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Understanding Epithelial Tissue: Structure, Types, and Functions

Epithelial tissue, or epithelium, consists of closely packed cells arranged in single or multiple layers. These cells have distinct surfaces: apical (free), lateral, and basal, with the basal layer adhering to the basement membrane. The basement membrane, composed of basal and reticular lamina, provides support. Epithelial tissue is categorized by layers—simple or stratified—and shape—squamous, cuboidal, or columnar. Each type plays a crucial role in functions such as absorption, secretion, and protection. Understanding these variations helps in recognizing their significance in the human body.

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Understanding Epithelial Tissue: Structure, Types, and Functions

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  1. Ch. 4 Part 2 Epithelial tissues

  2. Epithelial Tissue • Epithelial tissue or epithelium • Consists of cells arranged in continuous sheets in either single or multiple layers • Cells are closely packed and held tightly together by cell junctions • Have various surfaces • Apical (free) • Lateral • Basal

  3. Epithelial Tissue • Surfaces • Apical – faces body surface, body cavity, lumen (interior space), or tubular duct • Lateral – face adjacent cells on all sides; lateral surfaces contain junctions • Basal – opposite of apical; deepest layer of cells; adhere to basement membrane; have hemidesmosomes • Note: apical layer refers to most superficial basal layer refers to deepest layer

  4. Basement Membrane • Thin extracellular layer that consists of two layers: basal lamina and reticular lamina • Basal lamina (lamina = thin) – closer to epithelial cells • Contains proteins: collagen, laminin, glycoproteins, proteoglycans • Reticular lamina – closer to underlying connective tissue • Contains fibrous proteins (fibroblasts) • Function: point of attachment and support for overlying epithelial tissue

  5. Basement Membrane

  6. Epithelial Tissue Types • Based on 2 factors: layers and shape • Layers • Simple = single • Function: diffusion, osmosis, filtration, secretion, absorption • Stratified = layer • Function: protection from wear and tear • Pseudostratified (pseudo = false) • Actually simple, but appear stratified because of nuclei arrangement • Function: ciliated, secrete mucus

  7. Epithelial Tissue Types • Shape • Squamous • Arranged like floor tiles, thin • Function: rapid passage of substances • Cuboidal • Shaped like cubes or hexagons • Function: secretion or absorption • Columnar • Taller than wide, like columns • Function: protection, secretion or absorption • Transitional • Change shape from flat to cuboidal • Function: stretch (urinary bladder)

  8. Epithelial Tissue Types • Combine layers with shape to get all epithelial tissue types (plus some extra) • Ciliated – have cilia • Simple squamous, simple cuboidal, simple columnar, pseudostratified columnar • Stratified squamous, stratified cuboidal, stratified columnar, transitional • Keratinized – contains keratin (protein)

  9. Epithelial Tissue Types • Red book p. 113 – 117 • Blue book p. 100-105

  10. Simple Squamous

  11. Simple Cuboidal

  12. Nonciliated Simple Columnar

  13. Ciliated Simple Columnar

  14. Pseudostratified Columnar

  15. Stratified Squamous

  16. Stratified Cuboidal

  17. Stratified Columnar

  18. Transitional

  19. Checkpoint • Describe the various layering arrangements and cell shapes of epithelium. • What characteristics are common to all epithelial tissues?

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