Epithelial Tissue Quiz

Epithelial Tissue Part 1

• Epithelial tissue is one of four basic tissues, covering external body surfaces and lining internal body cavities and tubes.
• Other types of basic tissues include connective, nerve, and muscle tissue.
• Epithelial tissue is avascular, obtaining nutrition from blood vessels in the underlying tissue.
• It's composed of cells closely attached by cell-to-cell junctions.

Learning Objectives

• Differentiate and compare functions of 8 morphologically different types of epithelium.
• Determine and detail the characteristics of various body epithelia.
• Differentiate between endothelium and mesothelium.
• Understand exceptions to simple squamous designation in lymph nodes and spleen.
• Provide examples of how epithelium functions (protective, secretory, excretory, absorptive, reproductive) to maintain health.
• Match locations of epithelia with their specific functions.
• Explain apical, basal, and lateral surface modifications of epithelial cells.
• Define microvilli, stereocilia, and cilia correlating structure to function.
• Name and detail the functions of cell-to-cell and cell-to-matrix junctions.
• Identify structural elements contributing to these junctions.
• Define cytoskeleton elements and correlate distribution to function.
• Define glands, describe morphological patterns, and state general functions.
• Match and classify glands based on morphological features.
• Outline functional and morphological features of exocrine and endocrine glands, including examples.
• Compare and contrast mucous and serous glands.
• Identify microscopic characters of mucous and serous glands.
• Describe ultrastructural features of exocrine glands.
• Differentiate between various modes of exocrine gland secretion (merocrine, apocrine, holocrine).
• Identify histologically specific glands matching them to the different classifications (merocrine, apocrine, holocrine, endocrine, exocrine).
• Relate ultrastructural appearance of glands to their function.
• Identify serous and mucous membranes.

Epithelium

• Epithelial cells are arranged as sheets in single or multiple layers.
• They can be organized as glands.
• They're attached by cell-to-cell junctions, and display three distinct surface domains (apical, lateral, basal).
• These domains have specific properties due to lipids and membrane proteins.

Characteristics of Epithelial Cells

• Basal surface attached to underlying basement membrane.
• Basement membrane is noncellular and rich in proteins and polysaccharides.
• Best seen in LM when stained with PAS stain.

Epithelioids

• Aggregates of epithelial cells, often found in endocrine glands (e.g., islets of Langerhans, interstitial cells of Leydig, luteal cells, adrenal glands).
• Also found in many epithelium-derived tumors.

Functions of Epithelium

• Epithelial functions are diverse, including secretion (e.g., secretory columnar epithelium of the stomach), absorption (e.g., absorptive columnar epithelium of the intestines), transportation (e.g., fallopian tube epithelium), mechanical protection (e.g., stratified squamous, keratinized epithelium of the skin), and reception (e.g., taste buds, olfactory epithelium) .

Classification of Epithelium

• Classified by cell shape (squamous, cuboidal, columnar) and number of cell layers (simple, stratified).
• May also be specialized by presence of cilia, keratin, or goblet cells.
• Note: Classification is typically based on cell layers and shape, not function.

Simple Squamous Epithelium

• Epithelial cells are flattened with width greater than height, occurring in one layer.
• Function: Diffusion, filtration (e.g., kidney Bowman's capsule, respiratory spaces, blood/lymphatic vessels).
• Called endothelium when lining blood vessels or lymphatics and mesothelium when lining body cavities.

Simple Cuboidal Epithelium

• Cells are cube-shaped with roughly equal width and height, occurring in one layer.
• Locations include glands, kidney tubules, ducts of exocrine glands, and thyroid follicles.
• Function: Secretion, absorption (if the function is tied to absorption, the cells likely have mitochondria).

Simple Columnar Epithelium

• Tall cells, with heights exceeding their widths, occurring in one layer.
• Classified into ciliated or non-ciliated based on surface characteristics.
• Non-ciliated: absorption and secretion (e.g., small intestine).
• Ciliated: transport by ciliary action (e.g., fallopian tubes).

Stratified Squamous Epithelium

• Multiple layers of cells, with superficial cells being squamous.
• Classified as keratinized or non-keratinized based on the presence of keratin.
• Keratinized: protection from abrasion (e.g., epidermis).
• Non-keratinized: lining of oral cavity, pharynx, esophagus, and vagina.

Stratified Cuboidal Epithelium

• Multiple layers of cube-shaped cells.
• Located in larger ducts of exocrine glands (e.g., sweat glands).
• Function: Barrier, protection.

Stratified Columnar Epithelium

• Multiple cell layers; superficial cells are columnar.
• Located in the large excretory ducts of glands (e.g., salivary glands)
• Function: Barrier and transport.
• May be columnar in the superficial layer and have different other cell types beneath it.

Pseudostratified Columnar Epithelium

• Appears multilayered due to varying cell heights, but all cells are in contact with the basement membrane (simple arrangement).
• May be specialized for secretion or movement (e.g., respiratory system).
• Can be ciliated (e.g., upper respiratory tract), non-ciliated (e.g., large ducts), or contain stereocilia (e.g., epididymis).

Transitional Epithelium

• Cells vary in shape depending upon the functional state of the organ.
• Found in the urinary system to allow distension and relaxation (e.g., renal calyces, ureters).
• Called urothelium.

Mucous Membranes

• Line body cavities that connect to the external environment (e.g., digestive, respiratory, and urogenital tracts).
• Consist of an epithelial layer, basal lamina, and lamina propria (underlying connective tissue).
• May contain glands that produce mucus.

Serous Membranes

• Line closed cavities (e.g., peritoneal, pleural).
• Consists of simple squamous epithelium (mesothelium), basal lamina, and underlying connective tissue.
• Do not contain glands.

Basement Membrane

• The basal lamina (basement membrane) is an underlying layer supporting epithelial cells.
• It’s synthesized by the epithelium (secreted extracellularly), and it’s composed of collagen, laminin, and proteoglycans.
• It provides structural and metabolic support, and plays critical roles in compartmentalization, filtration, and tissue scaffolding/regeneration.
• Anchoring fibrils attach the basal lamina to the underlying reticular fibers or reticular lamina, critical for epithelial integrity and functions.
• LM methods such as PAS (periodic acid-Schiff) allow for visualization of the basement membrane for pathological analysis or research.

Clinical Scenario: Squamous Cell Carcinoma

• Abnormal squamous epithelium and excessive keratin production are clinical hallmarks.
• Keratin "nests of swirls" can aid in diagnosis.

Office Hours and Contact Information (provided in the original image)

• Dr. Mallika Indran, BDS, PhD, FICCDE
• Saba University School of Medicine
• Office Hours: 12:00 PM - 2:00 PM, Monday - Friday
• Email: [email protected]

Test your knowledge on the functions and characteristics of epithelial tissue with this comprehensive quiz. Explore various types, distinctions, and modifications of epithelial cells through a series of questions. Perfect for students studying anatomy and physiology.