Epithelial Tissue
covers exposed surfaces, lines internal passageways and chambers, and forms glands
Epithelial Tissue includes
epithelia and glands
epithelial
layers of cells that cover internal or external surfaces; covers every exposed surface of the body. forms the surface of the skin, line the digestive , respiratory, reproductive, and urinary tracts.
Glands
structures that produce fluid secretions; they are either attached to or derived from epithelia.
important characteristics of Epithelial
cellularity, polarity, attachment, avascularity, regeneration
polarity
refers to the presence of structural and functional differences between the exposed and attached surfaces.
basal lamina
basement membrane; a complex structure produced by the basal surface of the epithelium and the underlying connective tissue
avascular
lack blood vessels.
4 essential functions of epithelial tissue
provide physical protection, control permeability, provide sensation, produce specialized secretions
glandular epithelium
epithelial cells produce secretions, which are either discharged ontothe sufrace of the epithelium or released into the surrounding interstitial fluid and blood
Specializations of Epithelial Cells
the movement of fluids over the epithelial surface, providing portection and lubrication, movement of fluids through the epithelium to control permeability, or the production of secretions that provide physical protection or act as chemical messangers
Specialized Cells are broke into two functional regions called
apical surface, and basolateral surfaces
apical surface
where the cell is exposed to an internal or external environment
basolateral surfaces
which include both the base, where the cell attaches to the underlying epithelial cells or deeper tissues, and the sides, where the cell contacts its neighbors
Physical intergrity of an epithelium
intercellular connections, attachment to the basal lamina, and epithelial maintenance and repair
Cell junctions
specialized areas of the plasma membrane that attach a cell to another cell or to extracellular materials.
3 types of cell junctions
occluding junctions(tight) gap junctions, macula adherens (desmosomes)
occluding junction
lipid portions of the 2 plasma membranes are tightly bound together by interlocking membrane proteins.
gap junctions
2 cells are held together by interlocking junctional proteins called connexons; they form narrow passage ways that lets small molecules and ions pass from cell to cell.
Clear Layer
layer closer to the epithelium, acts as a barrier that restricts movement of proteins and other large molecules from underlying connective tissue into the epithelium
dense layer of the basal lamina
contains bundles of coarse protein fibers produced by connective tissue cells. It gives the basement of membrane its strength.
germinatice cells
stem cells, located near the basal lamina, in a relatively protected location
3 epithelial cell shapes
squamous, cuboidal, and columnar
simple epithlium
one layer of cells. They are necessarily thin and fragile. They cannot provide much mechanical protection, so simple epithelia are located only in protected areas INSIDE THE BODY. They line internal compartments and passageways, including the ventral body
Stratified epithelium
several layers of cells that cover the basal lamina. generally located in areas that need protection from mechanical or chemical stresses, such as the surface of the skin and the lining of the mouth.
squamous epithelium
thin, flat, and somewhat irregular in shape, like pieces of a jigsaw puzzle. The disc-shaped nucleus occupies the thickets portion of each cell
simple squamous epithelium
is the body's most delicate type of epithelium. located in protected regions such as the respiratory exchange surfaces of the lungs, lining of the ventral body cavities and lining of the heart and blood vessels.
mesothelium
simple squamous that lines the ventral body cavities
endothelium
simple squamous epithelium lining the inner surface of the heart and all blood vessels
stratified squamous epitheliu
located where mechanical stresses are severe, forms series of layers like in a sheet of plywood. Surface of the skin, lining of the mouth, esophagus, and anus.
Cuboidal epithelium
resemble hexagonal boxes
simple cuboidal epithelium
provides limited protection and occurs where secretion or absorption takes place; lines portions of the kidney tubules
stratified cuboidal epithelia
relatively rare; located along the ducts of sweat glands, and in larger ducts of the mammary glands
transitional epithelium
tolerates repeated cycles of stretching and recoiling(returning to its previous shape) without damage. Regions of the urinary system.
simple columnar epithelium
found in the small intestines stomach, and large intestines
Endocrine Glands
release their secretions into interstitial fluid
excorine glands
release their secretions into passageways called ducts
3 modes of secretion
merocrine secretion, apocrine secretion, and holocrine secretion
3 types of secretion
serous, mucous, and mixed exocrine glands.