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Introduction to Histology

Introduction to Histology

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Introduction to Histology

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  1. Introduction to Histology Cell Structures Dr. Rebecca A. Code Summer Scholars 2007

  2. 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

  3. 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.

  4. Cytoplasmic organelles – other clues to differentiate cell types and function • Ribosomes • Mitochondria • Golgi apparatus • Endoplasmic reticulum • Microfilaments • Secretory vesicles • Pigment granules • Lipid droplets

  5. 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.

  6. Microvillus Cilium

  7. 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

  8. Occluding – the most apical junction Zonula occludens, tight junctions Adhering – 2 types: Zonula adherentes Macula adherens = desmosomes Communicating Gap junctions Cell Junctions

  9. Histology = 2 dimensional image • A section is a slice of tissue • Orientation when sectioned affects what you see.

  10. Section of Round Solid Object A B B A

  11. Sections cut through a curved tube

  12. Light Microscope = tool of the histologist • Oculars (eyepieces) • Stage • Objective Lens • Condenser • Light source • Focus knobs

  13. Specimen Preparation • Fixation, dehydration, embedding • Sectioning • Staining: most common is H&E • 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.

  14. Kidney cells

  15. Heterochromatic and Euchromatic Nuclei

  16. Golgi Apparatus in Nerve Cells

  17. Mitochondria and Myofibrils

  18. Microvilli of Intestinal Epithelial Cells

  19. Cilia of Tracheal Epithelial Cells

  20. False Intercellular Bridges (Desmosomes)