cells and tissues

Question 1

define histology.

Answer 1

study of tissues at a microscopic level

Question 2

what are the 3 reasons to do histology?

Answer 2

Diagnosis- what things are
Prognosis- what is likely to happen
Treatment- Was it successful?
- Will a treatment be successful?

Question 3

what does fixation do to tissues?

Answer 3

Formation of cross links within tissue, either by denaturing proteins or forming covalent bonds within the tissue

Question 4

what are the two ways decay can be stopped?

Answer 4

Intrinsic- autolytic enzymes

Extrinsic- microbial, trauma

Question 5

what is the most common chemical for fixation?

Answer 5

formalin

Question 6

what are the benefits of using formalin?

Answer 6

Forms covalent bonds between proteins

Good tissue penetration

Question 7

what is formalin not good at?

Answer 7

Not good for cytoplasmic structure or nucleic acids

Question 8

what are the three alternatives to formalin?

Answer 8

Glutaraldehyde
Ethanol
freezing

Question 9

what are the +ves and -ves of using glutaraldehyde?

Answer 9

For electron microscopy

But poor tissue penetration

Question 10

what are the +ves and -ves of using ethanol?

Answer 10

For Nucleic acids

Poor for morphology

Question 11

what are the +ves and -ves of using freezing?

Answer 11

Good for nucleic acids, proteins etc
Poor for morphology
Refrigeration required

Question 12

what is the purpose of wax impregnation?

Answer 12

Gives tissue rigidity
Allowing sectioning
Protecting tissue

Question 13

describe the passage to wax in fixing

Answer 13

dehydrated in alcohol
alcohol replaced by xylene
xylene replaced with hot wax

Question 14

what is the wax block of tissue cut by?

Answer 14

a microtome

Question 15

what is the most common stain?

Answer 15

Haematoxylin and Eosin

Question 16

what does haematoxylin stain?

Answer 16

Basic dye that stains acidic structures blue or purple

e.g. DNA in nuclei

Question 17

what does eosin stain?

Answer 17

Acidic dye that stains basic structures pink

e.g. proteins (cytoplasm)

Question 18

which stains are in massons trichrome and what does it stain?

Answer 18

Haematoxylin
Acid fuschin
Methyl blue

Collagen = blue
Muscle, cytoplasm, RBC = red
Nuclei = black

Question 19

what is the clinical application of masons trichrome?

Answer 19

To highlight fibrosis (scarring) e.g. liver cirrhosis

Question 20

what stains can stain mucin?

Answer 20

Periodic Acid-Schiff (PAS)
Alcian blue (Acid mucins only)

Question 21

what is immunohistochemistry? describe the process.

Answer 21

to identify a specific molecule of interest ((antigen (Ag)) in a cell

The antibodies (Ab) to this Ag are generated by exposing an animal e.g. rabbit, to this antigen
This Ab is applied and binds to a section
A second, labelled anti-rabbit Ab is applied

Question 22

what is immunohistochemistry? describe the process.

Answer 22

to identify a specific molecule of interest ((antigen (Ag)) in a cell

The antibodies (Ab) to this Ag are generated by exposing an animal e.g. rabbit, to this antigen
This Ab is applied and binds to a section
A second, labelled anti-rabbit Ab is applied

Question 23

which embryological layer is epithelium derived from?

Answer 23

all of them
Ectoderm (e.g. skin)
Mesoderm (e.g. ovarian/peritoneal 
epithelium, vascular endothelium)
Endoderm (e.g. GI tract)

Question 24

what are the 5 key epithelial characteristics?

Answer 24

Cellularity: tightly bound cells
Polarity: have apical/basal surfaces
Attachment: lie on basement membrane
Avascularity: rely on diffusion
Regeneration: have germinative cell division

Question 25

what are the 5 key features of epithelia?

Answer 25

``` Provide physical protection Control absorption/secretion Movement Provide sensation Produce specialised secretions ```

Question 26

what are the 5 types of junction epithelial cells have to help provide their function?

Answer 26

``` tight junction adherens junction gap junction desmosome hemi-desmosome ```

Question 27

what do tight junctions do?

Answer 27

Occludin/claudin seals to protein movement/paracellular diffusion; apical

Question 28

what do adherens junctions do?

Answer 28

Transmembrane proteins connect across cell cytoskeletons, below TJs

Question 29

what do gap junctions do?

Answer 29

Small channels (nm wide) allow intercellular ion/small molecule exchange

Question 30

what do desmosomes do?

Answer 30

Transmembrane proteins connect to others (linked to intermediate filaments) from adjacent cells

Question 31

what do hemi-desmosomes do?

Answer 31

Provide attachment to underlying basal lamina

Question 32

what are the three types of secretion?

Answer 32

merocrine apocrine holocrine

Question 33

how does merocrine secretion work?

Answer 33

just secrete with the cell left intact

Question 34

how does apocrine secretion work?

Answer 34

a portion of the cell is pinched off as a secretion

Question 35

how does holocrine secretion work?

Answer 35

cell disintegrates and its contents are released

Question 36

what are the two possible structures for exocrine glands?

Answer 36

tubular and alveolar (simple and compound)

Question 37

where do endocrine glands secrete to?

Answer 37

the circulation

Question 38

what are the three shape types for epithelial cells?

Answer 38

Squamous (e.g. blood vessels) Cuboidal (e.g. kidney, thyroid) Columnar (e.g. small bowel)

Question 39

how can cells be categorised based on layers?

Answer 39

Stratified (e.g. skin, lower female reproductive tract) Pseudostratified (e.g. trachea, epidydymis) Transitional: multilayered cell appearance varies with stretch (e.g. bladder) simple

Question 40

what is Epidermolysis bullosa simplex?

Answer 40

congenital; affects keratin intermediate filament assembly; causes bullae in areas of stress