Chapter 6 – Bones and Bone Tissue

Functions of the Skeletal System

The skeletal system provides the structural framework for the human body and serves several essential functions.

• Support: Bones support the body and cradle soft organs.

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

• Movement: Bones act as levers for muscles to produce movement.

• Mineral Storage: Bones store minerals, especially calcium and phosphorus.

• Blood Cell Formation: Hematopoiesis occurs in the red marrow of certain bones.

• Triglyceride Storage: Yellow marrow stores fat as an energy reserve.

Bone Classification and Structure

Bones are classified by shape and internal structure, which relate to their function.

• Shape Classification: Long, short, flat, irregular, and sesamoid bones.

• Gross Structure: Compact bone (dense, outer layer) and spongy bone (porous, inner layer).

• Example: The femur is a long bone with a shaft (diaphysis) and two ends (epiphyses).

Longitudinal Section of a Long Bone

A typical long bone consists of several key anatomical structures.

• Diaphysis: Shaft of the bone.

• Epiphysis: Ends of the bone.

• Epiphyseal Line/Plate: Site of bone growth in children and adolescents.

• Articular Cartilage: Covers joint surfaces for smooth movement.

• Spongy Bone: Contains red marrow.

• Periosteum: Outer fibrous covering.

• Endosteum: Lines the internal bone surfaces.

• Medullary Cavity: Central cavity containing yellow marrow.

Blood Supply and Innervation

Bones are highly vascularized and innervated to support their metabolic needs and sensory functions.

• Nutrient arteries: Enter through nutrient foramina to supply bone tissue.

• Nerves: Accompany blood vessels and sense pain and injury.

Microscopic Structure of Bone Tissue

Bone tissue consists of compact and spongy bone, each with distinct microscopic features.

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

• Components of an Osteon:

  • Central canal

  • Perforating canals

  • Canaliculi

  • Lacunae

  • Concentric and interstitial lamellae

• Spongy Bone: Contains trabeculae, bone marrow, and spaces for hematopoiesis.

Bone Cells

Bone tissue contains several types of cells, each with specialized functions.

• Osteoblasts: Bone-forming cells.

• Osteocytes: Mature bone cells maintaining bone matrix.

• Osteoclasts: Bone-resorbing cells.

• Osteoprogenitor cells: Stem cells that differentiate into osteoblasts.

Bone Development and Growth

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

• Intramembranous Ossification: Forms flat bones (e.g., skull, clavicle) from mesenchymal tissue.

• Endochondral Ossification: Forms most bones from hyaline cartilage templates.

• Bone Growth: Occurs in length at the epiphyseal plate and in diameter by appositional growth.

Bone Remodeling and Hormonal Regulation

Bone is continuously remodeled throughout life, regulated by hormones and mechanical stress.

• Remodeling: Balance between bone formation (osteoblasts) and resorption (osteoclasts).

• Hormones:

  • Calcitonin: Lowers blood calcium levels.

  • Parathyroid hormone (PTH): Raises blood calcium levels.

  • Growth hormone: Stimulates bone growth.

  • Thyroid hormone: Regulates bone development.

  • Sex hormones: Promote growth and closure of epiphyseal plates.

• Mechanical Stress: Weight-bearing activities stimulate bone formation.

Red and Yellow Bone Marrow

Bone marrow exists in two forms, each with distinct functions and locations.

• Red Marrow: Site of hematopoiesis; found in spongy bone of flat bones and epiphyses of long bones.

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

• Age Differences: Red marrow predominates in children; yellow marrow increases with age.

Chapter 7 – The Skeleton: Structure and Function

Overview of the Skeleton

The skeleton is divided into axial and appendicular components, each with specific bones and functions.

• Axial Skeleton: Skull, vertebral column, and thoracic cage.

• Appendicular Skeleton: Limbs and girdles (pectoral and pelvic).

Bones and Bone Markings

Bones have distinct markings that serve as sites for muscle attachment, articulation, and passage of nerves and blood vessels.

• Bone Markings: Include foramina, processes, condyles, and ridges.

• Functional Significance: Markings relate to bone function and movement.

Cartilage and Joints

Cartilage tissues and joints connect bones and allow for movement and flexibility.

• Types of Cartilage: Hyaline, fibrocartilage, and elastic cartilage.

• Joints: Classified by structure (fibrous, cartilaginous, synovial) and function (immovable, slightly movable, freely movable).

Major Bones and Features

Students should be able to identify major bones and their features, including those of the skull, vertebral column, thoracic cage, and limbs.

• Skull: Cranial and facial bones, sinuses, and sutures.

• Vertebral Column: Cervical, thoracic, lumbar, sacral, and coccygeal vertebrae.

• Thoracic Cage: Ribs and sternum.

• Limbs: Bones of the arm, forearm, hand, thigh, leg, and foot.

Chapter 8 – The Skeletal System: Articulations

Joints and Articulations

Joints, or articulations, are sites where two or more bones meet, allowing for movement and flexibility.

• Definition: A joint (articulation) is the junction between bones.

• Classification:

  • Structural: Fibrous, cartilaginous, synovial.

  • Functional: Synarthroses (immovable), amphiarthroses (slightly movable), diarthroses (freely movable).

Synovial Joints

Synovial joints are the most movable type of joint, characterized by a fluid-filled cavity.

• Components:

  • Articular cartilage

  • Joint (synovial) cavity

  • Articular capsule

  • Synovial fluid

  • Reinforcing ligaments

  • Nerves and blood vessels

• Accessory Structures: Bursae, tendon sheaths, fat pads.

Movements at Synovial Joints

Synovial joints allow for a wide range of movements, classified by plane and axis.

• Types of Movement:

  • Flexion, extension, abduction, adduction, circumduction, rotation

  • Special movements: supination, pronation, elevation, depression, dorsiflexion, plantarflexion, inversion, eversion, protraction, retraction, opposition

Specific Joints and Their Features

Key joints include the elbow, hip, knee, and shoulder, each with unique anatomical structures and functions.

• Elbow Joint: Includes annular ligament and collateral ligaments.

• Hip Joint: Features acetabular labrum, articular capsule, and several ligaments.

• Knee Joint: Contains menisci, cruciate ligaments (ACL, PCL), and collateral ligaments.

• Shoulder Joint: Glenohumeral joint, rotator cuff muscles, and associated ligaments.

Table: Comparison of Bone Types

Key Equations

• Calcium Homeostasis:

Additional info:

• Some content inferred from standard Anatomy & Physiology curriculum to ensure completeness and clarity.

• Table entries and equations added for academic context.