introduction to histology

Question 1

define histology

Answer 1

the microscopic study of normal cells and tissues

Question 2

define pathology

Answer 2

the microscopic study of diseased cells and tissues

Question 3

name the four biomolecules of life

Answer 3

proteins, carbohydrates, lipids and nucleic acids (DNA/RNA)

Question 4

define tissues

Answer 4

groups of similar cells working together to perform a particular function

Question 5

define organs

Answer 5

two or more tissues interacting with each other

Question 6

define system

Answer 6

groups of organs interacting with each other

Question 7

name the four main tissue types

Answer 7

epithelial, muscle, nervous and connective

Question 8

describe the function of light microscopes

Answer 8

• reveal basic cellular structure
• 0.2 micrometre resolution
• most commonly used for histology

Question 9

describe the function of electron microscopes

Answer 9

• reveal ultrastructure
• 1 nanometre resolution

Question 10

why does microscopy require thin tissues?

Answer 10

to allow light/electrons to pass through

Question 11

what are the stages of microscopy preparation?

Answer 11

• specimen collection, fixation, dehydration, embedding

Question 12

what are the different methods of specimen collection?

Answer 12

• incision/punch biopsy
• needle biopsy
• endoscopic biopsy

Question 13

what is the purpose of fixation?

Answer 13

• preserves the structural arrangement between cells and extracellular components
• stops all biochemical reactions, stopping enzyme activity, preventing tissue decomposition and microbial growth (dead cells release enzymes which degrade the tissue)

Question 14

what are common fixative examples?

Answer 14

formaldehyde and glutaraldehyde

Question 15

what is the purpose of dehydration?

Answer 15

• paraffin embedding is NOT compatible with water so it must be removed from the tissue
• this is done using a series of graded alcohols
• the water is removed gradually to prevent the tissue being distorted

Question 16

describe tissue embedding

Answer 16

• thin tissues are required for microscopy however most tissues are too delicate to be cut and would distort, therefore, the tissues must be supported before they are cut
• resins and (paraffin) wax are used for this
• paraffin wax is NOT compatible with alcohol so here the alcohol is replaced with xylene

Question 17

describe tissue sectioning

Answer 17

• tissue sections must be thin and flat- ideally a single layer of cells
• tissue sections should be transparent
• sectioning is done on embedded specimens using a microtome
• ideally around 7 micrometers thick sections of tissue
• the tissue sections are mounted onto glass slides

Question 18

what is the need for tissue staining?

Answer 18

most cells are colourless and transparent so staining makes them visible

Question 19

what is the problem with staining following the use of wax?

Answer 19

stains are mainly aqueous therefore not compatible with paraffin wax, this means rehydration of the tissue sample is required to remove the wax

Question 20

what is H & E staining?

Answer 20

• haemotoxylin and eosin staining
• most common staining technique
• haemotoxylin is basic and dyes acid structures blue/ purple
• eosin is acidic and dyes basic structures red/pink

Question 21

what is PAS staining?

Answer 21

• periodic acid-schif reaction
• stains complex carbohydrates eg mucins magenta
• complex carbs are tightly packed so stain deeply
• muffins produced by goblet cells, brush borders and basement membranes are all PAS positive

Question 22

what is Masson trichrome staining?

Answer 22

• stains connective tissues
• nuclei and other basophilic structures stain blue/purple
• collagen stains green/blue
• cytoplasm, muscle, rbc and keratin stain red

Question 23

what is immunonistochemistry?

Answer 23

• uses antibodies to stain specific cellular proteins
• utilises antibody specificity for their antigen, to reveal these components by joining the antibody to a colour indicator

Question 24

name some other staining techniques

Answer 24

-rectulin- stains rectulin fibres blue/black
- alcian blue- stains cartilage
- van gieson- stains collagen red and cytoplasm yellow