Characteristic of epithelium
• cells
Epithelial tissue
Textus epithelialis
– foundation is basal lamina
– minimum of extra cellular matrix
– plenty of intercellular junctions
– various shapes – important for classification
– variability of functions
Štěpán Jelínek
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, Schwann‘s cells
and adipocytes
Function of basal lamina
• barier
– selection in transport - proteoglycans
– selection of cells – laminin
• regeneration
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
Polarity
• apical part of cell
– lumen of organ, surface of organ
• basal (basolateral) part of cell
– basal lamina in contact with lamina propria
– wound healing, NM junction
• polarisation and migration of epithelial
cells
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Lamina propria
• contains vessels and nerves
• mechanical support of epithelium
• connects epithelium to another layers
– usually undulated surface - papillae
Specialisations of cellular
surface
• free surface
– microvilli, stereocilia, cilia
• lateral surface
– intercellular junctions, interdigitations
• basal surface
– connection with BL, basolateral labyrinth
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
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
Intercellular junctions
• adhesive
– zonula adherens (belt desmosome)
– desmosome (macula adherens)
– hemidesmosome
• occluding
– zonula occludens (tight junction)
• communicating
– gap junction (nexus)
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
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
Synthesising and trasporting
cells
• proteins
– synthesis, modification, storage
– serous cells of sal. gl., serous cells of pancreas
• glycoproteins of mucus
Types of epithelial cells
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transporting cells
signalising cells
synthesizing and exporting cells
myoepithelial cells
stem cells
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
Myoepihelial cells
• cytokeratins, contractile microfilaments
• acins and tubules of sweat, salivary,
lacrimal gl.
– mucus (lighter than cells prod. proteins)
– mucous cells of sal. gl., goblet cells
• steroids
– lipid droplets, sER, tubular MIT
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Stem cells
• maternal
• undiferetiated
• regeneration of epithelium
Classification of epitheliums
• acording to spatial arrangement
– flat
– trabecular
– reticular
• according to function
Flat epithelium
• according to count of layers
– simple
– stratified
– pseudostratified, transitional
• according to shape of cells
– squamous
– cuboidal
– columnar
Trabecular epithelium
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cells in cords
cords form web
between cords are capillaries, nerves
liver, adrenal, pituitary
• keratinised and non-keratinised
Classification according to
function
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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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
Types of gland
• cells producing and releasing substrate
• this substrate is used by organism
• exocrine
• type of secretion
• endocrine
– merocrine (pancreas)
– apocrine (mammary gland)
– holocrine (sebaceous gland)
– excretion to lumen of organ
– have ducts
– do not have ducts
– excretion to blood capillaries
Types of exocrine glands
• according to shape of secretory and excretory
parts
The end
• simple glands
• compound glands
• tubular
• alveolar (acinar)
• tubulo-acinar
next week
• written test: Tissues
• slide test
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