Notes on Introduction to Histology

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Introduction and Methods:

• Model of "modern" cell:

Model of modern cell

Compartmentalization of Function

Levels of Organization:

1. Small molecules.

2. Macromolecules and aggregates.

3. Cells.

4. Tissues.

5. Organs.

6. Organ systems.

7. Organism.

Levels of Organization

Vital Activities of Cells:

1. Motility:

• External: whole cell migration.

• Internal: cytoplasmic movement of organelles.

2. Irritability:

• Result of various stimuli including physical, chemical, hormone, etc.

3. Metabolism:

a. Anabolism: storage.

b. Catabolism: cell respiration.

4. Reproduction.

Cell Populations:

1. Proliferating:

a. Cell renewal, birth rate = death rate. Gut lining, skin, blood.

b. expanding, birth rate > death rate.

Cleavage, cancer.

2. Static:

• Differentiated yet can still divide i.g., liver hepatocytes.

3. Non-dividing:

• Chemically and structurally terminally differentiated, no ability to divide e.g., RBC.

There are over 200 specialized cell types in humans, all derived from a single progenitor.

Cell Body Components:

1. Cells composed of proteins, nucleic acids, carbohydrates and fats.

2. Intercellular substances:

a. fibrous intercellular components.

b. amorphous intercellular substances.

3. Body fluids:

a. blood.

b. tissue fluid.

c. lymph.

body is composed of basic components

Body Fluids Coexist in a Dynamic Flow:

• Blood.

• Interstitial tissue fluid.

• Lymph.

Body fluids coexist in a dynamic flow

• Resolving power = smallest distance between 2 objects at which they can be seen as separate objects.

Minimum Resolvable Distance:

1. Inaided eye 0.2 mm.

2. Light microscope (LM) 200 nm.

3. Transmission electron microscope (TEM) 0.2 nm.

Minimum resolvable distance

Bright Field Microscopy:

Utilizes the visible portion of the spectrum.

Specimens can be alive.

Effective magnification 1,000-1,500 X.

Bright field
Bright field vs Phase contrast

TEM and SEM (Electron Microscopes):

Specimens are in a vacuum, therefore dead.

TEM and SEM
TEM and SEM

Freeze Fracture and Etch:

Freeze fracture and etch
Metal shadow replica
plasmalemma
fluorescent vs confocal

Specimen Preparation for LM and TEM:

• Fixation: generally aldehydes.

• LM: 37-40% formaldehyde gas in water.

Generally used as 4-10% formalin buffered to a biological pH. Small molecule with 2 binding sites.

• TEM: glutaraldehyde. Large molecule with 4 binding sites.

Specimen Preparation for LM and TEM
Specimen Preparation for LM and TEM
Specimen Preparation for LM and TEM
Rotary microtome
TEM use

Staining:

• LM - hematoxylin and eosin, H and E; Most common stain.

• TEM - uranyl acetate and lead citrate.

Histochemistry:

The chemical identification and localization of various components of cells or tissues by which the end products are characterized by a colored dye precipitate.

Acidic vs Basic Cell Dyes:

Acidic cell components (like nucleic acids) stain blue or black with basic dyes and are termed basophilic. Basic dyes include hematoxylin, toluidine blue and methylene blue.

From the 60's "Acid heads love bass." Structures that have affinity for acid dyes are acidophilic and stain pink with eosin, acid fuchsin or orange G. H and E, thus gives differential staining.

Staining

Metachromasia:

When a dye like toluidine blue is applied, much of the cytoplasm will stain the color of the dye (blue) but carbohydrate containing structures will stain purple to magenta. This metachromatic shift results from conversion of a monomeric form of the dye (blue) to a polymeric form (magenta).

Additional Reading:

Basic Histology

1. Introduction to Histology
2. Basic Cell Physiology
3. Actin, Microtubules, and Intermediate Filaments
4. Mitochondria, Nucleus, Endoplasmic Reticulum, Golgi
5. Epithelium (Epithelial Tissue)
6. Connective and Adipose Tissue
7. Types of Cartilage
8. Osteogenesis
9. Nervous Tissue
10. Muscle Tissue
11. Cardiovascular System
12. Blood and Hematopoiesis
13. Lymphoid Tissue
14. Digestive Tract I: Oral Cavity
15. Digestive Tract II: Esophagus through Intestines
16. Liver, Pancreas, and Gall Bladder
17. Respiratory System
18. Integument
19. Urinary System
20. Endocrine System
21. Male Reproductive System
22. Female Reproductive System
23. Eye and Ear

Medical Images

Useful Medical Images & Diagrams (link opens in a new window)

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