Tissues: Structure, Function, and Classification in Anatomy & Physiology

Tissues in Anatomy & Physiology

Introduction to Histology

Histology is the study of tissues, which are groups of similar cells that perform specific functions in the body. Understanding tissue structure and function is fundamental to the study of anatomy and physiology.

• Histology: The microscopic study of tissue structure and organization.

• Tissue: A group of similar cells and their extracellular products that perform a common function.

Basic Tissue Types

Overview of the Four Basic Tissue Types

• Nervous Tissue: Specialized for internal communication. Found in the brain, spinal cord, and nerves.

• Muscle Tissue: Contracts to cause movement. Includes skeletal, cardiac, and smooth muscle.

• Epithelial Tissue: Forms boundaries between different environments, protects, secretes, absorbs, and filters.

• Connective Tissue: Supports, protects, and binds other tissues together.

Epithelial Tissue

Functions of Epithelial Tissue

• Protection: Shields underlying tissues from mechanical and chemical damage.

• Absorption: Uptake of substances such as nutrients.

• Permeability: Regulates the movement of materials across surfaces.

Types and Characteristics of Epithelial Tissue

• Main types: Covering and lining epithelia (external and internal surfaces), glandular epithelia (secretory tissues in glands).

• Key characteristics:

  • Tightly packed cells

  • Specialized contacts (tight junctions, desmosomes)

  • Polarity (apical and basal surfaces)

  • Supported by connective tissue

  • Avascular but innervated

  • High regenerative capacity

Cell Polarity and Specialization

• Polarity: Cells have an apical (top) surface and a basal (bottom) surface.

• Specialized structures:

  • Cilia: Move substances along the surface.

  • Microvilli: Increase surface area for absorption/secretion.

  • Keratinization: Provides strength and water resistance.

Classification of Epithelia

• Simple epithelium: Single cell layer (absorption, secretion, filtration).

• Stratified epithelium: Multiple layers (protection).

• Shapes: Squamous (flat), cuboidal (cube-shaped), columnar (tall).

Table: Types of Epithelial Tissue

Type	Structure	Location	Function
Simple Squamous	Single layer, flat cells	Kidney, air sacs, blood vessels	Diffusion, filtration
Simple Cuboidal	Single layer, cube-shaped	Kidney tubules, glands	Secretion, absorption
Simple Columnar	Single layer, tall cells	Digestive tract, gallbladder	Absorption, secretion
Stratified Squamous	Multiple layers, flat surface cells	Skin, mouth, esophagus	Protection
Transitional	Multiple layers, shape varies	Bladder, ureters	Stretching

Glands

• Gland: One or more cells that make and secrete an aqueous (water-based) fluid.

• Endocrine glands: Ductless, secrete hormones into interstitial fluid.

• Exocrine glands: Secrete products into ducts (e.g., sweat, saliva).

• Unicellular exocrine glands: Goblet cells (produce mucus).

• Multicellular exocrine glands: Composed of a duct and secretory unit.

Connective Tissue

Functions of Connective Tissue

• Binding and support

• Protection

• Insulation

• Storing reserve fuel

• Transporting substances (blood)

Characteristics of Connective Tissue

• Highly vascularized (except cartilage)

• Derived from mesenchyme (embryonic tissue)

• Cells separated by extracellular matrix (ECM)

Components of Connective Tissue

• Extracellular matrix (ECM): Non-living material that surrounds cells, composed of ground substance and fibers.

• Ground substance: Gel-like material that fills space between cells.

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

• Cells: Fibroblasts, chondroblasts, osteoblasts, adipocytes, white blood cells, mast cells, macrophages.

Table: Types of Connective Tissue

Type	Main Fibers	Location	Function
Areolar	Collagen, elastic, reticular	Under epithelia	Cushions organs
Adipose	Few fibers, fat cells	Under skin, around organs	Insulation, energy storage
Reticular	Reticular	Lymphoid organs	Support for cells
Dense Regular	Collagen (parallel)	Tendons, ligaments	Strength in one direction
Dense Irregular	Collagen (irregular)	Dermis, joint capsules	Strength in many directions
Elastic	Elastic	Walls of large arteries	Stretch and recoil
Cartilage	Collagen, elastic	Joints, ear, nose	Support, flexibility
Bone	Collagen, calcium salts	Skeleton	Support, protection
Blood	None (fluid matrix)	Blood vessels	Transport

Specialized Connective Tissues

• Cartilage: Avascular, supports and reinforces, resists compression.

• Bone: Hard, calcified matrix, supports and protects, stores calcium.

• Blood: Fluid matrix (plasma), transports nutrients, wastes, and gases.

• Lymph: Contains white blood cells, involved in immunity and fluid balance.

Muscle Tissue

Types of Muscle Tissue

• Skeletal Muscle: Voluntary, striated, attached to bones, responsible for movement.

• Cardiac Muscle: Involuntary, striated, found in heart, pumps blood, contains intercalated discs.

• Smooth Muscle: Involuntary, non-striated, found in walls of hollow organs, moves substances.

Nervous Tissue

Structure and Function

• Main function: Conducts electrical impulses for communication and control.

• Location: Brain, spinal cord, peripheral nerves.

• Cells: Neurons (transmit signals), neuroglia (support and protect neurons).

Membranes

Types and Functions

• Physical barriers: Composed of epithelial and connective tissues.

• Functions: Line and protect body cavities and surfaces.

• Examples: Mucous membranes (digestive, respiratory, urinary, reproductive tracts), serous membranes (ventral body cavities), cutaneous membrane (skin), synovial membranes (joints).