cells and tissues Flashcards
define histology.
study of tissues at a microscopic level
what are the 3 reasons to do histology?
Diagnosis- what things are
Prognosis- what is likely to happen
Treatment- Was it successful?
- Will a treatment be successful?
what does fixation do to tissues?
Formation of cross links within tissue, either by denaturing proteins or forming covalent bonds within the tissue
what are the two ways decay can be stopped?
Intrinsic- autolytic enzymes
Extrinsic- microbial, trauma
what is the most common chemical for fixation?
formalin
what are the benefits of using formalin?
Forms covalent bonds between proteins
Good tissue penetration
what is formalin not good at?
Not good for cytoplasmic structure or nucleic acids
what are the three alternatives to formalin?
Glutaraldehyde
Ethanol
freezing
what are the +ves and -ves of using glutaraldehyde?
For electron microscopy
But poor tissue penetration
what are the +ves and -ves of using ethanol?
For Nucleic acids
Poor for morphology
what are the +ves and -ves of using freezing?
Good for nucleic acids, proteins etc
Poor for morphology
Refrigeration required
what is the purpose of wax impregnation?
Gives tissue rigidity
Allowing sectioning
Protecting tissue
describe the passage to wax in fixing
dehydrated in alcohol
alcohol replaced by xylene
xylene replaced with hot wax
what is the wax block of tissue cut by?
a microtome
what is the most common stain?
Haematoxylin and Eosin
what does haematoxylin stain?
Basic dye that stains acidic structures blue or purple
e.g. DNA in nuclei
what does eosin stain?
Acidic dye that stains basic structures pink
e.g. proteins (cytoplasm)
which stains are in massons trichrome and what does it stain?
Haematoxylin
Acid fuschin
Methyl blue
Collagen = blue
Muscle, cytoplasm, RBC = red
Nuclei = black
what is the clinical application of masons trichrome?
To highlight fibrosis (scarring) e.g. liver cirrhosis
what stains can stain mucin?
Periodic Acid-Schiff (PAS) Alcian blue (Acid mucins only)
what is immunohistochemistry? describe the process.
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
what is immunohistochemistry? describe the process.
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
which embryological layer is epithelium derived from?
all of them Ectoderm (e.g. skin) Mesoderm (e.g. ovarian/peritoneal epithelium, vascular endothelium) Endoderm (e.g. GI tract)
what are the 5 key epithelial characteristics?
Cellularity: tightly bound cells Polarity: have apical/basal surfaces Attachment: lie on basement membrane Avascularity: rely on diffusion Regeneration: have germinative cell division
what are the 5 key features of epithelia?
Provide physical protection Control absorption/secretion Movement Provide sensation Produce specialised secretions
what are the 5 types of junction epithelial cells have to help provide their function?
tight junction adherens junction gap junction desmosome hemi-desmosome
what do tight junctions do?
Occludin/claudin seals to protein movement/paracellular diffusion; apical
what do adherens junctions do?
Transmembrane proteins connect across cell cytoskeletons, below TJs
what do gap junctions do?
Small channels (nm wide) allow intercellular ion/small molecule exchange
what do desmosomes do?
Transmembrane proteins connect to others (linked to intermediate filaments) from adjacent cells
what do hemi-desmosomes do?
Provide attachment to underlying basal lamina
what are the three types of secretion?
merocrine
apocrine
holocrine
how does merocrine secretion work?
just secrete with the cell left intact
how does apocrine secretion work?
a portion of the cell is pinched off as a secretion
how does holocrine secretion work?
cell disintegrates and its contents are released
what are the two possible structures for exocrine glands?
tubular and alveolar (simple and compound)
where do endocrine glands secrete to?
the circulation
what are the three shape types for epithelial cells?
Squamous (e.g. blood vessels)
Cuboidal (e.g. kidney, thyroid)
Columnar (e.g. small bowel)
how can cells be categorised based on layers?
Stratified (e.g. skin, lower female reproductive tract)
Pseudostratified (e.g. trachea, epidydymis)
Transitional: multilayered cell appearance varies with stretch (e.g. bladder)
simple
what is Epidermolysis bullosa simplex?
congenital;
affects keratin intermediate filament
assembly; causes bullae in areas of stress
