Bio2140: ch4 partA

Chapter 4: Tissue - The Living Fabric

Overview of Tissues

  • Definition of Tissue: Groups of cells similar in structure that perform a common or related function, vital for maintaining homeostasis.

  • Histology: The study of tissues.

  • Primary Tissue Types:

    • Epithelial Tissue: Covers and forms boundaries.

    • Connective Tissue: Supports, binds, protects other tissues.

    • Muscle Tissue: Produces movement.

    • Nerve Tissue: Controls communication within the body.

Four Main Tissue Types

1. Nervous Tissue

  • Function: Internal communication.

  • Locations: Brain, spinal cord, nerves.

2. Muscle Tissue

  • Function: Contracts to cause movement.

  • Types:

    • Skeletal: Muscles attached to bones.

    • Cardiac: Found in the heart.

    • Smooth: Walls of hollow organs.

3. Epithelial Tissue

  • Function: Forms boundaries, protects, secretes, absorbs, filters.

  • Locations:

    • Lining of digestive tract organs and other hollow organs.

    • Skin surface (epidermis).

4. Connective Tissue

  • Function: Supports, protects, binds other tissues together.

  • Examples: Bones, tendons, fat, soft padding.

Characteristics of Epithelial Tissue

  • Polarity: Has an apical surface (upper free) and a basal surface (attached).

  • Specialized Contacts: Cells are tightly bound together.

  • Supported by Connective Tissues: Basement membrane provides support.

  • Avascular but Innervated: Nourished by diffusion; supplied with nerve fibers.

  • Regeneration Capacity: High ability to replace lost cells.

Types of Epithelial Tissue by Structure and Function

1. Simple Epithelia

  • Single layer of cells.

  • Types:

    • Simple Squamous: Thin, flattened cells; functions in diffusion.

    • Simple Cuboidal: Boxlike cells for secretion and absorption.

    • Simple Columnar: Tall, column-shaped cells; absorption and secretion.

2. Stratified Epithelia

  • Two or more layers of cells.

  • Classified by shape of the apical layer:

    • Stratified Squamous: Protects against abrasion; can be keratinized or non-keratinized.

    • Transitional Epithelia: Can stretch; found in urinary bladder.

Glandular Epithelial Tissue

  • Definition of Gland: One or more cells that make and secrete an aqueous fluid.

  • Types of Glands:

    • Endocrine: Ductless; secrete hormones into bloodstream.

    • Exocrine: Secrete products onto body surfaces or into cavities via ducts.

Exocrine Glands

  • Unicellular Glands: Goblet cells; produce mucin that forms mucus.

  • Multicellular Glands: Composed of duct and secretory units; classified by structure and mode of secretion:

    • Modes of Secretion:

      • Merocrine: Secrete via exocytosis; most common.

      • Holocrine: Entire cell ruptures releasing secretions.

      • Apocrine: Apex of the cell ruptures; debated whether exists in humans.

Summary of Epithelial Tissue Characteristics

  • Epithelial tissues play crucial roles in protection, absorption, secretion, and sensation, characterized by their structure and regenerative abilities. Each type serves specific functions essential for homeostasis and various bodily processes.