The tissue level of organization

The Tissue Level of Organization

Overview of Tissues

  • Tissues are groups of cells with similar structures performing common functions.

  • Four main types of tissues:

    • Nervous tissue

    • Epithelial tissue

    • Muscle tissue

    • Connective tissue

Tissue Membranes

  • Two broad categories:

    1. Connective tissue membranes (e.g., synovial membranes, organ capsules) - made only of connective tissue.

    2. Epithelial membranes - composites of both connective and epithelial tissue.

Epithelial Tissue

  • Functions: Covers body surfaces, lines cavities, and forms glands.

  • Characteristics:

    • Two distinct surfaces:

      • Apical surface: exposed to the outside or internal cavities.

      • Basal surface: attached to underlying connective tissue.

    • Epithelial cells are polar, having differing structures on each surface.

Organization of Epithelial Tissue

  • Simple epithelial tissue: single layer of cells.

  • Stratified epithelial tissue: multiple layers of cells.

  • Shapes of epithelial cells: squamous, cuboidal, columnar.

Goblet Cells

  • Found in the small intestine interspersed among columnar epithelial cells; responsible for mucus secretion.

Classification of Epithelial Tissue

  • Simple Squamous Epithelium: Lining of lungs, blood vessels; functions in diffusion and filtration.

  • Simple Cuboidal Epithelium: In glands and kidney tubules; absorbs and secretes.

  • Simple Columnar Epithelium: Found in digestive tract and uterus; absorbs and secretes.

  • Pseudostratified Columnar Epithelium: Lines bronchi and trachea; secretes mucus.

  • Stratified Squamous Epithelium: Lines esophagus, mouth; protects against abrasion.

  • Stratified Cuboidal Epithelium: In gland ducts; protective tissue.

  • Stratified Columnar Epithelium: In urethra and some glands; secretes and protects.

  • Transitional Epithelium: Lines bladder; allows stretching.

Exocrine Glands

  • Classified by structure:

    • Alveolar (acinar): E.g., simple branched alveolar.

    • Tubular: E.g., simple tubular, simple coiled tubular.

    • Compound: E.g., compound tubuloalveolar and compound tubular.

Modes of Glandular Secretion

  • Merocrine: Cell remains intact.

  • Apocrine: Apical portion of the cell is released.

  • Holocrine: Cell is destroyed as it releases product.

Sebaceous Glands

  • Secrete oils, are holocrine glands, cells are destroyed upon secretion.

Connective Tissue

  • Four types:

    1. Connective tissue proper

    2. Cartilage

    3. Bone

    4. Blood

  • Connective tissue is the most abundant tissue type.

Connective Tissue Classes

  • Loose connective tissue: Areolar, adipose, reticular.

  • Dense connective tissue: Regular and irregular.

  • Cartilage: Hyaline, elastic, fibrocartilage.

  • Bone: Compact and spongy.

  • Blood: Fluid connective tissue.

Specific Connective Tissues

  • Adipose Tissue: Stores fat for energy, provides insulation.

  • Reticular Tissue: Support for soft organs.

  • Dense Connective Tissue: Contains collagen; provides strength and support.

Types of Muscle Tissue

  • Skeletal Muscle: Striated, multinucleated; voluntary movement.

  • Cardiac Muscle: Striated, single nucleus, involuntary; found in heart.

  • Smooth Muscle: Non-striated, involuntary; found in walls of hollow organs.

Nervous Tissue

  • Composed of neurons and supporting cells (neuroglia).

  • Neurons are specialized for signal transmission; supporting cells protect and support neurons.

Neuron Structure

  • Cell body (soma) contains the nucleus.

  • Dendrites: receive signals.

  • Axon: transmits electrical impulses.

Tissue Repair

  • Involves inflammation, organization, and regeneration.

  • During healing, fibroblasts lay down collagen fibers to repair the tissue.