Types of Epithelium Quiz

Simple Epithelium

• Thin, scale-like cells
• Found in alveoli, endothelium of the heart and blood vessels, lymphatic and thyroid tissues
• Functions include diffusion, secretion, lubrication, and filtration

Stratified Squamous Epithelium

• Multiple layers of scale-like cells
• Found in skin, oral cavity, esophagus, vagina
• Protects against abrasion

Simple Cuboidal Epithelium

• Cube-shaped cells with equal height and width, nucleus in the center
• Found in kidney tubules and glands
• Functions include absorption and secretion of substances
• Facilitates transport without leakage

Stratified Cuboidal Epithelium

• Found in salivary glands, sweat gland ducts, mammary gland, and prostate gland
• Functions include transport and protection

Simple Columnar Epithelium

• Rectangular cells with height greater than width, may or may not have cilia
• Ciliated cells are found in the uterine tube, bronchi, and uterus
• Non-ciliated cells are found in the digestive tract
• Functions include absorption, secretion of mucus and enzymes, and protection

Stratified Columnar Epithelium

• Found in the conjunctiva of the eye, uterus, and pharynx
• Secretes chemicals for protection
• Functions include protection and transport

Pseudostratified Columnar Epithelium

• Appears stratified but all cells contact the basement membrane
• Found in the trachea and upper respiratory tracts
• Secretes and moves mucus

Stratified Squamous Epithelium

• Two sub-types: keratinized and non-keratinized
• Found in areas with high abrasion, such as skin and gums
• Keratinized stratified squamous epithelium provides an additional layer of protection

Transitional Epithelium (Urothelium)

• Dome-shaped cells
• Found in the urethra and ureter
• Specialized for stretching and expansion, allowing for changes in organ size
• Appears stratified

Epithelium Specialization

• Epithelial cells must adhere and communicate
• Tight junctions, adherens junctions, desmosomes, hemidesmosomes, and gap junctions facilitate these functions

Tight Junction (Zonula Occludens)

• Completely encircles the cell
• Seals between cells, preventing paracellular movement
• Allows transcellular movement
• Higher density in the bladder, lower density in the kidney
• Establishes apical and basal layers
• Proteins involved include ZO proteins
• Associated with Sjögren's syndrome and Clostridium perfringens infection

Adherens Junction (Zonula Adherens)

• Anchors cells to neighboring cells
• Similar to tight junctions but forms a "belt"
• Stabilizes and strengthens the bond between cells
• Cadherens bind to catenin, linking to actin filaments

Desmosomes (Macula Adherens)

• Identical structure in adjacent cells
• Extend filaments between cells
• Large cadherens (desmogleins, desmoplakin) bind to keratin intermediate filaments
• Provides mechanical stress resistance, especially in the heart

Hemidesmosomes

• Half of a desmosome, containing integrins
• Link keratin intermediate filaments to the basement membrane
• Focal adhesion junctions provide direct links to actin filaments

Gap Junction

• Facilitates cell-to-cell communication
• Allows exchange of nutrients and signaling molecules
• Connexons (composed of connexin proteins) form channels
• Enables highly coordinated functions, such as heart contraction
• Associated with heartache, calloused skin, and tooth abnormalities

Transcellular vs. Paracellular Transport

• Transcellular transport: movement through the cell
• Paracellular transport: movement between cells
• Types of transcellular transport: simple diffusion, aquaporin-mediated transport, gated ion channel transport, antiporter, symporter
• Examples of transcellular transport include oxygen and carbon dioxide diffusion, and the sodium-potassium pump

Aquaporins

• Allow water to pass through cells
• Amount of aquaporins determines water permeability
• Both transcellular (passive) and paracellular (ion channel) transport of water occur

Absorption (Sodium Absorption)

• Apical membrane: ENaC sodium channel
• Basal membrane: Na+/K+ ATPase, K+ channel
• Chloride and water transport are influenced by sodium transport
• Low sodium concentration inside the cell, high sodium concentration outside
• High potassium concentration inside the cell

Secretion

• Movement from blood or basal layer to the lumen
• Chloride secretion involves CFTR channels and other chloride channels in the apical membrane, and NKCC, ion exchangers, and sodium/bicarbonate exchangers in the basal membrane.
• Sodium moves paracellularly during chloride secretion
• CFTR plays a key role in fluid export