Chapter 6: Bones and Bone Structure

Bone Shapes and Landmarks

Bones are classified by their shapes and possess various anatomical landmarks that serve as points of attachment, articulation, or passage for nerves and blood vessels.

• Bone Shapes:

  • Flat bones: Thin, often curved (e.g., skull, sternum).

  • Long bones: Longer than wide (e.g., femur, humerus).

  • Irregular bones: Complex shapes (e.g., vertebrae).

  • Sesamoid bones: Small, round, embedded in tendons (e.g., patella).

  • Short bones: Nearly equal in length and width (e.g., carpals, tarsals).

• Bony Landmarks:

  • Head: Expanded articular end of a bone.

  • Tubercle: Small, rounded projection.

  • Epiphysis: End part of a long bone.

  • Diaphysis: Shaft of a long bone.

  • Metaphysis: Region between diaphysis and epiphysis.

  • Other landmarks: Trochlea, condyle, neck, trochanter, facet, canal, process, sinus, fissure, foramen, ramus, spine, crest, fossa, line.

• Number of Bones:

  • Total: 206 bones in adult human skeleton.

  • Axial skeleton: 80 bones (skull, vertebral column, thoracic cage).

  • Appendicular skeleton: 126 bones (limbs, girdles).

Compact vs. Spongy Bone

Bones contain two main types of tissue: compact and spongy bone, each with distinct structures and functions.

• Compact Bone:

  • Dense, forms outer layer.

  • Contains osteons (Haversian systems): concentric lamellae around a central canal.

  • Features: canaliculi, lacunae, central canal, lamellae, endosteum, periosteum.

• Spongy Bone:

  • Porous, found at ends of long bones and inside flat bones.

  • Contains trabeculae: lattice-like network.

  • Spaces filled with bone marrow.

• Comparison Table:

Cells of Cartilage and Bone

Bone and cartilage are maintained by specialized cells, each with unique functions.

• Mesenchymal cells: Stem cells that differentiate into other cell types.

• Chondroblasts: Produce cartilage matrix.

• Chondrocytes: Mature cartilage cells, maintain matrix.

• Osteogenic cells: Stem cells that become osteoblasts.

• Osteoblasts: Build bone matrix (osteoid).

• Osteocytes: Mature bone cells, maintain bone tissue.

• Osteoclasts: Break down bone matrix (resorption).

Bone Marrow: Red vs. Yellow

Bone marrow is a soft tissue found in bone cavities, with two main types.

• Red bone marrow: Site of hematopoiesis (blood cell production); found in flat bones and ends of long bones.

• Yellow bone marrow: Stores fat; found in diaphysis of long bones.

Bone Formation Processes

Bones form through two main processes: endochondral and intramembranous ossification.

• Endochondral Ossification: Bone replaces cartilage model; most bones form this way.

  1. Cartilage model develops.

  2. Primary ossification center forms in diaphysis.

  3. Secondary ossification centers form in epiphyses.

  4. Epiphyseal plate allows lengthwise growth.

• Intramembranous Ossification: Bone forms directly from mesenchymal tissue; flat bones (e.g., skull) form this way.

  1. Mesenchymal cells cluster and differentiate.

  2. Osteoblasts secrete osteoid.

  3. Mineralization occurs.

  4. Formation of spicules and trabeculae.

• Appositional Growth: Increases bone diameter by adding new layers to the periosteum.

Functions of the Skeletal System

The skeletal system serves multiple functions beyond protection.

• Mineral storage: Stores calcium and phosphate.

• Blood cell production: Hematopoiesis in red marrow.

• Support: Framework for the body.

• Leverage: Facilitates movement.

• Protection: Shields vital organs.

Bone Growth and Hormonal Regulation

Bone growth occurs at the epiphyseal plate and is regulated by hormones.

• Epiphyseal plate: Site of lengthwise growth.

• Growth hormone: Stimulates bone growth.

Bone Growth Abnormalities

Various disorders affect bone growth and development.

• Marfan syndrome: Connective tissue disorder, long limbs.

• Acromegaly: Excess growth hormone in adults, enlarged bones.

• Gigantism: Excess growth hormone in children, abnormal height.

• Club foot: Congenital deformity.

• Pituitary growth failure: Insufficient growth hormone.

• Achondroplasia: Impaired cartilage growth, short stature.

• FOP (Fibrodysplasia Ossificans Progressiva): Soft tissues turn to bone.

Fractures and Healing

Fractures are breaks in bone, classified as open or closed, and heal in four steps.

• Open fracture: Bone breaks through skin.

• Closed fracture: Bone does not break skin.

• Four Steps of Fracture Repair:

  1. Hematoma formation

  2. Callus formation

  3. Callus ossification

  4. Bone remodeling

Calcium Regulation and Hormones

Calcium levels are tightly regulated by hormones and organs.

• Hypocalcemia: Low blood calcium; causes muscle spasms.

• Hypercalcemia: High blood calcium; causes weakness.

• Hormones:

  • PTH (Parathyroid hormone): Increases blood calcium by stimulating osteoclasts, increasing intestinal absorption, and reducing renal excretion.

  • Calcitonin: Lowers blood calcium by inhibiting osteoclasts and increasing renal excretion.

  • Calcitriol: Active vitamin D, increases calcium absorption in intestines.

• Organs involved: Bones, kidneys, intestines.

Minerals in the Body

Minerals are essential for bone health and metabolic functions.

• Most abundant: Calcium, phosphate.

• Roles: Structure, nerve transmission, muscle contraction.

Chapter 7: The Skeleton

Axial vs. Appendicular Skeleton

The skeleton is divided into two main regions.

• Axial skeleton: Skull, vertebral column, thoracic cage.

• Appendicular skeleton: Limbs, pectoral and pelvic girdles.

Skull Bones and Sutures

The skull consists of cranial and facial bones, connected by sutures.

• Cranial bones: Frontal, parietal, temporal, occipital, sphenoid, ethmoid.

• Facial bones: Maxilla, mandible, zygomatic, nasal, lacrimal, palatine, inferior nasal concha, vomer.

• Sutures: Immovable joints; e.g., coronal, sagittal, lambdoid, squamous.

• Processes/foramina: Openings and projections for nerves and vessels.

• Associated bones: Auditory ossicles, hyoid bone.

• Infant skull: Fontanelles are soft spots between unfused bones.

Vertebral Column

The vertebral column supports the body and protects the spinal cord.

• Cervical: 7 vertebrae

• Thoracic: 12 vertebrae

• Lumbar: 5 vertebrae

• Sacrum: 5 fused bones

• Coccyx: 3-5 fused bones

• Normal curves: Cervical, thoracic, lumbar, sacral

• Abnormal curves: Scoliosis, kyphosis, lordosis

• Atlas (C1): Most superior, supports skull

• Axis (C2): Has dens, allows rotation

• Spinous process differences: Cervical (bifid), thoracic (long, downward), lumbar (short, blunt)

• Transverse foramina: Found in cervical vertebrae; transmit vertebral arteries.

Thoracic Cage

The thoracic cage protects vital organs and supports respiration.

• Components: Sternum, ribs, thoracic vertebrae

• True ribs: 1-7, directly attached to sternum

• False ribs: 8-12, not directly attached

• Floating ribs: 11-12, no anterior attachment

• Cartilage: Hyaline cartilage connects ribs to sternum

Pectoral and Pelvic Girdles

Girdles attach limbs to the axial skeleton.

• Pectoral girdle: Clavicle and scapula

  • Scapula structures: acromion, coracoid process, glenoid cavity

  • Clavicle articulates with sternum and scapula

• Pelvic girdle: Ilium, ischium, pubis

  • Landmarks: ischial tuberosities, obturator foramen, iliac crests, iliac spines

Upper Limb Bones

The upper limb includes the humerus, forearm, wrist, and hand.

• Humerus: Greater/lesser tubercles, capitulum, trochlea, epicondyles, olecranon fossa

• Forearm: Radius and ulna

• Wrist: 8 carpal bones

• Hand: Metacarpals and phalanges

• Thumb: Anatomical term is pollex

Lower Limb Bones

The lower limb includes the femur, patella, tibia, fibula, ankle, and foot.

• Femur: Greater trochanter

• Patella: Kneecap

• Tibia: Tibial tuberosity, medial malleolus

• Fibula: Lateral malleolus

• Ankle: Tarsal bones

• Foot: Metatarsals and phalanges

• Big toe: Anatomical term is hallux

Chapter 8: Joints

Joint Classification

Joints are classified by their structure and function.

• Bony joints: Bones fused together (e.g., epiphyseal lines)

• Fibrous joints: Connected by fibrous tissue

  • Sutures (skull)

  • Syndesmoses (radius/ulna)

  • Gomphoses (teeth)

• Cartilaginous joints: Connected by cartilage

  • Synchondroses (hyaline cartilage)

  • Symphyses (fibrocartilage)

• Synovial joints: Freely movable, contain synovial cavity

Anatomy of Synovial Joints

Synovial joints have specialized structures for movement and stability.

• Articular cartilage: Covers bone surfaces

• Joint capsule: Encloses joint

• Synovial fluid: Lubricates joint

• Tendons: Connect muscle to bone

• Ligaments: Connect bone to bone

• Bursa: Fluid-filled sacs reduce friction

• Tendon sheaths: Protect tendons

Classes of Synovial Joints

Synovial joints are classified by their shape and movement axes.

• Plane (gliding): Flat surfaces, sliding (e.g., carpals)

• Hinge: Flexion/extension (e.g., elbow)

• Pivot: Rotation (e.g., atlas/axis)

• Condyloid: Flexion, extension, abduction, adduction (e.g., wrist)

• Saddle: Similar to condyloid, more movement (e.g., thumb)

• Ball-and-socket: All axes (e.g., shoulder, hip)

Synovial Joint Movements

Joints allow various movements, including special movements for certain body parts.

• Flexion/Extension: Decrease/increase angle

• Abduction/Adduction: Move away/toward midline

• Rotation: Turn around axis

• Special movements: Elevation, depression, protraction, retraction, inversion, eversion, dorsiflexion, plantarflexion

• Example: Tilting head back is extension of the neck

Major Joint Features

Shoulder, elbow, knee, and hip joints have unique anatomical features.

• Shoulder: Glenoid cavity, acromion, coracoid process

• Elbow: Olecranon, trochlea, capitulum

• Knee: Menisci, cruciate ligaments, patella

• Hip: Acetabulum, femoral head

Arthritis Types

Arthritis is inflammation of joints, with several types.

• Osteoarthritis: Degenerative, wear and tear

• Rheumatoid arthritis: Autoimmune, chronic inflammation

• Gout: Uric acid crystals in joint

Summary Table: Joint Types

Key Equations

• Calcium Regulation:

Example: If blood calcium drops, PTH is released to restore normal levels.