cytology (Cell biology) 1 l General Histology revision for dental students

 

cytology (Cell biology) 1  l General Histology revision for dental students

Introduction

Light microscope (LM) and Electron microscope (EM):

•         In light microscope (LM) visible light and glass lenses are used to see colored photos magnified up to 1500 times.
•         In electron microscope (EM) invisible electrons and electro-magnetic coils are used to see non-colored photos magnified up to 400.000 times or more.

·        Light microscope (LM) is formed of:

• Metallic parts: base, arm and stage.
• Illumination system: light, mirror and condenser.
• Optical system:

1. Ocular lenses (7 or 10).
2. Objective lenses (3.5 - 8 - 10 - 20 - 40 or 100).

·        Magnification of LM :

•     power of ocular lens × power of objective lens.

·        Units:

• One meter (m) = million micro-meter (μm) while
• One micro-meter (μm) = million pico-meter (pm)

Resolution:

• is the capacity of the microscope to discriminate 2 adjacent points.

 

• Limit of resolution is the shortest distance to discriminate 2 adjacent points.

Its value in:

1. Human eye = 1 mm
2. Light microscope (LM) = 0.2 μm
3. Electron microscope (EM) = 3 nm
4. Atomic force microscope (AFM) = 50 pm

Light microscope (LM)

Body tube :

• non-vacuumed tube

Illumination system :

• visible beam of light (day or electric)

Optical system :

• glass lenses

Magnification :

• up to 1500 times

Resolution :

• around 0.2 μm

Examination:

• by human eyes
• to see many cells with colored photo-micro-graphs (according to stains)

Examples:

• Ordinary light microscope
• Phase contrast microscope

 

Electron microscope (EM)

Body tube :

• vacuumed tube

Illumination system :

• invisible beam of electrons

Optical system :

• electro-magnetic coils

Magnification :

• up to 400.000 times or more

Resolution :

• around 3 nm (0.003 μm)

Examination:

• by fluorescent screen
• to see 1 or 2 cells with non-colored photo-micro-graphs (only black and white)

Examples:

• Transmission EM® 2 dimensions
• Scanning EM ® 3 dimensions

Types of stains used in histology:

• The stains may be of animal origin (as carmine), of plant origin (as hematoxylin) or synthetic (as eosin).

1. Acidic stain (for acidophilic cytoplasm):

• as eosin, orange G, acid fuchsine … ® red color.

2. Basic stain (for basophilic nucleus):

• as hematoxylin, toluidine blue, methylene blue … ® blue color.

3. Neutral stain (for blood films):

• as Leishman stain (eosin + methylene blue absolute methyl alcohol).

4. Vital stain (for living cells inside the body):

• as trypan blue (for reticulo-endothelial cells).

5. Supra-vital stain (for living cells outside the body):

• as brilliant cresyl blue (for blood reticulocytes).

6. Physical stain (stain soluble in alcohol but more soluble in fat):

• as Sudan III (for fat cells).

7. Meta-chromatic stain (stain ® different color):

• as toluidine blue ® violet color (in mast cells).

8. Silver impregnation (for connective tissue fibers):

• leading to brown collagenous fibers - black reticular fibers.

9. Tri-chrome stains (3 stains that differentiate between various structures of the tissue):

• as Mallory stain ® blue collagenous fibers, yellow smooth muscle fibers and red nuclei.