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