Epithelial tissue

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Epithelial tissue

• Textus epithelialis
• tepán Jelínek

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Characteristic of epithelium

• cells
• foundation is basal lamina
• minimum of extra cellular matrix
• plenty of intercellular junctions
• various shapes important for classification
• variability of functions

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Basal lamina

• thin layer of extracellular matrix
• collagen IV. type, laminin, proteoglycans
• two layers
• lamina rara, lamina densa
• lamina reticularis part of connective tissue
• foundation for epithelial cells
• produced by epithelial, muscular, Schwanns cells
  and adipocytes

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Basement membrane

• two connected basal laminae
• on the border of two epitheliums
• lung, kidney
• two laminae rarea, one lamina densa
• basal lamina and lamina reticularis
• visible in light microscope
• PAS positive

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Function of basal lamina

• barier
• selection in transport - proteoglycans
• selection of cells laminin
• regeneration
• wound healing, NM junction
• polarisation and migration of epithelial cells

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Polarity

• apical part of cell
• lumen of organ, surface of organ
• basal (basolateral) part of cell
• basal lamina in contact with lamina propria

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Lamina propria

• contains vessels and nerves
• mechanical support of epithelium
• connects epithelium to another layers
• usually undulated surface - papillae

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Specialisations of cellular surface

• free surface
• microvilli, stereocilia, cilia
• lateral surface
• intercellular junctions, interdigitations
• basal surface
• connection with BL, basolateral labyrinth

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Microvilli, stereocilia, cilia

• microvilli
• non-branching projections of cell
• enlargement of cell surface
• stereocilia
• branched non motile projections
• cilia
• non-branching motile projections
• transport of extracellular mass

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Intercellular junctions

• adhesive
• zonula adherens (belt desmosome)
• desmosome (macula adherens)
• hemidesmosome
• occluding
• zonula occludens (tight junction)
• communicating
• gap junction (nexus)

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Intercellular junctions (belt)

• Zonula occludens
• cell. membranes without intercell. space
• five layers of membrane
• Zonula adherens
• intercell. space about 20 nm
• thicker membrane
• connected with cytoskeleton

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Intercellular junction (spot)

• Desmosome
• intercell. space about 30nm
• sometimes dark plate
• connected with cytoskeleton
• hemidesmosome
• connection between cell and BL
• Nexus (gap junction)
• intercell. space about 2 nm
• connexons forms pores for ion transport

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Regeneration of epithelium

• fast and complete
• faster with complete BL
• continual regeneration of cells
• stem cells
• small intestine 3 days
• skin - 27 days

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Types of epithelial cells

• transporting cells
• signalising cells
• synthesizing and exporting cells
• myoepithelial cells
• stem cells

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Transporting cells

• cells transporting ions (active)
• microvilli, basolateral labyrinth
• prox. a dist. tubule of kidney, striated ducts of
  sal. gl.
• cells transporting using pinocytosis
• transport of larger molecules
• pinocytic sacs
• endothelium

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Signalising cells

• release signal molecules
• neurocrine cells (neurons)
• distribution across synapse
• paracrine cells (DNES)
• distribution diffusely to ECM
• secretory granules in basal part of cell
• endocrine cells (suprarenal)
• distribution - transport by blood stream
• ultrastructure depends on type of substance

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Synthesising and trasporting cells

• proteins
• synthesis, modification, storage
• serous cells of sal. gl., serous cells of
  pancreas
• glycoproteins of mucus
• mucus (lighter than cells prod. proteins)
• mucous cells of sal. gl., goblet cells
• steroids
• lipid droplets, sER, tubular MIT

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Myoepihelial cells

• cytokeratins, contractile microfilaments
• acins and tubules of sweat, salivary, lacrimal gl.

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Stem cells

• maternal
• undiferetiated
• regeneration of epithelium

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Classification of epitheliums

• acording to spatial arrangement
• flat
• trabecular
• reticular
• according to function

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Flat epithelium

• according to count of layers
• simple
• stratified
• pseudostratified, transitional
• according to shape of cells
• squamous
• cuboidal
• columnar
• keratinised and non-keratinised

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Trabecular epithelium

• cells in cords
• cords form web
• between cords are capillaries, nerves
• liver, adrenal, pituitary

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Reticular epithelium

• cells are in contact only with their processes
• cells form web
• in holes of web are other cells
• thymus, bone marrow

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Classification according to function

• epithelium covering - skin
• epithelium resorbtional - intestine
• epithelium respiratory - lung
• epithelium sensory olfactory ep.
• epithelium muscular myoepithelial c.
• epithelium germinal testes
• epithelium secretory - glands

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Glandular epithelium

• cells producing and releasing substrate
• this substrate is used by organism
• type of secretion
• merocrine (pancreas)
• apocrine (mammary gland)
• holocrine (sebaceous gland)

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Types of gland

• exocrine
• excretion to lumen of organ
• have ducts
• endocrine
• do not have ducts
• excretion to blood capillaries

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Types of exocrine glands

• according to shape of secretory and excretory
  parts
• simple glands
• compound glands
• tubular
• alveolar (acinar)
• tubulo-acinar

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The end

• next week
• written test Tissues
• slide test