Epithelium Tissue

Overview and Functions

Epithelium tissue is a fundamental tissue type that covers exposed surfaces, lines internal passageways and chambers, and produces glandular secretions. It plays a critical role in controlling permeability, providing physical protection, absorption, filtration, lubrication, digestion, and reproduction.

• Definition: Epithelium is a layer of cells covering body surfaces and lining cavities.

• Key Functions: Protection, secretion, absorption, filtration, and sensation.

• Example: Simple squamous epithelium in blood vessels.

Types of Tissue

• Epithelium tissue: Covers exposed surfaces, lines passageways and chambers, produces glandular secretions. Avascular (no blood vessels).

• Connective tissue: Fills internal spaces, provides structural support, stores energy. Examples: fat, bone, blood, cartilage.

Diffusion

Diffusion is the process by which particles move from an area of high concentration to an area of low concentration, leading to equal distribution throughout a system.

• Application: Movement of oxygen and nutrients across epithelial surfaces.

Free Surface of Epithelium

• Definition: The surface of the epithelium exposed to the external environment or internal passageways/cavities.

Basement Membrane (Basal Lamina)

• Location: Between the epithelium and its connective tissue layer.

• Function: Provides attachment and support for epithelial cells.

Stratified Epithelium

• Function: Protection against friction, dehydration, and invasion by microbes and chemicals.

• Structure: Multiple layers; bottom layer at basement membrane, upper layers exposed to free surface.

• Location: Areas exposed to abrasion and friction, body surface, and digestive tract.

Simple Epithelium

• Structure: Single layer of cells touching the basement membrane and exposed to the free surface.

• Main Functions: Diffusion, absorption, secretion.

Stem Cells

• Function: Constantly produce new cells to replenish the tissue.

Transitional Epithelium

• Structure: Special stratified epithelium with cells of many shapes.

• Function: Permits tissue to stretch and recoil.

• Location: Urinary bladder.

Pseudostratified Ciliated Columnar Epithelium

• Structure: All cells touch the basement membrane but grow to different heights.

• Function: Protection, secretion, movement of mucus.

• Location: Nasal cavities, trachea, reproductive tract.

Simple Squamous Epithelium

• Structure: Irregularly shaped, flat, and scalelike cells.

• Function: Protection, secretion, diffusion, controls vessel permeability.

• Location: Lining of blood vessels, kidney tubules, air sacs of lungs.

Simple Cuboidal Epithelium

• Structure: Cube-shaped cells with large nuclei.

• Function: Secretion and absorption.

• Location: Glands, ducts, kidney tubules, thyroid glands.

Simple Columnar Epithelium

• Structure: Taller than wide cells.

• Function: Protection, secretion, absorption.

• Location: Lining of stomach, intestines, gallbladder, uterine tubes, collecting ducts of kidneys.

Stratified Squamous Epithelium

• Function: Physical protection against abrasion, friction, pathogens, chemicals.

• Location: Skin surface, lining of mouth, throat, esophagus, rectum, anus, vagina.

• Keratinized: Cells dehydrate and interlock to form a tough, protective barrier.

• Nonkeratinized: Moist lining cells on tissue surface.

Stratified Cuboidal and Columnar Epithelium

• Stratified cuboidal: Protection, secretion, absorption; rare, found in lining of ducts.

• Stratified columnar: Protection; found in areas such as pharynx, epiglottis, anus, mammary glands, salivary glands, urethra.

Connective Tissue

Overview and Functions

Connective tissue provides body support, structural framework, and joins various structures. It is the most abundant tissue type and is typically vascularized.

• Protein fibers + ground substance = extracellular matrix

• Ground substance: Composed of glycoprotein and polysaccharide molecules that surround cells and fibers.

Types of Connective Tissue Fibers

• Collagen fibers: Provide strength and support.

• Elastic fibers: Provide flexibility.

• Reticular fibers: Provide framework for soft organs (e.g., liver, spleen).

Adipose Tissue

• Definition: Connective tissue with thick liquid matrix; stores fat.

• Function: Energy storage, insulation, protection.

• Location: Under skin, around organs.

Connective Tissue Proper

• Loose connective tissue: Protein fibers in thick ground substance; fills space between structures for support and protection.

• Dense connective tissue: Little space between cells and fibers; provides strong support and resistance to stretching.

Loose Connective Tissue Types

• Areolar: Fills space between structures.

• Adipose: Fat storage; highly vascularized.

• Reticular: Internal supporting framework for soft tissues.

Dense Connective Tissue Types

• Dense regular: Parallel bundles of collagen; found in tendons and ligaments.

• Dense irregular: Collagen fibers in all directions; found in dermis, liver, spleen.

Fluid Connective Tissue

• Blood: Liquid matrix (plasma); transports cells and nutrients.

• Coagulation: Fibrin traps cells to stop bleeding.

• Red blood cells: Transport oxygen.

• White blood cells: Immune defense; includes phagocytes, eosinophils, neutrophils.

Supporting Connective Tissue

• Cartilage: Rubbery avascular tissue with gelatinous matrix; provides structural support and flexibility.

• Bone: Solid matrix of calcium phosphate and carbonate; provides rigid support and protection.

Cartilage Types

• Hyaline cartilage: Most common; lacks visible fibers; found in ribs, sternum, nose, and ends of long bones.

• Elastic cartilage: Many elastic fibers; found in external ear, larynx.

• Fibrocartilage: Irregular collagen fibers; toughest type; found in knee joints, vertebral discs, pubic symphysis.

Bone Structure

• Matrix: Calcium phosphate and carbonate crystallized on collagen fibers.

• Periosteum: Membrane covering bone surface; contains osteoblasts.

• Canaliculi: Small channels for nutrient diffusion.

• Concentric lamellae: Surround central canal with blood vessels.

• Osteoclasts: Dissolve bone matrix to release calcium.

Comparison of Cartilage and Bone

Structural and Functional Differences

The following table summarizes the main differences between cartilage and bone in terms of structure, function, and repair capabilities.

Additional info: Cartilage is essential for cushioning joints and providing flexible support, while bone forms the rigid framework of the body and serves as a reservoir for minerals.