Tissue level

Overview of Anatomy and Physiology

  • The first unit covered broad concepts of anatomy and physiology, including:

    • Chemical level

    • Cellular level of organization

  • This chapter concludes the foundation with tissue level organization.

  • Understanding chemistry and biology of cells sets the stage to discuss body systems:

    • Integumentary System

    • Skeletal System (Bones)

    • Muscular System

    • Nervous System

    • Endocrine System

    • Reproductive System

    • Other advanced systems (Cardiovascular, Gastrointestinal, Urinary)

Histology: The Study of Tissues

  • Tissues consist of cells organized for a common function, which can include different cell types.

  • Example: Epithelium in airways includes mucus-producing cells for protective lining.

Types of Tissues

  1. Epithelial Tissues

    • Line and cover body surfaces.

    • Examples: Intestinal lining (absorptive), stratified squamous epithelium (less permeable).

  2. Connective Tissues

    • Bind various body parts together.

  3. Muscle Tissues

    • Produce movement by contracting or shortening.

    • Movement occurs through attachment points.

  4. Nervous Tissues

    • Enable rapid communication within body.

Epithelial Tissue Characteristics

  • Covers and lines surfaces of the body.

  • Types of functional roles:

    • Absorption in intestines

    • Protective barriers in epidermis.

  • Polarity: Includes an exposed apical surface and a basolateral surface.

  • Avascular: Lacks blood supply; relies on underlying connective tissue for nutrients.

  • High regeneration capacity via stem cells.

Intracellular Junctions

  • Types of Junctions:

    • Gap Junctions: Allow communication between cells (e.g., in cardiac muscle).

    • Tight Junctions: Create seals between cells (e.g., in intestinal lining).

    • Desmosomes: Provide strength to withstand mechanical stress (e.g., in epidermis).

Epithelial Tissue Classification

  • Based on Layers:

    • Simple Epithelium: Single cell layer; all cells in contact with the underlying connective tissue.

    • Stratified Epithelium: Multiple layers; not all cells in contact with connective tissue.

    • Pseudostratified Epithelium: Appears stratified; all cells in contact with the underlying tissue but not all reach the surface.

  • Based on Cell Shape:

    • Squamous: Flat cells.

    • Cuboidal: Cube-shaped cells.

    • Columnar: Taller than wide; nuclei are uniformly positioned.

Specific Types of Epithelial Tissue

  • Simple Squamous Epithelium: Thin; allows for diffusion (e.g., alveoli).

  • Stratified Squamous Epithelium: Multiple layers; withstands abrasion (e.g., skin).

  • Simple Cuboidal Epithelium: Involved in secretion and absorption (e.g., renal tubules).

  • Simple Columnar Epithelium: Heightened absorption and secretion (e.g., intestines, uterine tubes).

  • Pseudostratified: Respiratory tract; often ciliated.

  • Transitional Epithelium: Stretches as bladder fills.

  • Glandular Epithelium: Forms glands which secrete substances.

Glandular Epithelium

  • Endocrine Glands: Secrete hormones into the bloodstream.

  • Exocrine Glands: Secrete onto surfaces via ducts. Can be classified based on:

    • Structure

    • Mode of secretion

    • Nature of secretion.

  1. Exocrine Gland Structure:

    • Unicellular: Single cell (e.g., goblet cells).

    • Multicellular: Classified by duct structure (simple vs. compound).

  2. Mode of Secretion:

    • Merocrine Secretion: Release products via exocytosis (e.g., sweat glands).

    • Apocrine Secretion: Release of apical portion of cell (e.g., mammary glands).

    • Holocrine Secretion: Entire cell disintegrates, releasing contents (e.g., sebaceous glands).

  3. Types of Secretions:

    • Serous: Thin, watery (e.g., tears).

    • Mucous: Thick, sticky (produces mucins).

    • Mixed: Contains both serous and mucous components.

Connective Tissue

  • The most abundant tissue by mass.

  • Key features:

    • Specialized cells embedded in a nonliving extracellular matrix (ECM).

    • ECM includes protein fibers and ground substance.

Functions of Connective Tissue

  • Structural Support: Bones and cartilage.

  • Transport: Blood transports nutrients and gases.

  • Protection: Protects delicate organs (e.g., reticular connective tissue).

  • Energy Storage: Adipose tissue for energy.

Types of Connective Tissue

  1. Connective Tissue Proper:

    • Loose Connective Tissue (e.g., areolar, adipose, reticular).

    • Dense Connective Tissue.

  2. Fluid Connective Tissues:

    • Blood and lymph.

  3. Supporting Connective Tissues:

    • Cartilage and bone.

Key Cell Types in Connective Tissue Proper

  • Fibroblasts: Produce protein fibers.

  • Macrophages: Immune response; eat foreign material.

  • Mast Cells: Secrete histamine (increases permeability) and heparin (inhibits clotting).

Types of Protein Fibers

  • Collagen Fibers: Provide tensile strength.

  • Reticular Fibers: Support soft tissues in organs.

  • Elastic Fibers: Provide elasticity and flexibility.

Specific Loose Connective Tissues

  • Areolar Connective Tissue: Sparse collagen; provides minimal structural integrity.

  • Adipose Tissue: Composed mainly of adipocytes; stores energy and provides insulation.

  • Reticular Connective Tissue: Net-like structure for holding soft organs together.