Lectures 3

1
Lectures 3 4

• Histology The Study of Tissues

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Tissues and Histology

• What is a Tissue?
• A collection of similar cells and noncellular
  substances (extracellular matrix) secreted by the
  cells
• Tissue Level of Organization
• Epithelial
• Connective
• Muscle
• Nervous
• Histology Microscopic Study of Tissues

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Epithelium Characteristics

1. Consists almost entirely of cells
2. Covers body surfaces and forms glands
3. Has free and basal surface
4. Avascular
5. Undergoes mitosis

Fig. 4.1
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Classification of EpitheliumHow to Make Sense
of It All?

• There are 2 basic features (or criteria) for
  classification of epithelium
• Number of cell layers
• Simple
• Single layer
• Stratified
• More than 1 layer
• Exceptions?
• Pseudostratified
• Single layer only some cells reach free surface
• Transitional
• Number of cell layers decreases as it is
  stretched

Fig. 4.2
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Classification of Epithelium

• Shape of cells
• Squamous (scaly)
• Cells flattened
• Cuboidal
• Cells cube-shaped
• Columnar
• Cells are taller than wide

Fig. 4.2
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Types of Epithelium

• Name of epithelium is combination of number of
  cell layers and shape of cell (Table 4.2)
• 3 types of simple simple squamous epithelium,
  simple cuboidal epithelium and simple columnar
  epithelium
• 3 types of stratified stratified squamous
  epithelium, stratified cuboidal epithelium and
  stratified columnar epithelium
• Pseudostratified columnar epithelium
• Transitional epithelium Cuboidal to columnar
  when not stretched and squamous-like when
  stretched

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Review Question

• Which of the following statements about
  epithelial tissue is correct?
• All cells of pseudostratified columnar epithelial
  tissue have a free surface.
• You would predict simple squamous epithelium
  lining the inside of an organ that absorbs
  substances.
• Transitional epithelium has multiple layers of
  cells that can change shape.
• The epithelium of your skin is a simple squamous
  epithelium.
• Cuboidal or columnar cell shapes are optimal for
  diffusion.

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Glands

• Secretory organs made mostly of epithelium
• Form as invaginations (ingrowths) of outer layer
  of epithelium in embryo

• Two basic types
• Exocrine
• Have ducts lined with epithelium

• Endocrine
• Have no ducts
• Examples include pituitary gland, pancreas,
  thyroid gland

Fig. 4.4
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Connective Tissue

• Abundant and diverse
• Consists of cells separated by extracellular
  matrix
• Specialized cells produce the extracellular
  matrix
• Suffixes
• -blasts create the matrix
• -cytes maintain the matrix
• -clasts break the matrix down for remodeling
• Performs variety of important functions

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Connective Tissue Categories

• Embryonic or mesenchyme

• Adult
• Loose
• Areolar
• Adipose
• Dense
• Cartilage
• Bone
• Blood

Table 4.6
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Loose Connective Tissue
Table 4.9

• Areolar tissue
• Loose packing material of most organs and tissues
• Attaches skin to underlying tissues
• Contains collagen, reticular, elastic fibers and
  variety of cells

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Loose Connective Tissue

• Adipose Tissue
• Consists of adipocytes
• Types
• Yellow (white)
• most abundant, white at birth and yellows with
  age
• Brown
• found only in specific areas of body as axillae,
  neck and near kidneys

Table 4.9
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Dense Regular Connective Tissue

• Has abundant collagen fibers
• Tendons Connect muscles to bones
• Ligaments Connect bones to bones

Table 4.10
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Dense Irregular Connective Tissue

• Forms most of dermis of the skin

Table 4.10
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Elastic Connective Tissue

• Ligaments in vocal folds
• In walls of elastic arteries

Table 4.10
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Review Question

• In which of the following locations would you
  expect to find dense irregular connective tissue?
• Nuchal ligament
• Dermis of skin
• Vocal cords
• Large arteries
• Tendon

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Points to Remember

• Two basic components to a tissue
• Similar cells specialized for a function
• Non-cellular matrix secreted by the cells
• Epithelial tissue is typically a covering or
  lining
• Connective tissue is diverse and extremely
  abundant

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Questions?