histology Flashcards
what is histology
study of microscopic structure of tissues to identify morphological changes in tissues that characterise disease to allow for accurate diagnosis
why study histology
essential for understanding function + pathological change to allow for accurate diagnosis. need to identify components in normal tissues
what is a cell
basic functional unit of all multi-cellular organisms
steps in tissue processing
1) fixation (dehydration + clearing )
2) embedding
3) sectioning
what is fixation
fixation preserves architecture by treating it with a chemical reagent. this holds tissue components in normal place and prevents tissue from rotting due to bacteria/fungus or autodigestation by enzymes leaking for lysosomes
how do fixatives work
they have binding sites enable them to form cross-links between adjacent tissue protiens = fixed shape. they protect from digestion by binding and inactivating microbes at spare binding site
what is the most common fixative
formaldehyde
what is a limitation of fixation
preserves proteins but not all other important cell components
what are the stages of fixation
dehydration and then clearing
dip tissue in increasing concentrations fo alochol starting at 50% going to 100% and then clearing - dip in xylene to completely remove water
what do you embed it in
wax or resin
how do you embed
place tissue in mould and pour wax in and solidify .
for electron microscope use resin
what happens during sectioning
fit wax into block and use knife to slice into thin slices using a microtome ( thinner = clearer)
differences between light microscope and electron microscope sections
for light microscope - wax sections, 4um + metal blade
for electron - resin sections, 100nm + diamond knife
what happens if blade is blunt for sectioning
crumpled sections (should have ribbons)
what happens during mounting
sections are floated on water and then mounted on a glass slide
what happens during dewaxing
opposite of fixation - to remove chemicals. use xylene to remove wax then go from 100% alcohol to 50% until water to remove xylene and reintroduce water
what are the routine stains for a light microscope
haematoxylin - purple, basic stain nuclei goes purple
eosin - acidic stain, protein goes red/pink
what do epithelial tissues do
cover and line internal + external surfaces of bodies , forming a barrier between other body tissues and internal/external environments across which all exchanges take place. Defends tissues.
Features that are common to all epithelial tissues x5
1) totally cellular (no connective fibres, only cell junctions)
2) no blood vessels
3) have stem cells within = self-regenerating
4) separated from underlying tissues by basal lamina
5) supported by underlying layer of connective tissue (mechanical support) which contains blood vessels (metabolic support)
2 main types of epithelia
simple - single cell layer
stratified - multiple layers of cell
What type of organisation do epithelial cells have
polarised = always attached to basal lamina and have a free surface towards cavity (apical)
define lumen
empty space within tubular organ
3 types of cell junctions
1) occluding = barrier, tight junction
2) anchoring = strength, desmosomes and hemidesmosomes (attach to basal lamina)
3) communicating = movement between cells, gap junction
types of simple epithelia x4
squamous, cuboidal, columnar and pseudostratified
types of stratified epithelia x2
squamous (squamous, keratinised and parakeratotic) and transitional
simple squamous epithelium structure + function
-single layer due to thin cytoplasm
-flattened nucleus + indistinct cytoplasm
-slick surface to allow flow of fluid
-irregular boundaries
-allow rapid transport (gas exchange)
-low-friction (cover internal organs)
structure + function of cuboidal epithelium
- single layer
- cell height ,width +depth are same
-centrally placed nucleus - cover internal surfaces
-cover duct walls (glands for secretion)
-equal cytoplasm around nucleus - no synthetic activity (except thryoid)
structure and function of simple columnar epithelium
- cell height is more than width
-nucleus arranged in ordered layer - no apical specialisations (top end)
-specialised for absorption and secretion (digestive system)
-nucleus towards basal membrane
types of apical specialisation for columnar epithelium
-microvilli (intestine) for absorption, bigger sa
-cilia (airways) draft particles away, move over epithelial surface, gaps
structure + function of pseudostratified columnar epithelium
- nuclei at different levels but still SINGLE layer (all in contact with basal lamina
- ciliated
-restricted to respirator system ( goblet cells = cells that secrete mucus)
stratified squamous epithelium
- basal layer is cuboidal
- upper layers are squamous
- defence against mechanical damage (oral cavity, oesophagus, skin)
-integrity provided from desmosomes - attachment by rete pegs (projections at basal lamina)
keratinised stratified squamous structure + function
- upper layers = squamous and keratohyalin (protein granules)
- superficial (outermost) layer = no cellular detail + keratin (red)
- epidermis = protect from mechanical damage + dessication (drying out)
-strong, semi-waterproof + chemically inert
parakeratotic stratified squamous structure + function
- ruminant forestomach only
-top layer = cellular detail + keratin - protection from coarse ingesta
- absorbs fermentation products (VFA)
transitional epithelium structure and function
- can stretch
- superficial layers are fatter and rounder ( look like frog spawn)
-no keratin or rete pegs - urinary system only
-stretches when bladder fills (tips when stretched look squamous, form troughs when relaxed)
