Chapter 4: The Tissue Level of Organization – Essentials of Anatomy & Physiology

Tissues of the Body

Introduction to Tissues

Tissues are collections of specialized cells and cell products that perform a limited number of functions. The study of tissues is known as histology.

• Tissue: A group of cells with similar structure and function.

• Histology: The scientific study of tissues.

Four Basic Types of Tissues

The human body contains four primary types of tissues, each with distinct functions and characteristics:

• Epithelial tissue: Covers body surfaces and lines internal passageways; forms glands.

• Connective tissue: Provides structural support, stores energy, and connects other tissues.

• Muscle tissue: Specialized for contraction and movement.

• Nervous tissue: Propagates electrical impulses and processes information.

Epithelial Tissue

Overview of Epithelial Tissue

Epithelial tissue covers both internal and external body surfaces and composes most glands. It serves essential functions in protection, secretion, and absorption.

• Covers surfaces: Forms sheets that cover surfaces exposed to the external environment and lines internal body surfaces.

• Glandular function: Composes most glands, which are fluid-secreting cells.

Characteristics of Epithelial Tissue

• Cells bound closely together: Form continuous sheets.

• Apical surface: Exposed to the environment or internal chamber.

• Basement membrane: Attaches epithelium to underlying connective tissue.

• Avascular: Lacks blood vessels; nutrients diffuse from underlying tissues.

• Regeneration: Cells are continually replaced or regenerated.

Locations and Functions of Epithelial Tissue

Epithelial tissue forms selective barriers and covers all surfaces exposed to the external environment, as well as lining internal body surfaces and cavities.

• External surfaces: Skin, passageways of digestive, urinary, respiratory, and reproductive tracts.

• Internal cavities: Cavities around lungs and heart.

• Functions:

  • Physical protection: Protects against abrasion, dehydration, and chemical/biological agents.

  • Control permeability: Regulates entry and exit of substances.

  • Sensation: Specialized cells detect environmental changes.

  • Specialized secretions: Glandular epithelium produces secretions.

Examples and Applications

• Skin: Protects underlying tissues from external environment.

• Digestive tract lining: Absorbs nutrients and secretes enzymes.

• Respiratory tract: Ciliated epithelium moves mucus.

Additional info:

• Epithelial tissue forms the interface between the body and its environment, playing a critical role in homeostasis.

Summary Table: Four Basic Types of Tissues

Type of Tissue	Main Functions	Examples
Epithelial	Protection, secretion, absorption	Skin, lining of digestive tract
Connective	Support, binding, energy storage	Bone, blood, fat
Muscle	Contraction, movement	Skeletal muscle, heart muscle
Nervous	Communication, control	Brain, spinal cord, nerves

Additional info:

• The organization of tissues is fundamental to understanding organ structure and function in Anatomy & Physiology.