Chapter 4: Tissues – The Living Fabric

Overview of Tissues

Tissues are groups of similar cells that perform a common function. The study of tissues is called histology. There are four basic tissue types in the human body, each with specialized roles.

• Definition of Tissue: A group of similar cells performing a specific function.

• Histology: The study of tissues.

• Four Basic Tissue Types: Epithelial, Connective, Muscle, Nervous.

General Characteristics of Tissue Types

• Epithelial Tissue: Covers body surfaces, lines cavities, forms glands, and lines blood vessels.

• Connective Tissue: Arises from mesenchyme, supports and binds other tissues, stores energy, and provides immunity.

• Muscle Tissue: Specialized for movement.

• Nervous Tissue: Makes up the brain, spinal cord, and nerves; specialized for communication.

Epithelial Tissue

Characteristics of Epithelial Tissue

Epithelial tissue forms boundaries between different environments, protects, secretes, absorbs, and filters.

• Polarity: Has an apical (free) surface and a basal (attached) surface.

• Specialized Contacts: Cells are closely packed with little extracellular material.

• Supported by Connective Tissue: Rests on a basement membrane.

• Avascular but Innervated: Contains no blood vessels but is supplied by nerve fibers.

• Regeneration: High regenerative capacity.

Classification of Epithelial Tissue

• Number of Layers: Simple (one layer), Stratified (multiple layers).

• Cell Shape: Squamous (flat), Cuboidal (cube-shaped), Columnar (tall).

Pseudostratified Epithelium: Appears layered but all cells touch the basement membrane (e.g., trachea).

Transitional Epithelium: Found in the bladder; stretches to allow filling.

Glandular Epithelium

• Endocrine Glands: Ductless, secrete hormones into the blood.

• Exocrine Glands: Secrete products onto body surfaces or into ducts (e.g., sweat, saliva).

Basement Membrane

• Definition: Thin, fibrous, extracellular matrix separating epithelium from underlying connective tissue.

• Components: Basal lamina (from epithelium) and reticular lamina (from connective tissue).

Connective Tissue

General Features

Connective tissue is the most abundant and widely distributed tissue type. It supports, protects, and binds other tissues together.

• Main Classes: Connective tissue proper, cartilage, bone, blood.

• Common Origin: All arise from mesenchyme (embryonic tissue).

• Three Basic Elements: Ground substance, fibers, and cells.

• Three Fiber Types: Collagen (strength), Elastic (stretch), Reticular (network).

• Matrix: Extracellular matrix composed of ground substance and fibers; can be fluid (as in blood).

Types of Connective Tissue

• Loose Connective Tissue: Areolar, adipose, reticular.

• Dense Connective Tissue: Dense regular (tendons, ligaments), dense irregular (dermis, fibrous capsules), elastic (walls of large arteries).

• Cartilage: Hyaline (ends of bones, trachea), elastic (ear), fibrocartilage (intervertebral discs).

• Bone: Skeleton; provides support and protection.

• Blood: Transports oxygen and nutrients.

Special Features

• Lacunae: Small spaces in cartilage and bone where cells reside.

• Vascularity: Varies; cartilage is avascular, bone is highly vascular.

Membranes

Types and Structure

• Components: Epithelium + connective tissue.

• Types: Cutaneous (skin – dry), mucous (lines body cavities open to exterior – moist), serous (lines closed cavities – moist).

• Locations: Pleura (lungs), pericardium (heart), peritoneum (abdomen).

Tissue Repair

Processes and Outcomes

• Regeneration: Replacement of destroyed tissue with the same kind of tissue.

• Fibrosis: Replacement with scar tissue (dense connective tissue).

• Steps of Tissue Repair: Inflammation → Organization (restores blood supply) → Regeneration and Fibrosis.

• Granulation Tissue: Delicate new tissue formed during the organization phase.

Practice Quick Facts

• Simple Squamous Epithelium: Air sacs of lungs.

• Simple Cuboidal Epithelium: Kidney tubules.

• Simple Columnar Epithelium: Digestive tract lining.

• Pseudostratified Columnar Epithelium: Trachea.

• Stratified Squamous Epithelium: Mouth, esophagus, skin.

• Transitional Epithelium: Urinary bladder.

• Adipose Tissue: Fat storage, insulation.

• Dense Regular Connective Tissue: Tendons, ligaments.

• Dense Irregular Connective Tissue: Dermis, fibrous capsules.

• Elastic Connective Tissue: Walls of large arteries.

• Hyaline Cartilage: Ends of bones, trachea.

• Elastic Cartilage: Ear.

• Fibrocartilage: Intervertebral discs.

• Bone: Skeleton.

• Blood: Transports oxygen, nutrients.

Table: Comparison of Major Tissue Types

Key Equations and Terms

• Histology: The study of tissues.

• Basement Membrane:

• Extracellular Matrix:

Additional info: These notes expand on the original flashcard questions by providing definitions, context, and examples for each tissue type, as well as a summary table for comparison.