Bones and Skeletal Tissues: Study Guide and Key Concepts

Chapter 6: Bones and Skeletal Tissues

Introduction

This study guide covers the essential concepts related to bones and skeletal tissues, focusing on their structure, function, classification, and physiology. Understanding these topics is fundamental for students of Anatomy & Physiology.

Functions of Bones

Main Functions

• Support: Bones provide a framework that supports the body and cradles soft organs.

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

• Movement: Skeletal muscles attach to bones and use them as levers to produce movement.

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

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

• Triglyceride Storage: Fat is stored in yellow bone marrow.

Classification of Bones

Types of Bones

• Long Bones: Longer than they are wide (e.g., femur, humerus).

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

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

• Irregular Bones: Complicated shapes (e.g., vertebrae, hip bones).

Example: The femur is a long bone, while the scapula is a flat bone.

Types of Skeletal Cartilage

Cartilage Types and Locations

• Hyaline Cartilage: Most abundant; provides support with flexibility (e.g., articular, costal, respiratory, nasal cartilages).

• Elastic Cartilage: Contains more elastic fibers; withstands repeated bending (e.g., external ear, epiglottis).

• Fibrocartilage: Highly compressible with great tensile strength (e.g., intervertebral discs, menisci of knee).

Bone Structure

Gross Anatomy

• Compact Bone: Dense outer layer; smooth and solid.

• Spongy Bone: Internal layer; honeycomb of trabeculae filled with marrow.

Microscopic Anatomy

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

• Lamellae: Concentric rings of bone matrix.

• Lacunae: Small spaces housing osteocytes.

• Canaliculi: Tiny canals connecting lacunae.

Bone Cells

Types and Functions

• Osteogenic Cells: Stem cells that differentiate into osteoblasts.

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

• Osteocytes: Mature bone cells; maintain bone matrix.

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

Bone Development (Ossification)

Types of Ossification

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

• Endochondral Ossification: Bone forms by replacing hyaline cartilage (e.g., most bones below the skull).

Bone Growth and Remodeling

Growth in Length and Width

• Longitudinal Growth: Occurs at the epiphyseal plate (growth plate).

• Appositional Growth: Increase in bone thickness.

Remodeling

• Bone is continuously renewed through resorption (by osteoclasts) and deposition (by osteoblasts).

• Remodeling is influenced by hormones (e.g., parathyroid hormone, calcitonin) and mechanical stress.

Bone Homeostasis and Calcium Regulation

Hormonal Control

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

• Calcitonin: Lowers blood calcium by inhibiting osteoclasts.

Equation:

$\text{Ca}^{2+}_{\text{blood}} \xleftrightarrow{\text{PTH/Calcitonin}} \text{Ca}^{2+}_{\text{bone}}$

Bone Fractures and Repair

Types of Fractures

• Simple (Closed): Bone does not penetrate skin.

• Compound (Open): Bone ends penetrate skin.

• Comminuted: Bone fragments into three or more pieces.

• Compression: Bone is crushed.

• Spiral: Ragged break due to twisting forces.

• Epiphyseal: Epiphysis separates from diaphysis at growth plate.

• Depressed: Broken bone portion is pressed inward.

• Greenstick: Incomplete break; one side of shaft breaks, other bends (common in children).

Repair Process

1. Hematoma formation

2. Fibrocartilaginous callus formation

3. Bony callus formation

4. Bone remodeling

Disorders of Bone

Common Disorders

• Osteomalacia/Rickets: Bones are inadequately mineralized; soft and weak (due to vitamin D deficiency).

• Osteoporosis: Bone resorption outpaces deposit; bones become fragile.

• Paget's Disease: Excessive and haphazard bone deposit and resorption.

Summary Table: Types of Bone Cells

Cell Type	Function	Location
Osteogenic Cell	Stem cell; differentiates into osteoblasts	Periosteum, endosteum
Osteoblast	Bone formation; secretes matrix	Growing bone surfaces
Osteocyte	Maintains bone tissue	Lacunae within bone matrix
Osteoclast	Bone resorption	Bone surfaces, resorption bays

Additional info:

• Students should also review laboratory objectives related to bone identification and skeletal features as indicated in their course materials.