epithelium
TRANSCRIPT
EPITHELIAL TISSUEBook Recommended:
Basic Histology Lec. By Dr. Habib Qureshi
DEFINITION
Epithelium is the collection of cells with very little intercellular substance lining internal and external surfaces of body
and performing similar function
epithelium
EPI = UPON THELE = NIPPLE DERIVED FROM ALL THREE EMBRYONIC
GERM LAYERS Basal layer of epithelium rest on
BASEMENT MEMBRANE
BASEMENT MEMBRANE
Basement membrane consists of Basal lamina proteoglycans, type 1V collagen, electron
microscopic- Forms limit of cell- Secreted by epithelial cells Reticular lamina- Consist of fine collagen fibers
CLASSIFICATION of EPITHELIUM
Simple Epithelium Simple Squamous Simple Cuboidal Simple Columnar
Stratified Epithelium Pseudostratified Epithelium Transitional Epithelim
Simple Squamous Epithelium
Single layer of flat cells. Rest on basement membrane Nucleus bulging Function: gas exchange, diffusion of fluids Endothelium = blood vessels Mesothelium = peritoneal, pleural and
pericardial cavities Sites= bowman’s capsule, alveoli of
lungs, mesothelium, endothelium, loop of Henle of kidney
Simple Squamous Epithelium
Simple cuboidal epithelium
SINGLE LAYER OF CUBOIDAL CELLS For secretion Sites=thyroid follicles, tubules of kidney,
surface of ovary All cells of same height and width and
rest on basement membrane
SIMPLE CLUMNAR
Tall cells on basement membrane Nucleus near base For absorption and secretion ciliated = uterus Non ciliated = GIT, (has brush border –
microvilli, folds of cell membrane to increase surface area
Stratified squamous epithelium
S. sq. keratinized Surface layer is squamous In between 3-7 layers are polygonal to flat Basal layer is cuboidal There is layer of keratin at the the top Sites. skin
S. Sq. Non-keratinized No keratin layer Same as other sites= esophagus, anal canal, vagina
Stratified Cuboidal epithelium Two to three layers of cells Mostly present in ducts of salivary glands.
Stratified Columnar epithelium Two to three layers of cells Present in ducts of salivary glands, Urethra.
Pseudostratified epithelium
ALL LAYERS REACH BASEMENT MEMBRANE
Nuclei at different levels Trachea Has goblet cells
Transitional epithelium
Empty urinary bladder Basal layer columnar Intermediate layers polygonal 2-3 layers Flask shaped layers Dome shaped( umbrella) at top
AٍStretched urinary bladder 2-3 layers of flat cells
Intercellular Junctions
Needed for cell aggregation and cohesion Marked in epithelial tissue Due to binding action of glycoproteins Lateral membranes have special
junctions For adhesion Act as seals for flow of materials
Present in definite order from apex to base
E/M Cellular Junctions
Cellular junctional complex
TYPES of INTERCELLULAR JUNCTIONS
Tight junctions – ZONULA OCCLUDENS Most apical Belt like , totally occluding (Closing) Have ridges and grooves forming net like structure Form tight seal (e.g Urinary bladder) to control
paracellular pathway
ZONULA ADHERENS Belt like Encircles cell For adhesion of neighbouring cells Forms terminal web on cytoplasmic surface of cell
membrane
Gap junctions –NEXUS Present anywhere Present in all tissues except skeletal muscle There is gap of 2 nm in between opposing
surfaces Protiens of junction make connexons which
control the flow Permits molecules less than 1500 Da. Eg. Heart muscle.
DESMOSOMES:MACULA ADHERENS Disc like structure Membrane > 30 nm apart Dense material in intracellular space
DESMOSIN for adhesion Attechment plaque protiens inside the cell
membrane
HEMIDESMOSOMES (Half Desmosomes)Are between basal surface of epithelial cells and
basement membrane.
E/M Cellular junctions
FUNCTIONAL CLASSIFICATION
Adhereing junctions Z. Adherens Hemidesmosomes desmosomes
Impermiable junctions Zonula occludens
Communicating Junctions Gap junctions
Specialization of cell surface
For specific activities at the cell mambrane
Microvilli Fingerlike folds of cell membrane Increase surface area Present in absorptive cells e. g. small intestine
where the make brush or striated border 1 um in height and 0.08 um wide Within mv are clusters of actin microfilaments
forming terminal web at the base
Microvilli
STEREOCILIA Long nonmotile processes of cell Long microvill Present in epididymis Increase surface area for molecular movement
CILIA AND FLAGELLA Long, motile hair like structures 5-10 um long and 0.2 in dia Surrounded by the cell membrane Contain central pair of microtubule
surrounded by9 pairs of microtubules Inserted into basal body, inside the cell Cilia eg. In trachea for movement of mucous Flagela eg in sperms. Tail like movement
Cilia
The End