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45 terms

Epithelium and Cell Surface Specialization

Dental Histology
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4 basic or fundamental tissue types
Epithelium
Connective tissue
Muscular tissue
Nervous tissue
Epithelial tissue
forms cellular sheets that covers body surfaces (ext/int), lines body cavities, forms glands
has very little extra- or intra-cellular substance (matrix or material)
Connective tissue
connecting and supporting
-surrounds and supports the other three basic tissues both structurally and functionally
-has abundance of extra-cellular substance
Muscular tissue
made up of contractile cells and responsible for movement of body and its parts
specialized function of contraction
Nervous tissue
function in coordination and communication
receives, transmits and generates info from outside and inside the body (nerve impulse) to control the activities of the body and its parts
Main characteristics of ET
Avascular, nourished by diffusion from CT
lots of sensory nerve ending
very little extracellular substance
has basement membrane
renewal, mitosis regeneration, rapid turnover rate
metaplasia - transformed to other type, abnormal, smoking - from PCCE to stratified squamous epithelium, hiatal hernia and bulemic - esophagus - from stratified squamous epithelium to simple columnar
Main functions of ET
covering external surfaces of body
lining body cavities
lining body tubes
absorption
secretion
sensation
contractility
excretion
lubrication
transportation by cilia
reproduction
Ectodermal origin
skin (epidermis only), hair, nail, glands, mouth, nose and anus
Mesodermal origin
endothelial lining of blood vessels
mesothelial lining of body cavities
UG systems
Endodermal origin
lining of respiratory tract
digestive tract and its glands (liver, pancreas)
Epithelial cells
vary in size and shape from flat to tall
Squamous cells (L=fish scales) with flattened nuclei
Cuboidal cells with spherical nuclei
Columnar cells with elongate nuclei
Two types of epithelia
Glandular epithelium
Covering epithelium can be classified according to number of cell layers - Simple Et (one cell layer) and Stratified Et (two or more cell layers)
Epithelia according to cell shape
Squamous
Cuboidal
Columnar
Simple squamous epithelium
endothelium
mesothelium (pleura, pericardium, peritoneum)
lung alveoli
Bowman's capsule of kidney
Simple cuboidal epithelium
collecting tubules of kidney
Simple columnar epithelium
lining of stomach, small and large intestines
Stratified epithelium
classified according to cell shape of its superficial layer
Stratified squamous keratinized epithelium
(skin, dry surface), keratin on top layer, no cell organelles
Stratified squamous non-keratinized epithelium
(mouth, esophagus, vagina, moist surfaces) alive cells with nuclei are at top layer, retain organelles
Stratified cuboidal epithelium
rare (sweat gland and ducts)
Stratified columnar epithelium
rare (large ducts of salivary ducts)
Transitional epithelium
(ureter, urinary bladder, upper urethra) - dome shaped cells on top layer, some may be binucleated
Pseudostratified ciliated columnar epi (PCCE)
(trachea, bronchi) - not true stratified, nuclei at different levels, all cells reach basal lamina, but not all cells reach the surface, with stereocilia in epididymis
Neuroepithelial cells
(tastebuds, retina, inner ear hair cells, olfactory epithelium) - for specialized sensory function
Myoepithelial or basket cells
(acini of salivary, mammary glands) - specialized for contraction
Apical surface specializations
microvilli, stereocilia, cilia, and flagella
Lateral surface specializations
junctional complexes, zonula occludens, zonula adherens, macula adherens (desmosomes), hemidesmosomes, gap junctions (nexus), interdigitation, intercellular canaliculi
Basal surface specializations
hemidesmosomes, basal invaginations/foldings and basement membrane or basal lamina
Microvilli
Actin filaments form core of microvilli
finger-like projections from apical surface
under light microscope microvilli clusters seen as
- striated border in small intestine epi, regular
- brush border in proximal renal tubules, irregular
under electron microscope seen as
- extension of cytoplasm covered by plasma membrane
each covered with glycocalyx which stains +ve with PAS
inside are clusters of actin microfilaments, connects to microfilaments in terminal web at the base of microvilli along apex of the cell
Stereocilia
found in epididymis
not a true cilia
non-motile
long anastomosing microvilli
seen in LM as cone-shaped structures
Cilia
found in trachea, bronchi, oviduct
long motile structures with rapid back and forth movement to propel mucus/egg in one direction
each arises from basal body (centriole)
each has axoneme core composed of 9 pairs of peripheral microtubules (doublets) and 2 single central microtubules (singlets)
doublets have dynein arms with ATPase activity to energize ciliary motion
abnormal respiratory problems
Flagella
only present in spermatozoa in humans
similar to cilia but much longer
only 1 flagellum per sperm cell
Kartagener's Immotile Cilia Syndrome
genetic defect in genes coding for dynein
uncoordinated or absent cilia beating
chest infection
infertility in male due to defected flagella
in females not present because egg moved by smooth muscle contractions
Junctional complex
seen as terminal bar in LM, encircles entire cell at apex, 3 components:
-Zonula occludens (tight or occluding junction)
-Zonula adherens (adhering junction)
-Macula adherens (desmosomes)
ZO and ZA encircle cell while MA does not
ZO or tight junction
most apical, zone-like
completely encircles cell
closes off intercellular space
fusion of outer leaflets of adjacent membranes form a tight seal (greatest resistance) to prevent flow of materials between cells
ZA or adhering junction
band-like
encircle the cell
adhesion of one cell to another
actin filaments attached to dense plague of material
MA or desmosomes
spot adhesions, patches, disk
do not encircle cell membranes are straight and further apart
hairpin loop of actin microfilaments attach to plagues called tonofilaments
only type of junction found or present in epidermis of skin and oral mucosa form firm adhesion between cells
Fascia adherens
intercalated discs of cardiac muscle
Gap junction
for communication, exchange between cells
Hemidesmosomes
half of a desmosome
Basal invaginations
found in proximal/distal tubules of kidney, striated duct of salivary glands, house longitudnally arranged mitochondria, for ion exchange/active transport
Basal membrane
Two components
- basal lamina
- reticular lamina
Basal lamina
epithelial derived, type IV collage (no form), glycoproteins and proteoglycan
has 2 parts
- lamina densa (dense layer, dark color)
- lamina lucida (electron lucent, light color)
Reticular lamina
connective tissue derived
type VII collagen in anchoring fibrils
Functions of Basal Laminae
structural support (epithelium)
filtering functions (in renal glomerulus)
influence cell polarity
regulate cell proliferation, differentiation and migration
influence cell metabolism
epithelial regeneration in wound healing
cell to cell interaction