Animal Tissues and Their Functions

Overview of Tissues

• Tissues are defined as collections of similar cells and their extracellular matrix, performing related functions.
• Histology is the study of tissues.

Four Primary Types of Tissue

• Epithelial tissue
• Connective tissue
• Muscle tissue
• Nervous tissue

Epithelial Tissue

• Covers body surfaces and cavities; characterized by tightly packed cells with minimal extracellular material.
• Avascular; relies on diffusion for nutrient uptake.
• Supported by a basement membrane.

Functions of Epithelial Tissue

• Protection: Outer skin layer, mucosa lining.
• Barrier Formation: Prevents substance passage (e.g., skin).
• Substance Passage: Facilitates gas exchange in lungs.
• Secretion: Produces mucus in glands.
• Absorption: Nutrient uptake in the intestine.

Classification of Epithelial Tissue

• By Shape:
  • Squamous (flat and thin)
  • Cuboidal (cube-shaped)
  • Columnar (tall and thin)
• By Arrangement:
  • Simple (single layer)
  • Stratified (multiple layers)
  • Pseudostratified (appears layered, but is not)
  • Transitional (can stretch)

Stratified Epithelium Types

• Stratified squamous
• Stratified cuboidal
• Stratified columnar
• Transitional epithelium

Functions of Epithelial Tissue by Type

• Mucous Membrane: Secretes mucus, enzymes, absorbs nutrients, protects.
• Glandular Epithelium: Forms glands for secretion.
• Endothelium: Lines blood and lymphatic vessels.
• Mesothelium: Lines body cavities without external openings.

Epithelial Tissue Glands

• Glands are structures secreting substances; classified as endocrine or exocrine.
• Endocrine Glands: Ductless, secrete hormones directly into blood.
• Exocrine Glands: Possess ducts, secrete onto surfaces or into cavities (e.g., sweat glands).

Structure of Exocrine Glands

• Simple: One duct.
• Compound: Branching ducts.
• Tubule-Ending: Ends in small tubes.
• Acini: Ends in saclike structures.
• Alveoli: Ends in hollow sacs.

Secretion Types of Exocrine Glands

• Merocrine: No cell loss (e.g., sweat glands).
• Apocrine: Part of the cell pinches off (e.g., mammary glands).
• Holocrine: Entire cell is lost in secretion (e.g., sebaceous glands).

Connective Tissue

• Consists of cells separated by an abundant extracellular matrix.

Functions of Connective Tissue

• Enclosing and Separating: Forms compartments within organs.
• Connecting Tissues: Ligaments and tendons connect structures.
• Support and Movement: Bones and cartilage support the body.
• Storage: Fat is stored in adipose tissue; minerals in bones.
• Cushioning and Insulating: Adipose tissue provides cushioning.
• Transporting: Blood transports nutrients and wastes.
• Protecting: Provides structural protection (e.g., bones).