Chapter 3: Tissues – Structure and Function in Human Anatomy

Chapter 3: Tissues

Overview of Tissue Types

Human tissues are collections of cells with similar structure and function, forming the foundation for organs and systems. There are four primary tissue types:

• Epithelial Tissue: Tightly bound, avascular sheets of cells covering surfaces and lining cavities.

• Connective Tissue: Diverse group with specialized cells, protein fibers, and ground substance; functions include support, protection, and transport.

• Muscular Tissue: Specialized for contraction; includes skeletal, cardiac, and smooth muscle.

• Nervous Tissue: Specialized for conducting electrical impulses throughout the body.

Germ Layers and Tissue Origins

During embryonic development, three primary germ layers give rise to all tissues:

• Ectoderm: Forms nervous system, epidermis, and associated glands.

• Mesoderm: Middle layer; gives rise to connective tissues, muscles, and some organs.

• Endoderm: Forms epithelia and glands of digestive, respiratory, and portions of urinary systems.

Epithelial Tissue

Structure and Characteristics

Epithelial tissue consists of layers of cells covering surfaces or lining internal passages. It includes both epithelia and glands.

• Cellularity: Cells are tightly joined.

• Polarity: Distinct apical (top) and basal (bottom) surfaces.

• Attachment: Anchored to a basement membrane (basal lamina and reticular lamina).

• Avascularity: Lacks blood supply; nutrients diffuse from underlying tissues.

• Regeneration: Damaged cells are rapidly replaced.

Functions of Epithelial Tissue

• Protection

• Lubrication

• Secretion

• Absorption

• Sensory reception

• Reproduction

Classification of Epithelial Tissue

Epithelial tissues are classified by layer arrangement and cell shape:

• Layer Arrangement: Simple (one layer), Stratified (multiple layers), Pseudo-stratified (appears layered, but is not).

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

Examples of Epithelial Types

• Simple Squamous: Lines heart, blood vessels, alveoli; reduces friction, controls permeability.

• Stratified Squamous: Skin, mouth, anus, vagina; protects against abrasion and pathogens.

• Simple Cuboidal: Kidney tubules; involved in secretion and absorption.

• Transitional: Bladder lining; stretches as bladder fills.

• Simple Columnar: Stomach, gall bladder; absorption and secretion.

• Pseudo-stratified (ciliated): Nasal cavity, bronchi; protection and secretion.

Glands

• Exocrine: Secrete via ducts (e.g., sweat, mammary, goblet cells).

• Endocrine: Ductless; secrete hormones directly into blood (e.g., pituitary, ovary).

Cell suffixes: -blast (immature, dividing), -cyte (mature, non-dividing).

Connective Tissue

Basic Components and Functions

Connective tissue is characterized by specialized cells, extracellular protein fibers, and ground substance. It supports, connects, protects, insulates, separates, and transports substances in the body.

• Specialized Cells: Fixed (maintenance, repair, storage) and wandering (defense, repair).

• Extracellular Protein Fibers: Collagen (strength), Reticular (network), Elastic (flexibility).

• Ground Substance: Amorphous, can be fluid, gel, or solid.

Classification of Connective Tissue

• Connective Tissue Proper: Many cell types, syrupy ground substance (e.g., adipose, tendons).

• Fluid Connective Tissue: Distinct cell populations in watery matrix (e.g., blood, lymph).

• Supporting Connective Tissue: Less diverse cells, matrix with closely packed fibers (e.g., bone, cartilage).

Connective Tissue Proper: Loose and Dense Types

Loose connective tissue has loosely arranged fibers and cells, while dense connective tissue has tightly packed fibers.

• Loose: Areolar (airy, all cell types), Adipose (fat storage), Reticular (network, support).

• Dense: Regular (parallel collagen, tendons/ligaments), Irregular (meshwork, dermis), Elastic (elastic fibers).

Supporting Connective Tissue: Cartilage and Bone

Supporting connective tissues provide structural strength and framework for the body. Cartilage is made of chondrocytes in lacunae, is avascular, and has a fibrous perichondrium. Bone is composed of osteocytes in lacunae, surrounded by a mineralized matrix.

• Cartilage: Matrix of chondroitin sulfate, avascular, growth via appositional (cellular dimension) and interstitial (matrix production).

• Bone: Collagen fibers surrounded by calcium; osteocytes in lacunae connected by canaliculi.

Comparison of Supporting Connective Tissue Types

Different types of cartilage and bone are distinguished by their cells, fibers, and matrix characteristics.

Supporting CT	Cells	Fibers	Matrix
Hyaline Cartilage	Chondrocytes	Not visible	Smooth, glassy appearance
Elastic Cartilage	Chondrocytes	Elastic	Very dark with fibers
Fibrous Cartilage	Chondrocytes	Collagen	Lots of fibers, no visible matrix
Bone	Osteocytes	Collagen	Hard, mineralized

Muscular Tissue

Types and Functions

Muscular tissue is specialized for contraction and movement.

• Skeletal Muscle: Striated, voluntary, multinucleate cells.

• Smooth Muscle: Non-striated, involuntary, found in organs and blood vessels.

• Cardiac Muscle: Striated, involuntary, found only in the heart.

Nervous Tissue

Structure and Function

Nervous tissue conducts electrical impulses and coordinates body functions. It consists of nerves and neurons, which transmit signals along their plasma membranes.

• Neurons: Specialized for impulse transmission.

• Functions: Sensory input, motor output, integration, and regulation.

Key Terms and Concepts

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

• Perichondrium: Fibrous layer surrounding cartilage.

• Appositional Growth: Increase in cellular dimension.

• Interstitial Growth: Production of additional matrix material.

Summary Table: Connective Tissue Proper

Connective Tissue	Cells	Visible Fibers	Matrix
Areolar	All cell types	All	Very airy
Adipose	Adipose	Not visible	Not visible
Reticular	Reticulocytes	Reticular	Loose
Dense Regular	Fibrocytes	Collagen packed tightly	Not visible
Elastic	Fibrocytes	Elastic	Some visible
Dense Irregular	Fibrocytes	Collagen in all directions	Some visible

Summary Table: Supporting Connective Tissue

Supporting CT	Cells	Fibers	Matrix
Hyaline Cartilage	Chondrocytes	Not visible	Smooth, glassy appearance
Elastic Cartilage	Chondrocytes	Elastic	Very dark with fibers
Fibrous Cartilage	Chondrocytes	Collagen	Lots of fibers, no visible matrix
Bone	Osteocytes	Collagen	Hard, mineralized

Additional info:

• Fat cells (adipocytes) are metabolically active and responsible for energy storage; they can increase in number but are not lost.

• Connective tissue cells include fibroblasts (fiber production), macrophages (immune defense), adipocytes (fat storage), mesenchymal cells (stem cells), melanocytes (pigment production), mast cells (histamine production), lymphocytes (antibody production), and microphages (phagocytosis).

• Blood is a fluid connective tissue with red blood cells (no nucleus, hemoglobin) and white blood cells (granulocytes and agranulocytes).