Understanding Tissues and Epithelial Functions

Understanding Tissues

• A tissue is a group of cells united by a common function within the body.
• Tissues are essential for forming organs.

Tissue Composition and Characteristics

• Tissues are differentiated by:
  • Cellular composition
  • Extracellular matrix (ECM) components
  • Functional roles
• The extracellular matrix consists of proteins, salts, water, and macromolecules.

General Functions of Epithelia

• Provides physical protection against water, chemicals, and physical injury.
• Exhibits selective permeability to control substance exchange.
• Engages in secretion (e.g., sweat, saliva) and absorption processes.
• Functions in sensation.

Characteristics of Epithelia

• High cell density with minimal extracellular matrix presence.
• Polarity: cells have distinct apical (free surface) and basal (attached) sides.
• Attachment to connective tissue on one side.
• Avascular: lacks direct blood supply.

Characteristics of Different Tissue Types

Epithelial Tissue

• Contains minimal extracellular matrix, primarily a basal lamina.
• Lacks direct blood supply.
• Surface features may include microvilli and cilia.
• Locations: Covers body surfaces, lines cavities, hollow organs, and forms secretory glands.
• Cell arrangement varies from single to multiple layers; shapes can be flattened, cuboidal, or columnar.

Connective Tissue

• Features an extensive extracellular matrix with varied types (liquid, gelatinous, firm, calcified).
• Cartilage is unique for its lack of blood supply.
• Cells are not arranged in layers and are usually dispersed in the matrix.
• Locations include supporting structures of the skin, cartilage, bones, and blood.
• Cell shapes can be irregular to round.

Muscle Tissue

• Specific characteristics of muscle tissue were not detailed in the provided text.