TISSUES Classification_ structure and function EPITHELIAL TISSUE by malj

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									 Charles University in Prague, First Faculty of Medicine

Classification, structure and function
 Institute of Histology and Embryology
           Doc. MUDr. Zuzana Jirsová, CSc.
          Histology and Embryology – B81131
                      19. 10. 2011

Aggregates of cells organized to perform one or
more specific functions

Common origin and morphological characteristic

Four basic types of tissues:

                   EPITHELIAL TISSUE
Origin: tissue developing from the ectoderm, mesoderm and
endoderm (all three germ layers )
Morphology: tissue composed of closely aggregated cells
Function: protection, secretion, absorption, transport,
           respiration, reception

                   CONNECTIVE TISSUE
Origin: tissue develops from mesenchyme
                     protein fibers and ground substance
Types: connective tissue proper (loose and dense)
        CT with special properties (mucous, reticular,
                                    elastic and adipose)
        supporting (cartilage, bone, dentin)

Functional specialization: supporting, structural, storage,
                           defense, nutrition
                           MUSCLE TISSUE
Origin: mesoderm (skeletal and cardiac muscles)
        mesenchyme (smooth muscles)
Functional property: contractibility. Actin and myosin form myofilaments,
actin–myosin interaction is responsible for contraction.
Two types: striated muscle (skeletal and cardiac muscles)
            smooth muscle
Structural unit: cell (cardiac and smooth muscles)
                 muscle fiber (skeletal muscle)

                           NERVE TISSUE
Origin: tissue develops from neuroectoderm
Structure: NT consists of two principal types of cells: nerve cells
(neurons), and supporting glial cells (neuroglia)
Neurons: functional units of nervous system, gather and process
   information and generate signal, conduct electrical impulses
Glial cells: protection, electric insulation, metabolic exchange,

  Cell adhesion and intercellular
    Cell surface modifications
            Cell polarity
Classification of the epitelial tissue
Cells are closely apposed and adhere to one another by
means of specific cell adhesion molecules (CAMs)
Specialized cell junctions:
OCCLUDING JUNCTIONS (link forming an impermeable
barrier, tight junction)
ANCHORING JUNCTIONS - provide mechanical stability
by linking of the cytoskeleton of one cell to the cytoskele-
ton of adjacent cell:
zonula adherens (focal contacts*) - actin filaments
macula adherens/desmosome (hemidesmosome*)
                                  - intermediate filaments
COMMUNICATING JUNCTIONS (gap junctions – allow
selective diffusion of molecules between adjacent cells)

                           *cell-to-extracellular matrix junctions
                         CELL POLARITY
Free surface or apical domain
         Special structural surface modifications
Microvilli – cytoplasmic processes (core consisting of actin filaments)
closed packed microvilli – brush border (absorptive epithelium)
Stereocilia – long immotile microvilli (hair cells of the inner ear, epithelium
              of the ductus epididymidis and ductus deferens)
Cilia – motile cytoplasmic processes (consisting of microtubule axoneme,
       basal bodies); epithelium of respiratory ways, and uterine tube

Lateral domain
In close contact with the opposed lateral domains of neighboring cells
Presence of unique proteins, cell adhesion molecules (CAMs)
Specialized cell-to-cell junctions (occluding, anchoring, communicating)
Folding - invagination and evagination (interdigitation) of lateral cell membrane

Basal domain
Attached to the basement membrane, cell-to-extracellular matrix junctions
(focal contacts, hemidesmosomes), basal cell membrane infoldings (ion –
transporting cells: striated ducts of salivary glands, kidney tubules)
   Zonula occludens                            CELL JUNCTIONS              Zonula adherens

bars in LM

Scheme: Ross, Pawlina, Histology, 2003   Focal contacts   Hemidesmosomes
                                                  Scheme, electron micrographs: Ross, Pawlina, Histology, 2003

ZO separates luminal space from the intercellular compartment. Focal
junctions between cells by transmembrane proteins (claudin,occludin).
Proteins that form these junctions are arranged as intertwining lines
(sealing strands)
Electron micrograph of ZO - close apposition of adjacent areas of cell membrane (a)
Freeze fracture technique shows ZO as anastomosing network of ridges – arrows (b)
                 ZONULA ADHERENS
 (Scheme, electron micrograph: Ross, Pawlina, Histology, 2003)

ZA is belt-like junction encircling the cell localized just bellow ZO. Actin filaments
of terminal web of adjacent cells are attached to E cadherin-catenin complex by
alfa-actinin and vinculin. Intercellular space measures 10-20 nm.
DESMOSOME, MACULA ADHERENS                        Electron micrograph, scheme: Stevens, Lowe, Histology, 1993

                                              (20 nm)

                                                                                      intercellular space
                                                                                      (25-30 nm)

Disc-like intercellular attachment. Intermediate filaments are anchored to the
attachment plaque located on the cytoplasmatic side of cell membrane. Dense
medial band, intermediate line (x) in the intercellular space represents
extracellular portions of transmembrane proteins (desmogleins, desmocollins –
cadherin family of Ca2+-dependent CAMs, “cadherin zipper” ).
 GAP JUNCTION, NEXUS – permit the direct passage of the ions, signaling molecules

                                          space – 2 nm

Gap junction proteins (connexins) form hexamers CONNEXONS with hydrophilic
pore (2 nm in diameter). Connexons in adjacent cell membranes are aligned to
form a cylindrical transmembrane channel. Conformational changes in connexins
lead to opening or closing of channels. Epithelium, smooth and cardiac muscles.
                                              Electron micrograph, scheme: Ross, Pawlina, Histology, 2003
   BASEMENT MEMBRANE (term used in light microscopy)
mediates attachment of epithelial cells to underlying connective tissue

Basal lamina (in electron   microscope)
Lamina densa - a layer of electron-dense material 40 – 60 nm thick
(between the epithelium and the adjacent connective tissue) composed of
laminins, type IV collagen, proteoglycans (heparan sulfate and
chodnroitin sulfate proteoglycans), entactin

Lamina rara is an electron-lucent area (40 nm thick) between the
lamina densa and epithelium (contains of extracellular portions of
CAMs, mainly their fibronectin and laminin receptors)

Attachment of the basal lamina to the underlying connective tissue:
anchoring fibrils (type VII collagen) and fibrillin microfibrils

A layer of reticular fibers underlies the basal lamina - reticular lamina
(is not product of the epithelium) belongs to the connective tissue

Basement membrane is PAS positive and stains with acidic dyes
Brush (striated) border                      Striated border of enterocytes (HE)
Enterocytes (intestinal absorptive cells)
Epithelium of proximal tubules in kidney
Scheme: Ross, Pawlina, Histology, 2003


                                            Striated border, PAS r. (glycocalyxx - x)



                                                             Photomicrographs: Collection of ÚHIEM
STEREOCILIA                                                  Pseudostratified columnar epithelium (epididymis)
long immotile microvilli                                      smooth muscle cells              spermatozoa

Scheme: Ross, Pawlina, Histology, 2003;   Photomicrograph: Kühnel, Color Atlas, 2003
                             Cilium Basal body              Ciliated cell in epithelium
                                                            of the uterine tube

                             Pseudostratified columnar ciliated epithelium
                             (with goblet cells)

Scheme of cilium
 Ross, Pawlina, Histology,

 Electron micrograph (c):
 Stevens, Lowe, 1993                               Photomicrographs: doc. Kraus, doc. Jirkovská
  Basal surface modification: ion-transporting epithelium (proximal and distal
  tubules of the kidney, striated ducts of the salivary glands). Infoldings at the basal
  plasmalemma enlarge basal surface, mitochondria provide energy for active transport
  of ions.
                                                                            G = Golgi complex


infoldings of the
basal plasma
Na+K+ ATP-ase

                                                      Scheme: Krstic, Illustrated Encycl. of Human Histology, 1984
Classification of epithelium
              according arrangement of cells:

a) PLANE: cells form tightly cohesive sheets
   traditional nomenclature is based on the:
   shape of cells:
   squamous, cuboidal, columnar
   number of layers:
   simple, stratified, pseudostratified

b) TRABECULAR: cells are arranged in cords or plates
   (liver, endocrine glands)

c) RETICULAR: cells form three-dimensional network
   (stroma of thymus, epithelium of crypts in tonsils,
    stellate reticulum of enamel organ)
Classification of epithelium
              according functional specialization:
Covering epithelium
Simple squamous, cuboidal, columnar, pseudostratified columnar
Stratified squamous, columnar
Transitional epithelium (urothelium)
Secretory epithelium – exocrine and endocrine; polarization of
cells, mechanism of secretion: merocrine, apocrine, holocrine
Absorptive epithelium
Respiratory epithelium: exchange of respiratory gases, in the
lung alveoli
Sensory epithelium: cells react on the external stimuli by change
of membrane potential. Primary and secondary sensory cells
Myoepithelium: cells with ability to contract
Germinal epithelium - production of cells (seminiferous epithelium
of testis produce spermatozoa)

Ion-transporting epithelium (modification of the basal cell surface)

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