ANP 1105 Lecture Notes - Lecture 4: Apocrine, Keratin, Bronchus

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ANP1105 – Lecture 4
7 Special Characteristics of Epithelial Tissue
1. Cellularity:
2. Specialized Contacts: epithelial cells fit closely together to form continuous sheets.
Tight junctions & desmosomes bind adjacent cells together. Tight junctions help keep
proteins in apical region of the plasma membrane from diffusing into basal region which
helps maintain epithelial polarity.
3. Polarity: apical and basal surfaces; differ in structure and function thus exhibit apical-
basal polarity.
Apical: smooth/slick surfaces with microvilli.
Basal: adjacent to its thin supporting sheet called basal lamina.
4. Basal Lamina: non-cellular, underlying supportive sheet of primarily glycoproteins.
Functions are, acting as a selective filter that determines which molecules diffusing from
underlying connective tissue can enter the epithelium. Also acts as scaffolding which
epithelial cells can migrate from to repair wounds.
5. Supported by Connective Tissue: all epithelia are supported by connective tissue. For
instance, deep to the basal lamina is reticular lamina (extracellular material containing
collagen protein fiber) which forms the basement membrane. The basement membrane
reinforces the epithelium and helps it resist stretching and tearing.
• An important feature of cancerous epithelial cells is failure to respect the boundary
imposed by the basement membrane which they penetrate to invade the tissues beneath.
6. Avascular but Innervated: Contains no blood vessels but supplies by nerve fibers.
Nourished by substances diffusing from blood vessels in the underlying connective
tissue.
7. Regeneration: high regenerative capacity. Reproduce rapidly because they are easily
destroyed from bacteria, smoke, acids, frictions etc. So when cells are destroyed they
need to regenerate to take the place of the destroyed cells. Can regenerate as long as cells
receive nutrition.
2 Criteria Used to Classify Epithelial Cells
Cell Shape:
• Squamous (flattened and scale like; nucleus flattened)
• Cuboidal (cube shaped, as tall as they are wide)
• Columnar (tall and column shaped; nucleus closer to cell base)
Layers:
• Simple epithelia (one layer so very thin and not very good at protecting; found where
absorption, secretion, filtration take place)
• Stratified epithelia (multiple layers)
4 Types of Simple Epithelia
1. Simple Squamous Epithelium: thin and permeable. Flattened cells with disc-shaped
central nuclei and sparse cytoplasm; the simplest of epithelia
Function: Allows material to pass by diffusion and filtration where protection is not
important. Also secretes lubricating substances in serosae
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