Tissues and Their Classification

Tissues and Their Classification

• Tissues are groups of similar cells working together to perform specific functions.
• Four primary tissue types in animals: epithelial, connective, muscle, and nervous.

Epithelial Tissue

• Covers body surfaces, lines body cavities, and forms glands.
• Characterized by tightly packed cells with minimal extracellular matrix.
• Functions include protection, secretion, absorption, excretion, filtration, diffusion, and sensory reception.
• Classified based on cell shape (squamous, cuboidal, columnar) and layers (simple, stratified).
  • Simple squamous: single layer of flattened cells, functions in diffusion and filtration (e.g., alveoli of lungs, lining of blood vessels).
  • Stratified squamous: multiple layers of flattened cells, providing protection against abrasion (e.g., epidermis of skin).
  • Simple cuboidal: single layer of cube-shaped cells, common in glands and kidney tubules (functions in secretion and absorption).
  • Stratified cuboidal: multiple layers of cube-shaped cells, less common than simple cuboidal (functions in secretion and absorption).
  • Simple columnar: single layer of elongated cells, common in digestive tract (functions in secretion and absorption).
  • Stratified columnar: multiple layers of elongated cells, rare and functions in protection and secretion.
• Glandular epithelium forms glands that secrete substances (e.g., hormones, mucus).
  • Endocrine glands secrete products directly into the bloodstream (e.g., hormones).
  • Exocrine glands secrete products into ducts that open onto body surfaces or cavities (e.g., sweat glands, salivary glands).

Connective Tissue

• Supports, connects, and separates different tissues and organs.
• Characterized by a matrix (ground substance and fibers) surrounding cells.
• Functions include binding, support, protection, insulation, transportation (blood).
• Various types of connective tissue:
  • Connective tissue proper: loose and dense connective tissues.
    • Loose connective tissue (areolar, adipose, reticular): supports and connects tissues, stores energy, and provides immune protection.
    • Dense connective tissue (regular, irregular, elastic): provides strength and support (e.g., tendons, ligaments).
  • Cartilage: firm, flexible connective tissue, with specialized cells (chondrocytes) in a matrix containing collagen fibers.
    • Hyaline cartilage: smooth, flexible support and reduces friction (e.g., articular cartilages, trachea).
    • Elastic cartilage: maintains shape while permitting flexibility (e.g., ear).
    • Fibrocartilage: strong and resists compression (e.g., intervertebral discs).
  • Bone: rigid connective tissue with calcium salts and collagen fibers supporting weight, protecting organs, and serving as storage for minerals.
  • Blood: fluid connective tissue that transports substances throughout the body.

Muscle Tissue

• Specialized for contraction and movement.
• Three types: skeletal, smooth, and cardiac muscle.
  • Skeletal muscle: attached to bones, voluntary movement (e.g., biceps, quadriceps).
  • Smooth muscle: in walls of internal organs, involuntary movement (e.g., stomach, intestines).
  • Cardiac muscle: heart, involuntary contractions for blood pumping.

Nervous Tissue

• Specialized for communication and control.
• Composed of neurons (nerve cells) and neuroglia (supporting cells).
• Functions include sensory input, integration, and motor output.
  • Neurons transmit nerve impulses.
  • Neuroglia support and protect neurons.
• Found in the brain, spinal cord, and nerves.