Epithelium Flashcards
Tissue
Aggregation go cells and extracellular substances
Four basic tissue types
Epithelial tissue
Connective tissue
Muscular tissue
Nervous tissue
Epithelium
A tissue composed of closely aggregated cells with very little extracellular substance.
3 types: Lining, Glandular, Special
Lining Epithelium
Form sheets that cover body surfaces or line luminal organs, tubular structures, and body cavities
Glandular Epithelium
have specialized cells that synthesize, story, and release various products
Special epithelium
Contain sensory nerve endings; found in the skin, ears, and on the tongue; (in nose and eyes there are modified neurons)
Origin
Ectoderm –> epidermis of skin
Mesoderm –> mesothelium (lining of body cavities), endothelium (lining of vessels and heart chambers)
Endoderm –> epithelial lining and glands of most of the GI tract, including liver and pancreas, of the respiratory system; of the urinary bladder
Functions of epithelial tissues
Protection (epidermis of skin)
Friction reduction (lining of the lumen of blood vessels and of the heart chambers)
Cleaning (internal lining of airways)
Diffusion (lining of the lumen of capillaries)
Absorption (special lining of the small intestine)
Secretion (glandular epithelia in glands)
Sensation (specialized epithelial tissue containing sensory nerve ending convey sensations from the skin, ear, and the tongue)
Characteristics of epithelium
Is a tissue with high cellular density and very little intercellular substance
Is closely associated to supporting connective tissue (CT) via basement membrane
Lining epithelium is avascular, with few nerve endings
Epithelial cells are polarized
Epithelial cells are cohesive
Epithelia are constantly renewed by a cycle of cell division
Low cellular density
Connective tissue
Lots of intracellular matriculates
Few cells
High cellular density
Hepatic tissue (glandular epithelium) Little intercellular matrix High cellular density
Interface with CT and basement membrane
Epithelial and connective tissue are interfaced by an extracellular basement membrane
Small blood capillaries never enter an epithelium across it, a few nerve ending do
Usually not visible under light microscopy
Stains prominently with PAS for carbohydrates
Epithelial cells have
Apical surface
Lateral surface
Basal surface
Epithelial cells are cohesive
Epithelial tissues are subject to pressure and traction have marked intercellular adhesion
Cohesivness due to transmembrane glycoproteins, E-caherins
Folds of plasma membranes between neighboring cells form intercellular junctions
Three types of intercellular junctions
Tight junctions
Desmosomes
Gap junctions
Gap junctions
Provide cytoplasmic channels or tunnels from one cell to an adjacent cell
Consist of special membrane proteins that surround a pore, through which ions, sugar, amino acids, and other small molecules may pass
Are necessary for communication (chemical and electrical signals) between cells in many types of tissues
Epithelial renewal
Epithelial cells are constantly lost and replaced
Stem cells are present, which have high mitotic potential
Location of stem cell varies but usually is near the bB<
Cells are pushed by the new layers away from the BM and shed off
Simple squamous epithelium
Composed of flat, elongated cells, with a round to oval nucleus, often centrally located
Common locations: lining of body cavities, generally called mesothelium (pleural, pericardial and peritoneal)
Alveolar walls in lungs
Inner lining of blood vessels and lymphatic vessels; called endothelium
Capsule of renal glomeruli
Simple cuboidal epithelium
Cuboidal shape, all sides are approximately the same size, cell limits are often well-defined Examples of cuboidal epithelium: -lining ducts of many glands -choroid plexus in brain -lining follicles of thyroid gland -lens of the eye
Simple columnar epithelium
Tall, narrow, cells with ovoid nucleus located near the base of the cell
Examples of simple columnar epithelium:
-lining the luminal surface of stomach, small and large intestine, gall bladder
-lining the uterus and uterine tube
Pseudostratified Epithelium
Composed of single layer of irregularly shaped and sized cells
All cells touch the basement membrane, but not all of them reach the apical surface
Ciliated
Examples:
-nasal cavity, upper respiratory tract
-male reproductive: duct of epididymis and vas deferens
Stratified squamous epithelium
Epithelium composed of several layers of cells
Superficial cells determine the name= the superficial cells have a squamous shape
There are 2 types of squamous epithelium
-non-keratinized
-keratinized
Stratified squamous epithelium, Keratinized
Cells on the surface lost their nuclei and are composed mainly of keratin, a protective, water-resistant protein
Cornification varies depending on how exposed and mechanically solicited the surface of a region is
Transitional epithelium
Lines urinary passages
The superficial cells have a specialized plasma membrane providing an osmotic barrier between urine and tissue fluids
