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
Glandular Epithelium
Criteria of classifications: -number of cells in the gland for multicellular -shape of duct and shape of secretory units -type of product -mode of secretion
Unicellular glands
Found in epithelial lining and glands of intestine and in the epithelial lining of the respiratory tract
Goblet cells have a “cup”- goblet shape due to presence of abundant mucinogen granules in the apical part of the cell
Exocrine glands
Secretion released on body surface or internal cavity/tract
Structure: duct and adenomere
(gastric glands, uterine glands, salivary glands)
Secretory Units
Secretory cells of exocrine glands are grouped in secretory units called adenomeres. This secretory unit manufactures the product, then specialized cells (my-epithelial cells) express it into a duct system
Ducts
Convey products to needed location (salivary gland to oral cavity)
Ducts may be simple (one opening) or compound (many branches of duct system)
Ducts may be lined with a simple cuboidal, simple columnar, or stratified cuboidal/columnar epithelium
Types of adenomeres
Tubular: straight or coiled (sweat gland, stomach gland, colon gland)
Acinar: pie-shaped, small lumen (pancreas, salivary glands)
Alveolar: larger luminal space (mammary gland, prostate, sebaceous glands)
Compound glands and Parenchyma
Compound glands are very large. The collective of secretory units and ducts of a compound gland is termed parenchyma; the connective tissue framework supporting it is called stroma. Large glands are divided into lobes. These are further subdivided by the stroma into lobules. Lobules contain multiple secretory units
Serous Gland
Watery product, contains enzymes (sweat)
Cells with round nuclei, the cytoplasm is basophilic in the basal portion and acidophilic in the apical part (zymogen granules)
Cerumen
the secretion of modified sweat glands in the skin go the external auditory canal
Mucous gland
Slick, viscous secretion (tracheal mucus)
Cells with flat heterochromatic nuclei at the base of each cell
Cytoplasm is vacuolated (frothy) and pale
Mucinogen granules are not detectable with routine stains
Mixed glands
A gland producing both mucus and serous secretion (saliva)
Mucus and serous star a common duct system, mucous acing units with associated crescent of serous cells, a serous demilune
Sebaceous gland
oily secretion, sebum
Centrally located nuclei
Cytoplasm is pale and foamy as lipid droplets are washed out during processing
Merocrine secretion
smooth lumen, no cytoplasm lost producing secretion
Cell remains intact; contents of small secretory granules are released as the secretory product
(exocrine pancreases, salivary glands)
Apocrine secretion
apex bulges, some cytoplasm is lost producing secretion
Cell bulges, a portion of cell is lost with the product
Predominant sweat gland of domestic mammals
Holocrine secretion
Entire cell is the product
Disintegrated cells with contents become the secretion
Sebaceous glands
Endocrine secretion
Secreted product is directed toward the blood vessels
