Lecture 7 GenMed_2nd semester

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Lecture 7 GenMed_2nd semester

• Epithelial tissue definition, classification
  and histogenesis
• Overview of covering and glandular epithelia.
  Characteristics of glandular cells
• Absorptive, respiratory, and sensory epithelia

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• Tissues of the adult and their classification
• a tissue a complex of similar cells specialized
  in common direction and able to perform a common
  function
• 4 primary (basic, fundamental) tissues
• - epithelial tissue (epithelium)
• - connective and supporting tissues
• - muscle (muscular) tissue
• - nerve tissue
• tissues form elementary components of organs
• the occurrence, arrangement and proportions of
  tissues in individual organs are different and
  are object of study in the microscopic anatomy

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• Epithelial tissue
• is composed of cells that are in close apposition
  with one another among cells there is present
  only a small amount of intercellular substance
• epithelial cells are usually of regular form
  without extensive cytoplasmic processes
• adhesion between the cells is very strong
• epithelia derive from the all germ layers
• Connective and supporting tissues
• unlike epithelia, contain cells that are
  separated from one another by intervening
  spaces, these contain intercellular material or
  substance produced by cells
• the intercellular substance consists of two
  components fibers and amorphous ground substance
• connective and supporting tissues are always of
  mesenchymal origin
• Muscle tissue
• is composed of elongated cells that are able to
  contract
• for this function cells are well adapted as they
  contain contractile proteins actin and myosin
• cells or muscle fibers tend to be aggregated in
  bundles that are conspicuously different from the
  surroundings tissues
• two types of muscle tissue are distinguished
  smooth, skeletal and cardiac
• smooth muscle tissue derives from the mesenchyme,
  striated muscle tissue from the mesoderm
• Nerve tissue
• consists of nerve cells - neurons, and associated
  supporting cells of various type called neuroglia
• neurons are highly specialized cells that show
  ability to receive, generate and transmit nerve
  impulses

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• Epithelial tissue
• is composed of cells that are in close apposition
  with one another among cells only a small
  amount of intercellular substance is present
• epithelial cells are usually of regular form
  without extensive cytoplasmic processes
• adhesion between cells is very strong
• epithelia derive from the all germ layers
• epithelial tissue is avascular - it contains no
  blood capillaries
• it exhibits a remarkable degree of physiologic
  regeneration

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• Classification of the epithelial tissue
• a) according to the arrangement of cells -2 forms
• - epithelial membranes either sheets -
  composed of one or more cell layers in
• thickness
• or
• - solid cords or tubules (rarely follicles) that
  have developed as out- growths from an
• epithelial sheet
• cords and tubulus especially occur in glands
• b) according to the function of cells
• covering or protective - cells cover external and
  internal surfaces of human body and protect
  underlying tissues against loss moisture and
  mechanical damage,
• secretory or glandular - cells are engaged in
  synthetic processes and product substances with
  defined functional destination,
• absorptive - cells transport substances from the
  alimentary canal and renal tubules into the
  systemic circulation,
• respiratory - cells take part in the transport of
  oxygen and carbon dioxide from alveoli into the
  blood,
• sensory - cells are specialized for reception of
  stimuli (olfactory epithelium, taste buds etc.)
• a given epithelium may serve one or more
  functions, depending upon the cell types
  presented,
• eg. protective and secretory functions of the
  epithelium in the stomach or protective and
  absorptive

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• Covering epithelia /epithelial membranes/
• common features
• cells always rest upon a basement membrane
• it attaches them to underlying connective tissue
• the basemenet membrane is thin and composed of
  delicate reticular fibers that are
• embedded in a gel-like mucopolysaccharide
  substance
• in ordinary staining procedures (eg. using
  hematoxyline and eosin), the membrane is
• not visible but it stains with PAS technique
• epithelial cells are mostly polarized
• lateral and apical aspects of cells are
• subjects of various modifications
• microvilli, motile cilia
• interdigitations
• and intercellular junctions

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• two types
• simple and stratified epithelia
• the simple epithelia consist of single layer of
  cells, all of which are in
• contact with the basement membrane
• the stratified epithelia are composed of two or
  more layers of cells, of
• which only basal is in contact with the basement
  membrane and remainder
• layer superimposed one upon other
• the both are further subdivided according to the
  shape of cells
• the component cells may be
• squamous - the width and depth of the cell is
  greater than its height
• cuboidal - the width, depth and height are
  approximately the same and
• columnar - the height of the cell appreciably
  exceeds the width and depth
• the classification based on both criteria is

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Simple epithelia - simple squamous epithelium
- simple cuboidal epithelium - simple columnar
epithelium - pseudostratified columnar
epithelium Stratified epithelia -
stratified squamous epithelium - stratified
columnar epithelium - transitional epithelium
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• Simple squamous epithelium
• cells are flattened
• viewed from the surface they appear as fairly
  large cells with clear cytoplasm and an oval
• nucleus cell boundaries are not visible in
  ordinary preparations but may be demonstrated by
• the use of impregnation technique
• in sections the cytoplasm is barely visible, but
  there is an enlargement of the
• cell at center where the nucleus is located
• chief distribution
• the parietal layer of capsule of
• Bowman and descending limb of the
• loop of Henle in the kidney
• inner surface of the wall of the
• membranous labyrinth and inner
• surface of the tympanic membrane
• the smallest excretory ducts of
• many glands

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• Simple cuboidal epithelium
• cells of cuboidal epithelium are smaller in
  surface view than those of the simple
• squamous type and are roughly hexagonal
• cell boundaries are often clearly visible
• in vertical sections the cells are square with a
  spherical nucleus in the center of each
• the square shape is modified to that of truncated
  prism when cells line small ducts
• chief distribution free surface of the ovary,
  the choroid plexus surface, the inner
• surface of the lens, the excretory ducts of many
  glands
• Simple columnar epithelium
• the surface view of columnar epithelium is like
  that of the cuboidal epithelium in
• sections,
• the cells are seen to be taller than they are
  broad
• their nucleus is near the base of the cell
• as in the case of the cuboidal epithelium, the
  rectangular shape of columnar cells is
• changed to pyramidal when they are grouped around
  small lumen
• in order to right diagnosis of this epithelium it
  is important to select a region, in

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a simple cuboidal epithelium
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simple columnar epithelium with striated border
(microvilli)
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a simple columnar ciliated epithelium (with
kinocilia)
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• Pseudostratified columnar epithelium
• all cells are in contact with the basement
  membrane but only a part of
• them extends to the free surface
• in pseudostratified epithelium cells are variable
  in shape and their nuclei lie at different
  levels
• according to cell height, three different cell
  types are distinguished
• small basal or supporting cells
• spindle-shaped cells
• tall superficial cells that are connected with
  the basement membrane via slender processes,
  apices of tall superficial cells are often
  ciliated
• goblet cells producing mucous
• secretion are usually present
• in this epithelium
• chief distribution
• the respiratory passages

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• Stratified epithelia
• small cuboidal or columnar cells lie next to the
  basement membrane
• above them one or more layers of polygonal cells
  are
• the free surface is covered by a layer of cells
  that are important for diagmosis
• Stratified squamous epithelium
• the thickness of the epithelium and number of
  cells vary in different parts of the body
• the shape and arrangement of component cells,
  however, follow the same general plan
• consists of small cuboidal or even columnar cells
  are are covered by a varying number of
• layers of more or less polygonal (polyhedral)
  cells
• they gradually begin to flatten out toward to the
  epithelium surface
• they become scale-like form, their nuclei are
  pyknotic but they may be yet considered as viable
• such epithelium is found in the mouth, the
  esophagus, the vagina, and on the surface
• of the cornea
• on the exposed outer surfaces, the stratified
  squamous epithelium is modified as cornified or

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stratified squamous epithelium
stratified squamous epithelium (cornified)
epidermis
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• Stratified columnar epithelium
• it differs from the pseudostratified epithelium
  in having a continuous layer of small, rounded
• cells next to the basement membrane, a varying
  number (3-4) of more or less polyhedral cells
• and by presence of superficial cells that are
  tall and prismatic
• the epithelium is truly stratified
• chief distribution the fornix of the
  conjunctiva, the cavernous part of the male
  urethra,
• large excretory ducts of some glands
• Transitional epithelium
• it consists of several layers of cells
• the basal cells are like those of stratified
  columnar epithelium
• above them there is a varying number of layers of
  polygonal or pear-shaped cells, the cell
• layer at the free surface is composed of large,
  rather flattened cells, usually described as
• dome shaped
• one of dome shaped cell often covers two or three
  pear-shaped cells that underlie it
• cells show unusual degree the ability to change
  their position, sliding over each other

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transitional epithelium
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• Secretory /glandular/epithelium
• the epithelium whose cells are able to synthesize
  special products - secretions
• substances that are for organism and right
  function of many organs very important
• in many cases they cannot be substituted
• secretory products are released either upon free
  surfaces or into blood
• (rarely lymphatic) vessels for distribution
  /hormones/
• Histophysiology of secretion
• secretory process involves 3 phases as follows
• ingestion of single substances or precursors from
  the surrounding or blood
• synthesis of secretory products including their
  segregation and accumulation
• release or extrusion of secretory products
• Ingestion of precursors is usually realized by 3
  ways
• - passive diffusion down a concentration
  gradient,
• - active transport against a concentration
  gradient using ATP as an energy source,

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• synthesis of secretory products
• under cooperation of many cell organelles - free
  ribosomes or unbounded polyribosomes and the
  rough endoplasmic reticulum
• synthesized products are then transferred from
  this compartment to the Golgi apparatus, where
  they become final form and are directed to
  their final destination in each cell
• synthetic processes need an energy - is produced
  by mitochondria
• all the mentioned cell organelles are typical of
  glandular cells
• release or extrusion of secretory
• products
• three modes have been distinguished
• - merocrine secretion
• - apocrine secretion
• - holocrine secretion

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Release of secretion products merocrine
secretion products are released through the
cell membrane without the loss any cytoplasm
(during the whole secretory cycle) the cell does
not change its shape goblet cells
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apocrine secretion by a loss of the apical
parts that contains an accumulated secretory
material glandular cells of follicles in
thyroid apocrine sweet glands
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holocrine secretion the discharge of product is
associated with a destruction of the whole
glandular cells cells of sebaceous glands
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• secretory cells constitute special organs
  called glands
• Classification of glands
• glands are classified in several different ways
• a) with respect to the mode of secretion
• exocrine glands - discharge their product via
  ducts at an external or internal
• surface,
• endocrine glands release their product into the
  blood or lymph vessels
• have no ducts (ductless glands)
• secretions are called hormones and regulate and
  coordinate the activities of all the
• cells in the body in cooperation with the nervous
  system
• b) with respect to the number of glandular cells
• unicellular glands - the glandular components
  consist of a single cell among
• other cells that are not glandular

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• Exocrine glands
• or glands of external secretion retain
  connections with surfaces
• exocrine glands occur as uni - and multicellular
  ones
• unicellular glands are
• - mucous cells or goblet cells and
• - enteroendocrine (GEP) cells
• goblet cells are scattered among the columnar
• cells of the simple columnar or
• pseudostratified columnar epithelia
• cells secrete mucin
• each cell has an expanded, oval apex filled with
• pale droplets of mucigen and a slender basal
• end containing a compressed nucleus and
• a small amount of deeply staining basophilic

goblet cells
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• multicellular glands
• intraepithelial glands
• are relative rare and are composed of small
  accumulations of glandular cells that lie wholly
• within the thickness of an epithelial membrane
• chief distribution mucous glands of lacunae
  urethrales Morgagni in the male urethra
• extraepithelial glands
• are always in the connective tissue of respective
  organ or often more deeper
• glnds develop as invaginations of the epithelial
  membrane into the underlying tissues
• the extraepithelial glands consist of secretory
  units and ducts
• secretory units are of three types
• tubules (unit is shaped like a tube)
• alveoli (acini) (unit is shaped like a flask)
• tuboalveolar portions (combination of the tube
  and alveolus which is located at
• one end of the tube)
• ducts may be short and unbranched - simple glands

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Multicellular glands
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• besides the anatomical classification of glands
• it may be taken in account the chemical
  properties of secreted product
• the secretory units are divided into
• mucous units - the shape of straight tubules
  with a small lumina
• cells are usually of cuboidal form or of
  truncated pyramids, nuclei are usually small,
  dark, and are flattened against the plasma
  membrane of the cells
• the cytoplasm stains light in HE preparation and
  may have a foamy appearance
• (alcian blue, mucicarmine, and the PAS reaction
  are used to demonstrate mucous tubules )
• serous units - are the form of alveoli and are
  composed of pyramidal cells whose nuclei are
  located centrally
• secretion granules are more or less acidophilic
  and are primarily protein in character
• the cytoplasm always stains in pink or pinkish
  purple, more darkly than that of mucous cells
• the lumen of alveoli (acini) is definite and and
  smaller in diameter than that of mucous tubules
• seromucous units - mixed units are composed of
  both mucous and serous cells
• a mixed unit is composed of mucous cells lining
  a tubular part (short tubule) to which one end
  is added a collection of serous cells arranged in
  a half-moon fashion
• these serous cells collections are called as
  demilune complexes or lunulae of Giannuzzi
• in a great number they are occurred in the human
  submandibular gland

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acinar / alveoli /
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tubular /tubules /
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tubuloacinar /tubules with serous demilunes/
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tubule with serous demilune demilune of Gianuzzi
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• Absorptive epithelium
• cells whose apices are provided with microvilli
• striated border (enterocytes)
• brush border (cells of proximal tubule of the
  nephron)

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• Respiratory epithelium
• is extremely thin and lines alveoli
• membranous pneumocytes (type I)
• granular pneumocytes (type II)

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• Sensory epithelium
• sensory organs
• sensory areas (fields)
• supporting cells
• sensory cells - receipt stimuli from external
  environment, stimuli induce a special status in
  their bodies - irritation
• sensory cells are of two types
• a) primary sensory cells (neuroepithelial cells
  or unipolar neurons)
• they consist of receptor area (can be
  photosensitive or registrate odoriferous
  substances), cell body and axon or neurite that
  conducts impulses to the next neuron
• in the human - olfactory cells in the olfactory
  epithelium and by rod cells and cone cells in the
  retina
• b) secondary sensory cells
• are only modified cells of covering epithelia
• cells have spindle-like or flask-like form and
  consist of only receptor area and body
• the process corresponding to the axon is always
  missing (signals from cells are conducted via
  dendritic processes of sensory nerves that endon
  the surface of these cells)
• cells of taste buds, and hair cells in the
  membranous labyrinth

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cone cell rod cell
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taste bud with taste cells
hair cells (utricle)