1. HISTOLOGY

2. INTRODUCTION
Definition: A science: study normal micro-structure & its related function of human body structural levels: Cell: the smallest structural & functional unit. Tissue: groups of cells (similar in morphology or related in function)＋intercellular materials 4 types of fundamental tissue 　　 epithelium 　　 connective tissue 　　 muscular tissue nervous tissue　

3. Organs: organizations of various kinds of tissues in particular ways & perform a specific function.
System: formed by several function-related organs which together perform a continuous physiological function.
For example: digestive system

5. Why to study histology ?
To complete the knowledge of human body’s structures----from gross to microscopic
Be able to understand how the different tissues function----the basis of physiology
Can find the diseases only after the normal is known----the basis of pathology
It is related to some modern science fields: cell apoptosis, cell recognition, implantation of embryo stem cells, eugenics and etc.
It is also a foundation of clinic sciences—for a good doctor needed in futrue

6. Unit used in microscope
1μm=1/1000 mm
1 n m=1/1000μm
Maximum resolution
Light microscope: μm
Transmission electron microscope: 0.2nm
Scanning electron microscope: 5nm

7. Investigative methods of histology
I. Light
microscopy

8. 1. Tissue preparation A. paraffin section preparation
Specimen: as fresh as possible
 Fixation: fixative: formalin solution;
purpose: to preserve the structural
organisation
Dehydration: replace the water in the tissue
by alcohol
Clearing: replace the alcohol by xylene
Embedding: replace the xylene w/ melted
paraffin
Sectioning & mounting
l                      

10. B. Frozen section:
Better for preserving chemical components
(e.g. enzymes)
Freezing→cryotomy→staining
C. the others:
Smear preparations:
for blood etc;
Grind preparations:
for bone

11. Basophilic: components bonded by basic
2. Staining
Purpose: To make tissue section pigment
for observation.
H-E Staining:
Hematoxylin: basic dye, purple-blue
Eosin: acid dye, pink color
Basophilic: components bonded by basic
dye (H); pruple-blue（nuclear chromatin
& basophilic substance in cytoplasm）
Acidophilic: components bonded by acidic
dye (E); pink (cytoplasm & collagenous fiber)

12. Neutrophilic: do not stain w/ both basic and
acid dyes
Metachromasia: a dye stains tissue a
different color from that of dye solution, e.g.
toluidine blue stains mast cells in purple color
Special staining:
Argyrophilia
Fluorescent staining

13. Silver staining of
the neuron and
the bile canaliculi
HO (Hoechst 33258)-PI staining shows the apoptosis in human HL-60 cells

14. II. Electron Microscopy
1. Transmission Electron Microscope (TEM)
Using a beam of electrons (short wave-lengths)
instead of visible light.
Section preparation:
similar to those for L.M mainly,
plastic instead of paraffin,
50-70nm thick,
heavy metal salts instead of HE.
 Resolution: nm (0.2nm)
Ultrastructrue: The structure in EM
Electron-dense / electron-lucent

15. Transmission Electron Microscope

17. Diagrams of TEM

18. 2. Scanning Electron Microscope (SEM)
Sowing the 3 dimensional surface
Architecture of cells and tissues
   Resolution: 5nm

19. III. Histochemistry & Cytochemistry
Reveal the chemical composition in situ (e.g. proteins, a.a., nucleic acid, lipids, enzymes etc.) w/ chemical, biochemical methods.
The product of chemical reaction should be insoluble / colored / electron- scattering, & be seen in LM or EM

20. For instance: PAS(Periodic Acid Schiff) reaction:
for manifesting polysaccharide and
proteoglycan (e.g. glycogen).
polysaccharide + HIO4
(hydroxyl group) (oxidise)
Aldehyde group + Shiff’s reagent (colorless)
Purplish red depositor

21. PAS reaction in the hepatocytes

22. Immunocytochemistry Based on antigen binds to specific antibody.
Tissue section w/ Antigen + labelled antibody
labelled Ag-Ab complex
Fluoresceinlabelling
enzyme labelling
colloidal gold labelling

23. NOS positive neuron in hypothalamus of rat
NOS & GnRH positive Neurons in hypothalamus of rat
NOS positive neuron in hypothalamus of rat

24. m-ATPase activity in skeletal muscles

25. VI. in situ hybridization (ISH)
IV. tissue culture
V. isotopic tracing
VI. in situ hybridization (ISH)
—nucleic acid molecular hybridization
Use nucleotide probe to check target
fragment of intracellular DNA or mRNA in
situ, in order to study the gene expression.

26. Expression of PSA and PSAmRNA in human prostate (histochemistry & ISH)

27. The method in learning histology
Combination of the 2 dimentional structure with 3 dimentional

28. Combination of the theory with
practice
Combination of the structure
with function
Concern the dynamic change