This document provides an overview of epithelial tissue, including its definition, classification, characteristics, and locations in the body. It discusses the four primary tissue types - epithelial, connective, muscle, and nerve tissue. It focuses on epithelial tissue, describing the two main types (simple and stratified), their subtypes based on cell shape, and examples of each epithelium's location and function. Key points covered include that epithelial tissue lines surfaces, derives from all germ layers, and lacks blood vessels.

1. Lecture 7 ESS_2nd semester Epithelial tissue – definition , classification and histogenesis Overview of covering and glandular epithelia . Characteristics of glandular cells Absorptive, respiratory, and sensory epithelia

2. T issues of the adult and their classification a tissue = a complex of similar cells specialized in common direction and able to perform a common function 4 primary (basic, fundamental) tissues - epithelial tissue (epithelium) - connective and supporting tissues - muscle (muscular) tissue - nerve tissue tissues form elementary components of organs t he occurrence, arrangement and proportions of tissues in individual organs are different and are object of study in the microscopic anatomy

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. Epithelial tissue is composed of cells that are in close apposition with one another; among cells only a small amount of intercellular substance is present e pithelial cells are usually of regular form without extensive cytoplasmic processes a dhesion between cells is very strong e pithelia derive from the all germ layers e pithelial tissue is avascular - it contains no blood capillaries it exhibit s a remarkable degree of physiologic regeneration

5. Classification of the epithelial tissue a) according to the arrangement of cells - 2 forms - epithelial membranes either sheets - composed of one or more cell layers in thickness or - solid cords or tubules (rarely follicles) that have developed as out- growths from an epithelial sheet cords and tubulus especially occur in glands b) according to the function of cells covering or protective - cells cover external and internal surfaces of human body and protect underlying tissues against loss moisture and mechanical damage, secretory or glandular - cells are engaged in synthetic processes and product substances with defined functional destination, absorptive - cells transport substances from the alimentary canal and renal tubules into the systemic circulation, respiratory - cells take part in the transport of oxygen and carbon dioxide from alveoli into the blood, sensory - cells are specialized for reception of stimuli (olfactory epithelium, taste buds etc.) a given epithelium may serve one or more functions, depending upon the cell types presented, eg. protective and secretory functions of the epithelium in the stomach or protective and absorptive

6. Covering epithelia /e pithelial membranes / common features: cells always rest upon a basement membrane it attach es the m to underlying connective tissue t he basemenet membrane is thin and composed of delicate reticular fibers that are embedded in a gel-like mucopolysaccharide substance i n ordinary staining procedures ( eg. using hematoxylin e and eosin ), the membrane is not visible but it stains with PAS technique epithelial cells are mostly polarized lateral and apical aspects of cells are subjects of various modifications : microvilli, motile cilia interdigitations and intercellular junctions spot and belt desmosome, gap junctions and occluding junctions)

7. two types: simple and stratified epithelia t he simple epithelia consist of single layer of cells, all of which are in contact with the basement membrane t he stratified epithelia are composed of two or more layers of cells, of which only basal is in contact with the basement membrane and remainder layer superimposed one upon the other the both are further subdivided according to the shape of cells : t he component cells may be squamous - the width and depth of the cell is greater than its height; cuboidal - the width, depth and height are approximately the same; and columnar - the height of the cell appreciably exceeds the width and depth t he classification based on both criteria is :

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. Simple squamous epithelium cells are flattened v iewed from the surface they appear as fairly large cells with clear cytoplasm and a n oval nucleus ; c ell boundaries are not visible in ordinary preparations but may be demonstrated by the use of impregnation technique i n sections the cytoplasm is barely visible, but there is an enlargement of the cell at center where the nucleus is locate d c hief distribution : the parietal layer of capsule of Bowman and descending limb of the loop of Henle in the kidney inner surface of the wall of the membranous labyrinth and inner surface of the tympanic membrane the smallest excretory ducts of many glands i n two locations, simple squamous epithelium is modified and has special functions there is a mesothelium - lines serous cavities and is deriving from the mesoderm a nd the endothelium - lines the lumina of blood and lymph vessels and arises from the mesenchyme

11. Simple cuboidal epithelium cells of cuboidal epithelium are smaller in surface view than those of the simple squamous type and are roughly hexagonal c ell boundaries are often clearly visible i n vertical sections the cells are square with a spherical nucleus in the center of each th e square shape is modified to that of truncated prism when cells line s mall ducts c hief distribution : free surface of the ovary, the choroid plexus surface, the inner surface of the lens, the excretory ducts of many glands Simple columnar epithelium the surface view of columnar epithelium is like that of the cuboidal epithelium i n sections, the cells are seen to be taller than they are broad; t he ir nucleus is near the base of the cell a s in the case of the cuboidal epithelium , the rectangular shape of columnar cells is changed to pyramidal when they are grouped around small lumen in order to right diagnosis of this epithelium it is important to select a region , in which the section passes through the tissue in a plane perpendicular to the surface c hief distribution: the stomach, larger excretory ducts, and uterus; in the case of oviduct and small bronchi, apices of some epithelial cells are ciliated

12. a simple cuboidal epithelium

13. simple columnar epithelium with striated border (microvilli)

14. a simple columnar ciliated epithelium (with kinocilia)

15. Pseudostratified columnar epithelium all cells are in contact with the basement membrane but only a part of them extends to the free surface i n pseudostratified epithelium cells are variable in shape and their nuclei lie at different levels ; a ccording to cell height, three different cell types are distinguished: small basal or supporting cells spindle - shape d cells tall superficial cells that are connected with the basement membrane via slender processes , a pices of tall superficial cells are often ciliated goblet cells producing mucous s ecretion are usually present in this epithelium chief distribution: the respiratory passages

16. Stratified epithelia small cuboidal or columnar cells lie next to the basement membrane above them one or more layers of polygonal cells are the free surface is covered by a layer of cells that are important for diag n osis Stratified squamous epithelium the thickness of the epithelium and number of cells vary in different parts of the body the shape and arrangement of component cells, however, follow the same general plan : consists of small cuboidal or even columnar cells are are covered by a varying number of layers of more or less polygonal (polyhedral) cells they gradually begin to flatten out toward to the epithelium surface they become scale-like form, their nuclei are pyknotic but they may be yet considered as viable such epithelium is found in the mouth, the esophagus, the vagina, and on the surface of the cornea on the exposed outer surfaces , t he stratified squamous epithelium is modified as cornified or keratinized t he surface cells loose their nuclei and undergo a transformation into dry and dead scales t he keratinized stratified squamous epithelium covers the skin as a epidermis

17. stratified squamous epithelium stratified squamous epithelium (cornified) = epidermis

19. Stratified columnar epithelium it differs f rom the pseudostratified epithelium in having a continuous layer of small, rounded cells next to the basement membrane , a varying number (3-4) of more or less polyhedral cells and by presence of superficial cells that are tall and prismatic the epithelium is truly stratified chief distribution : the fornix of the conjunctiva , the cavernous part of the male urethra , large excretory ducts of some glands Transitional epithelium it consists of several layers of cells t he basal cells are like those of stratified columnar epithelium a bove them there is a varying number of layers of polygonal or pear-shaped cells , t he cell layer at the free surface is composed of large, rather flattened cells, usually described as dome shaped o ne of dome shaped cell often covers two or three pear-shaped cells that underl ie it cells show unusual degree the ability to change their position, sliding over each other w hen an organ is distended, the epithelium is reduced to three or four layers and vice versa (by organ contraction the cells heap up forming several layers between the basal and surface cells) chief distribution: it covers the mucosa of the excretory passages from the renal calyces to the urethra

20. transitional epithelium

21. Secretory /glandular/epithelium the epithelium whose cells are able to synthesize special products - secretions substances that are for organism and right function of many organs very important in many cases they cannot be substituted (GLANDULAR CORDS AND NOT SHEATHS) Secretory products are released either upon free surfaces or into blood (rarely lymphatic) vessels for distribution / hormones / Histophysiology of secretion s ecretory process in volves 3 phases as follows: ingestion of single substances or precursors from the surrounding or blood synthesis of secretory products including their segregation and accumulation release of secretory products Ingestion of precursors is usually realized by 3 ways: - passive diffusion down a concentration gradient, - active transport against a concentration gradient using ATP as an energy source, - pinocytosis - the way providing of transport of macromolecules across the plasma membrane

22. synthesis of secretory products under cooperation of many cell organelles - free ribosomes or unbounded polyribosomes and the rough endoplasmic reticulum 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 s ynthetic processes need an energy - is produced by mitochondria a ll the mentioned cell organelles are typical of glandular cells release or extrusion of secretory products three modes have been distinguished: - merocrine secretion - apocrine secretion - holocrine secretion

23. Release of secretion products merocrine secretion products are released through the cell membrane without the loss any cytoplasm (during the whole secretory cycle ) the cell does not change its shape goblet cells

24. apocrine secretion by a loss of the apical parts that contain s an accumulated secret ory material glandular cells of follicles in thyroid apocrine sweet glands

25. holocrine secretion the discharge of product is a ssociated with a destruction of the whole glandular cells cells of sebaceous glands

26. secretory cells constitute special organs called glands Classification of glands With respect to the mode of secretion With respect to the number of glandular cells With respect to the chemical properties of secreted product a) with respect to the mode of secretion: exocrine glands - discharge their product via ducts at an external or internal surface, endocrine glands release their product into the blood or lymph vessels have no ducts (ductless glands) secretions are called hormones and regulate and coordinate the activities of all the cells in the body in cooperation with the nervous system b) with respect to the number of glandular cells: unicellular glands - the glandular components consist of a single cell among other cells t hat are not glandular multicellular glands - the glandular components consist of more than one cell

27. With respect to the mode of secretion With respect to the number of glandular cells With respect to the chemical properties of secreted product With respect to the ducts 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

28. Exocrine glands or glands of external secretion (eg. Directly into the GIT) retain connections with surfaces exocrine glands occur as uni - and multicellular ones u nicellular glands are - mucous cells or goblet cells and - enteroendocrine (GEP) cells goblet cells are scattered among the columnar cells of the simple columnar or pseudostratified columnar e pithelia c ells secrete mucin Mucous e ach cell has an expanded, oval apex filled with pale droplets of mucigen and a slender basal end containing a compressed nucleus and a small amount of deeply staining basophilic cytoplasm enteroendocrine (GEP) cells occur in the wall of the stomach, small and large intestine, bile ducts (hepatic, cystic or common bile) and islets of Langerhans produce catecholamines or peptidehormones ; for visualization of endocrine cells were formerly used impregnation techniques, recently is used TEM or immunohistochemistry goblet cells

29. M ulticellular glands I ntraepithelial glands are relative rare and are composed of small accumulations of glandular cells that lie wholly within the thickness of an epithelial membrane chief distribution: mucous glands of lacunae urethrales Morgagni in the male urethra E xtraepithelial glands are always in the connective tissue of respective organ or often more deeper glnds develop as invaginations of the epithelial membrane into the underlying tissues t he extraepithelial glands consist of secretory units and ducts secretory units are of three type s: tubules (unit is shaped like a tube) alveoli (acini) (unit is shaped like a flask) tuboalveolar portions (combination of the tube and alveolus which is located at one end of the tube) ducts may be short and unbranched - simple glands or ducts are long a branched - compound glands t he shape of secretory units and the length of ducts are used in the anatomical classification of glands as follows

30. Multicellular glands

34. b esides the anatomical classification of glands it may be taken in account the chemical properties of secreted product the secretory units are divided into m ucous units - the shape of straight tubules with a small lum ina 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 the cytoplasm stains light in HE preparation and may have a foamy appearance (alcian blue, mucicarmine, and the PAS reaction are used to demonstrate mucous tubules ) serous units - are the form of alveoli and are composed of pyramidal cells whose nuclei are located centrally secretion granules are more or less acidophilic and are primarily protein in character t he cytoplasm always stains in pink or pinkish purple, more darkly than that of mucous cells t he lumen of alveoli (acini) is definite and and smaller in diameter than that of mucous tubules seromucous units - mixed units are composed of both mucous and serous cells 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 t hese serous cells collections are called as demilune complexes or lunulae of Giannuzzi i n a great number they are occurred in the human subma ndibular gland

35. acinar / alveoli /

36. tubular /tubules /

37. tubuloacinar / tubules with serous demilunes /

38. tubule with serous demilune = demilune of Gianuzzi

39. Absorptive epithelium cells whose apices are provided with microvilli striated border (enterocytes) brush border (cells of proximal tubule of the nephron)

40. Respiratory epithelium is extremely thin and lines alveoli membranous pneumocytes (type I) granular pneumocytes (type II) secrete pulmonary surfactant

41. Respira tory epit h el ium the type I alveolar cell s or membranous pneumocyte s - flattened, with micropino - cytotic vesicles near basal and apical surfaces and thin processes ( 20–25 nm ), cells cover cca 97 % of the alveolar surface the type II alveolar cell s or granular pneumocyte s - cuboidal cell s with secretory granules in the cytoplasm ; they contain phospholipid- protein and are secreted on the surface of epithelium as monomolecular film "lining complex" (surfactant) that is primarily composed of dipalmitoyl lecithin t he layer of surfactant (about 30 nm thick) prevents from atelectasis (alveolar collapse) lamina basalis

42. Sensory epithelium sensory organs sensory areas (fields) supporting cells – basal cells sensory cells - receipt stimuli from external environment , stimuli induce a special status in their bodies - irritation s ensory cells are of two type s: a) primary sensory cells ( neuroepithelial cells or unipolar neurons ) 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 i n the human - olfactory cells in the olfactory epithelium and by rod cells and cone cells in the retina b) secondary sensory cells are only modified cells of covering epithelia cells have spindle-like or flask-like form and consist of only receptor area and body 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 ) cells of taste buds, and hair cells in the membranouslabyrinth

43. cone cell rod cell

44. taste bud with taste cells hair cells (utricle)