Epithelial Tissue

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Epithelial Tissue

• Chapter 4
• Anatomy and Physiology
• Liberty High School
• Mr. Knowles

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Tissue

• Collections of specialized cells and cell
  products that perform a specific function.

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Four Types of Tissue

• Epithelial- covers exposed surfaces, lines
  passageways, forms glands.
• Connective- fills internal space, structural
  support, storage of energy.
• Muscle -contracts for specific movements.
• Neural- carries information from one part of the
  body to another.

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Observe my Lunch on the Front Table!

• List three functions of the plastic bag.

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Epithelial Tissue

• Includes epithelia and glands.
• Epithelium- a layer of cells that forms a
  barrier. Epithelia- plural, many types
  Epithelial is the adjective.
• Examples surface of skin lining of the
  digestive, respiratory, reproductive tracts.

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Functions of Epithelia

• Provide Physical Protection- protect surfaces
  from abrasion, dehydration, chemical and
  biological agents.
• Control Permeability- regulates molecules that
  enter or leave through the surface.

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Permeability Can Change!
Corn
Callus
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Functions of Epithelia

• Provides Sensation- many sensory nerves Ex
  smell, taste, hearing.
• Produce Specialized Secretions- gland cells
  produce secretions

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Some Characteristics

• Cellularity tightly bound cells with little
  space between.
• Polarity has an exposed surface- apical surface
  (faces exterior surface ) and an attached
  surface-basal surface (attached to underlying
  tissue). Organelles are distributed unevenly in
  these cell.

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Characteristics

• Attachment basal surface of an epithelium is
  bound to a thin basement membrane- produced by
  the basal surface of epithelium and underlying
  connective tissue.
• Avascularity epithelia have no blood vessel
  epithelial cells receive nutrients by diffusion
  through apical and basal surfaces.

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Characteristics

• Regeneration cells damaged or lost at the
  apical surface are replaced constantly.

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How do epithelial cells do ALL of this?

• The answer is in their structure!
• Function ? Structure

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Specialized Epithelial Cells

• Some epithelial cells
• Produce secretions.
• Help with movement of fluids over epithelial
  surface.
• Help move fluids through the epithelium.
• These cells have a strong polarity (top and
  bottom).

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Apical Surface Structures

• Microvillus (i)- small projections of the cell a
  few to many on each cell.
• Function increase surface area (20X) of
  epithelial cell (transport specialists).
• Location epithelial surfaces where there is
  absorption and secretion along digestive and
  urinary tracts
• See Fig. 4-1, p. 110.

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Microvilli
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Apical Surface Structures

• 2. Cilia- different internal structure than
  microvilli many, long extensions that beat in a
  coordinated fashion.
• Function movement of material along the
  epithelium.
• Location respiratory tract (mucus) fallopian
  tubes (egg)

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Cilia
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Apical Surface Structures

• 3. Stereocilia- similar to microvilli but longer,
  but cannot move.
• Function detection of vibration.
• Location male reproductive tract receptor
  cells of inner ear.

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Stereocilia
Stereocilia
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Show me Ciliated Epithelia in Action!
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Damaged Epithelia and Emphysema
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The Effects of Emphysema
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Staying Together!

• 3 Ways Epithelial Cells Stay Together
• 1. Intercellular Connections
• 2. Attachment to Basal Membrane
• 3. Epithelial Maintenance and Repair

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1. Intercellular Connections or Cell Junctions

• Tight Junctions- fusion of cell membranes of
  neighboring cells.
• Function block water and solutes between
  cells protection.
• Location near apical surfaces of cells in
  digestive tract-keep enzymes and acids from
  damaging cells underneath.

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1. Intercellular Connections or Cell Junctions

• b. Desmosomes- strong connections of proteins
  (CAMs) between cells.
• Function Act as cross-braces between cells
  (tent ropes) to hold the shape of cells anchor
  cell to its base.
• Found basal and lateral superficial skin and
  cardiac muscle cells Ex. Dead skin comes off as
  sheet.

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1. Intercellular Connections or Cell Junctions

• c. Gap Junctions- interlocking membrane proteins
  (connexons) that form channels between cells.
• Function allow small molecules and cations to
  pass between cells-coordinate functions-beating
  cilia.
• Found lateral cardiac and smooth muscle

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Connexons or Channel Proteins
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2. Basement Membrane

• A layer of protein fibers to which epithelia can
  attach.
• Separates epithelial layer from connective
  tissue.

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3. Maintenance and Repair

• Epithelial cells must be replaced due to
  damage-bacteria, enzymes, toxic chemicals, etc.
• Use germinative cells (a type of stem cell) to
  replace them.
• Located in deepest layer near basement membrane.

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The Layers of Skin
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How many kinds of epithelia are there?

• Classified in Two Ways
• Number of Layers and Shape of Cell

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A. Layers

• Simple- a single layer covers the B.M.
• Characteristics thin layer, fragile no
  mechanical protection.
• Location lines internal passageways and
  compartments. Ex. Walls of blood vessels
  internal surface of lungs.
• Function absorption and secretion reduce
  friction in vessels.

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A. Layers

• Stratified- several layers of cells cover the
  B.M.
• Characteristics only one layer contacts the
  B.M. other layers lay on top of these cells.
• Location surface of the skin lining of the
  mouth.
• Function protect from mechanical and chemical
  stress.

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B. Shape

• Squamous- scale thin, flat cells look like
  fried eggs laid side by side.
• Ex. Simple Squamous Epithelium- walls of alveoli
  of lung walls of blood vessels and inner heart
  chamber- called Endothelium. Ex. Stratified
  Squamous Epithelium- surface of skin lines
  mouth, etc. provides protection.

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Simple Squamous Epithelium
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Apical View of Simple Squamous
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Simple Squamous Cross-Sectional View of Blood
Vessel
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Simple Squamous Cross-Sectional View of Lung
Alveoli
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Stratified Squamous Epithelium
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Stratified Squamous - Cheek Cells
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Stratified Squamous
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Stratified Squamous-Cross Section, Lower
Magnification
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Stratified Squamous-Cross Section, Higher
Magnification
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B. Shape

• Cuboidal- hexagonal boxes nuclei near center of
  cells.
• Ex. Simple Cuboidal- mostly secretion and
  absorption kidney tubules salivary glands.
• Stratified Cuboidal- rare in body lines the
  ducts of sweat and mammary glands.
• Transitional Epithelium- are a type of
  stratified cuboidal allows expansion and
  contraction lines urinary bladder.

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Simple Cuboidal Epithelium
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Simple Cuboidal X-Section of Kidney Tubules
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Transitional Epithelium Ureter, Lower
Magnification
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Transitional Epithelium Ureter, Higher
Magnification
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B. Shape

• 3. Columnar Epithelial- hexagonal cells but
  taller than they are wide columns nuclei are
  crowded near B.M.
• Ex. Simple Columnar- absorption and secretion
  inside small intestine secrete protective mucus
  may have microvillie at apical surface.

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Simple Columnar Epithelium
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B. Shape

• 3. Columnar-
• Ex. Pseudostratified Columnar- nuclei not in
  same plane- appear stratified, but not. All
  cells contact the B.M. Found- respiratory tract-
  have cilia line trachea, nasal cavity.
• Stratified Columnar- rare protective line
  epiglottis and pharynx

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Simple Columnar Small Intestine (Villi)
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Simple Pseudostratified
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Pseudostratified Epithelium
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Pseudostratified Ciliated Columnar
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Stratified Columnar
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Glandular Epithelia

• Endocrine Glands- release secretions into
  surrounding interstitial fluid they have no
  ducts.
• Glands may line the digestive tract or be
  separate.
• Example- hormones (insulin from the pancreas)

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Glandular Epithelia

• Exocrine Glands- secretions discharged onto
  epithelial surfaces released into tubular
  passageways-ducts that empty onto surface of
  other epithelial tissues.
• Examples- sweat, saliva, and tears.

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Lets see epithelia in action!

• National Geographic magazine, November 2002
• National Geographic video Skin, November 13, 2002