Cell systems Epithelial tissue 2009

Cell systems Systems of cells with typical features and specific function Epitheliocytes – intercellular junctions (epithelia and neural tissue) Mechanocytes – adhesion to the molecules of the intercellular space (connective tissue and muscles) Amebocytes – movable (blood cells)

Epithelial tissue It is composed from cells closely arranged with very little extracellular tissue Typical feature of epithelial cells is polarity, cells are lying on the lamina basalis. Important is the cell adhesion Nutrition – difusion from connectives (without vessels) Inervation – nerve ending are frequent Regeneration – good especially in covering epithelia – stem cells – proliferation and movement along basement membrane

Types of epithelial tissue Layers - flat sheets covering, lining the body surface, glands Cords (endocrine glands, liver) Reticulum – network (thymus) Development from all three embryonic germ layers – ectoderm, endoderm and mesoderm

Function: Covering and lining Absorption Secretion Sensation Contractility (myoepithelial cells)

Compartments of cell Apical: Microvilli, stereocilia,cilia Lateral: Intercellular junction Basal: Basal lamina and basement membrane

Apical differentiation: Microvilli - finger-like projection containing actin microfilaments – brush border – glycocalyx Terminal web – (actin and intermediate filaments) attachment to the zonula adherens by alfa actinin and vinculin.

Apical differentiation Stereocilia – long and branching processes (immobile) Kinocilia – mobile - till 10 μm – axial microtubules - 9 duplets + 2 central , basal body and rootlets

Kinocilia Kinocilia - peripheral- 9 duplets of microtubules and one pair of central microtubules Molecular motor - dynein = axial complex Basal body = centriol - 9 triplets of microtubules Rootlets – intermediate filaments

Intercellular junction Zonula occludens Zonula adherens Macula adherens, desmosome Gap junctions

Intercellular junction Tight junction – zonula occludens – controls and prevents free passage of substances across epithelium Determine cell polarity Occludins and claudins – barrier

Adhesive – anchoring junction Zonula adherens Cadherins + actin Desmosome (macula adherens) Cadherins + intermediate filaments (cytokeratins)

Communicating junction Gap junction – connexons – channel-like structures (connexins - proteins) exchange of small molecules till 1500 Da.

Attachment to the background Integrins –attachment to the extracellular matrix and basal lamina (Ca independent)-signaling Focal adhesion (actin) Hemidesmosome (intermediate filaments)

Basal lamina Structure – lamina densa and lamina rara (lucida) – collagen type IV, laminin, fibronectin, entactin and proteoglycans (heparan sulphate proteoglycan) Produced by epithelial cells (and others - adipocytes, muscle cells, Schwann cells) – barrier and attachment to extracellular matrix. Regulate proliferation and differentiation Loss of contact induces apoptosis

Basal lamina

Basement membrane Visible in light microscopy. Structure – basal lamina a lamina reticularis (connective tissue) – achoring collagen fibrils and reticular fibres – attachment to connective tissue Sometimes for the fusion of two basal laminae – kidney and lung alveoli

Cellular types Transporting cells Signaling cells Secretory and exporting cells Myoepithelial cells Stem cells

Transport through membrane Endocytosis – plasmatic membrane forms invaginations surrounding particle – vesicle (endosom):Pinocytosis (vesicle contains fluid), fagocytosis (vesicle contains dense particle). Exocytosis content of vesicle is secreated from cell. Proteins are syntetized on RER and GA. These vesicle migrate to the plasma membrane, where they either fused immediately with the membrane and discharge their content to the exterior (constitutive secretion) or they are stored near the membrane until a signal such as a neurotransmitter or hormone causes them to fuse with the membrane and release the enclosed content (regulated secretion ).

Transporting cells Pinocytotic invagination and vesicules – transport of macromolecules in the cell or through cells Transport through vascular endothelium - calveolae Clathrin – forms layer on the inner surface of plasmalemma and enables vesicule formation

Transporting cells Active transport – Na,K ATPase – sodium pump - invagination of basal cell membrane, mitochondria – source of energy Basolateral labyrinth Tight junction – compartments of cellular surface

Signaling cells Cells are specialized to production of signal molecules - hormones (different chemical structure - proteins, glycoproteins, lipids) They affect target cells, which are far from cells producing signal molecule (hormone) (endocrine signaling) or which are in their neighbourhood (paracrine signaling) Cells form cords (parathyroid gland, islets of Langerhans) Cells form follicle or vesicles filled by noncellular material (thyroid gland)

Steroid producing cells Lipids Tubular or vesicular types of mitochondria SER

Types of secretion Merocrine – secretory granuls Apocrine – granules and parts of apical cytoplasma Holocrine – destruction of cell – whole is changed in secretion

Myoepithelial cell Cytokeratins Actin and myosin

Stem cell Regeneration Self-renewal

Epithelial cell - derived tumors Metaplasia – transformation of cells into the other type Benign X malignant (carcinoma) Origin from stem cells (progenitor cells) – loss of typical features – polarity and basal lamina. It enables invasivity and metastasis formation. Loss of cadherins is jointed with tumor invasivity – loss of contact inhibition. Cells loosing typical features are more malignant - they grow faster Typical cytokeratins are used for diagnosis