Connective Tissues - Introduction

Connective Tissues - Introduction

• Connective tissues are the most abundant and widely distributed tissues in the body.
• They have many functions, including binding tissues together, providing support and strength, protecting and insulating internal organs, compartmentalizing and transporting, and storing energy reserves and participating in immune responses.

Four Types of Tissues

• Epithelial: Covers body surfaces and lines hollow organs, body cavities, ducts, and forms glands.
• Connective: Protects, supports, and binds organs; stores energy as fat, and provides immunity.
• Muscular: Generates the physical force needed for movement and creates body heat.
• Nervous: Detects changes in the body and responds by generating nerve impulses.

Development of Tissues

• Tissues develop from three primary germ layers: ectoderm, endoderm, and mesoderm.
• Epithelial tissues develop from all three germ layers.
• Most connective tissues and muscle tissues originate from mesoderm.
• Nervous tissue originates from ectoderm.

Connective Tissue

• Connective tissue is found between cells.
• It is composed of protein fibers and ground substance.
• Connective tissue is highly vascular and supplied with nerves, with exceptions such as cartilage and tendons, which have little to no blood supply and nerves.

Connective Tissue Cells

• Fibroblasts: Secretes fibers and components of ground substance.
• Adipocytes (fat cells): Store triglycerides (fat).
• Mast cells: Produce histamine.
• White blood cells: Participate in the immune response (Neutrophils and Eosinophils).
• Macrophages: Engulf bacteria and cellular debris via phagocytosis.
• Plasma cells: Secret antibodies.

Connective Tissue Extracellular Matrix

• Ground substance: Located between cells and fibers, it can be fluid, semi-fluid, gelatinous, or calcified; it supports and binds cells, stores water, and facilitates exchange between blood and cells; it's a complex combination of proteins and polysaccharides.
• Fibers: Include collagen, elastic, and reticular fibers.

Classification of Connective Tissues

• Embryonic connective tissue: Mesenchyme and mucous connective tissue (Wharton's Jelly, found in the umbilical cord of the fetus)
• Mature connective tissue (proper): Loose connective tissue (areolar, adipose, and reticular), Dense connective tissue (dense regular, dense irregular, and elastic)
• Cartilage: Hyaline, fibrocartilage, and elastic cartilage
• Bone tissue
• Fluid connective tissue: Blood and lymph

Loose Connective Tissue

• Areolar: Most widely distributed.
• Adipose: Contains adipocytes for insulation and energy storage, and produces hormones and cytokines.
• Reticular: Forms stroma of liver, spleen, and lymph nodes; made of delicate reticular fibers and cells.

Dense Connective Tissue

• Dense regular: Bundles of collagen fibers in parallel for strength; found in tendons and most ligaments.
• Dense irregular: Irregularly arranged collagen fibers for strength in many directions; found in the dermis of skin and heart.
• Elastic: Contains branching elastic fibers for strength and recoil ability; found in lung tissue and arteries.

Cartilage

• Composed of chondrocytes located in lacunae.
• Types include hyaline (most abundant, in the skeleton), fibrocartilage (strongest), and elastic (flexible).
• Supported by perichondrium (a dense irregular connective tissue covering).
• Avascular, so cartilage repair is slow.
• Growth occurs through interstitial and appositional growth.

Bone Tissue

• Bones are organs made of bone tissue, periosteum, and endosteum.
• Compact bone contains osteons (Haversian systems).
• Spongy bone lacks osteons but has trabeculae.

Fluid Connective Tissue

• Includes blood (plasma as the fluid extracellular matrix) and lymph.