Chapter 7: Skeletal System – Bone Structure and Function

Key Topics to Know

This chapter covers the structure, function, and physiology of bones, focusing on their anatomy, cellular composition, growth, and remodeling processes.

• Anatomy of a Long Bone: Understanding the major regions and features of a typical long bone.

• Microscopic Anatomy of Bone: Examining the cellular and matrix components at the microscopic level.

• Bone Cells and Their Functions: Identifying osteoblasts, osteocytes, and osteoclasts and their roles.

• Bone Composition: Describing the organic and inorganic components of bone tissue.

• Cartilage Growth: Outlining the types and mechanisms of cartilage growth.

• Ossification Types: Comparing endochondral and intramembranous ossification.

• Hormones & Bone Remodeling: Explaining hormonal regulation of bone metabolism.

• Fracture Repair and Classification: Understanding the stages of bone healing and types of fractures.

Bone Anatomy and Structure

Anatomy of a Long Bone

Long bones, such as the femur and humerus, have a characteristic structure that supports movement and weight-bearing.

• Diaphysis: The shaft of the bone, composed mainly of compact bone.

• Epiphyses: The expanded ends of the bone, containing spongy bone and red marrow.

• Medullary Cavity: The central cavity within the diaphysis, housing yellow marrow in adults.

• Periosteum: A dense connective tissue membrane covering the outer surface of bone.

• Endosteum: A thin membrane lining the medullary cavity.

Microscopic Anatomy of Bone

Bone tissue is organized into compact and spongy forms, each with distinct microscopic features.

• Osteons (Haversian systems): Cylindrical structures in compact bone, consisting of concentric lamellae around a central canal.

• Trabeculae: Lattice-like structures in spongy bone, providing strength with minimal weight.

• Bone Cells: Osteoblasts (build bone), osteocytes (maintain bone), and osteoclasts (break down bone).

Bone Composition

Organic and Inorganic Components

Bones are composed of both organic and inorganic materials, contributing to their strength and flexibility.

• Organic Matrix: Primarily collagen fibers, providing tensile strength and flexibility.

• Inorganic Matrix: Mainly hydroxyapatite (calcium phosphate crystals), providing hardness and resistance to compression.

Bone Growth and Ossification

Cartilage Growth

Cartilage grows by two mechanisms, important for bone development and repair.

• Interstitial Growth: Growth from within the cartilage, increasing length.

• Appositional Growth: Growth at the surface, increasing thickness.

Ossification Types

Bone formation occurs through two main processes:

• Endochondral Ossification: Bone replaces hyaline cartilage; responsible for forming most bones, especially long bones.

• Intramembranous Ossification: Bone develops directly from mesenchymal tissue; forms flat bones like the skull.

Bone Marrow and Blood Cell Production

Red vs. Yellow Bone Marrow

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

• Red Marrow: Produces blood cells; found in spongy bone of adults (e.g., pelvis, sternum).

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

Bone Remodeling and Hormonal Regulation

Osteoblasts vs. Osteoclasts

Bone remodeling is a dynamic process involving two main cell types:

• Osteoblasts: Synthesize new bone matrix and promote mineralization.

• Osteoclasts: Break down bone tissue, releasing minerals into the blood.

Hormonal Control

Several hormones regulate bone metabolism:

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

• Calcitonin: Lowers blood calcium by inhibiting osteoclasts.

• Estrogen and Testosterone: Promote bone growth and maintenance.

Fracture Repair and Classification

Stages of Fracture Healing

Bone repair involves several stages:

• Hematoma formation

• Fibrocartilaginous callus formation

• Bony callus formation

• Bone remodeling

Comparison of Compact and Spongy Bone

Compact and spongy bone differ in structure and function.

Sample Questions and Answers

Multiple Choice Questions

1. Which structure houses the red bone marrow in adults? Answer: B. Spongy bone

2. The central canal of an osteon contains: Answer: B. Blood vessels and nerves

3. Which hormone increases blood calcium levels by stimulating osteoclasts? Answer: C. Parathyroid hormone

Short Answer Questions

1. Compare compact and spongy bone in structure and function. Answer: Compact bone is dense and forms the outer layer of bones; spongy bone has trabeculae and contains marrow.

2. Describe how endochondral ossification forms long bones. Answer: Endochondral ossification replaces hyaline cartilage with bone in long bones.

3. What is the difference between red and yellow bone marrow? Answer: Red marrow produces blood cells; yellow marrow stores fat.

4. Explain the roles of osteoblasts vs. osteoclasts in bone remodeling. Answer: Osteoblasts build bone matrix; osteoclasts break down bone tissue.

Key Terms and Definitions

• Osteon: The structural unit of compact bone.

• Trabeculae: Lattice-like structures in spongy bone.

• Osteoblast: Bone-forming cell.

• Osteoclast: Bone-resorbing cell.

• Ossification: The process of bone formation.

• Periosteum: Membrane covering the outer surface of bone.

• Medullary Cavity: Central cavity in long bones containing marrow.

Formulas and Equations

• Calcium Homeostasis:

Additional info: Some explanations and definitions have been expanded for clarity and completeness.