Connective Tissues - Introduction

Connective Tissues - Introduction

• Connective tissues are the most abundant and widely distributed tissues in the body
• They perform numerous functions, including binding tissues together, support, strengthening, protecting and insulating internal organs, compartmentalizing, transporting energy reserves, and immune responses.

Four Types of Tissues

• Epithelial: Covers body surfaces and lines structures, ducts, and forms glands
• Connective: Protects, supports, and binds organs, stores energy, and provides immunity
• Muscular: Generates force for movement, and 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 tissue and muscle tissues derive from mesoderm.
• Nervous tissue develops from ectoderm.

Connective Tissue

• The extracellular matrix is important as it is positioned between cells.
• It consists of protein fibres and ground substance.
• Connective tissue is generally highly vascular (except for cartilage and tendon) and is supplied with nerves (except for cartilage and tendon)

Connective Tissue Cells

• Fibroblasts: Secrete fibres and components of the ground substance
• Adipocytes (fat cells): Store triglycerides (fat)
• Mast cells: Produce histamine
• White blood cells: Immune response (includes neutrophils and eosinophils)
• Macrophages: Engulf bacteria and cellular debris by phagocytosis
• Plasma cells: Secrete antibodies

Connective Tissue Extracellular Matrix

• Situated between cells and fibers
• Can be fluid, semifluid, gelatinous, or calcified
• Supports and binds cells
• Stores water and allows exchange between blood and cells
• Is a complex combination of proteins and polysaccharides

Classification of Connective Tissues

• Mature connective tissue (proper):
  • Loose connective tissue: Includes areolar, adipose, and reticular tissues.
  • Dense connective tissue: Includes dense regular, dense irregular, and elastic tissues.
• Cartilage: Includes hyaline, fibrocartilage, and elastic cartilages.
• Bone tissue
• Liquid connective tissue: Includes blood and lymph.

Embryonic Connective Tissue

• Mesenchyme: Found in the embryo, contains small, spindle shaped cells, cells extend processes to form networks, a viscous ground substance between cells with little collagen
• Mucous (Wharton's Jelly): Found in umbilical cord of the fetus.

Loose Connective Tissue

• Cellular tissue with thin and relatively sparse collagen fibers.

• Contains abundant ground substance with viscous consistency.

• Facilitates the diffusion of O2 and nutrients from circulation.

• Located primarily beneath epithelia at body surfaces.

• Surrounds glands and blood vessels.

• Areolar connective tissue: Most widely distributed in the body. Includes several types of cells and all three fiber types

Loose Connective Tissue: Adipose Tissue

• Contains adipocytes (fat cells) for insulation and energy reserves.
• Produces hormones and pro-inflammatory cytokines.
• Includes white (common) and brown adipose tissues.

Loose Connective Tissue: Reticular Connective Tissue

• Consists of fine interlacing reticular fibers and cells.
• Forms the stroma of liver, spleen, and lymph nodes.

Dense Connective Tissue

• Contains numerous, thicker, and denser fibers.

• Packed closely with fewer cells than loose connective tissue.

• Dense regular connective tissue: Bundles of collagen fibers are regularly arranged in parallel patterns for strength. Found in tendons and most ligaments.

• Dense irregular connective tissue: Collagen fibers are irregularly arranged. Found in the dermis of the skin and in the heart.

• Elastic connective tissue: Contains branching elastic fibers. Strong and can recoil to original shape after stretching. Found in lung tissue and arteries.

Cartilage

• A dense network of collagen and elastic fibers embedded in chondroitin sulfate.
• Chondrocytes: Cartilage cells found in spaces called lacunae.
• Perichondrium: Covering of dense irregular connective tissue surrounding cartilage. Two layers (outer fibrous layer and inner cellular layer)
• Generally has no blood vessels or nerves, except for perichondrium.
• Types include: hyaline, fibrocartilage, and elastic cartilages.

Hyaline Cartilage

• Most abundant cartilage in the body, surrounded by perichondrium, provides flexibility and support, reduces friction. Found in the skeleton, fetal bone, nose, trachea, and larynx.

Elastic Cartilage

• Located within a threadlike network of elastic fibers.
• Perichondrium is present.
• Provides strength and elasticity.
• Found in the auricle of the ear and epiglottis.

Fibrocartilage

• Contains chondrocytes scattered among bundles of collagen fibers.
• Lacks a perichondrium.
• Strongest type of cartilage.
• Found in intervertebral discs (between vertebrae), and in the knee and pubic symphysis.

Repair and Growth of Cartilage

• Cartilage grows slowly.
• Repair is slow due to avascular nature.
• Interstitial growth: Growth from within the tissue.
• Appositional growth: Growth at the outer surface

Bone Tissue

• Bones are organs composed of several different connective tissues
  • Bone (osseous) tissue
  • Periosteum
  • Endosteum
• Includes compact (osteon or Haversian system) and spongy (trabeculae) bone.

Fluid Connective Tissue

• Blood tissue: Connective tissue with a liquid extracellular matrix called plasma.
• Lymph: Another form of fluid connective tissue.