Obsah obrázku porcelán, keramické nádobí Popis byl vytvořen automaticky 1 2 EPITHELIAL TISSUE GENERAL FEATURES OF ALL EPITHELIAL TISSUES •Highly cellular, epithelial cells vary in shape and size •Numerous intercellular junctions for attachment and anchorage •Avascular •High proliferative capacity (especially in epithelial membranes, to replace continual sloughing of cells from free surface) •Most rest on a basement membrane: extracellular structure that separates epithelial cells from underlying connective tissue. It provides structural support to epithelial tissues and helps anchor the cells in place. is composed of proteins, glycoproteins, and collagen fibers, contributing to the overall stability and integrity of epithelial layers. It also plays a crucial role in regulating the exchange of molecules between the epithelium and the underlying tissue. • •The embryological origin: epithelial tissues are derived from all of the embryological germ layers (from ectoderm e.g., the epidermis; from endoderm e.g., the lining of the gastrointestinal tract; from mesoderm e.g., the inner linings of body cavities). • •Free and basal surfaces of epithelia •Basal surface contacts the basal lamina of the basement membrane. •Free surface interfaces with the external environment or spaces within the body. • • 3 EPITHELIAL TISSUE •Polarity – epithelia exhibit functional and morphologic polarity. A polarized cell is one that exhibits contrasting properties or structures on opposite sides of the cell. Because epithelial tissues face a free surface, the function of the apical surface is often very different from that at the base of the cell. This diversification is reflected by the non-homogeneous distribution of organelles. • •Function of epithelium: •Covering of external surfaces •Lining of internal surfaces •Protection •Absorbtion •Secretion •Sensory function •Contraction • •Types of epithelium: •Covering and lining epithelium •Glandular epithelium 4 EPITHELIAL TISSUE CLASSIFICATION OF LINING AND COVERING EPITHELIUM •Shape of superficial cells •Number of cell layers •Presence of specialized structures (cilia, microvili, keratin • •Shape of superficial cells •Squamous •Cells are much wider than tall. •Nucleus is highly flattened. • •Cuboidal •Cells are of equal height and width. •Nucleus is spherical. • •Columnar •Cells are much taller than they are wide. •Nucleus is oval shaped, generally located in the mid to lower portions of the cell. • • 5 EPITHELIAL TISSUE CLASSIFICATION OF LINING AND COVERING EPITHELIUM • •Number of cell layers •Simple epithelium •One cell layer thick •All cells rest on the basement membrane (basal surface) and all cells face the free surface. • •Simple squamous •Allows for rapid diffusion across the epithelium •Forms the lining of blood vessels, alveoli of the lungs, and internal body cavities •Simple cuboidal •Lines and absorbs •Forms the walls of ducts and tubules •Simple columnar •Lines and absorbs •Forms the lining of the intestines and gall bladder 6 F04_13.jpg F04_14.jpg 7 8 Mesovarium, mesothelium Kidney, Bowman´s capsule 9 10 11 F04_16.jpg 12 13 14 EPITHELIAL TISSUE CLASSIFICATION OF LINING AND COVERING EPITHELIUM • •Pseudostratified •Cells are of various heights. It appears stratified. All cells rest on the basement membrane, but only the tallest cells reach the free surface. Variation in height of the cells and the location of nuclei give the appearance of a stratified epithelium. Frequently ciliated. •Provides protection and surface transport when ciliated. •Forms the lining of much of the respiratory tract and much of the male reproductive system. F04_19.jpg 15 16 EPITHELIAL TISSUE CLASSIFICATION OF LINING AND COVERING EPITHELIUM •Stratified epithelium •More than one cell layer thick •Only the deepest layer of cells contact the basement membrane and only the superficial-most cells have a free surface. •Named according to the shape of the cells at the free surface. • •Stratified squamous •Protects from physical abrasion and prevents desiccation •Two types: •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. • • • F04_17.jpg C:\Users\Iveta\Desktop\GAHY002-002b.jpg 17 Stratified squamous nonkeratinized epithelium oesophagus 18 Stratified squamous keratinized epithelium skin Stratum spinosum - Wikipedia Stratum basale = s. germinosum: a single layer of cells, closest to the dermis. The cells can divide and some move up to the next layer. S. spinosum: „prickle cells“ with a lot of desmosomes, which anchor the cells to each other, with some amounts of keratin. When the cells shrink during fixation, the desmosomes from neighbouring cells remain bound to each other and look like 'prickles' or 'spines → „prickle cells“. S. granulosum: the cells lose their nuclei and organelles and become keratinised. The granules contain a lipid rich secretion, which acts as a water sealant. S. lucidum: only in thick skin. It is a thin transparent layer, difficult to recognise in routine sections. S. corneum: the keratinised layers of dead cells, filled with densely packed keratin. 19 EPITHELIAL TISSUE CLASSIFICATION OF LINING AND COVERING EPITHELIUM • •Stratified cuboidal/columnar •Lines the larger ducts of exocrine glands. • • Stratified cuboidal epithelium, tongue, duct from salivary gland 20 EPITHELIAL TISSUE CLASSIFICATION OF LINING AND COVERING EPITHELIUM •Transitional •Protective function; constructed to expand with distension of the hollow organs it lines •Unique to the urinary system; lines the urinary bladder and ureter 2_1 E:\ImgFiles\GAHY002-002d.jpg F04_18.jpg 21 22 23 EPITHELIAL TISSUE SURFACE SPECIALIZATIONS •Apical domain with special structural surface modification to carry our specific function Microvilli •Finger-like extensions from the free surface of the cell, about 1 micron in height •Are usually present in large numbers on each cell and, collectively, are called a brush or striated border •Contain a core of actin microfilaments •Are relatively non-motile •Increase surface area for absorption •Prominent on cells lining the digestive tract and proximal tubules in the kidney 24 F04_08.jpg F04_09.jpg 25 26 EPITHELIAL TISSUE SURFACE SPECIALIZATIONS •Stereocilia •Large, non-motile microvilli; not cilia •Contain a core of actin microfilaments •Increase surface area •Present on cells lining the epididymis and ductus deferens in the male reproductive tract epididimis 27 28 EPITHELIAL TISSUE SURFACE SPECIALIZATIONS •Cilia •Multiple hair-like extensions from free surface of the cell; 7-10 microns in height •Highly motile; beat in a wave-like motion •Function to propel material along the surface of the epithelium (e.g., in the respiratory system and the oviduct of the female reproductive system) •Core of a cilium is called the axoneme, in which nine pairs of microtubules surround two central, individual microtubules (9 + 2 arrangement). •The axomene of each cilium originates from a basal body that is located at the apex of the cell and is composed of nine triplets of microtubules. 29 Respiratory tract, LM, Mallory trichrome, x400 30 EPITHELIAL TISSUE INTERCELLULAR JUNCTIONS •Specialized structures of the plasma membrane that: •Attach and anchor cells •Establish apical and basolateral membrane domains by sealing adjacent plasma membranes •Provide channels for ionic and metabolic coupling • •Not restricted to epithelial cells; cell junctions occur, however, in large number in epithelial tissues to resist the physical forces acting on the cells. • •Types: Ocluding junctions: •Zonula occludens (tight junction) Adhesive and anchoring junctions: •Zonula adherens (belt desmosome) •Macula adherens (desmozome) •Hemidesmosome – in basal part of cell Communication between adjacent cells: •Gap junctions (nexus) 31 EPITHELIAL TISSUE Types of intercellular junctions • •Tight junction (zonula occludens) •Belt-like, barrier junction around apex of the cell •Provides close apposition of adjacent plasma membranes and occludes the intercellular space •Functions: •Prevents diffusion of material between the intercellular space and the lumen of the organ •Establishes apical and basolateral membrane domains in the cell by preventing the lateral migration of proteins in the plasma membrane F04_06.jpg 32 33 EPITHELIAL TISSUE Types of intercellular junctions • •Adherent junctions •Attach cells to each other or anchor them to the basal lamina; no fusion of the plasma membrane •Types of adherent junctions: •Belt desmosome (zonula adherens). Belt-like junction that encircles the apex of the cell like a barrel strap and is located immediately beneath the zonula occludens; serves to attach adjacent cells together; associated with actin filaments. •Spot desmosome (macula adherens). Disk-like junctions scattered over the surface of the cell, which are paired with similar structures in adjacent cells; associated with intermediate filaments (e.g., keratin filaments in epithelial cells). •Hemidesmosome. Represents a "half desmosome"; these junctions anchor the basal surface of the cell to the basal lamina. •Junctional complex. Consists of the zonula occludens, zonula adherens, and desmosomes; because these structures cannot be resolved as separate structures at the light microscopic level, they appear as a single, bar-shaped, dark region at the apical corners of adjacent cells. The term terminal bar was used by early microscopists to define the zonula occludens and zonula adherens at the light microscopic level. • 34 EPITHELIAL TISSUE Belt desmosome (zonula adherens). Belt-like junction that encircles the apex of the cell like a barrel strap and is located immediately beneath the zonula occludens; serves to attach adjacent cells together; associated with actin filaments. 35 EPITHELIAL TISSUE Spot desmosome (macula adherens). Disk-like junctions scattered over the surface of the cell, which are paired with similar structures in adjacent cells; associated with intermediate filaments (e.g., keratin filaments in epithelial cells). 36 EPITHELIAL TISSUE Hemidesmosome. Represents a "half desmosome"; these junctions anchor the basal surface of the cell to the basal lamina. 37 EPITHELIAL TISSUE Junctional complex. Consists of the zonula occludens, zonula adherens, and desmosomes; because these structures cannot be resolved as separate structures at the light microscopic level, they appear as a single, bar-shaped, dark region at the apical corners of adjacent cells. The term terminal bar was used by early microscopists to define the zonula occludens and zonula adherens at the light microscopic level. 38 39 40 EPITHELIAL TISSUE Gap junction •Gap junctions (protein channels connecting plasma membranes) consist of connexons, six transmembrane proteins clustered in a rosette that form a central pore. Connexons from adjacent cells abut one another, forming a continuity between cells. •Provides metabolic and electrical continuity (coupling) via the pores between cells 41 42 EPITHELIAL TISSUE MORPHOLOGIC SPECIALIZATIONS OF THE LATERAL CELL SURFACE Cellular interdigitations •Lateral cell surface folds create interdigitating cytoplasmatic processes of adjoining cells. •Infoldings increase the lateral surface. •Electrolyte active fluid transport (intestinal, gallblader epithelium) 43 EPITHELIAL TISSUE BASEMENT MEMBRANE •Basement membrane •The basement membrane is composed of a basal lamina and a reticular lamina. •The basal lamina is secreted by the epithelial cells and consists of the lamina lucida and the lamina densa. A similar structure is also present in muscle and nervous tissue, where it is referred to as an external lamina. •The reticular lamina is secreted by fibroblasts located in the underlying connective tissue. •Functions of the basement membrane: •Provides support and attachment for the epithelial cells •Acts as a selective diffusion barrier • F04_02 44 Ultrastructural components of the basal lamina. A: Basal lamina, hemidesmosomes (arrows) and underlying reticular fibres of the reticular lamina. B: The basal lamina (BL) is shown to have a dense layer with a clear on each side. The underlying dermis contain anchoring fibrils (arrows) of collagen which help anchor the epithelium to the underlying connective tissue. Hemidesmosome (H) occur at the epithelial-connective tissue junction. 45 fig084 46 47 48 EPITHELIAL TISSUE MORPHOLOGIC MODIFICATIONS OF THE BASAL CELL SURFACE Basal Labyrinth •Many cells that transport fluid have infoldings at the basal cell surface. •They significantly increase the surface area of the basal cell domain, allowing for more transport proteins and channels to be present. •Prominent infoldings – cells with active transport of molecules (e.g., in proximal and distal tubules of the kidney) •Mitochondria – typically concentrated, vertically oriented within the folds, energy for active transport fig083.jpg 49 Cell polarity - examples 50 EPITHELIAL TISSUE GLANDULAR EPITHELIAL TISSUES GENERAL CONCEPTS •Develop from or within a lining or covering epithelium •Secretory cells may •Differentiate but remain in the lining epithelium •Invaginate into the underlying connective tissue and remain attached to the lining epithelium •Invaginate into the underlying connective tissue but lose their connection to the epithelium • 51 EPITHELIAL TISSUE EXOCRINE VS. ENDOCRINE GLANDS Major classification of glands, which is based on the method by which their secretory product is distributed. •Exocrine glands (retains connection with surface epithelium) •Secretory products are released onto an external or internal epithelial surface, either directly or via a duct or duct system. •Secretory cells display polarized distribution of organelles. • •Endocrine glands (no connection with surface epithelium) •No ducts; secretory products are released directly into the extracellular fluid where they can affect adjacent cells (paracrine secretion) or enter the bloodstream to influence cells throughout the body (endocrine secretion). •No polarization of organelles, except the thyroid gland and enteroendocrine cells of the digestive tract. •Secretory products are called hormones. • 52 EPITHELIAL TISSUE GLANDULAR EPITHELIAL TISSUES METHODS OF PRODUCT RELEASE FROM GLANDULAR CELLS •Merocrine. Secretory product is released by exocytosis of contents contained within membrane-bound vesicles. This method of release is used by both exocrine and endocrine glands. Examples are digestive enzymes from pancreatic acinar cells and insulin from pancreatic islet cells. • •Apocrine. Secretory material is released in an intact vesicle along with some cytoplasm from the apical region of the cell. This method of release is used by exocrine glands only. An example is the lipid component of the secretory product of the mammary gland. • •Holocrine. Entire cell is released during the secretory process. Cells that are released may be viable (oocyte or sperm) or dead (sebaceous glands). This method of release is used by exocrine glands only. • •Diffusion. Secretory product passes through the cell membrane without the formation of secretory granules. Examples are steroid hormones. This method of release is used by endocrine glands only. • 53 EPITHELIAL TISSUE 54 55 EPITHELIAL TISSUE TYPES OF SECRETORY PRODUCTS (Exocrine glands) •Mucus. Thick, viscous, glycoprotein secretion •Secretory cells are usually organized into tubules with wide lumens. •Cytoplasm appears vacuolated, containing mucigen that, upon release, becomes hydrated to form mucus. •Nucleus is flattened and located in the base of the cell. • •Serous. Thin, watery, protein secretion •Secretory cells are usually organized into a flask-shaped structure with a narrow lumen, called an acinus. •Cytoplasm contains secretory granules. •Nucleus is round and centrally located in the cell. • 56 57 58 EPITHELIAL TISSUE CLASSIFICATION OF EXOCRINE GLANDS •Unicellular glands •Individual cells located within an epithelium, such as goblet cells that secrete mucus 59 EPITHELIAL TISSUE CLASSIFICATION OF EXOCRINE GLANDS • •Multicellular glands •Sheet gland. Composed of a surface epithelium in which every cell is a mucus-secreting cell. A sheet gland is unique to the lining of the stomach. 60 EPITHELIAL TISSUE CLASSIFICATION OF EXOCRINE GLANDS •The remaining multicellular glands are classified according to: •The shape(s) of the secretory units •Presence of tubules only •Presence of only acini (singular, acinus) or alveoli (singular, alveolus) (these two terms are synonymous), which are flask-shaped structures •Presence of both tubules and acini •The presence and configuration of the duct •Simple. No duct or a single, unbranched duct is present. •Compound. Branching duct system 61 EPITHELIAL TISSUE CLASSIFICATION OF EXOCRINE GLANDS •Classification and types of multicellular glands • •Simple tubular. No duct; secretory cells are arranged like a test tube that connects directly to the surface epithelium (e.g., intestinal glands). •Simple, branched tubular. No duct; tubular glands whose secretory units branch (e.g., fundic glands of stomach) •Simple, coiled tubular. Long unbranched duct; the secretory unit is a long coiled tube (e.g., sweat glands). •Simple, branched acinar (alveolar). Secretory units are branched and open into a single duct (e.g., sebaceous glands). 62 63 64 65 EPITHELIAL TISSUE CLASSIFICATION OF EXOCRINE GLANDS •Classification and types of multicellular glands • •Compound tubular. Branching ducts with tubular secretory units (e.g., Brunner's gland of the duodenum) •Compound acinar (alveolar). Branching ducts with acinar secretory units (e.g., parotid salivary gland) •Compound tubuloacinar (alveolar). Branching ducts with both tubular and acinar secretory units (e.g., submaxillary salivary gland) 66 67 68 EPITHELIAL TISSUE SPECIAL FEATURES OF SOME EXOCRINE GLANDS Serous demilunes •Consist of a "cap" of serous cells around the end of a mucous tubule; appear half-moon shaped in section Seromucous, compound tubuloacinar gland. The submandibular salivary glands have both mucous and serous secretory units, typicaly shaped as acini and tubules respectively. 69 EPITHELIAL TISSUE SPECIAL FEATURES OF SOME EXOCRINE GLANDS Myoepithelial cells •Resemble smooth muscle cells in their fine structure but are of epithelial origin; prominent in sweat and mammary glands, they surround secretory units, lying inside the basement membrane, and aid in the expulsion of secretory products from the gland. • F04_35.jpg 70 EPITHELIAL TISSUE DUCT SYSTEM OF COMPOUND, EXOCRINE GLANDS •Intralobular ducts. Contained within a lobule; simple cuboidal to columnar epithelium •Interlobular ducts. Receive numerous intralobular ducts; located in the connective tissue between lobules; stratified columnar epithelium •Excretory (main) duct. Macroscopic duct draining the entire gland • 71 72 EPITHELIAL TISSUE ENDOCRINE GLANDS •No ducts; generally, cells are not polarized • •Occurrence: •Unicellular (e.g., enteroendocrine cells of the digestive tract); these cells do show polarity because they are located within an epithelium and secrete away from the free surface of the epithelium. •Small clusters of cells (e.g., islet of Langerhans in pancreas) •Organs (e.g., thyroid gland, adrenal gland) • •Secretory cells of multicellular glands are usually arranged as plates or cords. The thyroid gland, where the cells form fluid-filled spheres, is an exception to this pattern. • •Highly vascular with fenestrated capillaries • •Secretory products are called hormones. Hormones can be: •Derived from amino acids (e.g, thyroxine and epinephrine) •Peptides and proteins (e.g., insulin and oxytocin) •Steroids (e.g., testosterone and cortisol); steroid-secreting cells display mitochondria with tubular cristae and contain large amounts of lipid droplets and smooth endoplasmic reticulum. • •Secrete by the merocrine or diffusion methods only 73 F04_36.jpg –Steroid-secreting cells display mitochondria with tubular cristae and contain large amounts of lipid droplets and smooth endoplasmic reticulum http://classes.kumc.edu/som/cellbiology/organelles/mito/img/nr08.gif 74 75 EPITHELIAL TISSUE EXAMPLES OF GLANDULAR EPITHELIAL CELLS •Ion transporting cells •Serous secretory cells •Mucous secretory cells •Neuroendocrine cells •Myoepithelial cells Ion-transporting cells •Deep invaginations of basal cell membranes •Zonula occludens •Mitochondria in basal cytoplasm provide energy for ion transport •Examples: proximal tubules in kidney 77 EPITHELIAL TISSUE Serous secretory cells •Large rounded nucleus and abundant rough ER, Golgi and secretory granules •Examples: pancreatic acinar cells, serous cells in salivary glands F04_27.jpg 78 EPITHELIAL TISSUE Mucous secretory cells •Abundant rough ER, Golgi and secretory granules •Produce mucins (protective, lubricant glycoproteins) •Examples: mucous cells in stomach, goblet cells in small and large intestine, and mucous cells in salivary glands • • F04_31.jpg Goblet cells in small intestine F04_30.jpg F04_33.jpg Mucous secretory cells, oesophagus 81 EPITHELIAL TISSUE Neuroendocrine cells •Dense secretory granules in cytoplasm contain polypeptides and/or amines (like epinephrine and norepinephrine) •Scattered throughout the body F04_34.jpg Myoepithelial cells •Spindle-shaped cells found in glandular epithelial between basal lamina and basal cytoplasm •Embrace gland acini •Contain actin: contract and squeeze out secretory product