Physiology of the Skeletal System - For PCL General Medicine Students Author: SB Thapaapa
Introduction
The skeletal system physiology focuses on the functioning of bones, joints, and supporting tissues that maintain posture, facilitate movement, protect vital organs, and serve as a storehouse for minerals like calcium and phosphorus. Bones are not lifeless structures — they are dynamic, living tissues that continuously remodel throughout life.
This chapter explains how bones grow, maintain themselves, adapt to mechanical stress, and repair damage. Understanding bone physiology helps NHPC students grasp the basis of orthopedic diseases, fractures, metabolic disorders, and calcium imbalance in clinical practice.
[Diagram Placeholder: Overview of skeletal physiology – growth, remodeling, repair, and mineral regulation]
1. Bone Growth and Development
Bone growth begins even before birth and continues until early adulthood. The process through which bones are formed is called ossification or osteogenesis.
Skeletal System – Bones, Joints, and Functions Anatomy & Physiology – NHPC Exam Guide (For PCL General Medicine Students
Introduction
The skeletal system forms the framework of the human body. It provides support, protection, and shape, allowing the body to move and function properly. It also plays vital roles in blood cell formation, mineral storage, and leverage for movement. For NHPC students, understanding the skeletal system is essential for diagnosing fractures, joint disorders, and metabolic bone diseases.
The adult human skeleton consists of about 206 bones, connected by joints, ligaments, and cartilage. These bones are classified by shape and function. The skeletal system works together with the muscular system to produce movement, forming the musculoskeletal system.
[Diagram Placeholder: Overview of human skeleton showing axial and appendicular divisions]
Functions of the Skeletal System
1. Support: Provides a rigid framework that supports the body and maintains its shape.2. Protection: Protects vital organs – skull protects brain, ribs protect heart and lungs, vertebrae protect spinal cord.3. Movement: Acts as levers for muscles; joints provide flexibility for motion.4. Mineral Storage: Stores calcium, phosphorus, and other minerals essential for body functions.5. Blood Cell Formation (Hematopoiesis): Bone marrow produces red and white blood cells and platelets.6. Energy Storage: Yellow marrow stores fat as an energy reserve.
Did You Know? A newborn baby has around 270 bones, which later fuse to form 206 bones in an adult.
Classification of Bones
Bones can be classified in several ways — by location, shape, or structure.
1. By Location
- Axial Skeleton: Bones of the skull, vertebral column, ribs, and sternum (total 80 bones). Supports and protects vital organs.- Appendicular Skeleton: Bones of the limbs and girdles (shoulder and pelvic) – total 126 bones. Helps in movement and locomotion.
2. By Shape
- Long bones: Longer than wide (e.g., humerus, femur, tibia). Act as levers.- Short bones: Cube-shaped bones that provide stability (e.g., carpals, tarsals).- Flat bones: Thin, flattened bones for protection (e.g., skull, sternum, ribs).- Irregular bones: Complex shapes (e.g., vertebrae, hip bones).- Sesamoid bones: Small, round bones embedded in tendons (e.g., patella).
[Diagram Placeholder: Classification of bones with labeled examples]
Structure of Bone
A typical long bone (like the femur) has several parts:- Diaphysis: Shaft of the bone, made of compact bone.- Epiphysis: Ends of the bone, made of spongy (cancellous) bone.- Metaphysis: Area between diaphysis and epiphysis; includes growth plate in children.- Periosteum: Outer covering of bone containing blood vessels and nerves; aids in repair and growth.- Medullary cavity: Central cavity containing bone marrow (yellow or red).- Articular cartilage: Smooth surface covering bone ends, allowing joint movement.
Types of bone tissue:1. Compact bone: Dense and strong, forms the outer layer of bones.2. Spongy bone (cancellous): Light and porous, contains bone marrow for blood formation.
[Diagram Placeholder: Long bone structure labeled]
Exam Focus: NHPC often asks which part of bone produces blood cells – the red bone marrow found in spongy bone.
Bone Cells
Bone is a living tissue made up of specialized cells:- Osteoblasts: Build new bone tissue (bone-forming cells).- Osteocytes: Mature bone cells that maintain the bone matrix.- Osteoclasts: Break down bone tissue for remodeling and calcium release.
Clinical Insight: In diseases like osteoporosis, osteoclast activity exceeds osteoblast activity, leading to weak bones.
Joints (Articulations)
Joints are places where two or more bones meet. They allow varying degrees of movement depending on their structure. Joints are supported by ligaments, tendons, and synovial fluid.
Classification of Joints
A. Structural Classification1. Fibrous joints: Bones joined by fibrous tissue; little or no movement (e.g., sutures of skull).2. Cartilaginous joints: Bones joined by cartilage; limited movement (e.g., between vertebrae, pubic symphysis).3. Synovial joints: Freely movable joints with synovial fluid (e.g., knee, shoulder, elbow).
B. Functional Classification1. Synarthrosis: Immovable joints.2. Amphiarthrosis: Slightly movable joints.3. Diarthrosis: Freely movable joints (all synovial joints).
[Diagram Placeholder: Synovial joint structure showing capsule, cartilage, and fluid]
Structure of a Synovial Joint
A typical synovial joint has:- Articular cartilage: Smooth surface covering bone ends.- Joint capsule: Fibrous outer covering enclosing the joint.- Synovial membrane: Inner lining that secretes synovial fluid.- Synovial fluid: Lubricates the joint and nourishes cartilage.- Ligaments: Connect bone to bone, providing stability.
Types of Synovial Joints
1. Hinge joint: Allows movement in one direction (e.g., elbow, knee).2. Ball and socket joint: Allows movement in all directions (e.g., shoulder, hip).3. Pivot joint: Rotation around an axis (e.g., between atlas and axis of neck).4. Gliding joint: Flat surfaces slide over each other (e.g., carpals).5. Saddle joint: Allows back-and-forth and side-to-side movement (e.g., thumb).6. Condyloid joint: Allows movement but no rotation (e.g., wrist joint).
Did You Know? The smallest joints in the human body are found between the ear bones (ossicles).
Clinical Correlation
Common skeletal and joint disorders include:- Fractures: Break in a bone due to trauma. Types include simple, compound, comminuted, and greenstick.- Arthritis: Inflammation of joints causing pain and stiffness.- Osteoporosis: Loss of bone mass leading to fragile bones, common in elderly women.- Rickets: Bone softening in children due to Vitamin D deficiency.- Osteoarthritis: Degeneration of joint cartilage, leading to pain and limited movement.
Clinical Tip: Adequate calcium, Vitamin D, and exercise help maintain bone strength and prevent osteoporosis.
Summary Table
| Classification | Example | Movement ||----------------|----------|-----------|| Fibrous Joint | Skull sutures | None || Cartilaginous Joint | Intervertebral discs | Slight || Synovial Joint | Knee, shoulder | Free |
Key Points to Remember:- Adult skeleton = 206 bones- Bone marrow forms blood cells- Joints allow flexibility and movement- Calcium and Vitamin D are essential for bone health
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