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Four types of tissues
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1. Epithelial tissue - covers exposed surfaces, lines internal passageways and chambers and forms glands.
2. Connective tissue - fills internal spaces, provides srtuctural support for other tissues, transports materials and stores energy reserves.
3. Muscle tissue - spezialized for contraction
4. Neural tisse - carries information in terms of electrical impulses.
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Epithelial tissue
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Consists of
Epithelia - layers of cells that cover internal or external surfaces.
Glands - structures that produce fluid secretions; either attached to or derived from epithelia.
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Characteristics of epithelia
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*Cellularity - cells very closely together by cell junctions.
*Polarity -
*Attachment - epithelia is attached to basal lamina.
*Avascularity - lacks blood vessels.
*Regeneration -
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Functions of Epithelial Tissue
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1. Provide physical protection - .
2. Control permeability - .
3. Provide sensations - .
4. Produce specialzed secretions - .
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Microvilli
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Covers epithelial cells that line internal passageways on their exposed surfaces. Abundant where absorbtion and secretion takes place, digestive and urinary tract.
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Cilia
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Moves substances over epithelial surface by synchronized beating - respiratory tract.
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Factors that help maintain the physical integrity of an epithelium -3
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1) Intracellular connections
2) attachment to the basal lamina
3) epithelial maintenance and repair
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A basal lamina
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Attaches epithelia to underlying connective tissues.
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Three major types of cell junctions
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1) Occluding junctions (tight)
2) Gap junctions
3) Macula adhernes (desmosomes)
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Occluding junction (tight junction)
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Prevents the diffuesion of fluids and solutes between cells.
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Gap junction
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Permits the free diffusion of ions and small molecules between two cells.
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Macula adhernes (desmosomes)
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Provides durable interconnections. Very strong and can resist stretching and twisting. Formed by two cells. Within each cell is a complex dense area, which is connected to the cytoskeleton - gives epithelium its strenght. Abundant in superficial layers of the skin. As a result skin is lost in sheets rather than cells. Two types: Spot desmosome and Hemidesmosome.
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Spot desmosome
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Kj
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Hemidesmosomes
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Attaches a cell to extracellular filaments in the basal lamina. This helps stabilze the position of the epithelial cell and anchors it to underlying tissues.
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Epithelial maintenance and repair
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Continual division of stem cells, also called germinative cells. Located near the basal lamina.
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