Week 6 - Bone Tissue

Chapter 7: Bone Tissue Anatomy & Physiology

Introduction

• The skeletal system is crucial for the body's structure, composed of bones, cartilages, and ligaments.

7. Tissues and Organs of the Skeletal System

Expected Learning Outcomes

• Identify the tissues and organs in the skeletal system.

• Understand the functions of the skeletal system.

• Differentiate between bones as a tissue versus an organ.

• Describe general features of long bones and flat bones.

Tissues and Organs of the Skeletal System—Introduction

• Skeletal system: Framework made of bones, cartilages, and ligaments.

• Osteology: The study of bones.

• Cartilage: Precursor to most bones and joint surface cover.

• Ligaments: Connect bones at joints.

• Tendons: Attach muscles to bones.

7.1a Functions of the Skeleton

Roles of the Skeleton

• Support: Limbs, vertebrae support body structure; jawbones support teeth.

• Protection: Shields vital organs like the brain, heart, and lungs.

• Movement: Facilitates limb movements and breathing through muscle interaction.

• Electrolyte Balance: Regulates calcium and phosphate levels.

• Acid–Base Balance: Aids in blood pH regulation.

• Blood Formation: Red bone marrow produces blood cells.

• Hormone Secretion: Bone cells secrete hormones impacting insulin action and stress responses.

7.1b Bones and Osseous Tissue

Definition and Composition

• Bone (Osseous Tissue): A connective tissue with a hardened matrix due to calcium phosphate and minerals.

• Mineralization/Calcification: The hardening process of bone.

• Bones as Organs: Consists of bone tissue, marrow, cartilage, adipose tissue, nervous tissue, and fibrous connective tissue.

7.1c General Features of Bones

Types of Bones

1. Flat Bones: Thin, curved plates (e.g., parietal bones, sternum).

2. Long Bones: Longer than wide; serve as levers (e.g., humerus, femur).

3. Short Bones: Similar length and width (e.g., wrist and ankle bones).

4. Irregular Bones: Elaborate shapes (e.g., vertebrae).

Anatomy of Long Bones

• Compact Bone: Dense outer shell surrounding the marrow cavity.

• Spongy Bone: Loosely arranged tissue within long bones; reduces weight.

• Diaphysis: Shaft providing leverage.

• Epiphysis: Enlarged ends of long bones providing joint strength and attachment points.

• Articular Cartilage: Covers joint surfaces.

• Periosteum: Protective sheath covering most bones.

• Endosteum: Lining of marrow cavity and internal bone surfaces.

• Flat bones contain layers of spongy bone sandwiched between compact bone.

7.2 Histology of Osseous Tissue

Expected Learning Outcomes

• Identify and describe bone cells and their functions.

• Understand that bone tissue is composed of cells, fibers, and ground substance.

• Compare two types of bone tissue: compact and spongy bone.

• Differentiate between two types of bone marrow.

Bone Cells

1. Osteogenic Cells: Stem cells that multiply and differentiate into osteoblasts.

2. Osteoblasts: Bone-forming cells responsible for osteogenesis, synthesizing the organic matrix, and promoting mineralization.

3. Osteocytes: Mature osteoblasts trapped in the bone matrix, residing in lacunae and connected by canaliculi.

4. Osteoclasts: Bone-resorbing cells responsible for osteolysis, derived from the same stem cells as blood cells.

Matrix Composition

• Organic Matter: 1/3 of bone, including collagen and carbohydrate–protein complexes.

• Inorganic Matter: 2/3 of bone, consisting of minerals like hydroxyapatite providing hardness and strength.

Compact Bone Structure

• Osteons: Basic structural units of compact bone consisting of concentric lamellae surrounding a central canal.

• Interstitial and circumferential lamellae fill spaces between osteons.

Spongy Bone

• Composed of trabeculae and spicules; filled with red bone marrow and provides structural support with minimized weight.

7.3 Bone Development

Expected Learning Outcomes

• Describe mechanisms of bone formation (ossification).

• Understand ongoing bone growth and remodeling processes.

Mechanisms of Bone Formation

1. Intramembranous Ossification: Development of flat bones (e.g., skull); involves deposition of osteoid tissue, calcification, and formation of spongy bone.

2. Endochondral Ossification: Development from hyaline cartilage; responsible for most bones, it includes several stages leading to the formation of marrow cavities and ossification centers.

Bone Growth and Widening

• Appositional Growth: Increase in diameter and thickness occurs through deposition of new tissue at the bone surface; osteoblasts and osteoclasts work together to remodel the bone.

Bone Remodeling

• Continuous process of repair and reshaping, occurring throughout life; involves resorption by osteoclasts and deposition by osteoblasts.

7.4 Physiology of Osseous Tissue

Expected Learning Outcomes

• Explain how minerals are moved into and out of bone tissue.

• Describe hormonal regulation of calcium and phosphate homeostasis.

Mineral Deposition & Resorption

• Mineral Deposition: Process where minerals from blood are deposited into bone by osteoblast activity.

• Mineral Resorption: Process of dissolving bone to release minerals into the blood, regulated by osteoclast activity.

Calcium Homeostasis

• Calcium is essential for several body functions, including bone structure and muscle contraction; regulated mainly by dietary intake and hormonal actions:

  • Calcitriol: Increases calcium absorption from diet, promotes resorption from bones, and aids calcium reabsorption in kidneys.

  • Calcitonin: Lowers blood calcium levels by inhibiting osteoclasts and stimulating osteoblasts.

  • Parathyroid Hormone (PTH): Raises blood calcium levels by stimulating osteoclast activity and promoting calcium reabsorption in kidneys.

7.5 Bone Disorders

Expected Learning Outcomes

• Identify various bone diseases and fracture types.

Fractures

• Types of Fractures:

  • Stress fracture: Result of abnormal stress (e.g., from a fall).

  • Pathological fracture: Occurs when a bone is weakened by disease.

Healing of Fractures

• Stages:

  1. Hematoma formation.

  2. Soft callus formation (collagen and fibrocartilage).

  3. Hard callus formation (temporary bony collar).

  4. Bone remodeling to restore compact bone structure.