Introduction to Histology

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Introduction to Histology

• Cell Structures
• Dr. Rebecca A. Code
• Summer Scholars 2007

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Histology the study of cellular structures of
the body

• Anatomy at the microscopic level (microanatomy)
• Cells---tissues---organs---organ systems
• 1015 cells in the human body
• 200 cell types in the body

Observation the key to identifying cell types
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Nucleus present in almost all cells, stains
well with hematoxylin.

• Size
• Shape
• Location
• Number
• Nucleolus site of rRNA synthesis
• Density
• Euchromatic light staining nucleus due to
  regions of chromosomes that are less coiled,
  indicating that the DNA is actively transcribing
  mRNA.
• Heterochromatic dense, darkly staining nucleus
  due to tightly coiled chromatin, presumably not
  transcriptionally active.

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Cytoplasmic organelles other clues to
differentiate cell types and function

• Ribosomes
• Mitochondria
• Golgi apparatus
• Endoplasmic reticulum
• Microfilaments
• Secretory vesicles
• Pigment granules
• Lipid droplets

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Cell Specializations

• Microvilli found on many epithelial cells 1-2
  mm long extensions of cell membrane increase
  surface area (15-20X) for absorption lots of
  microvilli brush border
• Cilia 7-10 mm long motile structures
  stabilized by microtubules function to move
  fluid over cells found in trachea, bronchi,
  oviducts, flagella of sperm.
• Stereocilia very long microvilli, non-motile
  for absorption in epidydimus and on hair cells
  of inner ear.

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Microvillus
Cilium
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Cell Adhesions/Junctions

• Nearly all cells are connected to neighboring
  cells by cell junctions
• Occluding junctions join cells together to form
  impermeable barrier
• Adhering junctions provide mechanical attachment
  between cells.
• Communicating junctions permit movement of ions
  or molecules between cells

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Cell Junctions

• Occluding the most apical junction
• Zonula occludens, tight junctions
• Adhering 2 types
• Zonula adherentes
• Macula adherens desmosomes
• Communicating
• Gap junctions

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Histology 2 dimensional image

• A section is a slice of tissue
• Orientation when sectioned affects what you see.

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Section of Round Solid Object
A
B
A
B
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Sections cut through a curved tube
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Light Microscope tool of the histologist

• Oculars (eyepieces)
• Stage
• Objective Lens
• Condenser
• Light source
• Focus knobs

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Specimen Preparation

• Fixation, dehydration, embedding
• Sectioning
• Staining most common is HE
• Hematoxylin cationic dye ( charge) that binds
  to negatively charged (acidic) structures in the
  cell. Example nucleus blue
• Eosin anionic dye (- charge) adheres to basic
  structures in the cell. Example amine groups
  (NH3) on proteins make cytoplasm pink.

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Kidney cells
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Heterochromatic and Euchromatic Nuclei
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Golgi Apparatus in Nerve Cells
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Mitochondria and Myofibrils
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Microvilli of Intestinal Epithelial Cells
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Cilia of Tracheal Epithelial Cells
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False Intercellular Bridges (Desmosomes)