Epithelial Tissue Notes

Tissues – Introduction •a group of similar cells specialized to carry on a particular function •Tissue = cells + extracellular matrix –The extracellular matrix is a nonliving portion of a tissue that supports cells. Cell living components Matrix (fiber &ground substances)non living There are (4) types of tissue: –Epithelial = protection, secretion, absorption –Connective = support soft body parts and bind structures together –Muscle = movement –Nervous = conducts impulses used to help control and coordinate body activities Epithelial Tissue •Epithelial tissues are composed of closely aggregated polyhedral cells with strong adhesion to one another and attached to a thin layer of ECM. Polyhedral Apics & base Cell more than matrix •Epithelia are cellular sheets that line the cavities of organs, covers and forms glands, cover the body surface. Two types of epithelial Covering and lining & glandular •The principal functions of epithelial tissues include the following: –Covering, lining, and protecting surfaces (eg, epidermis) –Absorption (eg, the intestinal lining) –Secretion (eg, glands) –Trans-cellular transport (through junction) –Selective permeability à they can control what substances can come in and what substance should stay out. –Detection of sensation.(because it has a nerve ending like in skin) Epithelial Tissues Characteristics • Cellularity Closely packed cells with little extracellular material – Cells are in close contact with each other with little or no intercellular space between them – Many cell junctions often provide secure attachment. – The main function for epithelium according to its structure and location is protection from biological samples, viruses, dehydration, ....etc. • Polarity epithelial tissues always have an apical and basal surface basement members epithelial tissue & connective tissue anchoring Base • Avascular without blood vessels • Nutrients and waste must diffuse • Good nerve supply • Ability to regenerate epithelial tissues have a high capacity for regeneration (ex. skin healing) Nutrition from connective to basement to epithelial waste Epithelial to basement to. Connective Epithelial Tissues Characteristics • Cells sit on basement membrane – Apical (upper) free surface Free surface open to the outside or an open internal space – Basal surface against basement membrane Supported by connective tissue . ❑ Lateral surface surface adjacent to neighboring cells Basement Membranes( non cellular structures) • All epithelial cells in contact with subjacent connective tissue have at their basal surfaces a specialized, feltlike sheet of extracellular material referred to as the basement membrane, which is a non-cellular structure (in general it compose of extracellular material, proteins, glycoproteins and proteoglycans). Collagen make anchoring • Basement membrane may be resolved into two structures: – Basal lamina (macromolecules of the basal lamina include the following: Laminin, Type IV collagen, adhesive glycoprotein and proteoglycan) – Reticular lamina (reticular laminae contains type III collagen and is bound to the basal laminae by anchoring fibrils of type VII collagen) • Basement membranes have many functions: – They provide structural support and polarity to epithelial cells and attach epithelia to underlying connective tissue. – Proteins of the layered meshwork help filter substances entering the epithelium from below, concentrate mitogenic growth factors, and form a scaffold for epithelial repair and regeneration. – Basal lamina components help organize proteins in the plasma membrane of epithelial cells. – Basement membrane proteins also mediate many cell-to-cell interactions involving epithelia and mark routes for certain cell migrations along epithelia. Embryonic Origin • It is derived from any embryonic layers. – Ectoderm the epithelium lining the outer surface of the skin – Mesoderm the epithelium lining the blood vessels and the heart. – Endoderm the epithelium lining the GI tract or the stomach Types of Epithelia • Epithelia can be divided into two main groups: – Covering (or lining) epithelia – Secretory (glandular) epithelia Epithelial Classifications • Classified based on shape and number of cell layers – Shape • Squamous = thin, flat cells • Cuboidal = cube-shaped cells • Columnar = tall, elongated cells – Number • Simple = single layer, all cells are in direct contact with basement membrane. • Stratified = two or more layers Simple Squamous Epithelium • Description – single layer of flat cells with discshaped nuclei • Special types – Endothelium (inner covering) • slick lining of hollow organs (e.g. blood vessels, lymphatic vessels, and the heart) Origin from endodermis and ectoderm – Mesothelium (cover the organ’s outer surface) • Lines peritoneal, pleural, and pericardial cavities • Covers visceral organs of those cavities Origin from mesoderm • Function – Passage of materials by passive diffusion and filtration – Secretes lubricating substances in serous membranes • Location – Renal corpuscles – Alveoli of lungs – Lining of heart, blood and lymphatic vessels – Lining of ventral body cavity (serosae/serous memb.) Simple Cuboidal Epithelium • Description – single layer of cube-like cells with large, spherical central nuclei • Function – secretion and absorption • Location – kidney tubules, secretory portions of small glands, ovary surface epithelial tissue Simple Columnar Epithelium • Description – single layer of column-shaped (rectangular) cells with oval nuclei • Some bear cilia at their apical surface • May contain goblet cells mucus • Function – Absorption; secretion of mucus, enzymes, and other substances – Ciliated type propels mucus or reproductive cells by ciliary action Cilia move fluid and structure that found at the surface like move move ova to uterus • Location – Non-ciliated form • Lines digestive tract, gallbladder, ducts of some glands – Ciliated form • Lines small bronchi, female fallopian tube, uterine tubes, and uterus Pseudostratified Columnar Epithelium • Description – All cells originate at basement membrane – Only tall cells reach the apical surface – May contain goblet cells and bear cilia – Nuclei lie at varying heights within cells • Gives false impression of stratification • Function – secretion of mucus; propulsion of mucus by cilia • Locations – Non-ciliated type • Ducts of male reproductive tubes • Ducts of large glands – Ciliated variety • Lines trachea and most of upper respiratory tract Stratified Epithelia • Contain two or more layers of cells • Regenerate from below • Major role is protection • Are named according to the shape of cells at apical layer Stratified Squamous Epithelium • Description – Many layers of cells – squamous in shape – Deeper layers of cells appear cuboidal or columnar – Thickest epithelial tissue – adapted for protection Stratified Squamous Epithelium • Specific types – Keratinized – contain the protective protein keratin • Surface cells are dead and full of keratin stratified squamous epithelium stratified squamous epithelium – Non-keratinized – forms moist lining of body opening • Function – Protects underlying tissues in areas subject to abrasion • Location – Keratinized – forms epidermis(skin) – Non-keratinized – forms lining of esophagus, mouth, and vagina(opining of body) Stratified Cuboidal Epithelium • Description – generally two layers of cube-shaped cells • Function – protection • Location – Forms largest ducts of sweat glands – Forms ducts of mammary glands and salivary glands Stratified Columnar Epithelium • Description ‫اﻟﻧﺳﯾﺞ ھﺎد ﻧﺎدر‬ – several layers; basal cells usually cuboidal; superficial cells elongated • Function base – protection and cuboidal secretion columnar • Location apical – Rare tissue type – Found in male urethra and vas deferens (reproductive system), largest ducts of salivary glands, nasopharynx. base Transitional Epithelium(stratified ) • Description – Basal cells usually cuboidal or columnar – Superficial cells dome-shaped or squamous • Function – stretches and permits distension of urinary Bladder • Location – Lines ureters, urinary bladder and part of Urethra apical apical like dome stretch and relaxed stretch its shape is squamous relaxing is cuboidal or columnar Apical features of epithelial cells • The apical ends of many tall or cuboidal epithelial cells face an organ’s lumen and often have specialized projecting structures. • These function either to increase the apical surface area for absorption or to move substances along the epithelial surface. • Apical surfaces presented either: •Microvilli •Stereocilia •Cilia Microvilli • In cells such as those lining the small intestine (,Absorption so we need to surface area) increase surapical surfaces are densely covered with uniform microvilli. • Under light microscope they are visible as brush or striated border. • In the kidney they called brush border • In the intestine they called striated border. • Under electron microscope finger like finger cytoplasmic extension covered by a layer of glycocalyx.(Glycoproteins + glycolibids) • The average microvillus is about 1 μm long and 0.1 μm wide, but with hundreds or thousands present on the end of each absorptive cell, the total surface area can be increased by 20- or 30-fold. • Function: increase the surface area •Each microvillus contains a core of actin filaments capped and crosslinked to each other and to the surrounding plasma membrane by many different actin-binding proteins. •Terminal web network of cytoskeletal elements (actin filament, intermediates filament and other proteins) in the apical cytoplasm, microvilli are inserted into these filament. •Microvili are non-motile structure but they are dynamic structure (they become longer or shorter depending on the cell activity) •Microvilli help maintain optimal conditions for absorption via numerous channels, receptors, and other proteins in the plasmalemma. Myosin 1 anchoring F-actin bind keratin with surface area Actin and myosin’s function is increase an decrease tall of microvilli myosin 11 ‫ و‬myosin 1 Myosin 11 bind between actin with terminal web &terminal web with cytoskeleton Myosin1 anchoring F-actin bind keratin with surface area