Histology: The Study of Tissues

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Lecture 3

• 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

• Consists almost entirely of cells
• Covers body surfaces and forms glands
• Has free and basal surface
• Avascular
• 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
• But, of course, there are exceptions!
• Pseudostratified
• Single layer only some cells reach free surface
• Transitional
• Number of cell layers decreases as it is
  stretched

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Classification of Epithelium

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

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Types of Epithelium

• Name of epithelium is combination of number of
  cell layers and shape of cell
• 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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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

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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
• Connective tissue proper - Loose and Dense
• Adipose
• Cartilage
• Bone
• Blood

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Loose Connective Tissue
Fig. 4.7a

• Also known as 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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Dense Regular Connective Tissue
Fig. 4.7b
Fig. 4.7c

• Dense regular collagenous
• Has abundant collagen fibers
• Tendons Connect muscles to bones
• Ligaments Connect bones to bones

• Dense regular elastic
• Ligaments in vocal folds

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Dense Irregular Connective Tissue
Fig. 4.7e
Fig. 4.7d

• Dense irregular collagenous
• Forms most of skin dermis

• Dense irregular elastic
• In walls of elastic arteries

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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

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Cartilage

• Composed of chondrocytes located in spaces called
  lacunae
• Next to bone firmest structure in body
• Types of cartilage
• Hyaline
• Fibrocartilage
• Elastic

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Hyaline Cartilage
Fig. 4.7h

• Found in areas for strong support and some
  flexibility
• Rib cage and cartilage in trachea and bronchi
• Forms most of skeleton before replaced by bone in
  embryo
• Involved in growth that increases bone length

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Fibrocartilage
Fig. 4.7i

• Slightly compressible and very tough
• Found in areas of body where a great deal of
  pressure is applied to joints
• Knee, jaw, between vertebrae, between halves of
  pelvic girdle

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Elastic Cartilage

• Rigid but elastic properties
• External ears, epiglottis

Fig. 4.7j
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Bone

• Hard connective tissue that consists of living
  cells and mineralized matrix
• Organic (primarily collagen fibers) and inorganic
  (mineral hydroxyapatite) portions of matrix

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Blood

• Matrix between the cells is liquid
• Hemopoietic tissue
• Forms blood cells
• Found in bone marrow
• Yellow
• Red

Fig. 4.7m
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Muscle Tissue

• Property
• Contracts or shortens in length to generate force
• Types
• Skeletal
• Cardiac
• Smooth

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Nervous Tissue

• Found in brain, spinal cord and nerves
• Property
• Ability to produce action potentials (electric
  signals
• Cells
• Nerve cells or neurons
• Neuroglia or support cells

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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
• Muscle tissue is specialized for contraction
• Nervous tissue is specialized to generate and
  conduct nerve impulses

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Questions?