4) Epithelial les 4.pptx

INTRODUCTIE 4 basisweefsels: epitheel, bindweefsel, spierweefsel, zenuwweefsel, Weefsel Cellen Functie Extracellulaire matrix Epitheel Aaneengesloten Zeer gering Bedekking van lichaamsoppervlak en inwendige holten; klierfunctie Bind- en steunweefsel Verschillende typen van vaste en vrij bew...

INTRODUCTIE 4 basisweefsels: epitheel, bindweefsel, spierweefsel, zenuwweefsel, Weefsel Cellen Functie Extracellulaire matrix Epitheel Aaneengesloten Zeer gering Bedekking van lichaamsoppervlak en inwendige holten; klierfunctie Bind- en steunweefsel Verschillende typen van vaste en vrij bewegende cellen Zeer veel Steunfunctie en bescherming Spierweefsel Contractiel Redelijk aanwezig Beweging Zenuwweefsel Vele uitlopers Geen Voortgeleiding van impulsen EPITHEEL WEEFSEL Dicht aaneengesloten veelhoekige cellen Heel weinig extracellulaire matrix FUNCTIES • bedekken en afgrenzen (huid) • absorptie (darmepitheel) • secretie (klieren) • gevoel (neuroepithelium) helpen ons voelen • samentrekken (myoepitheliale cellen) GRENZEN interne oppervlaktes externe oppervlaktes Alles wat door ons lichaam wordt opgenomen of uitgescheiden moet een VORMEN VAN EPITHEELCELLEN Vorm: van cilindrisch over kubisch tot plaveiselepitheel (plat)  dood Hebben geen celkern Polyhedrisch: in functie van de beschikbare ruimte  nemen de vorm aan van de beschikbare ruimte Nucleaire vorm ± cel vorm (van bolvormig tot plat); de as van de kern ligt meestal parallel met de as van de cellen Lagen De basale membraan Karakteristiek voor epitheel weefsel: Basale laminae (4-1), (4-2) - extracellulaire structuur - EW cellen in contact met BW - Basale oppervlakten in contact met elkander (43) BL= netwerk van fibrillen (collageen, glycoproteïnen, proteoglycanen) Aanhechting aan het onderliggende BW door verankeringsvezels (collageen) Figure 4–1. A: Section of human skin showing hemidesmosomes (H) at the epithelial–connective tissue junction. Note the anchoring fibrils (arrows) that apparently insert into the basal lamina (BL). The characteristically irregular spacing of these fibrils distinguishes them from collagen fibrils. x54,000. (Courtesy of FM Guerra Rodrigo.) B: Section of skin showing the basal lamina (BL) and hemidesmosomes (arrows). This is a typical example of a basement membrane formed by a basal lamina and a reticular lamina (to the right of the basal lamina in this micrograph). x80,000. Figure 4–2. Two types of basement membranes. A: The thickness of this type of membrane results from fusion of 2 basal laminae produced by an epithelial and an endothelial cell layer, as found in the kidney glomerulus (shown here) and in the alveoli of the lung. It consists of a thick central lamina densa with a lamina lucida (lamina rara) on either side. B: The more common type of basement membrane that separates and binds epithelia to connective tissue is formed by association of the basal and reticular laminae. Note the presence of the anchoring fibrils formed by type VII collagen, which binds the basal lamina to the subjacent collagen. Figure 4–3. Kidney section showing the collagen type IV of the glomerular and tubular basement membranes (arrows). In the glomeruli the basement membrane, besides having a supporting function, has an important role as a filter. Picrosiriushematoxylin (PSH) stain. Medium magnification. LB komt voor wanneer cellen in contact komen met BW > Spier > Vetcellen > Schwanncellen helpt voor de vorming van myeline LB aaneenliggende epitheliale lagen > long alveoli > renale glomerus LB wordt aangemaakt door de respectievelijke cellen Functies van de LB: > structureel > barriére  Invloed op de celpolariteit Intercellulaire verbindingen (4-4) Prominent in epithelia (ook aanwezig in andere weefsels)  Cohesie en communicatie Intercellulaire adhesie door transmembranaire glycoproteïnen Laterale specialisaties: intercellulaire verbindingen => adhesie => afdichten (verhinderen van transport door de intercellulaire ruimte) => communicatie Figure 4–4. Junctional complexes of epithelial cells. Three cuboidal epithelial cells, emptied of their contents, show the four major types of junctional complexes between cells. The tight junction (zonula occludens) and adherent junction (zonula adherens) are typically close together and each forms a continuous ribbon around the cell’s apical end. Multiple ridges of the tight, occluding junctions prevent passive flow of material between the cells, but are not very strong; the adhering junctions immediately below them serve to stabilize and strengthen these circular bands around the cells and help hold the layer of cells together. Both desmosomes and gap junctions make spotlike plaques between two cells. Bound to intermediate filaments inside the cells, desmosomes form very strong attachment points which supplement the role of the zonulae adherens and play a major role to maintain the integrity of an epithelium. Gap junctions, each a patch of many connexons in the Junctional complexes of epithelial cells. Most cuboidal or columnar epithelial cells have intercellular junctional complexes with the different types of junctions shown schematically here. At the apical end, tight junctions (zonulae occludens) and adherent junctions (zonulae adherens) are typically close together and each forms a continuous band around the cell. Multiple ridges of the tight junction prevent passive flow of material between the cells but are not very strong; the adhering junctions immediately below them serve to stabilize and strengthen the circular occluding bands and help hold the cells together. Both desmosomes and gap junctions are spot-like, not circular, structures between two cells. Bound to intermediate filaments inside the cells, desmosomes form very strong attachment points that supplement the zonula adherens and play a major role to maintain the integrity of an epithelium. Gap junctions, each a patch of many connexons in the adjacent cell membranes, have little strength but serve as intercellular channels for flow of molecules. All of these junctional types are also found in certain other cell types besides Van de apex naar de basale zijde van de cel (4-5) - (1) tight junction of zonula occludens –afsluitingsverbinding band rond de cel fusie van de membranen (sluiting van intercellulaire ruimte) het # fusies is gecorreleerd met de doorlaatbaarheid Functie: verhinderen van passage => compartementalisatie - (2)zonula adherens - hechtingszone * een verbindingsband rondom de cel * Transmembranaire adhesiemoleculen (cadherinen) * insertie van AF in plaques * AF zijn deel van het terminale web Functie: adhesie (1) en (2) vormen samen de kitlijst - (3) gap junction (communicatie kanalen) > Membranen van aaneenligende cellen heel dicht >bevatten connexonen: connexines vormen hexameren met een hydrofiel kanaaltje >connexonen in aanliggende membranen zijn geäligneerd => hydrofiel kanaal >Dynamische structuren: ze kunnen gevormd worden in de afwezigheid van proteïnsynthese > Functie: uitwisseling van moleculen voor - MW <1500 - hormonen - c-AMP - GMP - Ionen - (4) desmosoom of macula adherens (4-10NL) > complexe schijfvormige structuur > gematched met een identische structuur in de aanliggende cel > rechte celmembranen, iets verder uiteen dan de normale 20 nm - aanhechtingsplaat (proteïne) - IF(cytokeratine) zijn aangehecht aan de plaat en aan het cytoskelet - desmogleïnen in de intercellulaire ruimte - Functie: adhesie - (5) hemidesmosoom > connectie tussen EW en LB >de plaat bevat transmembranaire proteïnen die verbonden zijn met extracellulair collageen van het BW Figure 4–4. The main structures that participate in cohesion among epithelial cells. The drawing shows 3 cells from the intestinal epithelium. The cell in the middle was emptied of its contents to show the inner surface of its membrane. The zonula occludens and zonula adherens form a continuous ribbon around the cell apex, whereas the desmosomes and gap junctions make spotlike plaques. Multiple ridges form the zonula occludens, where the outer laminae of apposed membranes fuse. (Redrawn and reproduced, with permission, from Krstíc RV: Ultrastructure of the Mammalian Cell. Springer-Verlag, 1979.) Figure 4–5. Electron micrograph of a section of epithelial cells in the large intestine showing a junctional complex with its zonula occludens (ZO), zonula adherens (ZA), and desmosome (D). Also shown is a microvillus (MV). x80,000. Electron micrograph of a section of epithelial cells), zonula occludens Figure 4–7. A: Model of a gap junction (oblique view) depicting the structural elements that allow the exchange of nutrients and signal molecules between cells without loss of material into the intercellular space. The communicating pipes are formed by pairs of abutting particles, which are in turn composed of 6 dumbbell-shaped protein subunits that span the lipid bilayer of each cell membrane. The channel passing through the cylindrical bridges (arrow in A) is about 1.5 nm in diameter, limiting the size of the molecules that can pass through it. Fluids and tracers in the intercellular space can permeate the gap junction by flowing around the protein bridges. (Reproduced, with permission, from Staehelin LA, Hull BE: Junctions between living cells. Sci Am 1978;238:41. Copyright © 1978 by Scientific American, Inc. All rights reserved.) B: Gap junction between living cells as seen on a cryofracture preparation. The junction appears as a plaquelike agglomeration of intramembrane protein particles. x45,000. (Courtesy of P Pinto da Silva). C: Gap junction between 2 rat liver cells. At the junction, 2 apposed membranes are separated by a 2-nm-wide electron-dense space, or gap. x193,000. (Courtesy of MC Williams.) SPECIALISATIES VAN HET CELOPPERVLAK > Vergroting van het celoppervlak > Verplaatsen van deeltjes - Microvilli (4-8), (4-9) > Korte of lange cytoplasmatische uitstulpingen > Van enkele tot heel veel >Bevatten 20 tot 30 AF, crosslinked aan elkander en aan de plasmamembraan door eiwitten > Bedekt beschermende laag: cell coat, glycocalix ( slijmlaag die microvili beschermt/ mucus) > Borstelzoom Figure 4–8. Electron micrograph of the apical region of an intestinal epithelial cell. Note the terminal web composed of a horizontal network that contains mainly actin microfilaments. The vertical microfilaments that constitute the core of the microvilli are clearly seen. An extracellular cell coat (glycocalyx) is bound to the plasmalemma of the microvilli. x45,000. Figure 4–9. Electron micrograph of a section from the apical region of a cell from the intestinal lining showing crosssectioned microvilli. In their interiors, note the microfilaments in a cross section. The surrounding unit membrane can be clearly discerned and is covered by a layer of glycocalyx, or cell coat. x100,000. Microvilli. Absorptive cells lining the small intestine demonstrate the highly uniform microvilli of a striated or brush border particularly well. (a)A pseudo-colored TEM of one such cell shows many parallel microvilli and their connections to the terminal web (TW) in the underlying cytoplasm. (X6500) (b)SEM of a sectioned epithelial cell shows both the internal and surface structure of individual microvilli and the association with actin filaments and intermediate filaments of the terminal web. (X7000; TW) (c)TEM of microvilli sectioned longitudinally and transversely (inset) reveals the microfilament arrays that form the core of these projections. The terminal web (TW) of the cytoskeleton is also seen. The glycocalyx (G) extending from glycoproteins and glycolipids of the microvilli plasmalemma contains certain enzymes for late stages of macromolecule digestion. (X15,000) (d)The diagram shows a few microfilaments in a microvillus, with various actin-binding proteins important for F-actin assembly, capping, cross-linking, and movement. Like microfilaments in other regions of the cytoskeleton, those of microvilli are highly dynamic with treadmilling and various myosin-based interactions. Myosin motors import various microvilli components along the actin filaments. (Figure 4–8b, used with permission from Dr John Heuser, Washington University School of Medicine, St. Louis, MO.) -Cilia & Flagella >Cilia (4-10) >> Lange beweegbare uitstulpingen >> Bevatten 9+2 MT >> Zitten vast op een basaal lichaampje: structureel analoog aan de centriolen >> beweging: transportbandfunctie (e.g. trachea) >>verbruik van ATP > Flagella (22-9) >> In spermatozoa >> Langer in vergelijking met >> 1 flagellum/cel cilia Figure 4–10. Electron micrograph of the apical portion of a ciliated epithelial cell. Cilia are seen in longitudinal section. At the left, arrowheads point to the central and peripheral microtubules of the axoneme. The arrowhead at right indicates the plasma membrane surrounding the cilium. Each cilium has a basal body (B) from which it grows. Microvilli (MV) are shown. x59,000. Inset: Cilia in cross section. The 9 + 2 array of microtubules in each cilium is evident. x80,000. (Reproduced, with permission, from Junqueira LCU, Salles LMM: Ultra-Estrutura e Função Celular. Edgard Blücher, 1975.) Ciliary axoneme. (a)A diagram of a cilium with the axoneme consisting of two central microtubules surrounded by nine peripheral microtubular doublets associated with other proteins. In the doublets, microtubule A is complete, consisting of 13 protofilaments, whereas microtubule B shares some of A’s protofilament heterodimers. The axoneme is elastic but relatively stiff, with its structure maintained by nexins linking the peripheral doublets and other protein complexes forming a sheath and radial spokes between the doublets and the central microtubules. The axoneme is continuous with a basal body located in the apical cytoplasm. Basal bodies are structurally very similar to centrioles, consisting of nine relatively short microtubular triplets linked together in a pinwheel-like arrangement. A dynamic pool of tubulin and other proteins exists distally in cilia, and proteins are transported into and out of the structure by kinesin and cytoplasmic dynein motors moving along the peripheral doublets of microtubules. (b)Ciliary movement involves a rapid series of changes in the shape of the axoneme. Along the length of each doublet, a series of paired “arms” with axonemal dynein is bound to microtubule A, with each pair extended toward microtubule B of the next doublet. When Classificatie van EPITHELIA Bedekkend > < Klier Bedekkend epitheel (4-11), (4-12) De cellen zijn georganiseerd in lagen Classificatie ifv : > het aantal cellagen Eenlagig > < Meerlagig > De vorm van de cellen plaveisel, kubisch of cilinderisch * Eenlagig: plaveisel, kubisch of cilinderisch (4-13), (4-14), (4-15), (416) * Meerlagig (naar de vorm van de bovenste laag) > Meerlagig gekeratiniseerd plaveisel epitheel (bv. huid) Figure 4–11. Diagrams of simple epithelial tissue. A: Simple squamous epithelium. B: Simple cuboidal epithelium. C: Simple ciliated columnar epithelium. All are separated from the subjacent connective tissue by a basement membrane. In C, note the terminal bars that correspond in light microscopy to the zonula occludens and the zonula adherens of the junctional complex. Figure 4–12. Diagrams of stratified and pseudostratified epithelial tissue. A: Stratified squamous epithelium. B: Transitional epithelium. C: Ciliated pseudostratified epithelium. The goblet cells secrete mucus, which forms a continuous mucous layer over the ciliary layer. Figure 4–13. Section of a vein. All blood vessels are lined with a simple squamous epithelium called endothelium (arrowheads). Smooth muscle cells in the vein wall are indicated by arrows. Pararosaniline–toluidine blue (PT) stain. Medium magnification. Figure 4–14. Simple squamous epithelium covering the peritoneum (mesothelium). Some blood capillaries are indicated by arrows. PT stain. Medium magnification. Figure 4–15. Simple cuboidal epithelium from kidney collecting tubules. Cells of these tubules are responsive to the antidiuretic hormone and control the resorption of water from the glomerular filtrate, thus affecting urine density and helping retain the water content of the body. PT stain. Low magnification. Figure 4–16. Simple columnar epithelium that covers the inner cavity of the uterus. Note that the epithelium rests on the loose connective tissue of the lamina propria. The epithelium and the lamina propria constitute the mucosa. H&E stain. Medium magnification. Figure 4–17. Stratified squamous nonkeratinized (moist) epithelium of the esophagus. PT stain. Medium magnification. Figure 4–19. Stratified transitional epithelium of the urethra. The basement membrane between the epithelium and the underlying loose connective tissue is indicated by arrows. PSH stain. Medium magnification. Figure 4–20. Section of large intestine showing goblet cells secreting mucus to the extracellular space. The mucus precursor stored in the cytoplasm of the goblet cells is also stained in a dark color. PAS-PT stain. Medium magnification. Simple squamous epithelium. This is a single layer of thin cells, in which the cell nuclei (arrows) are the thickest and most visible structures. Simple epithelia are typically specialized as lining of vessels and cavities, where they regulate passage of substances into the underlying tissue. The thin cells often exhibit transcytosis. Examples shown here are those lining the thin renal loops of Henle (a), covering the outer wall of the intestine (b), and lining the inner surface of the cornea (c). The simple squamous epithelium lining the vasculature or the cornea is also called endothelium, while that lining large body cavities is called mesothelium and secretes a lubricant film called serous fluid. (a, c X400; b X600; H&E) Simple cuboidal epithelium. Cells here are roughly as tall as they are wide. Their greater thickness allows cytoplasm to be rich in mitochondria and other organelles for a high level of active transport across the epithelium and other functions. Examples shown here are from a renal collecting tubule (a), a large thyroid follicle (b), and the thick mesothelium covering an ovary (c). (All X400; H&E) Simple columnar epithelium. Cells here are always taller than they are wide, with apical cilia or microvilli, and are often specialized for absorption. Complexes of tight and adherent junctions, sometimes called “terminal bars” in light microscopic images, are present at the apical ends of cells. The examples shown here are from a renal collecting duct (a), the oviduct lining, with both secretory and ciliated cells (b), and the lining of Stratified epithelium. Stratified squamous epithelia usually have protective functions: protection against easy invasion of underlying tissue by microorganisms and protection against water loss. These functions are particularly important in the epidermis (a) in which differentiating cells become keratinized, that is, filled with keratin and other substances, eventually lose their nuclei and organelles, and form superficial layers oof flattened squames that impede water loss. Keratinized cells are sloughed off and replaced by new cells from more basal layers, which are discussed fully with the skin in Chapter 18. Nonkeratinized stratified squamous epithelia occur in many organs, such as the esophageal lining (b) or outer covering of the cornea (c). Here cells accumulate much less keratin and retain their nuclei but still provide protection against microorganisms. Stratified cuboidal or columnar epithelia are fairly rare but occur in excretory ducts of certain glands, such as sweat glands (d) where Pseudostratified epithelium. Cells of pseudostratified epithelia appear to be in several layers, but their basal ends all rest on the basement membrane. The pseudostratified columnar epithelium of the upper respiratory tract shown here contains many ciliated cells, as well as other cells with their nuclei at different levels. (X400; H&E) Klierepitheel >Synthese, stockering en secretie van proteïnen, lipiden, KH-proteïne complexen OF > Transfer van substanties uit het bloed (zweet) Klieren ontstaan uit bedekkend epitheel > Proliferatie en invasie van het BW Soorten klierepitheel: classificatie (1) Unicellulaire klieren (4-20) > < multicellulaire klieren(4-21) (2) Exocrien (verbinding met het weefsel waaruit ze ontstaan zijn) > <endocrien (geen verbinding –secretie naar het bloed) (4-21) (3) secretiewijze merocrien > apocrien (4-23)> holocrien (18-16) Figure 4–21. Formation of glands from covering epithelia. Epithelial cells proliferate and penetrate connective tissue. They may—or may not—maintain contact with the surface. When contact is maintained, exocrine glands are formed; without contact, endocrine glands are formed. The cells of endocrine glands can be arranged in cords or in follicles. The lumens of the follicles accumulate large quantities of secretions; cells of the cords store only small quantities of secretions in their cytoplasm. (Redrawn and reproduced, with permission, from Ham AW: Histology, 6th ed. Lippincott, 1969.) Figure 4–21. Functional classification of exocrine glands. Different cellular secretion processes are used in exocrine glands, depending on what substance is being secreted. (a): Merocrine glands secrete products, usually containing proteins, by means of exocytosis at the apical end of the secretory cells. Most exocrine glands are merocrine. (b): Holocrine gland secretion is produced by the disintegration of the secretory cells themselves as they complete differentiation which involves becoming filled with product. Sebaceous glands of hair follicles are the best examples of holocrine glands. (c): Apocrine gland secretion involves loss of a large membrane—enclosed portion of apical cytoplasm, usually containing one or more lipid droplets. This apical portion of the cell may subsequently break down to release its contents during passage into the duct. Apocrine secretion, along with merocrine secretion, is seen in General structure of exocrine glands. Exocrine glands by definition have ducts that lead to another organ or the body surface. Inside the gland, the duct runs through the connective tissue of septa and branches repeatedly, until its smallest branches end in the secretory portions of the gland. Mechanisms of exocrine gland secretion. Three basic types of secretion are used by cells of exocrine glands, depending on what substance is being secreted. (a)Merocrine secretion releases products, usually containing proteins, by means of exocytosis at the apical end of the secretory cells. Most exocrine glands are merocrine. (b)Holocrine secretion is produced by the disintegration of the secretory cells themselves as they complete their terminal differentiation, which involves becoming filled with product. Sebaceous glands of hair follicles are the best examples of holocrine glands. (c)Apocrine secretion involves loss of membrane-enclosed apical cytoplasm, usually containing one or more lipid droplets. Apocrine secretion, along with merocrine secretion, is seen in mammary glands. Holocrine secretion in a sebaceous gland. In holocrine secretion, best seen in the sebaceous gland adjacent to hair follicles, entire cells fill with a lipid-rich product as they differentiate. Mature (terminally differentiated) cells separate and completely disintegrate, releasing the lipid that serves to protect and lubricate adjacent skin and hair. Sebaceous glands lack myoepithelial cells; cell proliferation inside a dense, inelastic connective tissue capsule continuously forces product into the duct. (X200; H&E) Figure 4–23. Section of the secreting portion of a mammary gland; apocrine secretion is characterized by the discharge of the secretion product with part of the cytoplasm (arrows). PSH stain. Medium magnification. Serous cells. The small serous acini of the exocrine pancreas each have 5-10 cells facing a very small central lumen. Each acinar cell is roughly pyramidal, with its apex at the lumen. (a) As seen by light microscopy, the apical ends are very eosinophilic due to the abundant secretory granules present there. The cells’ basal ends contain the nuclei and an abundance of RER, making this area basophilic. A small duct (D) is seen, but lumens of acini are too small to be readily visible. The enclosed area is comparable to that shown in part b. (X300; H&E) (b) A portion of one acinar cell is shown ultrastructurally, indicating the abundant RER (R), a Golgi complex (G), apical secretory HISTOFYSIOLOGIE VAN EPITHEEL WEEFSELS Lamina propria = BW onder de lamina basalis Functie: > ondersteuning van het epitheel >Hechten van het epitheel aan de aanliggende structuren Papillae (evaginaties) om het oppervlakte te vergroten # papillae ~ stress Polariteit > Epithelia hebben een apicale en basale kant > Geen bloedvaten (capillairen tot in de lamina propria) => diffusie van nutriënten door de LP Vernieuwing van epithelia Continue vernieuwing door mitotische activiteit (stamcellen) Regeneratievermogen: van 1 dag tot maanden > Metaplasie: transformatie van een soort epitheel in een ander >> b.v.: geciliëerd pseudo-stratified epitheel in de bronchi wordt plaveisel epitheel SPECIFIEKE METABOLE FUNCTIES Ion transporterende cellen Alle cellen zijn in staat om ionen te transporteren b.v.: actief transport van Na ionen van intracellulair (5-15mmol/L) naar extracellulair (140mmol/L). Transcellulair transport (b.v. renale tubulus) van apex naar basaal (424) - Apex: permeabel voor Na+ Basale oppervlakte (actief transport): > Diepe invaginaties van de basale plasmamembraan > interdigitatie van basale uitsteeksels > Na+/K+-ATPase in deze invaginaties van de PM > Mitochondria tussen de invaginaties > Tight junctions aan de apicale zijde! > Richting: beiden Figure 4–24. Ultrastructure of a proximal convoluted tubule cell of the kidney. Invaginations of the basal cell membrane outline regions filled with elongated mitochondria. This typical disposition is present in ion-transporting cells. Interdigitations from neighboring cells interlock with those of this cell. Protein being absorbed by pinocytosis and digested by lysosomes is shown in the upper left portion of the diagram. Sodium ions diffuse passively through the apical membranes of renal epithelial cells. These ions are then actively transported out of the cells by Na+/K+-ATPase located in the basolateral membranes of the cells. Energy for this sodium pump is supplied by nearby mitochondria. Features of absorptive cells. A diagram and TEM photo showing the major ultrastructural features of a typical epithelial cell highly specialized for absorption, cells of proximal convoluted tubule of the kidney. The apical cell surface has a brush border consisting of uniform microvilli (MV) that increase the area of that surface to facilitate all types of membrane transport. Vesicles formed during pinocytosis may fuse with lysosomes as shown in (a) or mediate transcytosis by secreting their contents at the basolateral cell membrane. The basal cell surface is also enlarged, here by invaginations of the cell membrane, which are associated with mitochondria (M) providing ATP for active transport. Basolateral membrane infoldings from neighboring cells (the more heavily stippled structures) also with mitochondria interdigitate with those of this cell. Various ions entering through the apical membranes of renal epithelial cells undergo active transport out of the cells across the basolateral membrane. Immediately below the basal lamina shown in (b) is a capillary (C) that removes water and other substances absorbed across the epithelium. Junctional complexes between individual cells separate the apical and basolateral compartments on either side of the epithelium. Epithelial cells also show lateral membrane interdigitations with neighboring cells. Figure 4–25. Ion and fluid transport can occur in different directions, depending on which tissue is involved. A: The direction of transport is from the lumen to the blood vessel, as in the gallbladder and intestine. This process is called absorption. B: Transport is in the opposite direction, as in the choroid plexus, ciliary body, and sweat gland. This process is called secretion. Note that the presence of occluding junctions is necessary to maintain compartmentalization and consequent control over ion distribution. Ion and water absorption and secretion. Ion and water transport across epithelia can occur in either direction, depending on the organ involved. (a) Absorption is the process of transport from an organ or duct’s lumen to capillaries near the epithelial basement membrane and involves movement from the apical to the basolateral cell membrane domains. Absorption occurs, for example, in the epithelium of the gallbladder and intestine where it serves to concentrate bile or obtain water and ions from digested material. (b) Secretion involves transport in the other direction from the capillaries into a lumen, as in many glands and the choroid plexus. Secretion by epithelial cells removes water from the neighboring interstitial fluid or plasma and releases it as part of the specialized aqueous fluids in such organs. No matter whether an epithelium is involved in absorption or secretion, apical occluding junctions are necessary to maintain tight separation of the apical and basolateral compartments of either side of the epithelium. Sereuze cellen (4-26) (4-27) (4-28) (4-29) b.v. Acinaire pancreas (proteases, amylase, lipase, nucleases => proenzymes) > Polyhedrische of pyramidale cellen Centrale ronde nucleus Sterke polariteit >Basaal: stapeling van veel RER > Apicaal: sterk ontwikkeld GC secreet granula >> zymogeen granulen: maturatie >> secretie na stimulatie (exocytosis) >>> functie van de motor Figure 4–26. Diagram of a serous (pancreatic acinar) cell. Note its evident polarity, with abundant basal rough endoplasmic reticulum. The Golgi complex and zymogen granules are in the apical region. To the right is a scale indicating the approximate time necessary for each step. Figure 4–27. Electron micrograph of a pancreatic cell. Note the nucleus, mitochondria, Golgi complex, secretory (zymogen) granules in various stages of condensation, and rough endoplasmic reticulum. x13,000. (Courtesy of KR Porter.) Figure 4–28. Electron micrograph of part of a pancreatic acinar cell showing a condensing vacuole (C), which is presumed to be receiving a small quantity of secretory product (arrow) from the Golgi complex (G). M, mitochondrion; RER, rough endoplasmic reticulum; S, mature condensed secretory (zymogen) granule. x40,000. Mucus-Secreterende cellen b.v. goblet cel (4-30) (4-31) (4-32) Apicale zijde: mucines = hydrofiele glycoproteïnes Basale zijde: > nucleus > RER GC: goed ontwikkeld Boven de nucleus Glycolisatie van proteïnen in het ER en het GC Mucines worden gehydrateerd na vrijstelling => mucus = elastische gel (4-33) (4-34) Mucus secretie in Darm Maag Speeksel klieren luchtwegen Genitale tractus Figure 4–30. Diagram of a mucus-secreting intestinal goblet cell showing a typically constricted base, where the mitochondria and rough endoplasmic reticulum (RER) are located. The protein part of the glycoprotein complex is synthesized in the endoplasmic reticulum. A well-developed Golgi complex is present in the supranuclear region. (Redrawn after Gordon and reproduced, with permission, from Ham AW: Histology, 6th ed. Lippincott, 1969.) Figure 4–31. Electron micrograph of a goblet cell from the small intestine. The rough endoplasmic reticulum is present mainly in the basal portion of the cell (R), while the cell apex is filled with light secretory vesicles or granules (SG) some of which are being discharged. The Golgi complex (G) lies just above the nucleus. Typical columnar absorptive cells with microvillar borders (M) lie adjacent to the goblet cell. x7000. (Reproduced, with permission, from Junqueira LCU, Salles LMM. Ultra-Estrutura e Função Celular, Edgard Blücher, 1975.) Figure 16–4. Ultrastructure of serous and mucous cells. A micrograph of a mixed acinus from a submandibular gland shows both serous and mucous cells. Mucous cells (upper area shown here) have large, hydrophilic granules like those of goblet cells. Serous cells (lower area) have small, dense granules that stain more intensely with most stains. X2500. (With permission, from John D. Harrison, Department of Oral Pathology, King’s College, London.) Figure 4–32. Intestinal villi stained by the PAS technique, a procedure that detects some polysaccharides. Note the positive reaction in the goblet cells and brush border, which consists of microvilli. Counterstained with hematoxylin. Myoepitheliale cellen (4-36) > Rond exocriene klieren >Tussen de lamina basale en de basale kant van de secretoire of ductale cellen >Gap junctions en desmosomes verbinden MEP en epitheelcellen Bevatten: actine-myosine Kunnen samentrekken Figure 4–36. Electron micrograph of salivary gland showing secretory cells in the upper left; in the lower right is a myoepithelial cell that embraces the secretory acinus. Contraction of the myoepithelial cell compresses the acinus and aids in the expulsion of secretory products. Myoepithelial cells. (a) The TEM shows two salivary gland cells containing secretory granules, with an associated myoepithelial cell (M). (X20,000) (b) A myoepithelial cell immunostained brown with antibodies against actin shows its association with cells of an acinus stained by H&E. Contraction of the myoepithelial cell compresses the acinus and aids in the expulsion of secretory products into the duct. (X200) Steroid-Secreterende cellen(4-37) v. in de testes, bijnierschors, ovarium Centrale nucleus Rijk in lipiden druppels Veel SER (met enzymes om cholesterol te synthetiseren – transformatie tot hormonen) Mitochondria (tubulaire cristae) > energie productie > enzymes om cholesterol zijketens te splitsen tot pregnolon > samenwerking ts. SER en mitochondriën > geen opslag Figure 4–37. Diagram of the ultrastructure of a hypothetical steroid-secreting cell. Note the abundance of the smooth endoplasmic reticulum (SER), lipid droplets, Golgi complex, and lysosomes. The numerous mitochondria have mainly tubular cristae. They not only produce the energy necessary for the activity of the cell but are also involved in steroid hormone synthesis. Rough endoplasmic reticulum (RER) is also shown. Figure 20–13. Ultrastructure of cortical adrenalocytes. TEM of two adjacent steroid—secreting cells from the zona fasciculate shows features typical of steroid —producing cells: lipid droplets (L) containing cholesterol esters, mitochondria (M) with tubular and vesicular cristae, abundant smooth endoplasmic reticulum (SER), and autophagosomes (A), which remove mitochondria and SER between periods of active steroid synthesis. Also seen are the euchromatic nuclei (N), a Golgi apparatus (G), RER and lysosomes. X25,700.