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

Test your knowledge on the various types of epithelial tissues, including simple and stratified epithelium. This quiz covers characteristics, locations, and functions of different epithelial cells like squamous, cuboidal, and columnar. Perfect for students studying biology or anatomy!