02 EPITHELIAL TISSUE.pdf

EPITHELIAL TISSUE Line internal closed cavities and body tubes TABLE OF CONTENTS that communicate with...

EPITHELIAL TISSUE Line internal closed cavities and body tubes TABLE OF CONTENTS that communicate with the outside A. The Four Fundamental Tissues environment (GIT, respiratory and GUT) B. What is an epithelial tissue? ○ Ex.) Gastrointestinal Tract - it is a a. Function tubular structure, lie internally by a b. General Characteristics mucosa which is compose of a c. Two Kinds of Epithelial Tissue epithelial tissue C. Lining Epithelium Make up the secretory portions of glands a. Simple b. Stratified and their ducts c. Pseudostratified Sensory receptive regions of certain sensory d. Transitional organs (e.g. ear, eyes, & nose) D. Surface Specializations ○ Neuroepithelial tissue - a special type a. Microvilli of epithelial tissue b. Stereocilia c. Cilia FUNCTION E. Membrane Specialization on Lateral Surface Absorption (e.g. the intestine) a. Tight Junction b. Adherent Junction o Reflected in Morphology c. Gap Junction ▪ Cuboidal / Columnar in F. Glandular Epithelium shape a. Exocrine Secretion (e.g. glands) b. Endocrine Filtration (e.g. Kidneys) G. Key Concepts to Remember Diffusion (e.g. Capillaries) Sensory (e.g. neuroepithelium) REFERENCES: Dr. Dennis Ivan Bravo’s PPT; Junqueira’s Contractile (e.g. myoepithelial cells) Basic Histology Text and Atlas (16th ed.) GENERAL CHARACTERISTICS THE FOUR FUNDAMENTAL TISSUES Consists of closely packed cells Epithelial Inside or outside lining of body areas. Connective - cells with abundant Little intercellular material. extracellular matrix ○ in contrast to connective tissue Muscle - elongated cells for contraction Avascular and movement ○ Cannot find any blood vessels within Nervous - cells with long, fine processes epithelial tissue ○ Nutrition is obtained through diffusion WHAT IS AN EPITHELIAL TISSUE? from the neighboring tissues, like Thin tissues that cover all the exposed connective tissue. surfaces of the body. Rests on basement membrane o Include the skin ○ Basement membrane is composed of type IV collagen 1 ALABAN BAUTISTA BULANHAGUI FERNANDEZ FORMENTO LEONCIO NENENG PEREZ RAYMUNDO SOMERA  High regenerative capacity, especially in SIMPLE epithelial membranes, to replace continual sloughing of cells from free surface. ○ Capable of mitosis TWO KINDS OF EPITHELIAL TISSUE Lining/covering epithelium covers outside surfaces of the body and lines internal organs Glandular/secretory epithelium secretes hormones or other products LINING EPITHELIUM SUBTYPES Based on layers: o Simple - single layer of cells Single layer of cells o Stratified - multiple layers of cells Direct contact with the basement o Pseudostratified - single layer of cells Common apical surface. but appear like stratified Alveoli of lungs, kidney, thyroid, female Based on cell shape reproductive system and in the digestive o Squamous - thin cells tract o Cuboidal - cell width and thickness Simple Squamous are roughly similar ○ Allows for rapid diffusion across the o Columnar - cells taller than wide epithelium. Function: Diffusion and Nutrition ○ Forms the lining of blood vessels, alveoli of the lungs, and internal body cavities ○ Main functions Facilitates movement of viscera Active transport by pinocytosis Secretion of biologically active molecules ○ E.g. Parietal layer of the Bowman’s capsule in the kidney 2 ALABAN BAUTISTA BULANHAGUI FERNANDEZ FORMENTO LEONCIO NENENG PEREZ RAYMUNDO SOMERA  Simple Cuboidal STRATIFIED ○ Lines, secretes and absorbs ○ Forms the lining of the thyroid follicle; covering of ovary ○ Thyroid follicle Composed of several (two or more) layers of cells Only one layer is in direct contact with the basement membrane. Simple Columnar Only one layer of cells has the apical ○ Cells are much taller than cuboidal surface ○ Lines, secretes and absorbs; Protective role protection ○ capable of mitosis to replace the ○ Forms the lining of the intestines and cells that have been slough off on gallbladder the surface ○ Gallbladder Usually seen in subtype lining epithelium in organs that are subjective to constantly abrasion or mechanical stress 3 ALABAN BAUTISTA BULANHAGUI FERNANDEZ FORMENTO LEONCIO NENENG PEREZ RAYMUNDO SOMERA  Stratified squamous epithelia are found in Stratified Cuboidal skin, oesophagus, vagina. ○ Lines, secretes and absorbs Stratified cuboidal epithelia are found in ○ Lines exocrine ducts ducts of many glands ○ Sweat gland Stratified columnar epithelium also found in ducts but they are rare Stratified Squamous ○ Protects from physical abrasion and prevents desiccation Nonkeratinized (moist) - lining of wet cavities, including the mouth, esophagus, rectum, and anal canal; surface cells are nucleated and living. Keratinized (dry) - epidermis of the skin; surface cells are nonliving. ○ Epidermis Stratified Columnar ○ Lines, secretes and absorbs ○ Rare. ○ Lines exocrine ducts (Larger ducts than Strat. Cuboidal) ○ Parotid gland duct ○ Conjunctiva 4 ALABAN BAUTISTA BULANHAGUI FERNANDEZ FORMENTO LEONCIO NENENG PEREZ RAYMUNDO SOMERA  PSEUDOSTRATIFIED TRANSITIONAL Stratified epithelium Protective function; constructed to expand with distension of the hollow organs it lines Shape of the surface cells changes (undergoes transitions) depending on the degree of stretch. When not stretched, cells of the surface layers are large and rounded. (Relax) When stretched the cells of the surface layers are pulled into a flatter shape. (Distended) Can be found in the urinary tract (urethra and urinary bladder) One single layer but the nuclei are located at a different levels Protective function Cells appear stratified, or layered, because they are so tightly packed together that their nuclei are forced into what looks like two or more layers. Most commonly found along respiratory airways. Cells contain cilia on their apical surface. Ex. Mucosa of a Trachea SURFACE SPECIALIZATIONS MICROVILLI Collectively, are called a brush or striated border Composed of fingerlike extensions of the cytoplasmic membrane (usually uniform in length) Relatively nonmotile Increase surface area for absorption Prominent on cells lining the digestive tract and proximal tubules in the kidney e.g Kidney, ileum Kidney 5 ALABAN BAUTISTA BULANHAGUI FERNANDEZ FORMENTO LEONCIO NENENG PEREZ RAYMUNDO SOMERA  ○ The glomerulus is surrounded by the parietal layer of the bowman’s capsule called the renal corpuscle. It is surrounded by a cross section of convoluted tubules. Proximal convoluted tubule- thicker, lumen is dirty because of the presence of microvilli Distal convoluted - Thinner CILIA Lumen Multiple motile hair-like extensions from free Focus on the apical surface. It looks surface of the cell; 7-10 microns in height fuzzy because of the brush borders Highly motile; beat in a wave-like motion( of microvilli. It increases the surface synchronized motion) area to allow efficient absorption of Function to propel material along the nutrients. surface of the epithelium (e.g., in the respiratory system and the oviduct of the female reproductive system) Respiratory system- removes debris that becomes the booger in our nose. Oviduct of the reproductive system- propel oocyte during ovulation Trachea ○ Focus on the apical surface. Fuzzy layer ( cilia) is present. In living tissue, they are motile, beat in a wavelike STEREOCILIA manner to help propel materials up Large, nonmotile microvilli; not a true cilia in the airway. Longer version of microvilli Oviduct (Mucosa of the fallopian tube) Contain a core of actin microfilaments ○ The surface is fuzzy because of the Increase surface area presence of Cilia. They are motile, Present on cells lining the epididymis and helping the oocyte propel out from ductus deferens in the male reproductive the fallopian tube into the uterus. tract Epididymis, Ductus deferens Epididymis ○ Hairy because of the stereocilia. Ductus deferens ○ The surface is hairy because of the presence of stereocilia 6 ALABAN BAUTISTA BULANHAGUI FERNANDEZ FORMENTO LEONCIO NENENG PEREZ RAYMUNDO SOMERA  MEMBRANE SPECIALIZATION ON LATERAL ADHERENS JUNCTION SURFACE Zonula adherens Lateral surface TIGHT JUNCTION Hold together two adjacent epithelial cells. a.k.a. Zonula occludens Lies below the tight junction Belt-like, barrier junction around apex of the Inside the cell, actin filaments join up the cell ( Keyword : Barrier) adhesion junctions. Provides close apposition of adjacent Contains two interdigitating cadherin plasma membranes and occludes the proteins that anchors two adjacent intercellular space epithelial cells. Prevents diffusion of material between the Major transmembrane link proteins: intercellular space and the lumen of the E-cadherin, catenin complexes organ. ○ Loss of E-cadherin in epithelial cell Claudin and Occludin tumors (carcinomas) promotes tumor ○ Produces a tight interaction that seal invasion and the shift to malignancy the two cell membranes Cytoskeletal components: Actin filaments The tight junction is near the apical surface Provides points linking the cytoskeletons of and it is composed of interdigitating tight adjacent cells; strengthens and stabilizes junction proteins. They provide a barrier on nearby tight junctions the apical surface of the cell. The lining epithelium becomes “water-tight”, that means it prevents the passage of material in between the adjacent cells of the lining epithelium so the material instead of passing through the middle, they pass through the cell. They function to prevent paracellular diffusion. GAP JUNCTION Intercellular channels some 1.5-2 nm in diameter. Permit the passage between the cells of ions and small molecules. Constructed from 6 copies of transmembrane proteins called connexins. ○ Connexins form hexameric complexes called connexons 7 ALABAN BAUTISTA BULANHAGUI FERNANDEZ FORMENTO LEONCIO NENENG PEREZ RAYMUNDO SOMERA  Adjacent cells are exchanging materials by ○ System of ducts (ductus glandulae) - allowing passage through tunnels (Gap transport the secretion to the exterior Junction). of the gland Mediate intercellular communication rather than adhesion or occlusion between cells Can be classified functionally according to secretory mechanism GLANDULAR EPITHELIUM ○ Merocrine/Eccrine - secretory Develop from lining epithelium product is released by exocytosis; Formed by cells specialized to produce a pancreas, salivary glands. fluid secretion On the apical surface, we Glandular epithelium forms two kinds of have the secretory vesicles glands: that contain the secretory ○ Exocrine - secrete their substances materials. Whenever they are into tubes or ducts going to be released, this ○ Endocrine - secrete hormones vesicle fuses with the cell directly into bloodstream (ductless) membrane. When it fuses, the secretory material is EXOCRINE released. This is what we call Remains connected with the surface exocytosis. epithelium, the connection forming the tubular ducts lined with epithelium that deliver the secreted material where it is used. Histologically, composed from two parts: ○ Secretory portion (portio secretoria) - contains the cells responsible for the secretory process contains cells that produces sections 8 ALABAN BAUTISTA BULANHAGUI FERNANDEZ FORMENTO LEONCIO NENENG PEREZ RAYMUNDO SOMERA  part of the secretory material. Can be classified according to morphology ○ Apocrine - apical part of cytoplasm ○ Simple glands (Composed of single of the cells is lost together with the main duct) secretory product; female mammary Simple tubular (straight tube) gland. Simple branched tubular The apical part of the cell (secretory portion has collapses and becomes part branches) of the secretory material Simple coiled tubular (coiled) Simple acinar (Dilated) Simple branched acinar (acinar has several branches) ○ Compound glands (Duct has branched points) Compound tubular Compound acinar Compound tubuloacinar ○ Holocrine - breakdown and discharge of the entire secretory cell and its products; sebaceous glands of the skin. Not just the apical part collapses, the entire cell disintegrates and becomes 9 ALABAN BAUTISTA BULANHAGUI FERNANDEZ FORMENTO LEONCIO NENENG PEREZ RAYMUNDO SOMERA  KEY CONCEPTS TO REMEMBER Epithelial tissue is one of four fundamental tissue types Lining or Grandular Lining epithelium is divided into four subtypes ○ Simple ○ Stratified ○ Pseudostratified ○ Transitional Specific subtype is based on ○ Layers ○ Shapes Glandular epithelium - invaginations of lining epithelium Secretory Classified based on morphology or type of secretion Secretory mechanism ○ Merocrine ○ Apocrine ○ Holocrine 10 ALABAN BAUTISTA BULANHAGUI FERNANDEZ FORMENTO LEONCIO NENENG PEREZ RAYMUNDO SOMERA