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Types of Tissues
- Epithelial
- Connective
- Muscle
- Neural
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Epithelial tissue functions
- Protection - lines body surfaces and cavities, and covers organs
- Absorption - special cells able to absorb nutrient molecules
- Secretion - cells in exocrine and endocrine glands able to produce and secrete materials
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Epithelial tissue characteristics
- One surface always exposed to fluid or air
- Totally cellular
- No blood vessels, this tissue is avascularCells rest on a basement membrane for attachment to underlying connective tissue
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Epithelial classification
- Number of layers of cells (simple, stratified, pseudostratified)
- Shape of cells (squamous, cuboidal, columnar)
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Simple (epithelial tissue)
Single layer of cells resting on a basement membrane
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Stratified
Two or more layers with deepest layer resting on a basement membrane
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Pseudostratified
Appears multiple but all cells rest on the basement membrane
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Squamous
Flattened cells (squishy footballs with squished nucleus)
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Cuboidal
As tall as they are wide (cubes, with circular nucleus)
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Columnar
Taller than they are wide (columns with taller nucleus)
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Simple squamous epithelium
- composed of one layer of flat cells
- needed in places we need thin walls
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Simple squamous epithelium locations
- Alveoli of lungs (helps for easy breathing)
- Endothelium (forms innermost lining of blood vessels and heart)
- Mesothelium (superficial later of cells in serous membranes lining ventral body cavity)
- Pleural membrane (surrounds lungs)
- Pericardial membrane (surrounds heart)
- Peritoneal membrane (surrounds abdominopelvic organs)
- Inner lining of vessels
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Simple cuboidal epithelium
- composed of one layer of cubed shaped cells
- usually in general tubing
- Found in walls of kidney tubules (most common), surface of ovaries, and ducts of glands
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Simple columnar epithelium
- composed of one layer of columnar shaped cells
- contains goblet cells
- lines lots of gut organs, gall bladder, small intestine, and gut from stomach to rectum
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Goblet cells
- unicellular
- secretes mucus to help move stuff through
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Stratified squamous epithelium
- composed of numerous layers of flattened shaped cells (lots of squishy footballs!)
- found in epidermal layer of skin, lining of mouth, tongue, pharynx, esophagus, anus, vagina, and any areas subject to abrasion
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Pseudostratified ciliated columnar epithelium with goblet cells
- single layer of tall and short cells with nuclei appearing at two levels, but actually the basal surface of all cells rest on basement membrane (falsely-layered)
- goblet cells interspersed amongst epithelial cells and function to secrete mucus
- tallest cells have cilia on apical surface
- only ex is lining of the respiratory tract - in bronchioles and trachea (respiratory type epithelium)
- every cell will touch basement membrane, but not all will necessarily touch apical surface
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Transitional epithelium
- appearance of tissues changes upon stretch and recoil of organ as cells slide to accommodate change
- stratified epithelium lining distensible (stretchable) organs such as urinary bladder and ureters
- always changing
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Glandular epithelium
- epithelial cells capable of producing and secreting a specific substance
- may be unicellular (goblet cell) or multicellular
- develops as an invagination from an epithelial surface
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Exocrine glands
- gland is connected to an epithelial surface by a duct
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Secretory portion (of glands)
- made of glandular cells that produce material
- are either tubular or alveolar/acinar
- Ex: salivary glands, sweat glands, sebaceous glands, mammary glands
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Alveolar / acinar
bulbous
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Duct portion (of glands)
- lined with ductal cells that channels secreted materials
- either simple or compound
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Simple glands
Continuous, no branching
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Compound glands
displays some degree of branching
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Endocrine glands
- glandular cells that have no duct (connection) to an epithelial surface
- cellular products are secreted directly into blood
- Ex: pituitary gland, suprarenal gland, thyroid gland
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