General Introduction

Question 1

What is histology?

Answer 1

Histology is the study of the tissues of the body and how they are arranged to constitute organs

Question 2

What are the two interacting components of tissues?

Answer 2

Cells and extra cellular matrix

Question 3

What is extra cellular matrix?

Answer 3

Extra-cellular matrix (ECM) is the area between two cells

Question 4

What are the functions of the ECM?

Answer 4

• Surrounds the cell
• Provides mechanical support
• Controls the flow of nutrients and signals to the cells

Question 5

What is the ECM composed of?

Answer 5

Fibrous: collagen, elastin, fibronectin, laminin and non-fibrous: proteoglycans and polysaccharides

Question 6

Why is histology dependent on the use of microscopes and other molecular methods of study?

Answer 6

Because of the small size of the cells and matrix components

Question 7

Why are tissues sliced?

Answer 7

Because most tissues and organs are too thick for light to pass through them, so they must be sliced to obtain thin, translucent sections that are attached to glass slides for microscopic examination

Question 8

What is the name of the instrument used to slice tissues?

Answer 8

A microtome

Question 9

What are the steps of tissue preparation?

Answer 9

1. Fixation: small pieces of tissue are placed in solutions of chemicals that preserve by cross-linking proteins and inactivating degradative enzymes
2. Dehydration: the tissue is transferred through a series of increasingly concentrated alcohol solutions, ending in 100%, which removes all the water
3. Clearing: alcohol is removed in toluene or other agents in which both alcohol and paraffin are miscible
4. Infiltration: the tissue is then placed in melted paraffin until it becomes completely infiltrated with this substance
5. Embedding: the paraffin-infiltrated tissue is placed in a small mold with melted paraffin and allowed to harden

Question 10

What are the fixatives used in tissue preparation?

Answer 10

• Formalin- buffered isotonic solution of 37% formaldehyde
• formaldehyde
• glutaraldehyde
• osmium tetroxide (preserve lipid and proteins)

Question 11

What cell components are stained with basic dyes and why?

Answer 11

Anionic components such as nucleic acids are stained more readily with basic dyes because they have a net negative charge. They are called basophilic

Question 12

What cell components are stained with acidic dyes and why?

Answer 12

Cationic components such as proteins with many iodized amino groups. They are termed acidophilic

Question 13

What are some examples of basic dyes?

Answer 13

Toluidine blue, alcian blue, methylene blue and hematoxylin

Question 14

What are some examples of acidic dyes?

Answer 14

Eosin, orange G and acid fuchsin

Question 15

What are some of the organelles stained by basic dyes?

Answer 15

DNA, RNA and glycosaminoglycans

Question 16

What are some of the organelles stained by acidic dyes?

Answer 16

Mitochondria, secretory granules and collagen

Question 17

What is the most common stain in histology?

Answer 17

Hematoxylin and Eosin (H&E) stain. Hematoxylin stains acidic structures dark blue or purple and eosin stains basic structures a pink or red color.

Question 18

What are some special stains in histology?

Answer 18

PAS (Periodic Acid Schiff Stain) which stains DNA, glycogen, glycoproteins, glycosaminoglycans, proteoglycans and colloids a pink color.

Alcian blue stain which stains glycosaminoglycans and polysaccharides a blue color.

Prussian blue stain which identifies iron storage diseases, hemochromatosis and hemosiderosis.

Question 19

What is a biopsy?

Answer 19

A biopsy is a tissue sample that is removed during surgery or routine medical procedures. They are fixed in vials of formalin for later processing and microscopic analysis in a pathological lab.

If the results of the analyses are needed before the procedure is over, a more rapid process involving freezing the biopsy with liquid nitrogen is used.