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 specific functions within the body. 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 is composed of four primary tissue types, each with distinct roles:

• Epithelial tissue: Covers surfaces, lines cavities, and forms glands.

• Connective tissue: Provides support, protection, and connects other tissues.

• Muscle tissue: Specialized for contraction and movement.

• Nervous tissue: Specialized for communication via electrical impulses.

Epithelial Tissue

Overview of Epithelial Tissue

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

• Covers surfaces exposed to the environment and lines internal cavities.

• Forms selective barriers between body tissues and the external environment.

• Examples: Skin, digestive tract, respiratory tract, reproductive tract.

Characteristics of Epithelial Tissue

• Cells bound closely together: Forms continuous sheets.

• Apical surface: Exposed to environment or internal chamber.

• Basement membrane: Attaches epithelium to underlying connective tissue.

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

• Regeneration: Rapid replacement of damaged or lost cells.

Locations and Functions of Epithelial Tissue

• Forms large sheets covering all surfaces exposed to the external environment and lining internal body surfaces.

• Examples: Skin, internal passageways (digestive, urinary, respiratory, reproductive tracts).

• Acts as selective barriers separating deep tissues from the external environment and internal cavities.

• Prevents friction, regulates fluid composition, and restricts communication between body tissue fluids.

• Examples: Cavities around lungs and heart.

Essential Functions of Epithelia

• Physical protection: Shields underlying tissues from abrasion, dehydration, and chemical/biological agents.

• Control permeability: Regulates entry and exit of substances.

• Provide sensation: Contains specialized cells that detect environmental changes.

• Produce secretions: Glandular epithelium produces fluids such as enzymes, mucus, and hormones.

Glandular Epithelium

• Exocrine glands: Discharge secretions onto epithelial surfaces (e.g., sweat, digestive enzymes).

• Endocrine glands: Release hormones into surrounding tissue fluid and blood (e.g., pancreas, thyroid).

Summary Table: Types of Tissues and Their Functions

Tissue Type	Main Functions	Examples
Epithelial	Protection, secretion, absorption, sensation	Skin, lining of digestive tract, glands
Connective	Support, protection, transport, energy storage	Bone, blood, fat, tendons
Muscle	Contraction, movement	Skeletal muscles, heart, walls of hollow organs
Nervous	Communication, control	Brain, spinal cord, nerves

Additional info:

• Histology is a foundational discipline in Anatomy & Physiology, providing insight into how tissues contribute to organ function.

• Understanding tissue types is essential for recognizing how organs are structured and how they respond to injury or disease.