Epithelial Tissue Overview

Epithelial Tissue

• Avascular tissue that covers external body surfaces and lines internal closed cavities.
• Forms the secretory portion of glands and their ducts, as well as receptors in sensory organs.

Epithelial Cell Characteristics

• Arranged in sheets.
• Possess intercellular junctions (junctional complexes).
• Display distinct surface domains (apical, lateral, basal).
• Properties determined by specific membrane proteins.
• Rest on a basal lamina (non-cellular, protein-polysaccharide-rich layer).

Epithelial Tissue Functions

• Transport: Moves particles and mucus (e.g., in trachea and bronchi) via motile cilia.
• Sensory Reception: Receives stimuli (e.g., taste buds, retina, smell, hearing) via neuroepithelia.
• Lubrication: Secretes mucous and serous fluids.
• Excretion: Filters blood, produces urine and sweat.
• Reproductive: Participates in reproductive functions through epithelial cells in ovaries and testes.

Epithelial Tissue Classification

• Classified by cell arrangement and cell shape, not function.
• Simple: One cell layer thick.
• Stratified: Two or more cell layers thick.

Simple Epithelia Cell Types

• Squamous: Width greater than height.
  • Simple Squamous: Single layer. Found lining blood vessels, Bowman's capsule, and respiratory spaces in lungs. Function includes exchange, barrier in CNS, and lubrication/barrier between compartments.
• Cuboidal: Width, depth, and height are approximately the same.
  • Simple Cuboidal: Single layer. Found in thyroid follicle walls, kidney tubules (especially collecting ducts), ovary surface, and small ducts of exocrine glands.
• Columnar: Height greatly exceeds width.
  • Low Columnar: Height only slightly exceeds width.
  • Simple Columnar: Single layer. Found in the intestinal tract (stomach to rectum), uterus, cervix, and gallbladder. Functions include absorption and secretion.

Stratified Epithelia

• Pseudostratified: Appears stratified but is actually simple; all cells rest on the basal lamina. Found in respiratory tract (trachea, bronchi - ciliated), epididymis (stereocilia), and ductus deferens.
• Transitional: Stratified epithelium that functionally accommodates distension (e.g., urinary bladder, parts of urethra and ureter, renal calyces). Serves as a barrier.
• Stratified Squamous: Multiple layers; superficial layer is squamous. Functions as a protective barrier (keratinized or non-keratinized).
  • Keratinized: Found in the epidermis.
  • Non-keratinized: Found in the lining of oral cavity, vagina, esophagus, and tongue.

This quiz covers the characteristics, functions, and types of epithelial tissue. Understand its role in the body, including transport, sensory reception, and secretion. Test your knowledge of how epithelial tissue is structured and its various physiological functions.