Epithelium Flashcards
Tissue
an aggregation of cells and extracellular substances
Epithelium
a tissue composed of closely aggregated cells with very little extracellular substance
Four basic types of tissues
epithelial tissue
connective tissue
muscular tissue
nervous tissue
surface or lining epithelia
epithelial cells form sheets that:
cover body surfaces
line luminal organs, tubular structures, and body cavities
glandular epithelia
secretory epithelia, their functions are synthesize, store and release its product
special epithelia
receptors for taste and hearing
Function: Protection
epithelium covering protects underlying tissue from mechanical abrasion/injury, harmful chemicals, invading microbes and from excessive loss of water
Function: Secretion
specialized to secrete specific chemical substances such as enzymes, hormones and lubricating fluids
Function: Absorption
lining of intestine absorb nutrients from digestion
epithelial cells of kidney tubules
Function: Diffusion
simple squamous epithelium promotes the diffusion of gases, liquids and nutrients
Function: Friction Reduction
smooth, tightly interlocking endothelial cells that line circulatory system reduce friction between blood and walls of blood vessels
Function: Cleaning
ciliated respiratory epithelium assists in removing dust particles from air passages
Function: Sensation
contain sensory nerve endings is found in the skin, ears and on the tongue
modified neurons in nose and eyes
ectoderm
epidermis of skin and its derivatives
mesoderm
comprised of mesothelium and endothelium
mesothelium
epithelium lining
THREE serous body cavities:
peritoneal, pleural, pericardial
endothelium
epithelium lining blood and lymphatic vessels and heart chambers
Endoderm
epithelial lining and glands most of the gastrointestinal tract and respiratory systems; liver; pancreas; urinary bladder
Epithelium Characteristics
covers surfaces and lines lumens may have specialization like glands high cellular density very little intercellular substance basement membrane present lining epithelium is avascular few nerve endings polarized, cohesive and closely associated to supporting CT
Mesenchymal Cell
lots of intercellular matrix
few cells
(connective tissue)
Hepatocyte
specialized epithelial cell
high cellular density
little intercellular matrix
Layout of Epithelial Cells
Apical (free) surface
lateral surface
basal surface next to basement membrane/lamina
nucleous close to basal lamina
Basal Lamina
when visible in light microscopy called basement membrane
interface of epithelial and connective tissue
selective barrier
provides structural support
formed by epithelial cells
Basement Membrane
basal lamina when this layer is visible with light microscopy
stains with PAS (periodic acid- Schiff) for carbs
semipermeable barrier
Tight Junctions
prevent leakage of fluid across a layer of epithelial cells
form continuous hermetic seals around the cell
bound by specific proteins
Desmosomes
anchoring junctions
function like rivets, fastening cells together into strong sheets
intermediate filaments made of sturdy keratin proteins anchoring in cytoplasm
adhere epithelial cells of the skin
velcro
Gap Junctions
communicating junctions
cytoplasmic channels or tunnels form one cell to another
membrane proteins that surround a pore
necessary for communcation
simple squamous epithelium
flat, elongated cells with a round to oval nuclei, centrally located
located in:
lining of all moist internal surfaces (called mesothelium)
alveolar walls
luminal surface of blood vessels
capsule of renal glomeruli
Simple cuboidal epithelium
all sides are approximately the same, cell limits are well defined examples: lining ducts of many glands choroid plexus in brain lining follicles of thyroid glands lens of eye
simple columnar epithelium
tall narrow cells with ovoid nucleus located near base
examples:
lining luminal surface of stomach, small and large intestine, gall bladder
lining the uterus and uterine tube
Pseudostratified epithelium
composed of a single layer of irregularly shaped and sized cells
all cells contact the underlying basement membrane, not all reach the surface
examples:
nasal cavity, upper respiratory tract
male reproductive
Kartagener’s Syndrome
immotile cilia syndrome
dynein arms are missing cilia and sperm tails
chronic respiratory infection
male sterility
Stratified squamous epithelium
several layers of cells
superficial cells have squamous shape
non keratinized
ex. cornea, esophagus, oral cavity, vagine
keratinized
provides extra protection
no nuclei, water resistant
ex. epidermis, proventricles, oral cavity, vagina in estrus
Transitional Epithelium
aka urothelium
lines urinary passages
superficial cuboidal cells bulge into lumen
superficial cells become flattened or squamous when organ is distended
superficial cells have specialized plasma membrane providing osmotic barrier between urine and tissue fluids
Unicellular glands
epithelial linings and glands of intestine and respiratory tract
ex. goblet cells
mucinogen droplets are seen in apical part
Multicellular Glands
exocrine- have a duct and adenomere
endocrine- ductless- straight into blood stream
Adenomere
cells of the exocrine secretory end piece
manufacture the product, then specialized cells express it into duct system
simple ducts
one opening
compound ducts
many branches of duct system
Tubular Adenomere
straight of coiled
ex. sweat gland, stomach glands, colon glands
Acinar Adenomere
pie shaped, small lumen
ex. pancreas, salivary glands
Alveolar Adenomere
large lumen, smaller cells
ex. mammary gland, prostate, sebaceous glands
serous
watery product, contains enzymes
ex. sweat
round nuclei, cytoplasm is basophilic in basal portion and acidophilic in apical portion because of zymogen granules
mucus glands
cells with flat heterochromatic nuclei at the base of each cell
cytoplasm is vacuolated (frothy) and pale
mucinogen granules are not detectable without special stianing
Mixed gland
mucous and serous cells sharing a common duct system
mucous acinar units with crescent serous cells
Sebaceous gland
centrally located nuclei
cytoplasm is pale and foamy
lipid is washed out during preperation
merocrine
smooth lumen, no cytoplasm lost producing secretion
Apocrine
apex bulges, some cytoplasm is lost producing secretion
droplets of apical portion become part of secretion
ex. sweat gland of domestic animals, prostate gland, mammary gland
Holocrine
entire cell is the product
endocrine
secreted product is directed toward the vasculature
