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
Flat Bones: Thin, curved plates (e.g., parietal bones, sternum).
Long Bones: Longer than wide; serve as levers (e.g., humerus, femur).
Short Bones: Similar length and width (e.g., wrist and ankle bones).
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
Osteogenic Cells: Stem cells that multiply and differentiate into osteoblasts.
Osteoblasts: Bone-forming cells responsible for osteogenesis, synthesizing the organic matrix, and promoting mineralization.
Osteocytes: Mature osteoblasts trapped in the bone matrix, residing in lacunae and connected by canaliculi.
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
Intramembranous Ossification: Development of flat bones (e.g., skull); involves deposition of osteoid tissue, calcification, and formation of spongy bone.
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:
Hematoma formation.
Soft callus formation (collagen and fibrocartilage).
Hard callus formation (temporary bony collar).
Bone remodeling to restore compact bone structure.