Chapter 4: Tissues – Anatomy and Physiology I Study Notes

Introduction to Tissues

The Living Fabric

Tissues are groups of cells that are similar in structure and perform related functions, contributing to the maintenance of homeostasis in the body. The study of tissues is known as histology.

• Specialization: Cells within tissues are specialized to carry out specific functions.

• Homeostasis: Tissues work together to maintain the body's internal balance.

• Main Tissue Types: There are four primary tissue types in the human body: epithelial, connective, muscle, and nervous tissue.

Microscopy and Tissue Preparation

Viewing Tissues Under a Microscope

To study tissues, samples must be prepared and viewed under a microscope using specific techniques.

• Fixed: Tissue is preserved using a solvent to prevent decay.

• Sectioned: Tissue is sliced thin enough to allow light or electrons to pass through for imaging.

• Stained: Dyes or heavy metal salts are used to enhance contrast and visualize structures.

  • Light Microscopy: Uses colored dyes.

  • Electron Microscopy: Uses heavy metal salts.

    • Transmission Electron Microscopy (TEM): Shows internal structures.

    • Scanning Electron Microscopy (SEM): Shows surface features.

• Artifacts: Distortions may occur during preparation, so images may not perfectly represent living tissues.

Epithelial Tissue

Definition and Functions

Epithelial tissue (epithelium) consists of sheets of cells that cover body surfaces or line body cavities. It serves as a protective barrier and is involved in absorption, secretion, and sensation.

• Covering and Lining Epithelium: Forms the outer layer of skin, lines open cavities, and covers walls and organs of the ventral body cavity.

• Glandular Epithelium: Forms glands of the body, such as salivary glands.

Characteristics of Epithelial Tissues

Epithelial tissues have five distinguishing characteristics:

• Polarity: Cells have an apical (top) surface exposed to the exterior or cavity, and a basal (bottom) surface attached to underlying tissue.

• Specialized Contacts: Cells are closely packed and held together by tight junctions and desmosomes, forming continuous sheets.

• Supported by Connective Tissue: The basal surface rests on a basement membrane, which provides support and anchors the epithelium.

• Avascular but Innervated: Epithelial tissues lack blood vessels but are supplied by nerve fibers. Nutrients diffuse from underlying connective tissues.

• High Regeneration: Epithelial cells have a high capacity for regeneration, allowing rapid repair after injury or damage.

Additional info:

• Apical Surface: May have microvilli (for absorption) or cilia (for movement of substances).

• Basal Lamina: An adhesive sheet that helps attach epithelial cells to underlying tissues.