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