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Tissue Levels
Body Tissues
Question | Answer |
---|---|
Histology | The study of tissues |
Define "TISSUES" | A group of cells performing similar functions |
Extracellular Matrix | A substance produced by the cells of a specific tissue and CAN contain protein fibers, salts, H2O and dissolved macromolecules |
4 Types of Tissue | Epithelial tissue, Connective tissue, Muscle tissue, Nervous tissue |
Epithelial Tissue | Lines EVERY body surface and ALL body cavities. Organs are lined on the outside and inside by epithelial tissue. The majority of glands are derived from epithelial tissue. Has little to no extracellular matrix |
Characteristics of Epithelial Tissue | Avascularity, Innervation, Regeneration |
Avascular | All epithelial tissues lack blood vessels. The cells receive their nutrients by diffusion from underlying tissues. |
Innervation | Highly innervated to give info about the outside |
REGENERATION | Because apical surface is constantly exposed to the environment, epithelial cells are frequently damaged or die. They are replaced as quickly as they are lost |
Functions of Epithelial Tissue | - Physical protection - Selective permeability – regulates the passage of certain molecules in or out of a certain region of the body- Secretion- Sensations |
BASEMENT MEMBRANE | - Specialized structure of epithelium- Between the epithelium & underlying connective tissue (CT)- Provides physical support & anchoring of epithelial tissue- Acts as barrier to regulate passage of lg molecules between epithelium & underlying CT |
2 LAYERS OF BASEMENT MEMBRANE | - Basal lamina - Reticular lamina |
Epithelial cells are strongly bound by | Intercellular Junctions |
TYPES OF INTERCELLULAR JUNCTIONS | - Tight junctions- Adhering junctions- Desmosomes- Gap junctions |
TIGHT JUNCTIONS | - Encircle cells near their apical surface- Prevent molecules from traveling between epithelial cells. Molecules must go through the epithelial cells rather than in between them- “gatekeepers” between an external and internal environment |
ADHERING JUNCTIONS | - Formed completely around the cell deep to the tight junction - Microfilaments act like a purse-string to stabilize the apical surface of the epithelial cell |
DESMOSOMES | -Dsn't encircle cell(like a button or snap between 2 adjacent cells)-Sites of mechicanical stress-Thickened protein plaque on ea of the apposed cell membranes w/ a network of proteins spanning intercellular space between plaques (cytoplasm side) |
GAP JUNCTIONS | - Fluid-filled channels that directly connect the cytoplasms of apposed cells sharing these structures- These structures allow adjacent cells to communicate with each other by the flow of ions and other small molecular messengers |
CLASSIFICATION OFEpithelial Tissue | Classified according to two criteria:1. Number of layers of cells2. Shape of the cells |
NUMBER OF LAYERS | 1. Simple epithelium 2. Stratified epithelium3. Pseudostratified epithelium |
SIMPLE EPITEHLIUM | a single layer of cells with all cells having an apical surface and attached to the basement membrane |
STRATIFIED EPITHELIUM | two or more layers of cells. Not all cells have an apical surface nor do all cells attach to the basement membrane |
PSEUDOSTRATIFIED EPITHELIUM | two or more layers of cells. Not all cells have an apical surface nor do all cells attach to the basement membrane |
SHAPE OF THE CELL | - Squamous – flattened and similar to the shape of a fried egg- Cuboidal – about the same size on all sides. The nucleus is usually centrally located- Columnar – taller than they are wide and nucleus is oval and located in the basal region of the cell |
TRANSITIONAL EPITHELIUM | - Found lining the inside of the urinary bladder- Changes shape between squamous and cuboidal depending on whether bladder is full and its wall is stretched or empty and its wall is contracted |
CONNECTIVE TISSUE (CT) | Most diverse, abundant, widely distributed and structurally varied of all 4 tissue typesFunction is to “connect” one structure to another structure; CT is the “glue” and “filler” of the body |
Examples of CT | tendons, ligaments, body fat, bones, cartilage, and blood |