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Tissues
groups of similar cells and extracellular matrix/material that carry out a common function
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Four body tissues
epithelium, connective tissue (CT), muscle, nerve
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Extracellular matrix
fibers + interstitial fluid
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Characteristics of epithelia
- nCovering or lining epithelia
- ¨Skin, lining of digestive and respiratory tract, blood vessels, etc.
- nGlandular epithelia
- ¨Adenocarcinoma – cancer originating in glandular tissue
- nColon cancer, breast cancer, pancreatic cancer, etc.
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Characteristics of covering/lining epithelia
- nTissue is almost all cells with very little extracellular matrix
- nPolarity: apical surface facing space, basal surface attached to body tissues at basement membrane
- n
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Characteristics of epithelia
- nBasement membrane: extracellular material located at the basal surface
- nAvascular: no blood vessels
- nInnervation: may have sensory nerve receptors within or nearby
- nHigh regenerative capacity: mitosis carried out at basal layers
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Functions of epithelia
- nPhysical protection against dehydration, abrasion, foreign substances (skin)
- nSelective permeability: regulation of movement of material into and out of cells, i.e., into and out of body tissues (digestive system)
- nSecretion: many epithelial cells synthesize and exocytose material, some cells form glands (salivary glands)
- nSensations: sensory nerve endings in or near epithelia detect changes in the environment and relay the information to the CNS
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Classification of epithelia
- nNumber of cell layers: simple = one layer,
- stratified = >1 layer,
- pseudostratified = one layer with cells of varying heights
- nLook for
- nuclei
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Classification of epithelia
nCell shape: based on the shape of cells at the apical surface. Three shapes are found: squamous, cuboidal, and columnar.
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Types of epithelium
- nSimple squamous epithelium
- nSimple cuboidal epithelium
- nSimple columnar epithelium
- nStratified squamous epithelium
- nPseudostratified columnar epithelium
- nTransitional epithelium
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Simple squamous epithelium
- nSingle layer of flat cells
- ¨Flattened nucleus, little cytoplasm
- ¨Delicate epithelium (little protection)
- ¨Allows diffusion, osmosis, and/or filtration across epithelium
- ¨Locations: alveoli in lungs, lining blood vessels (endothelium)
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Simple cuboidal epithelium
- nSingle layer of cells with similar width and height
- ¨Spherical nucleus
- ¨Functions in transport and secretion (more organelles than simple squamous cells)
- ¨Locations: kidney tubules, ducts of glands
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Simple columnar epithelium
- nSingle layer of tall cells
- ¨Oval nucleus at basal region
- ¨Functions in secretion and absorption
- ¨May contain cilia or microvilli
- ¨Locations: digestive tract, uterine tubes
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Stratified squamous epithelium
- nSeveral layers of cells
- ¨Apical cells are flat
- ¨Basal cells have varied shapes
- ¨Serves to protect underlying tissues from abrasion and friction
- ¨Basal cells undergo mitosis
- ¨Oldest cells at superficial layer
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Pseudostratified columnar epithelium
- nOne cell layer thick
- nCells are of different heights with nuclei at different levels
- nPseudostratified ciliated columnar (PSCC) with goblet cells
- (respiratory tract)
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Transitional epithelium (urinary sys)
- nStratified epithelium with variable shape
- ¨Able to stretch
- ¨Cells change from cuboidal to squamous
- nLocation: urinary bladder and ureter
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Connective tissue structure
- nComponents
- ¨Cells
- ¨Extracellular matrix
- nFibers
- nGround substance
- nCT is mainly extracellular matrix, with scattered cells (vs. epithelium)
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Types of connective tissue
- nConnective tissue proper – between organs; tendons and ligaments
- nSupporting connective tissue – cartilage and bone
- nFluid connective tissue - blood
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Connective tissue functions
- nPhysical protection: skeletal system cavities, padding with fat
- nSupport and structural framework: skeletal system, cartilage (e.g., trachea), capsules (e.g., liver)
- nBinding of structures: ligaments, tendons, soft tissues between organs
- nStorage: calcium and phosphate in bone, fat
- nTransport: blood and blood cells
- nImmune protection: white blood cells in connective tissues protect against infections
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Connective tissue proper components
- nCells
- nFibers
- nGround substance
- n
- nContrast with epithelium
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Connective tissue proper cells
- nFibroblasts – tapered at ends, elongated nuclei, produce fibers and fluid of ECF
- nAdipocytes – contain fat droplet (inclusion body)
- nFixed macrophages – phagocytize foreign material or cellular debris
- nMesenchymal cells – CT stem cells
- nLeukocytes (white blood cells)
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Connective tissue proper fibers
- nCollagen fibers
- ¨Made of protein collagen
- ¨Strong, flexible, resist stretching
- ¨Make up tendons and ligaments (e.g., anterior cruciate ligament)
- ¨Other locations: dermis, organ capsules
- ¨Usually stains pink with blue fibroblast nuclei
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Connective tissue proper fibers
- nElastic fibers
- ¨Made up protein elastin
- ¨Stretches easily and returns to original length (elasticity)
- ¨Branched fibers
- ¨Located in skin, lungs, arteries
- ¨Seen as internal elastic
- membrane in medium
- arteries.
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Connective tissue proper fibers nReticular fibers
- ¨Made up of protein collagen
- ¨Thin, branching fibers form a network
- ¨Flexible and strong
- ¨Forms a support like scaffolding
- for spleen, liver, and lymph nodes
- nLymphocytes and liver cells cling to
- reticular fiber network
- ¨Requires special staining
- (black/blue)
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Connective tissue proper - types
- nLoose connective tissue – scattered cells and fibers, between organs
- ¨Areolar connective tissue
- ¨Adipose connective tissue
- ¨Reticular connective tissue
- nDense connective tissue – mainly fibers
- ¨Dense regular connective tissue
- ¨Dense irregular connective tissue
- ¨Elastic connective tissue
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