Histology

Histology

1. If you see a lesion...

   • 1. make a diagnosis
     • Asymmetry | Border | Colour | Diameter | Evolving
   • 2. Determine a prognosis - is it malignant/aggressive?
   • 3. Plan treatment
     • biopsy - what needs to be done?
     • excision - is it comepletley out?
     • related to prognosis: is additional/aggressive treatment needed?
   • 4. Predict/confirm response to drugs
     • will a post-operative (adjuvant) treatment be beneficial?
     • did a pre-operative (neoadjuvant) treatment show an effect?

2. fixation

   • preserves the tissue by...
     • stopping intrinsic autolytic enzyme action
     • prevents putrefication/decay
     • increases mechanical strength to preserve morphology
   • fixatives
     • aldehyde
       • e.g. formalin (formaldehyde solution) | forms protein cross-links, good mechanical strength and penetration | poor nucleic acid preservation
       • e.g. glutaraldehyde (like formalin but larger) | needs smaller tissue samples | works well at low temperatures | used for electron microscopy
     • alcohol
       • e.g. ethanol | reduces protein solubility --> percipitation | nucleic acid research (doesn't cross link) | used in cytology smears
     • oxidative - forms protein cross-links
     • freezing (quick but poor morphology)
   • tissue processing: dehydration via ethanol, replace alcohol with xylene (clearing), replace xylene with wax (wax infiltration), formalin fixed
   • Periodic Acid Schiff (PAS): detection of mucin --> fungal organisms and visualisation of basement membranes. Problem = glycogen is PAS positive
     • detection of mucin --> fungal organisms and visualisation of basement membranes. Problem = glycogen is PAS positive
   • combined with diastase (DPAS) - enzyme diastase removes glycogen

3. epithelial cells

   • main features
     • line all body surfaces except articular cartillage, tooth enamel and anterior iris
     • cellular
     • sits on basal lamina
     • stuck tightly together by intracellular junctions
     • polarity - apical or basal
     • avascular
     • rapid turn-over
   • classification
     • number of cells
       • 1 layer = simple
       • multi-layered = stratified
       • psuedo-stratified - single layer of columnar cells e.g. upper airways - cillia and goblet cells
       • transitional - multiple layers but changes shape (squamous and flat), bladder and urinary tract
     • shape of cells
       • squamous (flat)
       • cuboidal
       • columnar
   • specialisation
     • cillia - push mucus along
     • secretory - release stuff
     • microvilli increase SA of epithelium
   • epithelium
     • for protection
       • prevents dehydration, chemical, mechanical etc. damage
       • covering of inter/outer surfaces
       • stratified
       • replicative to replace sloughed (shed) cells
       • tight seals between cells
       • keratinisation
       • locations
         • squamous: oesophagus, skin, vagina
         • transitional: bladder, urinary tract
     • for absorption
       • epithelial lining of gut specialised for absorption e.g. glucose, ions, water
       • relies on cell polarity
       • adaptations such as brush border
     • for surface movement
       • cilia move in co-ordination to provide unidirectional movement
       • locations
         • airways - mucus
         • testes - sperm
         • fallopian tubes - ova
     • for gas exchange
       • simple squamous cells that line blood vessels - minimal distance for diffusion
   • endothelium
     • for surface lubrication
       • mesothelium is simple epitheloium e.g. serosa (which secrete a lubricating fluid which reduces friction from muscle movement)
       • lines all body cavities
       • potential spaces contain protein rich fluid (serous)
     • for sensation
       • sensory organs are highly specialised epithelia
       • ectoderm - nervouse system - all senses
     • for secretion
       • isolated epithelial cells e.g. goblet cells
       • organised multicellular glandular structures
       • secretory glands
         • endocrine glands - product released into blood
         • exocrine glands - product is released onto surface
           • classification
           • mechanisms of exocrine secretion
             • mercorine
               • fused plama membrane recycled by endocytosis
               • e.g. breast milk casein
             • apocrine
               • apical membrane is pinched off (loss of membrane)
               • e.g. breast milk lipids
             • holocrine
               • cell disintegrates to release product (cell suicide)
               • e.g. sebum in sebaceous glands
   • disorders of epithelial function
     • epidermolysis bullosa
       • blistering skin disorder
       • inherited gene mutation of adhesion molecules that stick epithelium to basement membrane - abnormal anchoring of epidermis to dermis
     • congenital cilliary dyskinesia / Kartagener's syndrome
       • autosomal recessive
       • abnormal cilliary function - secretion accumulation
         • brinchiectasis | sinusitis | situs inversus
     • cystic fibrosis
       • mutation in CFTR gene
         • defective Cl channel on apical surface of epithelila cells - less water in mucus - thickens and builds up

4. mesenchymal (connective tissue)

Images and files in the map