Study Guide: Tissues – The Living Fabric (Anatomy & Physiology)

Chapter 4: Tissues, The Living Fabric

Introduction

This chapter introduces the four basic types of tissue found in the human body: epithelial, connective, muscle, and nervous tissue. Each tissue type has unique structural and functional characteristics essential for maintaining homeostasis and supporting organ function.

Epithelial Tissue

Structural Characteristics of Epithelia

Epithelial tissue forms the surface coverings and inner linings of the body. It functions as barriers and selective filters.

• Cellularity: Epithelial tissues are composed almost entirely of tightly packed cells with minimal extracellular material.

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

• Attachment: The basal surface is attached to a thin basement membrane.

• Avascularity: Epithelia lack blood vessels and receive nutrients by diffusion from underlying tissues.

• Regeneration: Epithelial cells have a high capacity for renewal and repair.

Classification of Epithelia

Epithelia are classified based on the number of cell layers and the shape of the cells:

• Simple epithelium: Single layer of cells; functions in absorption, secretion, and filtration.

• Stratified epithelium: Multiple layers; provides protection against abrasion.

• Cell shapes: Squamous (flat), cuboidal (cube-shaped), columnar (tall and column-like).

Types of Epithelia and Their Functions

Type	Description	Function/Location
Simple Columnar	Single layer, tall cells	Lines most of the GI tract
Stratified Squamous	Multiple layers, flat cells	Tough outer barrier of the body (e.g., skin)
Transitional	Multiple layers, variable shape	Bladder; can stretch and recoil

Glands: Endocrine vs. Exocrine

• Endocrine glands: Ductless; secrete hormones directly into the bloodstream (e.g., thyroid gland).

• Exocrine glands: Have ducts; secrete products onto body surfaces or into body cavities (e.g., sweat glands).

• Goblet cells: Unicellular exocrine glands that secrete mucus.

Connective Tissue

General Characteristics

Connective tissue (CT) is the most abundant and widely distributed tissue in the body. It supports, protects, and binds other tissues together.

• Extracellular Matrix (ECM): CT has an abundance of ECM, which consists of ground substance and fibers.

• Ground substance: Unstructured material that fills the space between cells; contains water, proteins, and polysaccharides.

• Fibers: Collagen (strength), elastic (stretch), and reticular (support).

Major Classes of Connective Tissue

• Connective tissue proper: Includes loose (areolar, adipose, reticular) and dense (regular, irregular, elastic) types.

• Cartilage: Hyaline, elastic, and fibrocartilage.

• Bone: Osseous tissue; supports and protects.

• Blood: Fluid tissue; transports nutrients and waste.

Connective Tissue Proper

• Loose CT: Found underlying epithelia; supports and cushions organs.

• Dense CT: Forms tendons and ligaments; provides strength and resistance to stretching.

• Most abundant fiber: Collagen fibers are the most abundant in CT proper.

Muscle Tissue

Types and Functions

Muscle tissue is specialized for contraction and movement. There are three types:

• Skeletal muscle: Voluntary control; striated; attached to bones for movement.

• Cardiac muscle: Involuntary control; striated; found only in the heart.

• Smooth muscle: Involuntary control; non-striated; found in walls of hollow organs (e.g., intestines, blood vessels).

Cardiac muscle is the type found in the heart. Skeletal muscle is under voluntary control.

Nervous Tissue

Structure and Function

Nervous tissue forms the brain, spinal cord, and peripheral nerves. It is highly specialized for communication via electrical and chemical signals.

• Neuron: The basic functional unit; consists of a cell body, dendrites (receive signals), and axon (transmits signals).

• Neuroglia: Supporting cells that protect and assist neurons.

Membranes

Types of Body Membranes

Membranes are sheets of tissue that cover or line body surfaces and cavities. The four major types are:

• Serous membrane: Lines body cavities not open to the exterior; produces serous fluid for lubrication.

• Mucous membrane: Lines cavities open to the exterior (e.g., digestive, respiratory tracts); secretes mucus.

• Cutaneous membrane: The skin; protects the body surface.

• Synovial membrane: Lines joint cavities; produces synovial fluid.

Serous Membrane Composition

• Visceral layer: Covers organs.

• Parietal layer: Lines cavity walls.

• Serous fluid: Lubricates and reduces friction.

Some membranes, such as mucous membranes, have a thick lamina propria (connective tissue) and stratified squamous epithelium.

Tissue Repair

Key Steps in Tissue Repair

Tissue repair is a programmed response to injury that involves regeneration of damaged tissue and fibrosis (scar tissue formation).

• Inflammation: Damaged tissues release chemicals that cause blood vessels to dilate and become permeable; immune cells migrate to the site.

• Organization: Granulation tissue forms, restoring blood supply and supporting cell migration.

• Regeneration and fibrosis: Epithelial cells proliferate to replace lost tissue; fibroblasts produce collagen fibers, forming scar tissue if regeneration is incomplete.

Example: After a skin injury, inflammation occurs first, followed by the formation of granulation tissue, and finally regeneration of the epithelium or formation of scar tissue.

Additional info: Academic context and definitions have been expanded for clarity and completeness. Table entries and membrane types have been logically inferred and completed based on standard Anatomy & Physiology curriculum.