Functions and Anatomy of Bones

Functions of Bones

• Bones provide support for the body.
• Bones protect internal organs.
• Bones serve as levers for movement.
• Bones store minerals like calcium and phosphorus.
• Bones produce blood cells in red bone marrow.
• Bones store energy in yellow bone marrow.

Classification of Bones

• Bones are classified by shape: long, short, flat, irregular.
• Long bones are the most common type of bone in the body.

Anatomy of a Long Bone

• Diaphysis: shaft of the bone
• Epiphysis: ends of the bone
• Epiphyseal plate: growth plate where bone lengthens
• Articular cartilage: covers the ends of the bone at joints, reducing friction
• Medullary cavity: hollow space in the diaphysis, filled with bone marrow
• Periosteum: tough outer membrane, provides blood supply and attachment for tendons and ligaments.
• Endosteum: thin inner membrane that lines the medullary cavity

Bone Cells

• Osteoblasts: responsible for bone formation.
• Osteoclasts: responsible for bone resorption (breakdown).
• Osteocytes: mature bone cells, help maintain bone matrix.
• Bone lining cells: found on the surface of bone, regulate bone formation and resorption.

### Bone Matrix

• The organic component (collagen) provides flexibility to bone.
• The inorganic component (calcium phosphate) provides hardness to bone.

Compact Bone

• Found in the diaphysis of long bones.
• Provides strength and support.
• Functional unit: osteon
• Rings of calcified bone matrix are called lamellae.

Spongy Bone

• Found in the epiphysis of long bones, and in flat bones.
• Lighter than compact bone.
• Trabeculae (interconnected rods) help distribute stress.

Ossification

• Begins in utero, at about 8 weeks.
• Intramembranous ossification: flat bones, bone forms directly from mesenchyme.
• Endochondral ossification: most bones, bone forms from hyaline cartilage model.
• Endochondral ossification is the more common type of bone formation.

Bone Growth

• Interstitial growth: occurs in length, at epiphyseal plate.
• Appositional growth: occurs in width, adds bone tissue to the periosteal surface.

Calcium Homeostasis

• Hormones regulate calcium levels in bone and blood.
• Parathyroid hormone (PTH): released when blood calcium decreases, increases calcium levels.
• Calcitonin: released when blood calcium increases, decreases calcium levels.
• Exercise promotes bone growth, increasing mechanical stress, which stimulates osteoblast activity.

The Skeletal System

• Axial skeleton: skull, vertebral column, thoracic cage.
• Appendicular skeleton: bones of the limbs and girdles.

The Skull

• Cranial vault: bones that protect the brain.
• Facial bones: bones of the face.
• Mandible: only mobile bone of the skull.
• The skull consists of 22 bones: 8 cranial bones and 14 facial bones.

### The Vertebral Column

• Cervical region: 7 vertebrae.
• Thoracic region: 12 vertebrae.
• Lumbar region: 5 vertebrae.
• Sacral region: 5 fused vertebrae.
• Coccygeal region: 4 fused vertebrae.
• The vertebral column is divided into regions, each specialized for different functions.
• Intervertebral discs: cushioning and absorbing shocks between vertebrae, allowing for a flexible spine.

The Thoracic Cage

• Protects internal organs (heart and lungs).
• Ribs: 12 pairs; 7 vertebrosternal ribs connect to sternum directly.
• Sternum: breastbone, anterior part of thoracic cage.

The Upper Limb

• Pectoral girdle: clavicle and scapula, connects upper limbs to axial skeleton.
• Humerus: bone of the upper arm.
• Radius and ulna: bones of the forearm.
• Carpal bones: wrist bones.

The Lower Limb

• Pelvis: formed by two coxal (hip) bones and sacrum.
• Femur: thigh bone, longest and strongest bone in the body.
• Tibia and fibula: bones of the lower leg.
• Tarsal bones: ankle bones.

Classification of Joints

• Structural classification
  • Fibrous: bones held together by fibrous connective tissue.
  • Cartilaginous: bones held together by cartilage.
  • Synovial: bones separated by a joint cavity containing synovial fluid.
• Functional classification:
  • Synarthroses: immovable joints.
  • Amphiarthroses: slightly movable joints.
  • Diarthroses (synovial joints): freely movable joints.

Synovial Joints

• Articular capsule: surrounds the joint, encloses synovial cavity.
• Ligaments: dense fibrous connective tissue, connect bone to bone.
• Tendons: connect muscle to bone.
• Bursa: fluid-filled sac, reduces friction between tendons and bones.
• Meniscus: fibrocartilaginous pad that cushions the joint (knee).

Types of Synovial Joints

• Pivot joint: uniaxial movement, allows for rotation (e.g., radius and ulna)
• Hinge joint: uniaxial movement, allows flexion and extension (e.g., elbow and knee)
• Conyloid joint : biaxial movement, allows flexion, extension, abduction, adduction and circumduction (e.g., metacarpophalangeal joints).
• Saddle joint: biaxial movement, allows flexion, extension, abduction, adduction and circumduction (e.g., carpometacarpal joint of the thumb)
• Plane joint: multiaxial movement, allows for gliding motions (e.g., intercarpal joints and intertarsal joints).
• Ball and socket joint: multiaxial movement, allows for flexion, extension, abduction, adduction, circumduction, and rotation (e.g., hip and shoulder)

Body Movements at Joints

• Flexion: decreases the angle between bones.
• Extension: increases the angle between bones.
• Abduction: movement away from the midline of the body
• Adduction: movement toward the midline of the body.
• Circumduction: circular motion of a limb.
• Rotation: turning a bone around its longitudinal axis.
• Pronation: rotation of the forearm so that the palm faces posteriorly.
• Supination: rotation of the forearm so that the palm faces anteriorly.
• Eversion: turning the sole of the foot outward.
• Inversion: turning the sole of the foot inward.

Important Synovial Joints

• The intervertebral joints (between vertebrae) are synovial joints.
• Atlanto-occipital joint: articulation between the atlas (C1) and the occipital bone, allows for nodding and shaking the head.
• Temporomandibular joint: articulation between the temporal bone and the mandible, allows for opening and closing the mouth, as well as moving the mandible side to side.
• Glenohumeral (shoulder) joint: articulation between the humerus and glenoid fossa of the scapula, very mobile.
• Elbow joint: articulation between the humerus, radius, and ulna, allows for flexion, extension and some rotation.
• Hip joint: articulation between the femur and acetabulum of the hip bone, very stable.
• Knee joint: most complex joint in the body, articulation between the femur, tibia, and patella. Allows for flexion, extension, and some rotation.
• Ankle joint: articulation between the tibia, fibula, and talus, allows for dorsiflexion, plantar flexion, inversion, and eversion.

Explore the essential functions of bones in the human body, including support, protection, and blood cell production. Learn about the classification and anatomy of long bones, as well as the various types of bone cells responsible for bone health.