy and follow-up appointments.

Practical Applications for Nursing Practice

Assessment Techniques

• Inspection: Observe for deformity, swelling, or asymmetry.
• Palpation: Assess for tenderness, warmth, or abnormal movement.
• Range of Motion (ROM): Evaluate joint mobility and function.
• Neurovascular Assessment: Check pulses, capillary refill, sensation, and movement distal to injury.

Patient Education

• Explain the nature of skeletal injuries or conditions in simple terms.
• Demonstrate exercises and safe movement techniques.
• Instruct on the use of assistive devices and the importance of medication adherence.
• Advise on fall prevention strategies, especially in the elderly.

Documentation

• Accurate recording of assessment findings, interventions, and patient responses.
• Use of standardised tools and terminology for clarity and continuity of care.
• Timely communication of changes in condition to the wider healthcare team.

Key Takeaways

• The skeletal system provides the body’s framework, supports movement, protects organs, and is central to blood cell production and mineral storage.
• Bones are classified by shape and structure, each serving specific functions.
• Joints enable movement and are classified by their structure and the degree of movement they permit.
• Common skeletal disorders include fractures, osteoporosis, and arthritis, all of which have significant implications for nursing care.
• Effective nursing practice requires thorough assessment, patient education, and documentation related to the skeletal system.
• Continuous learning and application of anatomical knowledge enhance patient outcomes and professional development.

REFERENCES

1. Ross and Wilson, Anatomy and Physiology in Health and Illness, Fourteenth Edition, 1 July 2022, ISBN-13: 978-0323834612.
2. Roger Watson, Anatomy and Physiology for Nurses, 14th Edition, 12-06-2018, ISBN: 9780702077418
3. P.R Asha Latha, Text Book of Applied Anatomy & Physiology for Nurses, 7th Edition,3 January 2024, ISBN-13: 978-9356968622.
4. Bryan H. Derikson, Tortora’s Principles of Anatomy and Physiology, 16th Edition, August 2023, ISBN: 978- 1119400066.
5. Standring S, ed. Gray’s Anatomy: The Anatomical Basis of Clinical Practice. 42nd ed. London: Elsevier; 2020. pp. 75–102. ISBN 978-0702077050.
6. Rohen JW, Yokochi C, Lutjen-Drecoll E. Color Atlas of Anatomy: A Photographic Study of the Human Body. 9th ed. Philadelphia: Lippincott Williams & Wilkins; 2021. pp. 14–34. ISBN 978-1975151346.
7. Anatomy.co.uk, Skeletal System, Last updated on April 24, 2025, https://anatomy.co.uk/skeletal-system

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