Bones and Skeletal Tissues: Structure, Function, and Development

Study Guide - Smart Notes

Tailored notes based on your materials, expanded with key definitions, examples, and context.

Chapter 06: Bones and Skeletal Tissues

Why This Matters

Understanding bone anatomy and the process of bone remodeling is essential for diagnosing and treating bone diseases such as osteoporosis. Knowledge of skeletal tissues enables effective communication and care for patients with musculoskeletal disorders.

Bones and Cartilages of the Human Skeleton

Overview of Skeletal Components

The human skeleton is composed of bones and cartilage, which provide structure, protection, and facilitate movement. Cartilage is found in specific locations such as joints, the rib cage, and respiratory structures.

Bones: Rigid organs forming the skeleton, providing support and protection.
Cartilage: Flexible connective tissue found in joints, the rib cage, ear, nose, and respiratory tract.
Types of Cartilage: Hyaline, elastic, and fibrocartilage, each with distinct properties and locations.
Axial Skeleton: Includes skull, vertebral column, and rib cage.
Appendicular Skeleton: Includes limbs and girdles (shoulder and pelvic).

Functions of Bones

Seven Major Functions

Bones perform several vital functions necessary for overall health and movement.

Support: Provide a structural framework for the body and soft organs.
Protection: Shield vital organs such as the brain, spinal cord, and thoracic organs.
Movement: Serve as levers for muscle action, enabling locomotion.
Mineral and Growth Factor Storage: Reservoir for minerals like calcium and phosphate, and growth factors.
Blood Cell Formation (Hematopoiesis): Occurs in red marrow cavities of spongy bone.
Triglyceride (Fat) Storage: Fat stored in bone cavities serves as an energy reserve.
Hormone Production: Bones produce osteocalcin, which helps regulate bone formation and protects against obesity and diabetes. Additional info: This function is inferred from current academic knowledge.

Classification of Bones

Based on Shape

Bones are classified according to their shapes, which relate to their functions and locations.

Long Bones: Longer than they are wide; found in limbs (e.g., femur, humerus).
Short Bones: Cube-shaped; found in wrist and ankle (e.g., carpals, tarsals).
Flat Bones: Thin, flattened, and usually curved; found in the skull, ribs, sternum, and scapula.
Irregular Bones: Complex shapes; found in vertebrae and hip bones.
Sesamoid Bones: A Special type of short bone formed within tendons (e.g., patella).

Structure of Bone Tissue

Compact and Spongy Bone

Bones consist of two types of tissue: compact and spongy bone, each with distinct structural and functional properties.

Compact Bone: Dense outer layer providing strength and protection.
Spongy Bone (Cancellous Bone): Internal network of trabeculae, reducing bone weight and housing marrow.

Structure of Flat and Long Bones

Flat bones have a layer of spongy bone sandwiched between two layers of compact bone. Long bones have a shaft (diaphysis), ends (epiphyses), and membranes (periosteum and endosteum).

Diaphysis: Shaft of a long bone, composed of compact bone surrounding the medullary cavity.
Epiphyses: Ends of long bones, mostly spongy bone covered by compact bone.
Periosteum: Outer fibrous membrane covering bone.
Endosteum: Membrane lining internal bone surfaces.

Microscopic Anatomy of Bone

Bone Cells

Five major types of bone cells contribute to bone formation, maintenance, and remodeling.

Osteogenic Cells: Stem cells that differentiate into osteoblasts.
Osteoblasts: Bone-forming cells responsible for synthesizing bone matrix.
Osteocytes: Mature bone cells maintain bone tissue.
Bone-Lining Cells: Flat cells on bone surfaces, involved in maintenance.
Osteoclasts: Multinucleated cells that resorb bone matrix.

Structure of Compact Bone

Compact bone is organized into osteons (Haversian systems), which are cylindrical structures containing lamellae, central canals, and canaliculi.

Osteon: Structural unit of compact bone.
Lamellae: Concentric rings of bone matrix.
Central Canal: Contains blood vessels and nerves.
Canaliculi: Small channels connecting osteocytes.

Bone Development (Ossification)

Overview

Ossification is the process of bone tissue formation, beginning in the embryo and continuing through early adulthood.

Intramembranous Ossification: Bone develops from fibrous membrane; forms flat bones of skull and clavicle.
Endochondral Ossification: Bone forms by replacing hyaline cartilage; it forms most bones of the body.

Bone Growth

Longitudinal and Appositional Growth

Bones grow in length at the epiphyseal plate and in thickness by appositional growth.

Epiphyseal Plate: Cartilage plate where bone lengthening occurs during childhood and adolescence.
Appositional Growth: Increase in bone thickness by addition of new bone tissue at the surface.
Epiphyseal Line: Remnant of the epiphyseal plate in adults, indicating cessation of growth.

Bone Remodeling and Repair

Remodeling in Response to Stress (Wolff's Law)

Bones adapt to mechanical stress by remodeling, which involves both bone deposition and resorption.

Wolff's Law: Bone grows and remodels in response to the forces placed upon it.
Remodeling: Continuous process of bone renewal throughout life.

Calcium Homeostasis

Blood calcium levels are tightly regulated by parathyroid hormone (PTH), which controls bone resorption and formation.

Parathyroid Hormone (PTH): Increases blood calcium by stimulating osteoclast activity.
Homeostatic Imbalance: Hypocalcemia (low calcium) causes hyperexcitability; hypercalcemia (high calcium) causes nonresponsiveness and can lead to kidney stones.

Bone Fractures and Healing

Common Types of Fractures

Fractures are classified based on their characteristics and the nature of the break.

Type	Description
Comminuted	Bone fragments into three or more pieces
Compression	Bone is crushed
Spiral	Ragged break due to twisting forces
Epiphyseal	Epiphysis separates from diaphysis
Depressed	Broken bone portion pressed inward
Greenstick	Bone breaks incompletely

Stages of Bone Healing

Bone healing occurs in several stages following a fracture.

Hematoma Formation: A Blood clot forms at the fracture site.
Fibrocartilaginous Callus Formation: Soft callus of cartilage and connective tissue stabilizes the break.
Bony Callus Formation: New bone replaces the soft callus.
Bone Remodeling: Bone is reshaped to its original form.

Bone Disorders

Major Bone Diseases

Imbalances in bone deposition and resorption can lead to various skeletal disorders.

Osteomalacia and Rickets: Softening of bones due to vitamin D deficiency; rickets occurs in children.
Osteoporosis: Reduced bone mass and increased fragility, common in older adults.
Paget's Disease: Excessive and disorganized bone remodeling, leading to weak and deformed bones.

Developmental and Age-Related Changes

Bone Development Over the Lifespan

Bone formation and resorption rates change throughout life, influenced by genetics, hormones, and environmental factors.

Embryonic Development: Skeleton ossifies predictably; fetal age can be determined by bone development.
Childhood and Adolescence: Bone formation exceeds resorption; growth plates persist until adulthood.
Young Adulthood: Bone formation and resorption are balanced.
Older Age: Bone resorption exceeds formation, leading to decreased bone mass and increased risk of fractures.
Genetic Factors: Genes influence bone density, mineralization, and healing ability.