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Tissue: group of cells that are similar in structure and function
Histology: study of tissues
Types of Tissues:1. Epithelium (covering)2. Connective (support)3. Muscle (movement)4. Nervous (control)
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Preparing tissues for microscopy
• Specimen is fixed (preserved)• Cut into thin sections (slices)• Stained with colored dyes
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Epithelial Tissue• “epithe” = laid on, covering• Structure:
1. Covering and lining epithelium2. Glandular epithelium
• Function:– Protection– Absorption– Filtration– Secretion
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Special Properties1. Polarity
– Apical surface = exposed free surface or edge (some with microvilli, cilia)
– Basal surface = lower, attached surface2. Specialized contacts
– Fits close together to form continuous sheets
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Special Properties
3. Supported by connective tissue– Rests on basement membrane
4. No blood supply (avascular)– Rely on diffusion and underlying connective
tissue for food/O2
5. Regeneration – Replace lost cells
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Classification• Two names = (# cell layers) + (shape of cells)• Cell Layers: simple or stratified• Shapes: squamous, cuboidal, or columnar
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Simple Epithelium
Absorption, secretion, filtration Very thin
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Simple Epithelium Simple squamous
Filtration, rapid diffusion Capillary walls, air sacs in lungs, kidney
filtration Serous membranes: slick layer lining ventral
body cavity and its organs
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Simple Epithelium Simple cuboidal
Secretion & absorption Lines ducts of glands (salivary), kidney
tubules, ovary surface
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Simple Epithelium• Simple columnar
– Absorption and secretion– Lines digestive tract– Microvilli, cilia– Mucous membranes:
lubricating mucus
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Simple Epithelium• Pseudostratified columnar
– Rests on basement membrane – false impression (pseudo) of being multi-layered
– Secretes or absorbs– Respiratory tract – cilia propels mucus from
lungs
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Stratified Epithelium
• 2+ layers, more durable• Main function = protect
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Stratified Epithelium• Stratified squamous
– Withstand abuse, friction– Esophagus, mouth, outer portion of skin
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Stratified Epithelium• Stratified cuboidal
– Usually 2 layers– Mainly in ducts of large glands (sweat,
mammary, salivary)
Sweat Gland Esophageal Gland
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Stratified Epithelium• Stratified columnar
– Thick, waterproof layer– Pharynx, male urethra, lining ducts
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Transitional Epithelium• Able to change shape (cuboidal
squamous)• Lining of hollow urinary organs (bladder,
ureter, urethra)• Stretches when filled with urine
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Glandular Epithelium• Gland: make and secrete a particular product• 2 Types:
– Endocrine gland: produce hormones secreted into tissue fluid or bloodstream
– Exocrine gland: secrete products into ducts onto body surfaces or body cavities• Eg. mucous, sweat, oil, saliva, bile
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Exocrine Glands
Unicellular• Mucus cells or goblet
cells
Multicellular• Duct structure
