HISTOLOGY

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HISTOLOGY

• The study of Tissues

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Overview of Tissues

• Tissues are groups of cells with a common
  structure (form) and function (job).
• All the organs of the body are made up of four
  basic tissues (1) Epithelial, (2) Connective
  Tissue, (3) Muscle Tissue and (4) Nervous Tissue.

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Epithelial Tissue

• Cells that line surfaces
• Epithelium is the name given to the cells that
  line a surface (surface of the body- epidermis
  surface of body cavity and internal organs inner
  surface of ducts and tubes and glands (sweat,
  salivary, etc.) are also formed by epithelial
  cells.

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Functions of Epithelial Tissue

• Form barriers protects us from the outside
  world, are always contiguous with one another and
  are usually joined by special junctions. (tight
  gaps, etc.) intercellular space between
  epithelial cells is very limited.
• Permeability some are much more impermeable
  than others. The epidermis of the skin is an
  impermeable barrier the epithelium lining the
  intestine, while providing a barrier, must also
  absorb nutrients.
• Secretory Function- (eg. stomach, glands)

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Characteristics (Traits)

• 1) Closely attached to each other forming a
  protective barrier.
• 2) Always has one free (apical) surface open to
  outside the body or inside (cavity) an internal
  organ.
• 3) Always had one ?xed (basal) section attached
  to underlying connective tissue.
• 4) Has no blood vessels but can soak up nutrients
  from blood vessels in connective tissue
  underneath.
• 5) Can have lots of nerves in it (innervated).
• 6) Very good at regenerating (?xing itself). i.e.
  sunburn, skinned knee.

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Terminology

• Free surface All epithelia have a free surface,
  that is to say a surface to which no cellular or
  extracellular formed elements adhere. The free
  surface may contain specialized modifications,
  such as microvilli (increase the absorptive
  surface) or cilia (move secretions).
• Basement Membrane All epithelia rest on a
  basement membrane, through which it is attached
  to the underlying tissue.

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Types of Epithelial Tissue

• Epithelia are classified according to the number
  of layers of cells they contain and the shape of
  the cells.
• Layers Shape of Cell
• Simple 1 layer Squamous flattened cells
• Stratified 2 or more layers Cuboidal same
  height, width, depth
• Columnar height exceeds their
  width
• Note if there are multiple layers and they dont
  look similar you comment on the outermost layer
  regarding the shape

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Simple Squamous Epithelium

• Figure 1 shows the simple squamous epithelium
  lining within the capsule of the kidney

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Simple Squamous Epithelium
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Simple Squamous Epithelium

• Figure 2 shows the aorta lined by a layer of
  flattened cells called endothelial cells (arrows).

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Simple Cuboidal Epithelium

• Figure 4 shows parts of several thyroid gland
  with cuboidal cells in a roughly circular
  pattern.

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Simple Cuboidal Epithelium

• Figure 5 shows parts of the kidney tubules
  consisting of simple cuboidal epithelium.

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Simple Columnar Epithelium

• Figure 6 shows the tall simple columnar
  epithelium of the duodenum with bears a brush
  border formed by microvilli which greatly
  increase the absorptive surface.

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Stratified Squamous Epithelium

• This type of epithelium is found on tissues
  likely to encounter friction.
•  Figure 7 shows the stratified squamous
  epithelium of the esophagus (the shape of the
  cells can be inferred from the shape of the
  nuclei and that they are identifiable in all
  layers)

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Stratified Squamous Epithelium
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Stratified Squamous Epithelium

• Figure 8 shows another example of stratified
  squamous epithelium of the epidermis of skin. The
  cells can be seen to become more flattened toward
  the deep-staining red layer. The deep stained
  area are cells filled with keratin (protein)
  through a process known as keratinization. More
  specifically this epithelium is known as
  keratinized stratified squamous cell epithelium
  or cornified stratified squamous epithelium
  associated with the soles and palms.

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Stratified Squamous Epithelium
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Stratified Squamous Epithelium
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Stratified Cuboidal Epithelium

• Figure 9 demonstrates stratified cuboidal
  epithelium associated with ducts of various
  glands (sweat glands, sebaceous glands)

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Stratified Columnar Epithelium

• Figure 10 Found associated with the largest
  ducts of glands (submandibular).

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• In addition to the above, there are two special
  types of epithelium called Pseudostratified and
  Transitional.

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Pseudostratified Epithelium

• Figure 11 demonstrates Pseudostratified
  epithelium which has the appearance of being
  stratified, because it has cell nuclei at
  different heights within the epithelium. This is
  because it has some low cells which do not reach
  the free surface, and some tall cells, which do.
  However, all the cells rest on the basement
  membrane, so it is in fact a simple epithelium.
  In sections of pseudostratified epithelium, it is
  quite often difficult to discern that all the
  cells sit on the basement membrane. The
  distribution of pseudostratified epithelium is
  fairly limited. It is found in parts of the
  respiratory and male reproductive systems.

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Pseudostratified Epithelium
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Transitional Epithelium

• Figure 12 shows Transitional epithelium found in
  parts of the urinary system (kidney, ureter,
  urinary bladder urethra) that can be distended by
  the pressure of urine. The thickness of
  transitional epithelium depends on the state of
  distension (full) or contraction (empty). When
  the ureter or bladder is empty, the epithelium
  can be six or more layers deep, when it is
  distended, the epithelium is only two or three
  layers deep.

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Transitional Epithelium
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