Bones, Skeletal System, and Articulations: Study Guide for ANP College Students

Chapter 6 – Bones and Bone Tissue

Functions of the Skeletal System

• Support: Provides a structural framework for the body and supports soft tissues.

• Protection: Shields vital organs (e.g., skull protects the brain, rib cage protects the heart and lungs).

• Movement: Acts as levers for muscles to produce movement.

• Mineral Storage: Stores minerals, especially calcium and phosphorus, which can be released into the bloodstream as needed.

• Blood Cell Production: Houses red bone marrow, which produces blood cells (hematopoiesis).

• Fat Storage: Yellow bone marrow stores triglycerides (energy reserves).

Types of Bone Tissue: Compact vs. Spongy Bone

• Compact Bone: Dense, strong outer layer; provides strength and protection.

• Spongy Bone (Cancellous Bone): Porous, lighter, found at the ends of long bones and inside flat bones; contains trabeculae and spaces for marrow.

Classification of Bones by Shape

• Long Bones: Longer than wide (e.g., femur, humerus); have a shaft and two ends.

• Short Bones: Cube-shaped (e.g., carpals, tarsals).

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

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

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

Gross Structure of a Long Bone

• Diaphysis: Shaft of the bone; composed mainly of compact bone.

• Epiphysis: Ends of the bone; mostly spongy bone covered by compact bone.

• Epiphyseal Plate: Hyaline cartilage in growing bones; site of lengthwise growth.

• Epiphyseal Line: Remnant of the epiphyseal plate in adults; marks where growth occurred.

• Articular Cartilage: Hyaline cartilage covering joint surfaces; reduces friction and absorbs shock.

• Periosteum: Dense connective tissue membrane covering the bone (except at joints); contains osteoblasts and osteoclasts.

• Endosteum: Thin membrane lining the medullary cavity; contains bone-forming cells.

• Medullary Cavity: Central cavity in diaphysis; contains yellow marrow in adults.

Blood Supply and Innervation of Bone

• Bones are highly vascularized; blood vessels enter through nutrient foramina.

• Nerves accompany blood vessels, providing sensation and regulating blood flow.

Bone Matrix: Organic and Inorganic Components

• Organic: Collagen fibers and ground substance; provide flexibility and tensile strength.

• Inorganic: Hydroxyapatite (calcium phosphate crystals); provide hardness and resistance to compression.

Microscopic Structure of Bone

• Osteon (Haversian System): Structural unit of compact bone.

• Central Canal: Contains blood vessels and nerves.

• Concentric Lamellae: Rings of bone matrix around the central canal.

• Lacunae: Small spaces housing osteocytes.

• Canaliculi: Tiny canals connecting lacunae; allow for nutrient/waste exchange.

• Perforating (Volkmann's) Canals: Connect central canals of adjacent osteons.

• Interstitial Lamellae: Fill spaces between osteons.

Spongy Bone Structure

• Trabeculae: Lattice-like network of bone tissue; spaces filled with marrow.

• Diploe: Spongy bone in flat bones (e.g., cranial bones).

Bone Marrow: Red vs. Yellow

• Red Marrow: Site of hematopoiesis; found in spongy bone of children and some adult bones (e.g., pelvis, sternum).

• Yellow Marrow: Stores fat; found in medullary cavities of long bones in adults.

• Location Differences: Children have more red marrow; adults have more yellow marrow.

Bone Cells

• Osteoprogenitor Cells: Stem cells that differentiate into osteoblasts.

• Osteoblasts: Bone-forming cells; secrete bone matrix.

• Osteocytes: Mature bone cells; maintain bone tissue.

• Osteoclasts: Bone-resorbing cells; break down bone matrix.

Primary vs. Secondary Bone

• Primary (Woven) Bone: First bone formed; irregular collagen arrangement; later replaced by secondary bone.

• Secondary (Lamellar) Bone: Mature bone; organized collagen fibers; stronger and more resilient.

Bone Formation (Ossification)

• Intramembranous Ossification: Bone develops from a fibrous membrane; forms flat bones (e.g., skull, clavicle).

• Endochondral Ossification: Bone forms by replacing hyaline cartilage; forms most bones (e.g., long bones, vertebrae).

Bone Growth

• Longitudinal Growth: Occurs at epiphyseal plates; increases bone length.

• Appositional Growth: Increases bone diameter; new bone added to surface.

• Comparison: Longitudinal growth lengthens bones; appositional growth thickens bones.

Bone Remodeling

• Continuous process of bone formation and resorption; adapts bone to stress and repairs microdamage.

Hormonal Regulation of Bone Growth

• Calcitonin: Lowers blood calcium by inhibiting osteoclasts.

• Parathyroid Hormone (PTH): Increases blood calcium by stimulating osteoclasts.

• Vitamin D (Calcitriol): Increases calcium absorption from the gut.

• Growth Hormone: Stimulates bone growth in children.

• Thyroid Hormone: Regulates bone growth and development.

• Sex Hormones (Estrogen, Testosterone): Promote bone growth and closure of epiphyseal plates.

Regulation of Blood Calcium

• PTH and calcitriol increase blood calcium; calcitonin decreases it.

Mechanical Stress and Bone Remodeling

• Weight-bearing exercise stimulates bone formation and increases bone density.

Chapter 7 – The Skeletal System

Structural Divisions of the Skeleton

• Axial Skeleton: Skull, vertebral column, rib cage; supports and protects organs.

• Appendicular Skeleton: Limbs and girdles; enables movement.

Bone Markings and Their Functions

• Foramen: Opening for nerves and blood vessels.

• Process: Projection for muscle/ligament attachment.

• Fossa: Depression for articulation or muscle attachment.

• Crest, Spine, Tubercle, Trochanter: Various projections for attachment.

Cartilage in the Skeleton

• Hyaline Cartilage: Most common; found in joints, nose, ribs.

• Fibrocartilage: Strong, found in intervertebral discs, pubic symphysis.

• Elastic Cartilage: Flexible, found in ear and epiglottis.

Major Bones of the Axial and Appendicular Skeleton

• Axial: Skull, vertebral column, thoracic cage (ribs, sternum).

• Appendicular: Pectoral girdle (clavicle, scapula), upper limbs, pelvic girdle (hip bones), lower limbs.

Cranial and Facial Bones

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

• Main Sutures: Coronal, sagittal, lambdoid, squamous.

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

• Hyoid Bone: Supports tongue, not attached to other bones.

Special Features: Orbit, Nasal Cavity, Paranasal Sinuses

• Orbit: Eye socket; formed by several bones.

• Nasal Cavity: Air passage; formed by ethmoid, vomer, and others.

• Paranasal Sinuses: Air-filled spaces; lighten skull, resonate voice.

Skull Differences: Fetus/Infant vs. Adult

• Infant skulls have fontanelles (soft spots) for growth; adult skulls have fused sutures.

Vertebral Column

• Regions: Cervical (7), thoracic (12), lumbar (5), sacrum, coccyx.

• Curves: Cervical and lumbar (concave), thoracic and sacral (convex).

• Vertebral Foramen: Contains spinal cord.

• Intervertebral Foramina: Exit for spinal nerves.

• Intervertebral Disc: Annulus fibrosus (outer), nucleus pulposus (inner).

• Functions: Support, protect spinal cord, allow movement.

Joints of the Skull and Vertebral Column

• Atlanto-occipital Joint: Nodding "yes" (occipital condyles and atlas).

• Atlanto-axial Joint: Shaking "no" (atlas and axis).

Pelvic Bones: Male vs. Female

• Female pelvis is wider, shallower, larger pelvic inlet for childbirth.

• Male pelvis is narrower, deeper, more robust.

Bones of the Lower Limb

• Thigh: Femur.

• Leg: Tibia (medial), fibula (lateral).

• Ankle: Tarsals.

• Foot: Metatarsals, phalanges.

Arches of the Foot

• Medial and lateral longitudinal arches, transverse arch; provide support and distribute weight.

Chapter 8 – The Skeletal System: Articulations

Definition and Classification of Joints

• Joint (Articulation): Where two or more bones meet.

• Structural Classification:

  • Fibrous: Bones joined by dense connective tissue; immovable or slightly movable (e.g., sutures).

  • Cartilaginous: Bones joined by cartilage; slightly movable (e.g., intervertebral discs).

  • Synovial: Bones separated by a joint cavity; freely movable (e.g., knee, shoulder).

• Functional Classification:

  • Synarthrosis: Immovable.

  • Amphiarthrosis: Slightly movable.

  • Diarthrosis: Freely movable.

Cartilaginous Joints

• Synchondroses: Hyaline cartilage; immovable (e.g., epiphyseal plates).

• Symphyses: Fibrocartilage; slightly movable (e.g., pubic symphysis).

Fibrous Joints

• Sutures: Immovable, found in skull.

• Syndesmoses: Bones connected by ligaments; slightly movable (e.g., distal tibiofibular joint).

• Gomphoses: Peg-in-socket (e.g., teeth in sockets).

Synovial Joints

• Components: Articular cartilage, joint (synovial) cavity, articular capsule, synovial fluid, ligaments, nerves, blood vessels.

• Synovial Fluid: Lubricates, nourishes cartilage, absorbs shock.

• Accessory Structures: Bursae (reduce friction), tendon sheaths (protect tendons), fat pads (cushion).

Types of Synovial Joints and Movements

• Plane: Gliding (e.g., intercarpal joints).

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

• Pivot: Rotation (e.g., atlas-axis).

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

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

• Ball-and-Socket: All movements (e.g., shoulder, hip).

Movements at Synovial Joints

• Flexion/Extension: Decrease/increase angle between bones.

• Abduction/Adduction: Movement away/toward midline.

• Circumduction: Circular movement.

• Pronation/Supination: Rotation of forearm.

• Depression/Elevation: Lowering/raising a body part.

• Dorsiflexion/Plantarflexion: Upward/downward movement of foot.

• Eversion/Inversion: Turning sole of foot outward/inward.

• Protraction/Retraction: Moving a part forward/backward.

• Opposition: Thumb movement to touch fingers.

Examples of Specific Joints and Structures

• Elbow Joint: Annular ligament, medial/lateral collateral ligaments, ulnar/radial collateral ligaments.

• Shoulder (Glenohumeral) Joint: High mobility, low stability; susceptible to dislocation.

• Hip Joint: Acetabular labrum, articular capsule, ligament of head of femur, iliofemoral, ischiofemoral, pubofemoral ligaments; stable, less mobile than shoulder.

• Knee Joint: Patellar ligament, lateral/medial meniscus, ACL, PCL; allows flexion/extension, slight rotation.

• Rotator Cuff Muscles: Supraspinatus, infraspinatus, teres minor, subscapularis; stabilize shoulder.

Table: Comparison of Joint Types

Joint Type	Structural Features	Movement	Example
Fibrous	Dense connective tissue	Immovable/slightly movable	Sutures, syndesmoses
Cartilaginous	Cartilage	Slightly movable	Intervertebral discs, pubic symphysis
Synovial	Joint cavity, synovial fluid	Freely movable	Knee, shoulder

Additional info:

• Some explanations and examples were expanded for clarity and completeness.

• Table content inferred from standard anatomy and physiology textbooks.