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  • covering or protective - cells cover external and internal surfaces of human body and protect underlying tissues against loss moisture and mechanical damage,
  • Goblet cells are glandular simple columnar epithelial cells whose sole function is to secrete mucin , which dissolves in water to form mucus .
  • Lecture7

    1. 1. Lecture 7 ESS_2nd semester <ul><li>Epithelial tissue – definition , classification and histogenesis </li></ul><ul><li>Overview of covering and glandular epithelia . Characteristics of glandular cells </li></ul><ul><li>Absorptive, respiratory, and sensory epithelia </li></ul>
    2. 2. <ul><li>T issues of the adult and their classification </li></ul><ul><li>a tissue = a complex of similar cells specialized in common direction and able to perform a common function </li></ul><ul><li>4 primary (basic, fundamental) tissues </li></ul><ul><li> - epithelial tissue (epithelium) </li></ul><ul><li> - connective and supporting tissues </li></ul><ul><li> - muscle (muscular) tissue </li></ul><ul><li> - nerve tissue </li></ul><ul><li>tissues form elementary components of organs </li></ul><ul><li>t he occurrence, arrangement and proportions of tissues in individual organs are different and are object of study in the microscopic anatomy </li></ul>
    3. 3. Epithelial tissue is composed of cells that are in close apposition with one another; among cells there is present only a small amount of intercellular substance e pithelial cells are usually of regular form without extensive cytoplasmic processes a dhesion between the cells is very strong e pithelia derive from the all germ layers Connective and supporting tissues unlike epithelia, contain cells that are separated from one another by intervening spaces , these contain intercellular material or substance produced by cells t he intercellular substance consists of two components: fibers and amorphous ground substance c onnective and supporting tissues are always of mesenchymal origin Muscle tissue is composed of elongated cells that are able to contract f or this function cells are well adapted as they contain contractile proteins: actin and myosin cells or muscle fibers tend to be aggregated in bundles that are conspicuously different from the surroundings tissues t wo types of muscle tissue are distinguished: smooth , skeletal and cardiac s mooth muscle tissue derives from the mesenchyme, striated muscle tissue from the mesoderm Nerve tissue consists of nerve cells - neurons , and associated supporting cells of various type called neuroglia n eurons are highly specialized cells that show ability to receive, generate and transmit nerve impulses e xcept the microglia, the nervous tissue derives from the neuroectoderm
    4. 4. <ul><li>Epithelial tissue </li></ul><ul><li>is composed of cells that are in close apposition with one another; among cells only a small amount of intercellular substance is present </li></ul><ul><li>e pithelial cells are usually of regular form without extensive cytoplasmic processes </li></ul><ul><li>a dhesion between cells is very strong </li></ul><ul><li>e pithelia derive from the all germ layers </li></ul><ul><li>e pithelial tissue is avascular - it contains no blood capillaries </li></ul><ul><li>it exhibit s a remarkable degree of physiologic regeneration </li></ul>
    5. 5. <ul><li>Classification of the epithelial tissue </li></ul><ul><li>a) according to the arrangement of cells - 2 forms </li></ul><ul><li>- epithelial membranes either sheets - composed of one or more cell layers in </li></ul><ul><li>thickness </li></ul><ul><li>or </li></ul><ul><li>- solid cords or tubules (rarely follicles) that have developed as out- growths from an </li></ul><ul><li>epithelial sheet </li></ul><ul><li>cords and tubulus especially occur in glands </li></ul><ul><li>b) according to the function of cells </li></ul><ul><li>covering or protective - cells cover external and internal surfaces of human body and protect underlying tissues against loss moisture and mechanical damage, </li></ul><ul><li>secretory or glandular - cells are engaged in synthetic processes and product substances with defined functional destination, </li></ul><ul><li>absorptive - cells transport substances from the alimentary canal and renal tubules into the systemic circulation, </li></ul><ul><li>respiratory - cells take part in the transport of oxygen and carbon dioxide from alveoli into the blood, </li></ul><ul><li>sensory - cells are specialized for reception of stimuli (olfactory epithelium, taste buds etc.) </li></ul><ul><li>a given epithelium may serve one or more functions, depending upon the cell types presented, </li></ul><ul><li>eg. protective and secretory functions of the epithelium in the stomach or protective and absorptive </li></ul>
    6. 6. <ul><li>Covering epithelia /e pithelial membranes / </li></ul><ul><li>common features: </li></ul><ul><li>cells always rest upon a basement membrane </li></ul><ul><li>it attach es the m to underlying connective tissue </li></ul><ul><li>t he basemenet membrane is thin and composed of delicate reticular fibers that are </li></ul><ul><li>embedded in a gel-like mucopolysaccharide substance </li></ul><ul><li>i n ordinary staining procedures ( eg. using hematoxylin e and eosin ), the membrane is </li></ul><ul><li>not visible but it stains with PAS technique </li></ul><ul><li>epithelial cells are mostly polarized </li></ul><ul><li>lateral and apical aspects of cells are </li></ul><ul><li>subjects of various modifications : </li></ul><ul><li>microvilli, motile cilia </li></ul><ul><li>interdigitations </li></ul><ul><li>and intercellular junctions </li></ul><ul><li>spot and belt desmosome, gap junctions </li></ul><ul><li>and occluding junctions) </li></ul>
    7. 7. <ul><li>two types: </li></ul><ul><li>simple and stratified epithelia </li></ul><ul><li>t he simple epithelia consist of single layer of cells, all of which are in </li></ul><ul><li>contact with the basement membrane </li></ul><ul><li>t he stratified epithelia are composed of two or more layers of cells, of </li></ul><ul><li>which only basal is in contact with the basement membrane and remainder </li></ul><ul><li>layer superimposed one upon the other </li></ul><ul><li>the both are further subdivided according to the shape of cells : </li></ul><ul><li>t he component cells may be </li></ul><ul><li>squamous - the width and depth of the cell is greater than its height; </li></ul><ul><li>cuboidal - the width, depth and height are approximately the same; and </li></ul><ul><li>columnar - the height of the cell appreciably exceeds the width and depth </li></ul><ul><li>t he classification based on both criteria is : </li></ul>
    8. 8. Simple epithelia: - simple squamous epithelium - simple cuboidal epithelium - simple columnar epithelium - pseudostratified columnar epithelium Stratified epithelia: - stratified squamous epithelium - stratified columnar/ cuboidal epithelium - transitional epithelium
    9. 9. <ul><li>Simple squamous epithelium </li></ul><ul><li>cells are flattened </li></ul><ul><li>v iewed from the surface they appear as fairly large cells with clear cytoplasm and a n oval </li></ul><ul><li>nucleus ; c ell boundaries are not visible in ordinary preparations but may be demonstrated by </li></ul><ul><li>the use of impregnation technique </li></ul><ul><li>i n sections the cytoplasm is barely visible, but there is an enlargement of the </li></ul><ul><li>cell at center where the nucleus is locate d </li></ul><ul><li>c hief distribution : </li></ul><ul><li>the parietal layer of capsule of </li></ul><ul><li>Bowman and descending limb of the </li></ul><ul><li>loop of Henle in the kidney </li></ul><ul><li>inner surface of the wall of the </li></ul><ul><li>membranous labyrinth and inner </li></ul><ul><li>surface of the tympanic membrane </li></ul><ul><li>the smallest excretory ducts of </li></ul><ul><li>many glands </li></ul><ul><li>i n two locations, simple squamous epithelium is modified and has special functions </li></ul><ul><li>there is a mesothelium - lines serous cavities and is deriving from the mesoderm a nd </li></ul><ul><li>the endothelium - lines the lumina of blood and lymph vessels and arises from </li></ul><ul><li>the mesenchyme </li></ul>
    10. 11. <ul><li>Simple cuboidal epithelium </li></ul><ul><li>cells of cuboidal epithelium are smaller in surface view than those of the simple </li></ul><ul><li>squamous type and are roughly hexagonal </li></ul><ul><li>c ell boundaries are often clearly visible </li></ul><ul><li>i n vertical sections the cells are square with a spherical nucleus in the center of each </li></ul><ul><li>th e square shape is modified to that of truncated prism when cells line s mall ducts </li></ul><ul><li>c hief distribution : free surface of the ovary, the choroid plexus surface, the inner </li></ul><ul><li>surface of the lens, the excretory ducts of many glands </li></ul><ul><li>Simple columnar epithelium </li></ul><ul><li>the surface view of columnar epithelium is like that of the cuboidal epithelium i n </li></ul><ul><li>sections, </li></ul><ul><li>the cells are seen to be taller than they are broad; </li></ul><ul><li>t he ir nucleus is near the base of the cell </li></ul><ul><li>a s in the case of the cuboidal epithelium , the rectangular shape of columnar cells is </li></ul><ul><li>changed to pyramidal when they are grouped around small lumen </li></ul><ul><li>in order to right diagnosis of this epithelium it is important to select a region , in </li></ul><ul><li>which the section passes through the tissue in a plane perpendicular to the surface </li></ul><ul><li>c hief distribution: the stomach, larger excretory ducts, and uterus; in the case of oviduct </li></ul><ul><li>and small bronchi, apices of some epithelial cells are ciliated </li></ul>
    11. 12. a simple cuboidal epithelium
    12. 13. simple columnar epithelium with striated border (microvilli)
    13. 14. a simple columnar ciliated epithelium (with kinocilia)
    14. 15. <ul><li>Pseudostratified columnar epithelium </li></ul><ul><li>all cells are in contact with the basement membrane but only a part of </li></ul><ul><li>them extends to the free surface </li></ul><ul><li>i n pseudostratified epithelium cells are variable in shape and their nuclei lie at different levels ; </li></ul><ul><li>a ccording to cell height, three different cell types are distinguished: </li></ul><ul><li>small basal or supporting cells </li></ul><ul><li>spindle - shape d cells </li></ul><ul><li>tall superficial cells that are connected with the basement membrane via slender processes , a pices of tall superficial cells are often ciliated </li></ul><ul><li>goblet cells producing mucous </li></ul><ul><li>s ecretion are usually present </li></ul><ul><li>in this epithelium </li></ul><ul><li>chief distribution: </li></ul><ul><li>the respiratory passages </li></ul>
    15. 16. <ul><li>Stratified epithelia </li></ul><ul><li>small cuboidal or columnar cells lie next to the basement membrane </li></ul><ul><li>above them one or more layers of polygonal cells are </li></ul><ul><li>the free surface is covered by a layer of cells that are important for diag n osis </li></ul><ul><li>Stratified squamous epithelium </li></ul><ul><li>the thickness of the epithelium and number of cells vary in different parts of the body </li></ul><ul><li>the shape and arrangement of component cells, however, follow the same general plan : </li></ul><ul><li>consists of small cuboidal or even columnar cells are are covered by a varying number of </li></ul><ul><li>layers of more or less polygonal (polyhedral) cells </li></ul><ul><li>they gradually begin to flatten out toward to the epithelium surface </li></ul><ul><li>they become scale-like form, their nuclei are pyknotic but they may be yet considered as viable </li></ul><ul><li>such epithelium is found in the mouth, the esophagus, the vagina, and on the surface </li></ul><ul><li>of the cornea </li></ul><ul><li>on the exposed outer surfaces , t he stratified squamous epithelium is modified as cornified or </li></ul><ul><li>keratinized </li></ul><ul><li>t he surface cells loose their nuclei and undergo a transformation into dry and dead scales </li></ul><ul><li>t he keratinized stratified squamous epithelium covers the skin as a epidermis </li></ul>
    16. 17. stratified squamous epithelium stratified squamous epithelium (cornified) = epidermis
    17. 19. <ul><li>Stratified columnar epithelium </li></ul><ul><li>it differs f rom the pseudostratified epithelium in having a continuous layer of small, rounded </li></ul><ul><li>cells next to the basement membrane , a varying number (3-4) of more or less polyhedral cells </li></ul><ul><li>and by presence of superficial cells that are tall and prismatic </li></ul><ul><li>the epithelium is truly stratified </li></ul><ul><li>chief distribution : the fornix of the conjunctiva , the cavernous part of the male urethra , </li></ul><ul><li>large excretory ducts of some glands </li></ul><ul><li>Transitional epithelium </li></ul><ul><li>it consists of several layers of cells </li></ul><ul><li>t he basal cells are like those of stratified columnar epithelium </li></ul><ul><li>a bove them there is a varying number of layers of polygonal or pear-shaped cells , t he cell </li></ul><ul><li>layer at the free surface is composed of large, rather flattened cells, usually described as </li></ul><ul><li>dome shaped </li></ul><ul><li>o ne of dome shaped cell often covers two or three pear-shaped cells that underl ie it </li></ul><ul><li>cells show unusual degree the ability to change their position, sliding over each other </li></ul><ul><li>w hen an organ is distended, the epithelium is reduced to three or four layers and vice versa </li></ul><ul><li>(by organ contraction the cells heap up forming several layers between the basal and surface </li></ul><ul><li>cells) </li></ul><ul><li>chief distribution: it covers the mucosa of the excretory passages from the renal calyces to the </li></ul><ul><li>urethra </li></ul>
    18. 20. transitional epithelium
    19. 21. <ul><li>Secretory /glandular/epithelium </li></ul><ul><li>the epithelium whose cells are able to synthesize special products - secretions </li></ul><ul><li>substances that are for organism and right function of many organs very important </li></ul><ul><li>in many cases they cannot be substituted (GLANDULAR CORDS AND NOT SHEATHS) </li></ul><ul><li>Secretory products are released either upon free surfaces or into blood </li></ul><ul><li>(rarely lymphatic) vessels for distribution / hormones / </li></ul><ul><li>Histophysiology of secretion </li></ul><ul><li>s ecretory process in volves 3 phases as follows: </li></ul><ul><li>ingestion of single substances or precursors from the surrounding or blood </li></ul><ul><li>synthesis of secretory products including their segregation and accumulation </li></ul><ul><li>release of secretory products </li></ul><ul><li>Ingestion of precursors is usually realized by 3 ways: </li></ul><ul><li>- passive diffusion down a concentration gradient, </li></ul><ul><li>- active transport against a concentration gradient using ATP as an energy source, </li></ul><ul><li>- pinocytosis - the way providing of transport of macromolecules across the plasma </li></ul><ul><li>membrane </li></ul>
    20. 22. <ul><li>synthesis of secretory products </li></ul><ul><li>under cooperation of many cell organelles - free ribosomes or unbounded polyribosomes and the rough endoplasmic reticulum </li></ul><ul><li>s ynthesized products are then transferred from this compartment to the Golgi apparatus, where they become final form and are directed to their final destination in each cell </li></ul><ul><li>s ynthetic processes need an energy - is produced by mitochondria </li></ul><ul><li>a ll the mentioned cell organelles are typical of glandular cells </li></ul><ul><li>release or extrusion of secretory </li></ul><ul><li>products </li></ul><ul><li>three modes have been distinguished: </li></ul><ul><li>- merocrine secretion </li></ul><ul><li>- apocrine secretion </li></ul><ul><li>- holocrine secretion </li></ul>
    21. 23. <ul><li>Release of secretion products </li></ul><ul><ul><li>merocrine secretion </li></ul></ul><ul><ul><li>products are released through the cell membrane without the loss any cytoplasm (during the whole secretory cycle ) </li></ul></ul><ul><ul><li>the cell does not change its shape </li></ul></ul><ul><ul><li>goblet cells </li></ul></ul>
    22. 24. <ul><ul><li>apocrine secretion </li></ul></ul><ul><ul><li>by a loss of the apical parts that contain s an accumulated secret ory material </li></ul></ul><ul><ul><li>glandular cells of follicles in thyroid </li></ul></ul><ul><ul><li>apocrine sweet glands </li></ul></ul>
    23. 25. holocrine secretion the discharge of product is a ssociated with a destruction of the whole glandular cells cells of sebaceous glands
    24. 26. <ul><li>secretory cells constitute special organs called glands </li></ul><ul><li>Classification of glands </li></ul><ul><li>With respect to the mode of secretion </li></ul><ul><li>With respect to the number of glandular cells </li></ul><ul><li>With respect to the chemical properties of secreted product </li></ul><ul><li>a) with respect to the mode of secretion: </li></ul><ul><li>exocrine glands - discharge their product via ducts at an external or internal </li></ul><ul><li>surface, </li></ul><ul><li>endocrine glands release their product into the blood or lymph vessels </li></ul><ul><li>have no ducts (ductless glands) </li></ul><ul><li>secretions are called hormones and regulate and coordinate the activities of all the </li></ul><ul><li>cells in the body in cooperation with the nervous system </li></ul><ul><li>b) with respect to the number of glandular cells: </li></ul><ul><li>unicellular glands - the glandular components consist of a single cell among </li></ul><ul><li>other cells t hat are not glandular </li></ul><ul><li>multicellular glands - the glandular components consist of more than one cell </li></ul>
    25. 27. <ul><li>With respect to the mode of secretion </li></ul><ul><li>With respect to the number of glandular cells </li></ul><ul><li>With respect to the chemical properties of secreted product </li></ul><ul><li>With respect to the ducts </li></ul>Exocrine Endocrine Unicellular Multicellular Serous Mucous Seromucous Simple Compound mucous cells or goblet cells and - enteroendocrine (GEP) cells I ntraepithelial glands E xtraepithelial glands secretory units and ducts
    26. 28. <ul><li>Exocrine glands </li></ul><ul><li>or glands of external secretion (eg. Directly into the GIT) </li></ul><ul><li>retain connections with surfaces </li></ul><ul><li>exocrine glands occur as uni - and multicellular ones </li></ul><ul><li>u nicellular glands are </li></ul><ul><li>- mucous cells or goblet cells and </li></ul><ul><li>- enteroendocrine (GEP) cells </li></ul><ul><li>goblet cells are scattered among the columnar </li></ul><ul><li>cells of the simple columnar or </li></ul><ul><li>pseudostratified columnar e pithelia </li></ul><ul><li>c ells secrete mucin Mucous </li></ul><ul><li>e ach cell has an expanded, oval apex filled with </li></ul><ul><li>pale droplets of mucigen and a slender basal </li></ul><ul><li>end containing a compressed nucleus and </li></ul><ul><li>a small amount of deeply staining basophilic </li></ul><ul><li>cytoplasm </li></ul><ul><li>enteroendocrine (GEP) cells </li></ul><ul><li>occur in the wall of the stomach, small and large intestine, bile ducts (hepatic, cystic or common bile) and </li></ul><ul><li>islets of Langerhans </li></ul><ul><li>produce catecholamines or peptidehormones ; for visualization of endocrine cells were formerly used </li></ul><ul><li>impregnation techniques, recently is used TEM or immunohistochemistry </li></ul>goblet cells
    27. 29. <ul><li>M ulticellular glands </li></ul><ul><li>I ntraepithelial glands </li></ul><ul><li>are relative rare and are composed of small accumulations of glandular cells that lie wholly </li></ul><ul><li>within the thickness of an epithelial membrane </li></ul><ul><li>chief distribution: mucous glands of lacunae urethrales Morgagni in the male urethra </li></ul><ul><li>E xtraepithelial glands </li></ul><ul><li>are always in the connective tissue of respective organ or often more deeper </li></ul><ul><li>glnds develop as invaginations of the epithelial membrane into the underlying tissues </li></ul><ul><li>t he extraepithelial glands consist of secretory units and ducts </li></ul><ul><li>secretory units are of three type s: </li></ul><ul><li>tubules (unit is shaped like a tube) </li></ul><ul><li>alveoli (acini) (unit is shaped like a flask) </li></ul><ul><li>tuboalveolar portions (combination of the tube and alveolus which is located at </li></ul><ul><li>one end of the tube) </li></ul><ul><li>ducts may be short and unbranched - simple glands </li></ul><ul><li>or </li></ul><ul><li>ducts are long a branched - compound glands </li></ul><ul><li>t he shape of secretory units and the length of ducts are used in the anatomical </li></ul><ul><li>classification of glands as follows </li></ul>
    28. 30. Multicellular glands
    29. 34. <ul><li>b esides the anatomical classification of glands </li></ul><ul><li>it may be taken in account the chemical properties of secreted product </li></ul><ul><li>the secretory units are divided into </li></ul><ul><li>m ucous units - the shape of straight tubules with a small lum ina </li></ul><ul><li>cells are usually of cuboidal form or of truncated pyramids , nuclei are usually small, dark, and are flattened against the plasma membrane of the cells </li></ul><ul><li>the cytoplasm stains light in HE preparation and may have a foamy appearance </li></ul><ul><li>(alcian blue, mucicarmine, and the PAS reaction are used to demonstrate mucous tubules ) </li></ul><ul><li>serous units - are the form of alveoli and are composed of pyramidal cells whose nuclei are located centrally </li></ul><ul><li>secretion granules are more or less acidophilic and are primarily protein in character </li></ul><ul><li>t he cytoplasm always stains in pink or pinkish purple, more darkly than that of mucous cells </li></ul><ul><li>t he lumen of alveoli (acini) is definite and and smaller in diameter than that of mucous tubules </li></ul><ul><li>seromucous units - mixed units are composed of both mucous and serous cells </li></ul><ul><li>a mixed unit is composed of mucous cells lining a tubular part (short tubule) to which one end is added a collection of serous cells arranged in a half-moon fashion </li></ul><ul><li>t hese serous cells collections are called as demilune complexes or lunulae of Giannuzzi </li></ul><ul><li>i n a great number they are occurred in the human subma ndibular gland </li></ul>
    30. 35. acinar / alveoli /
    31. 36. tubular /tubules /
    32. 37. tubuloacinar / tubules with serous demilunes /
    33. 38. tubule with serous demilune = demilune of Gianuzzi
    34. 39. <ul><li>Absorptive epithelium </li></ul><ul><li>cells whose apices are provided with microvilli </li></ul><ul><ul><li>striated border (enterocytes) </li></ul></ul><ul><ul><li>brush border (cells of proximal tubule of the nephron) </li></ul></ul>
    35. 40. <ul><li>Respiratory epithelium </li></ul><ul><li>is extremely thin and lines alveoli </li></ul><ul><ul><li>membranous pneumocytes (type I) </li></ul></ul><ul><ul><li>granular pneumocytes (type II) secrete pulmonary surfactant </li></ul></ul>
    36. 41. <ul><li>Respira tory epit h el ium </li></ul><ul><li>the type I alveolar cell s or membranous pneumocyte s - flattened, with micropino - </li></ul><ul><li>cytotic vesicles near basal and apical surfaces and thin processes ( 20–25 nm ), cells cover cca </li></ul><ul><li>97 % of the alveolar surface </li></ul><ul><li>the type II alveolar cell s or granular pneumocyte s - cuboidal cell s with secretory </li></ul><ul><li>granules in the cytoplasm ; they contain phospholipid- </li></ul><ul><li>protein and are secreted on the surface of </li></ul><ul><li>epithelium as monomolecular film &quot;lining </li></ul><ul><li>complex&quot; (surfactant) that is primarily </li></ul><ul><li>composed of dipalmitoyl lecithin </li></ul><ul><li>t he layer of surfactant (about 30 nm thick) </li></ul><ul><li>prevents from atelectasis (alveolar collapse) </li></ul><ul><li>lamina basalis </li></ul>
    37. 42. <ul><li>Sensory epithelium </li></ul><ul><li>sensory organs </li></ul><ul><li>sensory areas (fields) </li></ul><ul><ul><li>supporting cells – basal cells </li></ul></ul><ul><ul><li>sensory cells - receipt stimuli from external environment , stimuli induce a special status in their bodies - irritation </li></ul></ul><ul><li>s ensory cells are of two type s: </li></ul><ul><li>a) primary sensory cells ( neuroepithelial cells or unipolar neurons ) </li></ul><ul><li>they consist of receptor area (can be photosensitive or registrate odoriferous substances), cell body and axon or neurite that conducts impulses to the next neuron </li></ul><ul><li>i n the human - olfactory cells in the olfactory epithelium and by rod cells and cone cells in the retina </li></ul><ul><li>b) secondary sensory cells </li></ul><ul><li>are only modified cells of covering epithelia </li></ul><ul><li>cells have spindle-like or flask-like form and consist of only receptor area and body </li></ul><ul><li>the process corresponding to the axon is always missing (s ignals from cells are conducted via dendritic processes of sensory nerves that endon the surface of these cells ) </li></ul><ul><li>cells of taste buds, and hair cells in the membranouslabyrinth </li></ul>
    38. 43. cone cell rod cell
    39. 44. taste bud with taste cells hair cells (utricle)