Connective Tissues: Overview and Types

Connective Tissues: Overview

• Connective tissues are diverse tissues supporting, connecting, and separating body tissues and organs.
• They are defined by a large extracellular matrix (ECM) separating cells.
• The ECM comprises ground substance (a gel-like material filling spaces) and fibers (protein structures giving strength and flexibility).
• Connective tissue cells vary by tissue type.
• Connective tissues function in structural support, material transport, energy storage, and pathogen defense.

Types of Connective Tissues

• Connective Tissue Proper: Subtypes include:
  • Loose Connective Tissue: Has a loose arrangement of cells and fibers, supporting and cushioning structures and filling spaces.
    • Contains fibroblasts, macrophages, mast cells, and adipocytes.
    • Contains collagen, elastic, and reticular fibers.
  • Dense Connective Tissue: Tightly packed collagen fibers providing strength and support to stressed structures.
    • Dense regular connective tissue forms tendons and ligaments, primarily parallel collagen fibers.
    • Dense irregular connective tissue, found in the dermis, has more irregular collagen fiber patterns, allowing for strength in multiple directions.
• Cartilage: A flexible, strong connective tissue supporting and cushioning joints.
  • Contains chondrocytes within lacunae, spaces in the extracellular matrix.
  • The firm matrix is rich in collagen and proteoglycans.
  • Three types: hyaline, elastic, and fibrocartilage, varying in flexibility and strength.
• Bone: A rigid connective tissue providing support, protection, and mineral storage.
  • Contains osteocytes within lacunae.
  • The matrix is composed of collagen fibers and mineral crystals (calcium phosphate) providing hardness and strength.
• Blood: A fluid connective tissue transporting oxygen, nutrients, hormones, and other substances.
  • Contains formed elements (red and white blood cells and platelets) suspended in plasma, a fluid matrix.

Components of Connective Tissue

• Cells: Vary by tissue type, including fibroblasts, chondrocytes, osteocytes, and blood cells.
• Extracellular Matrix (ECM): Non-cellular material surrounding cells.
  • Ground Substance: Viscous fluid with water, proteoglycans, and glycoproteins; varying consistency.
    • Proteoglycans trap water, impacting viscosity and tissue support.
    • Ground substance facilitates cell signaling and nutrient diffusion.
  • Fibers: Providing strength, elasticity, and support.
    • Collagen: Strongest and most abundant fiber, providing tensile strength.
    • Elastic: Provides recoil to original shape.
    • Reticular: Form a supportive network in organs like spleen and lymph nodes.

Common Characteristics of Connective Tissues

• Vascularity: Some (e.g., bone, blood) are well-vascularized, others (e.g., cartilage) are avascular, impacting repair and nutrient exchange.
• Origin: Connective tissues develop from mesenchyme, an embryonic connective tissue.
• Abundant ECM: ECM composition greatly influences tissue properties.

Functions of Connective Tissues

• Support: Provides structural framework (e.g., bone, tendons/ligaments).
• Protection: Protects internal organs.
• Transport: Blood transports substances.
• Storage: Adipose tissue stores energy, and bone stores minerals.
• Connection: Tendons and ligaments connect muscles to bones and bones to each other.