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What is one principal function of epithelial tissue?
Which cell shapes are characteristic of epithelial cells?
What is a function of the basement membrane?
What type of junction forms a seal between adjacent epithelial cells?
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Which feature is associated with the apical cell surface in epithelial tissue?
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What does the basal lamina help to maintain in epithelial cells?
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How do adherent junctions function in epithelial tissue?
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Which of the following features does not describe the basement membrane?
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What is the primary structural component of cilia?
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Which type of epithelium is characterized by layers of cells that can change shape?
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What is the length and diameter of cilia on average?
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Which type of epithelial cell is specialized for secretion and production of macromolecules?
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What structural feature distinguishes stereocilia from microvilli?
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What is the main function of the primary cilium found in epithelial cells?
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Which type of glandular epithelium produces lipids?
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What is the composition of the axoneme structure in cilia?
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Study Notes
Principal Functions of Epithelial Tissue
- Covers, lines, and protects surfaces (e.g., epidermis)
- Absorbs substances (e.g., intestinal lining)
- Secretes substances (e.g., parenchymal cells of glands)
Characteristic Features of Epithelial Cells
- Cells range in shape from columnar, cuboidal, to squamous
- Cell nuclei vary in shape: elliptic (oval), spherical, or flattened
- Epithelial cells are typically adjacent to connective tissue containing blood vessels
- Epithelial cells exhibit polarity: organelles and membrane proteins are unevenly distributed within the cell
Basement Membranes
- Thin, extracellular, felt-like sheet of macromolecules
- Acts as a semipermeable filter for substances reaching epithelial cells from below
- Composed of two layers:
- Basal lamina: thin, electron-dense, sheet-like layer of fine fibrils
- Reticular lamina: more diffuse and fibrous layer beneath the basal lamina
Functions of Basement Membranes
- Filters substances reaching epithelial cells from below
- Provides structural support for epithelial cells
- Attaches epithelia to underlying connective tissue
- Mediates cell-to-cell interactions involving epithelia
- Marks routes for cell migration along epithelia
- Serves as a scaffold for epithelial repair and regeneration
- Helps organize integrins and other proteins in the plasma membrane of epithelial cells
- Maintains cell polarity
- Localizes endocytosis, signal transduction, and other activities
Intercellular Adhesion & Other Junctions
- Tight/Occluding junctions: seal between adjacent cells
- Adherent/Anchoring junctions: sites of strong cell adhesion
- Gap junctions: channels for communication between adjacent cells
Specializations of the Apical Cell Surface
- Microvilli:
- Uniform length, densely packed
- Visible as a brush or striated border projecting into the lumen (e.g., small intestine)
- Approximately 1 µm long and 0.1 µm wide
- Increase surface area by 20-30 fold
- Contain bundled actin filaments capped and bound to the plasma membrane by actin-binding proteins
- Stereocilia:
- Longer and less motile than microvilli
- Specialized mechanosensory function in cells (e.g., inner ear)
- Involved in absorption (e.g., male reproductive tract - epididymis)
- Cilia:
- Long, highly motile, larger than microvilli
- Contain internal arrays of microtubules
- Most epithelial cells have at least one primary cilium (non-motile, enriched with receptors and signal transduction complexes)
- Abundant on cuboidal or columnar cells
- 5-10 µm long and 0.2 µm in diameter
Cilia Structure
- Axoneme: consists of 9 peripheral microtubule doublets arrayed around 2 central microtubules (9+2 assembly of microtubules)
- Basal Bodies: apical cytoplasmic structures below the cell membrane, similar to centrioles, consisting of 9 microtubular triplets
Types of Epithelia
- Covering or lining epithelia
- Secretory (glandular) epithelia
Covering (Lining) Epithelia
- Simple squamous epithelium
- Simple cuboidal epithelium
- Simple columnar epithelium
- Stratified epithelium
- Transitional epithelium (Urothelium)
- Pseudostratified epithelium
Secretory (Glandular) Epithelia
- Epithelial cells that produce and secrete macromolecules through glands
- Secreted macromolecules include:
- Proteins (e.g., pancreas)
- Lipids (e.g., adrenal, sebaceous glands)
- Carbohydrate and protein complexes (e.g., salivary glands)
- Proteins, lipids, and carbohydrates (e.g., mammary glands)
- Water and electrolytes (e.g., sweat glands)
- Scattered secretory cells (unicellular glands) are common in simple cuboidal, simple columnar, and pseudostratified epithelia.
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Description
This quiz explores the principal functions and distinctive characteristics of epithelial tissue, including its types of cells and the role of basement membranes. Learn how epithelial tissue covers, lines, and protects surfaces while also engaging in absorption and secretion. Test your knowledge of these essential biological components.
