epithelial tissue
TRANSCRIPT
Epithelial Tissue :-D
Tissues are groups of cells that are similar in structure and function.
* EpitheliumCoveringsLinings of surfaces
* ConnectiveSupportBone, ligaments, fat
* MuscleMovement
* NervousControlBrain, nerves, spinal
cord
Epithelial Tissue Function
Protection Skin protects from sunlight & bacteria & physical damage.
AbsorptionLining of small intestine, absorbing nutrients into blood
FiltrationLining of Kidney tubules filtering wastes from blood plasma
SecretionDifferent glands produce perspiration, oil, digestive enzymes and mucus
Classification of Epithelial Tissue
Cell Shape-Squamous – flattened like fish scales-Cuboidal - cubesColumnar - columns
Cell Layers-Simple (one layer)-Stratified (many layers)
- Named for the type of cell at the apical surface.
Simple Squamous Epithelium
StructureSingle Layer of flattened cells
FunctionAbsorption, and filtrationNot effective protection – single layer of cells.
LocationWalls of capillaries, air sacs in lungsForm serous membranes in body cavity
Simple Cuboidal Epithelium
StructureSingle layer of cube shaped cells
FunctionSecretion and transportation in glands, filtration in kidneys
LocationGlands and ducts (pancreas & salivary), kidney tubules, covers ovaries
Simple Columnar Epithelium
StructureElongated layer of cells with nuclei at same level
FunctionAbsorption, Protection & SecretionWhen open to body cavities – called mucous membranes
Special FeaturesMicrovilli, bumpy extension of apical surface, increase surface area and absorption rate.Goblet cells, single cell glands, produce protective mucus.
LocationLinings of entire digestive tract
Pseudostratified Epithelium
StructureIrregularly shaped cells with nuclei at different levels – appear stratified, but aren’t.
All cells reach basement membrane
FunctionAbsorption and Secretion
Goblet cells produce mucus
Cilia (larger than microvilli) sweep mucus
LocationRespiratory Linings & Reproductive tract
Stratified Squamous Epithelium
StructureMany layers (usually cubodial/columnar at bottom and squamous at top)
FunctionProtection
Keratin (protein) is accumulated in older cells near the surface – waterproofs and toughens skin.
LocationSkin (keratinized), mouth & throat
Transitional Epithelium
StructureMany layersVery specialized – cells at base are cuboidal or columnar, at surface will vary.Change between stratified & simple as tissue is stretched out.
FunctionAllows stretching (change size)
LocationUrinary bladder, ureters & urethra
Glands
One or more cells that make and secrete a product.Secretion = protein in aqueous solution: hormones, acids, oils.Endocrine glands
No duct, release secretion into blood vessels Often hormonesThyroid, adrenal and pituitary glands
Exocrine glandsContain ducts, empty onto epithelial surfaceSweat, Oil glands, Salivary glands, Mammary glands.
Shapes of Exocrine glands
Branching
Simple – single, unbranched duct
Compound – branched.
Shape: tubular or alveolar
Tubular – shaped like a tube
Alveolar – shaped like flasks or sacs
Tubuloalveolar – has both tubes and sacs in gland
Apical epithelial surfaces
These surfaces may possess specialized structures such as microvilli, stereocilia, and cilia.
1- Microvilli are finger like projections of epithelia (1µm length) extend into a lumen to increase the surface area
- Glycocalyx is present on their surfaces
- composed of actin filaments run longitudinally inserted in the terminal web
- they constitute the brush and striated borders
2- Stereocilia are very long microvilli (not cilia) and are located in the epididymis and vas deferens of the male reproductive system
3- Cilia are actively motile processes (5-10 µm in length) extending from certain epithelia which propel substance along their surfaces-They contain microtubules (axoneme) which arise from the basal bodies-The axoneme consists of nine doublets microtubules uniformly spaced around two central microtubules-The basal body is a cylindrical structure located at base of each cilium that consists of nine triplets microtubules arranged in radially like a pinwheel
THANK YOU MAM ALMOND :-D