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Epithelial tissue
- 1. EPITHELIAL TISSUE ClarenceWitty H. Mendoza, RMT
- 2. TISSUES Are largerstructural and functional units of cells having closely related functions joined together by intercellular substances and/or cell- to-cell junctions
- 3. BASIC TYPES OFTISSUES Epithelial tissues Connective tissues Muscular tissues Nervous tissues These tissues function in close association with each other.
- 4. CHARACTERISTICS OF EP.TISSUES high cellularity avascular exhibit polarity
- 5. PRINCIPAL FUNCTIONS OFEP. TISSUES Covering, lining, and protecting surfaces (e.g. skin) Absorption (e.g. intestines) Secretion (e.g. epithelial cells of glands) Contractility (e.g. myoepithelial cells)
- 6. EMBRYONIC ORIGIN OFEPITHELIAL TISSUES EPITHELIUM Ectoder m Endoderm Mesoderm
- 7. BASAL LAMINA amorphousextracellular material where the deepest layers of the epithelium rests a mixture of glycoproteins, collagen and proteoglycans secreted by the ep. Functions: provides structural support to the overlying ep. serves as an impermeable barrier that allows only water & small molecules to pass through
- 8. BASAL LAMINA Layers: laminarara externa (lamina lucida) lamina densa lamina interna
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- 11. GENERAL CLASSIFICATION OFEP. TISSUES • Covering ep. (skin) • Lining ep. (luminal surfaces of visceral organs) Surface epithelium • Elaborate (synthesize; produce) • Release (secretions) Glandular epithelium NOTE: Some surface epithelium are also secretory epithelium
- 12. SURFACE EPITHELIUM - dependson its location e.g. skin – protective GI tract – absorptive neuroepithelial cells of the taste buds – sensory cells olfactory cells in the nose – sensory cells kidney – excretion and maintenance of fluid balance testes – germ cells
- 13. CLASSIFICATION OF SURFACEEP. TISSUES ACCDG TO NUMBER OF LAYERS Simple Ep. Stratified Ep. These tissues are further classified according to their: shape surface modifications
- 14. SIMPLE EPITHELIAL TISSUES SimpleSquamous Epithelium Simple Cuboidal Epithelium Simple Columnar Epithelium Pseudostratified Columnar Epithelium
- 15. 1. SIMPLE SQUAMOUSEPITHELIUM - single layer, thin, flattened cells Functions Lining Lung alveoli, parietal layer of the Bowman’s capsule (kidneys) MESOTHELIUM - Serous cavities (pericardium, peritoneum, pleura) ENDOTHELIUM – lining of vessels/luminal surface (heart, blood, lymphatic vessels) Movement Facilitates the movement of the viscera (mesothelium) Active transport by pinocytosis (mesothelium and endothelium) Secretion Secretion of biologically active molecules (mesothelium)
- 16. Nuclei of thesimple sq. ep. (KIDNEYS)
- 17. 2. SIMPLE CUBOIDALEPITHELIUM - single layer, square, round nucleus at center, roughly as tall as they are wide Functions: absorption barrier secretion Ex: small ducts of exocrine glands, surface of ovary, kidney tubules, thyroid follicles, pancreas
- 18. pancreatic duct mesothelium covering anovary renal collecting tubule
- 19. 3. SIMPLE COLUMNAREPITHELIUM - Single layer, tall cells, nuclei form a single row at the basal part of the cell Functions: absorption secretion lubrication protection Ex. lining of fallopian tube, gallbladder, stomach, intestine, ducts of exocrine glands
- 20. 3. SIMPLE COLUMNAREPITHELIUM CILIATED SIMPLE COLUMNAR EP. – fallopian tube, uterus, ovary
- 21. renal collecting duct oviductlining, with both secretory and ciliated cells lining of the gall bladder
- 22. 4. PSEUDOSTRATIFIED COLUMNAR EPITHELIUM “Falsestratified epithelium” - Cells are attached to basal lamina even though their nuclei lie at different levels. - The height of some cells does not extend to the surface Functions: protection transport of particles trapped in mucus out of air passages secretion
- 23. 4. PSEUDOSTRATIFIED COLUMNAR EPITHELIUM Ex:lining of the membranous and spongy part of the male urethra Ciliated pseudostratified ep. (respiratory ep.) - lining of trachea, bronchi, nasal cavity
- 25. STRATIFIED EPITHELIAL TISSUES StratifiedSquamous Epithelium Stratified Cuboidal Epithelium Stratified Columnar Epithelium Transitional Epithelium
- 26. 1. STRATIFIED SQUAMOUS EPITHELIUM•“dry”; superficial layers are dead cells; no nucleus & organelles •Cells closer to the underlying connective tissue are usually cuboidal or low columnar •Impervious to water •Ex. epidermis Keratinized •“wet”; kept moist by glandular secretions •Flattened cells retain their nuclei •Lines wet cavities •Ex. Mouth, vagina, esophagus, urethra, cornea Non- keratinized
- 28. 2. STRATIFIED CUBOIDAL EPITHELIUM Functions: Protection Secretion Ex. Sweat glands, salivary glands, developing ovarian follicles
- 29. 3. STRATIFIED COLUMNAR EPITHELIUM -Lines large ducts of some glands
- 30. 4. TRANSITIONAL EPITHELIUM/ UROTHELIUM -Unique to mammals - manifest features that are between stratified squamous and stratified cuboidal - designed to withstand stretching Cuboidal (basal cells) Umbrella cells – domelike cells that are protective against hypertonic and potentially cytotoxic effects of urine(superficial cells)
- 31. 4. TRANSITIONAL EPITHELIUM/ UROTHELIUM Location:lining of the renal calyces, renal pelvis, urinary bladder, ureter, and upper part of the urethra - the form of the surface cells changes according to the degree of distention of the bladder wall
- 32. SURFACE MODIFICATION OF EPITHELIALCELLS Apical surface microvilli cilia flagella stereocila Lateral surface Zonula occludens Zonula adherens Desmosome Gap junction Basal surface hemidesmosome Basal infoldings of the plasmalemma
- 33. 1. APICAL MODIFICATION MICROVILLI -minute fingerlike projections that extend from the apical surface of the cell Striated border/ brush border (stomach)
- 34. • Within eachmicrovillus are bundles of actin filaments cross-linked to each other and to the surrounding plasma membrane by other proteins
- 35. 1. APICAL MODIFICATION CILIA(KINOCILIA) - Elongated, highly motile, longer and two times wider that microvillus - Exhibit rapid back and forth movements coordinated to propel a current of fluid and suspended matter in one direction
- 36. 1. APICAL MODIFICATION FLAGELLA -Long cilia - Functions to propel the cell - Spermatozoon (called tail)
- 37. 1. APICAL MODIFICATION stereocila -microvilli that are as long as cilia - non-motile and core consists of actin filaments Location: vas deferens, testes, hair cells of the inner ear
- 38. 2.LATERAL SURFACE MODIFICATION INTERCELLULAR JUNCTIONS Zonulaoccludens Zonula adherens Desmosomes Gap junctions Juxtaluminal junction complex/ terminal bar
- 39. 2. LATERAL MODIFICATIONS INTERCELLULARJUNCTIONS Zonula Occludens (Tight junction/ Closing Belt) - Most apically situated Zonula – indicates that junctions form bands completely encircling each cells Occludens – refers to membrane fusions that close off the space between the cells Principal function: Seals to prevent the flow of materials between the cells (paracellular pathway)
- 40. 2. LATERAL MODIFICATIONS INTERCELLULARJUNCTIONS Zonula Adherens (Adhering belt/ Belt desmosome/ Band desmosome) - Also encircles the cell usually immediately below the zonula occludens - cell membrane of adjoining cells neither adhere nor fuse; they are separated by intercellular space filled with cadherins (extracellular material) that provides firm adhesion of one cell to its neighbors
- 41. 2. LATERAL MODIFICATIONS INTERCELLULARJUNCTIONS Desmosomes(Macula adherens/ Spot Desmosome) - form button-like adhesions arranged in a line around the cell - appear as thickening of the cell - with intermediate filaments converging and inserting into each half disc Location: epidermis Principal function: Provides firm adhesion among cells
- 42. 2. LATERAL MODIFICATIONS INTERCELLULARJUNCTIONS Gap Junctions (Nexus/ Communicating Junction) - broad area where the plasma membranes of adjoining ep. cells are closely apposed w/ each other - perforated by tiny tubes called connexons Principal function: permit the rapid exchange between cells of molecules with small
- 45. 3. BASAL SURFACEMODIFICATIONS - For better attachment or for more efficient functioning Hemidesmosomes - Identical to half a desmosome - Exists in the stratum basale of the skin Basal infoldings of the plasmalemma - Present in cells lining segments of the renal tubule - increase the absorptive capacity of the cell
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- 48. ENDOCRINE GLANDS - Ductlessglands - Arise in the embryo as invagination of the covering epithelium Secretions: HORMONES (chemical messengers) Ex: adrenal gland, thyroid gland, islets of Langerhans (pancreas)
- 49. EXOCRINE GLANDS Unicellular glands -Exemplified by the goblet cells - Lines respiratory and digestive tract
- 50. EXOCRINE GLANDS Multicellular glands -All other glands Secretory ep. sheet (e.g. ependymal – lines the choroid plexus w/c produces CSF) Intraepithelial gland (e.g. penile urethra – secretory cells that gather around a small orifice and form shallow invaginations) Glands with ducts – (e.g. major salivary glands, pancreas, liver - possess “true” ducts)
- 51. CLASSIFICATION OF EXOCRINEGLANDS BASED ON MORPHOLOGY OF DUCT • single, unbranched duct Simple • duct with branches Compound
- 52. SECRETORY UNITS OF EXOCRINEGLANDS TUBULAR GLANDS Secretory tubules – blind ending tubes ACINOUS OR ALVEOLAR GLANDS Acini; alveoli – globular or basket-like structures TUBULOALVEOLAR (TUBULOACINOUS) GLAND Further classified into BRANCHED or COILED
- 53. SIMPLE TUBULAR Crypts ofLieberkuhn (intestinal glands)
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- 55. SIMPLE BRANCHED TUBULAR Cardiacglands (stomach)
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- 60. COMPOUND TUBULO-ACINAR Major salivaryglands (parotid, submandibular, sublingual)
- 61. BASED ON TYPEOF SECRETION MUCOUS CELLS (mucus secreting) Mucin containing – forms mucus that lubricates the covering epithelia Ex. Sublingual gland SEROUS CELLS (serous secreting) enzymes Ex. Parotid gland, pancreas Mixed gland – both are present; mucinous cell capped by serous demilunes (“mucoserous”) Ex. submandibular gland
- 62. BASED ON MECHANISMOF PRODUCT RELEASE (MODE OF SECRETION) Merocrine (eccrine) - exocytosis, cell remains intact Ex. Pancreatic acinar cells, major salivary glands Apocrine - secretes product with apical portion of cell; Ex. Sweat glands, lactating mammary glands, ceruminous glands in the skin Holocrine - whole cell disintegrates when it secretes
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Editor's Notes
- #5 High cellularity – closely packed tog w/ minimal intervening intercellular substance Avascular – no blood vessels Exhibit polarity
- #7 Ectoderm – lining the external surfaces (e.g. skin, appendages, cornea, mouth, anus) Endoderm – innermost layer (e.g. digestive system – liver, pancreas, gallbladder, respiratory tract, urinary bladder, urethra) Mesoderm- (e.g. heart, blood vessels, lymphatic vessels, serous cavities)
- #8 Lamina lucida – electron lucent layer; made up of glycoproteins (laminin) and proteoglycans Lamina densa – electron dense layer; made up of collagen IV and proteoglycans Lamina interna – morphologically similar to rara externa but thinner; collagen IV, fibronectin, thrombospondin, proteoglycans
- #9 Lamina lucida – electron lucent layer; made up of glycoproteins (laminin) and proteoglycans Lamina densa – electron dense layer; made up of collagen IV and proteoglycans Lamina interna – morphologically similar to rara externa but thinner; collagen IV, fibronectin, thrombospondin, proteoglycans
- #10 Lamina fibroreticularis
- #27 Keratinized - As they accumulate keratin in process the cells become irregular in shape and flatten and move closer to the surface and lack nuclei
- #62 Mucinous secretions- light colored cytoplasm; nucleus pushed to the basal part of epithelial cells (“slimy”). Has large acini Ex. sublingual gland Serous - darker colored cytoplasm because of granules; pyramidal shaped cells lining serous gland (“watery”). Smaller acini Ex. parotid gland, pancreas