Human Anatomy: Bone Types and Functions

Bone Classification

• Long Bones: Leverage for movement; cylindrical shape; found in arms, legs, hands, and feet.
• Short Bones: Support and facilitate movement; cube-shaped; carpals and tarsals.
• Flat Bones: Protect internal organs; thin, round, or flat; skull (upper), ribs, hips, sternum.
• Sesamoid Bones: Reinforcement and stress reduction on tendons; small, round, embedded in tendons (often near joints).
• Irregular Bones: Protect internal organs; complex shapes; vertebrae, sacrum, and parts of the face (lower).

Axial Skeleton

• Vertebral Column: Central vertical axis; protects vital organs.
  • Cervical: Neck (C1-C7). C1 (atlas) holds skull, C2 (axis) with dens to hold C1.
  • Thoracic: Mid/upper back, heart shape; T1-T12. Longer transverse processes for rib attachment.
  • Lumbar: Lower back, boxy; L1-L5; wider for weight-bearing.
• Thoracic Cage: Sternum anchors ribs; 12 pairs of ribs.
  • True Ribs: 1-7; connect to sternum with costal cartilage.
  • False Ribs: 8-10; costal cartilages attach to the cartilage of the next higher rib.
  • Floating Ribs: 11-12; attach only to the vertebral column (back for kidneys).
• Skull: Includes ossicles (inner ear) and hyoid (tongue base); floating. Sacrum and coccyx are separate at birth and fuse by age 20.

Appendicular Skeleton

• Pectoral Girdle: Clavicle (collarbone) and scapula (shoulder blade); attach upper limbs to axial skeleton.
  • Arms: Humerus, radius, ulna.
  • Hands: Carpals, metacarpals, phalanges.
• Pelvic Girdle: Hip bone, pubic symphysis; attach lower limbs to axial skeleton.
  • Legs: Femur, patella, fibula, tibia.
  • Feet: Tarsals, calcaneus, metatarsals, phalanges.

Epiphyseal Plates

• Growth plates; hyaline cartilage at the end of long bones, for new cell addition to the bone.

Joint Classification

• Fibrous Joints: Protection, strength, stability; mostly immovable, a few slightly movable; no joint cavity.
  • Sutures: Skull.
  • Syndesmosis: Between tibia and fibula.
  • Gomphosis: Tooth sockets.
• Cartilaginous Joints: Strength, shock absorption, limited movement; bones connected by cartilage; no joint cavity.
  • Ribs, pubic symphysis, intervertebral discs.
• Synovial Joints: Stability, movement, friction reduction, shock absorption; freely movable, closed space (joint cavity) with synovial fluid.
  • Knee, elbow, hip, hands, and feet.

Supporting Structures

• Ligaments: Connect bone-to-bone/cartilage; tough, fibrous bands for stability, preventing dislocations, and protecting joints.
• Tendons: Connect muscle to bone; thick, fibrous cords; create movement when muscles contract.
• Cartilage: Smooth, flexible tissue at bone ends and in joints; reduces friction, absorbs shock, and cushions.

Internal Bone Structure

• Osteoblast: Secrete collagen and hydroxyapatite; create new bone tissue.
• Osteocyte: Trapped within bone matrix; maintain bone health.
• Osteoclast: Secrete enzymes to reabsorb old bone.

Bone Chemistry

• Calcium Absorption: Vitamin D diffuses across intestinal cells, binds to intracellular receptors, triggering channel protein production for increased calcium absorption.
• Osseous Bone Tissue: Collagen fiber matrix, living cells, and inorganic compounds (calcium carbonate, hydroxyapatite, inorganic salts).

Fracture Repair

• Hematoma Formation: Blood vessels break, form clots, disrupt blood flow, and kill surrounding bone cells.
• Internal Callus Formation: Chondrocytes secrete fibrocartilaginous matrix between broken ends (48 hrs after).
• External Callus Formation: Periosteal chondrocytes and osteoblasts add hyaline cartilage and new bone; stabilize externally.
• Endochondral Ossification: Begins inside callus.
• Healed Fracture: Internal and external calluses unite; compact bone replaces spongy.

Motion Terms

• Abduction: Movement away from the body.
• Adduction: Movement toward the body.
• Extension: Increases angle of a joint.
• Flexion: Decreases angle of a joint.
• Supination: Palm up.
• Pronation: Palm down.
• Dorsiflexion: Flexed foot.
• Plantar Flexion: Pointed foot.
• Lateral Rotation: Rotating outward.
• Medial Rotation: Rotating inward.
• Circumduction: Rotation from a joint like shoulder.