6.10.1 Tissues

Body Organization and Tissues

General Overview

  • The human body is composed of various levels of organization, starting from cells and progressing to tissues, organs, and systems.

Definitions

  • Tissues: Groups of similar cells that perform a specific function.

  • Organs: Structures composed of two or more tissue types.

  • Systems: Groups of organs that work together to perform complex functions.

Types of Tissues

Epithelial Tissue

  • Functions: Covers surfaces and forms glands.

    • Properties:

      • Covers and lines surfaces.

      • Forms glands for secretion.

Connective Tissue

  • Functions: Connects, supports, and protects other tissues and organs.

    • Properties:

      • Most abundant tissue type in the body.

      • Specialized cells are embedded in an extracellular matrix.

Muscle Tissue

  • Functions: Responsible for contraction and movement of the body.

    • Types:

      • Skeletal Muscle: Striated and voluntary.

      • Smooth Muscle: Non-striated and involuntary.

      • Cardiac Muscle: Striated and found only in the heart, involuntary.

Nervous Tissue

  • Functions: Conducts impulses and coordinates bodily functions.

    • Contains neurons for signaling and neuroglia for support.

Epithelial Tissue Details

Properties of Epithelial Tissue

  1. Divisions:

    • Coverings and linings.

    • Glandular (formation of glands).

  2. Cellularity: Composed of cells tightly packed in continuous sheets.

  3. High Regeneration Rate: Rapid mitotic activity allows for recovery from injury, but many cancers arise from epithelial tissues.

  4. Avascular: Lacks blood vessels, relies on diffusion for nutrients.

  5. Polarity: Has a distinct top (apical) and bottom (basal) surface.

Types of Epithelial Tissue

  • Simple: One cell layer.

  • Stratified: Two or more cell layers.

  • Shapes:

    • Squamous: Flat and irregular.

    • Cuboidal: Cube-shaped with large nuclei.

    • Columnar: Tall and thin.

  • Special Types:

    • Pseudostratified Columnar: Appears layered but is one layer, often with cilia.

    • Transitional: Changes shape depending on stretching.

Glandular Epithelium

  • Functions: Forms glands in the body.

    • Types of Glands:

      • Endocrine Glands: Secrete hormones into the blood.

      • Exocrine Glands: Secrete substances into ducts.

Connective Tissue Properties

General Functions

  • Most diverse tissue type, providing support and connectivity.

  • Specialized cells within a varying matrix (ground substance and protein fibers).

Types of Connective Tissue

  1. Connective Tissue Proper:

    • Loose Connective: Areolar, adipose, reticular.

    • Dense Connective: Dense regular, dense irregular.

  2. Fluid Connective Tissue: Blood, lymph.

  3. Supporting Connective Tissue: Cartilage, bone.

Connective Tissue Fibers

  1. Collagen Fibers: Thick, pink/orange, resist stretching.

  2. Elastic Fibers: Thin, brown/black, provide elasticity.

  3. Reticular Fibers: Form a mesh framework, stains black.

Specific Types of Connective Tissue

Loose Connective Tissue

  • Areolar Tissue: Widely distributed, supports organs, connects tissues.

  • Adipose Tissue: Contains fat cells, provides insulation and energy storage.

  • Reticular Tissue: Forms a network around organs, supports tissue structure.

Dense Connective Tissue

  • Dense Regular: Provides strength in one direction (tendons, ligaments).

  • Dense Irregular: Strength in multiple directions (skin, arterial walls).

Supporting Connective Tissue

  • Bone: Strongest connective tissue, supports and protects organs.

  • Cartilage: Provides flexible support, limited blood supply.

    • Types: Hyaline, fibrocartilage, elastic cartilage.

Fluid Connective Tissue

  • Blood: Transports nutrients and wastes, found in circulatory system.

  • Lymph: Part of the immune system, removes excess fluid from tissues.

Muscle Tissue Characteristics

General Properties

  • Responsible for body movement, contraction involves specialized structures.

  • Types: Skeletal, smooth, cardiac.

Skeletal Muscle

  • Striated, under voluntary control, multi-nucleated.

Smooth Muscle

  • Involuntary control, found in organs, single central nucleus.

Cardiac Muscle

  • Found only in the heart, involuntary, striated with intercalated discs.

Nervous Tissue Properties

Functions

  • Coordinates body functions and processes information.

  • Composed of neurons (conducting cells) and neuroglia (support cells).

Cell Junctions

  • Tight Junctions: Create leak-proof seals (e.g., in the urinary system).

  • Adhesion Junctions: Hold cells together, allowing for stretch (e.g., heart, skin).

  • Gap Junctions: Allow communication between cells through small cytoplasmic connections.

Exocrine Glands

  • Types:

    • Sweat glands: Produce sweat.

    • Sebaceous glands: Secrete oils.

    • Salivary glands: Produce saliva.

    • Mammary glands: Produce milk.

    • Pancreas: Largest exocrine gland involved in digestion.

Additional Exocrine Glands

  • Include lacrimal, Brunner, and stomach glands, each with specific secretion functions.