Histology Lecture 1

Question 0

What 3 purposes of histology?

Answer 0

1. Understand tissue structure at levels not visible to unaided eye
2. Understand relationship between tissue structure and function
3. Establish basis of histopatholgy ie. relationship between abnormal tissue and abnormal function

Question 1

What is histology?

Answer 1

Study of cells and body tissues. Requires use of microscopy.

Question 2

What are the major types of microscopy?

Answer 2

Light microscopy (LM) and Electron microscopy (EM)

Question 3

Definition of light microscopy

Answer 3

Based in interactions of light and tissue components
Magnification: 1000 - 1500
Max. Resolving power: 0.2 micrometers

Question 4

Definition of electron microscopy

Answer 4

Based in interactions of electrons and tissue components.
Magnification: 100x LM
Max. Resolving Power: 1000x LM
1. Transmission EM: white is electron-lucent, dark is electron-dense
2. Scanning EM: pseudo-3D, surface detail

Question 5

Definition of Resolution

Answer 5

Smallest distance at which 2 points can be distinguished from each other.

Question 6

What are the steps for LM tissue preparation?

Answer 6

Fixation, dehydration, embedding, sectioning, and staining

Question 7

How is tissue fixed for LM preparation?

Answer 7

1. Chemical fixation with formalin or,

2. Physical fixation by freezing

Question 8

How do formalin-fixed tissues undergo dehydration, clearing, and embedding for LM preparation ?

Answer 8

Water replaced by organic solvent (unusually ethanol), ethanol replaced by clearing agent (unusually xylene), xylene replaced by paraffin.

Question 9

What are the two main stains?

Answer 9

Hematoxylin and Eosin

Question 10

How does a Hematoxylin stain work?

Answer 10

Hematoxylin stains basophilic, negatively charged tissue components (ie. DNA / RNA) blue.

Question 11

How does an Eosin stain work?

Answer 11

Eosin stains acidophilic, positively charged tissue components (ie. mitochondria, collagen, and secretory granules) pink.

Question 12

What are 5 special dyes and their uses?

Answer 12

1. Orcein: visualizes elastin and elastic fibers
2. Sudan black: visualizes lipids
3. Impregnation with silver salts: visualizes reticular fibers
4. Periodic acid-Schiff (PAS) reagent: visualizes carbohydrates
5. Imunoctyochemistry: based on specific antibody binding

Question 13

What are the preparation steps for EM?

Answer 13

1. Fixation with gluteraldehyde
2. Staining with heavy metals to enhance contrast
3. Freeze fracture and freeze etch: used in TEM and SEM, do not require fixation or embedding. Allows study of membranes

Question 14

What is an artifact?

Answer 14

Structural abnormality resulting from tissue preparation ie. Tissue shrinkage, loss of lipids

Question 15

What is the biological yardstick?

Answer 15

RBC, diameter is 7-8 micrometers