Cells- Histology, epithelial tissues and mesenchymal tissues Flashcards
Ways to assess a legion
A-asymmetry B-border C-colour D-diameter E-evolving
How to perform histology on a legion- Tissue and fixation
Tissue- Need to remove the tissue
Fixation- Need to preserve the tissue.
- Stopping intrinsic autolytic enzyme action (autolysis)
- Prevention of bacterial contamination (putrefaction)
- Increasing mechanical strength to preserve structure / morphology
Ways to preserve tissue is by different fixatives:
– Aldehyde fixatives form protein covalent cross-links
– Alcohol fixatives denature proteins causing aggregation/ fixation
– Oxidizing fixatives form protein cross-links via oxidation
– Freezing – very quick (intra-operative FS) – but poor morphology
Examples of fixatives :
Formalin (formaldehyde solution):
– Forms protein covalent cross-links
– Good penetration / mechanical strength
– Good tissue morphology (the study of the forms of things) preservation
– Poor nucleic acid preservation (DNA/RNA)
Glutaraldehyde:
– Similar to formalin but larger molecule
– Needs smaller tissue samples
– Works well at low temperatures
– Used for electron microscopy- very important
How to perform histology on a legion- Cut up/ block selection and tissue processing
Cut up/ block selection- Cut up/ block selection- Cut up tissue into blocks and place tissue in plastic cassette
Tissue processing-
Aim – Thin slice of tissue to examine under microscope
• To slice thinly enough, the tissue must be stiff & resistant to mechanical trauma. Fixation helps.
• The tissue is placed in wax to allow thin sections to be cut.
• Remove water from tissues by alcohol (dehydration)
• Replace alcohol with xylene (clearing)
• Replace xylene with paraffin wax (wax infiltration)
• Orientate tissue to form a block (embedding / blocking out)
Why can’t we put straight in wax?- tissue is rich in water, wax is hydrophobic. Thus remove water from tissue and replace with wax
The end product of tissue processing is called the paraffin box. This is Formalin Fixed Paraffin Embedded (FFPE) Tissue.
How to perform histology on a legion- Section cutting and mounting and section staining
Section cutting- Make a thin slice of tissue from the wax box, put on water, put on glass slide, stain it.
Section staining- Dyeing the tissue
• An unstained tissue section/slide is translucent to light
• To make visible we use dyes
Haematoxylin and eosin stain (H&E)- most common tinctorial stain
Haematoxylin (purple)- basic dye, stains acidic structure purple thus DNA are purple
Eosin (pink)- acidic dye, stains basic structures pink thus proteins in cytoplasm are pink
How to perform histology on a legion- Section scanning and microscopy and diagnosis and prognosis
Last two steps
Epithelium/epithelia
Layer or layers of cells that cover body surfaces or line body cavities
Structure of basement membrane
Epithelial cells Hemidesmosome Lamina lucida-part of basal lamina Lamina densa- part of basal lamina Reticular lamina
Main features of epithelial tissues
- Derived from endoderm, mesoderm and ectoderm
- They line all the bodies surfaces except- articular cartilage / tooth enamel / anterior iris
- Cellular
- Sit on a layer of connective tissue called the basal lamina
- Stuck tightly together- intra-cellular junctions/complexes
- Polarity-apical/basal i.e. top/bottom
- Avascular-rely on diffusion
- Regeneration- rapid turn-over of new cells
Main functions of epithelial tissues
- Absorption (e.g. stomach / small / large intestine)
- Surface movement (e.g. cilia in airways / fallopian tube)
- Secretion of substances (e.g. glands such as sweat, pancreas)
- Gas exchange (lungs)
- Surface lubrication (pleural / pericardial / peritoneal mesothelium)
- Sensation
- Protection
Why are cell-cell adhesion complexes important to epithelial function?
Epithelium is about adhesion (sticking). CAMS (Cellular adhesion molecules) are critical for epithelium integrity, adherence to underlying basal lamina and intrinsic function.
Structure of an epithelia- TAG DH
Tight junction- Occludin/claudin seals to protein movement/paracellular diffusion; apical
Adherens junction- TM proteins connect across cytoskeletons, below TJs
Gap junctions- small channels allow intracellular ion/small molecule exchange
Desmosome- TM protein connect to others (linked to intermediate filaments) from adjacent cells
Hemi-desmosome- provide attachment to underlying basal lamina
How to name epithelial cells
Specialisation, number of layers, type of layer, epithelium
Epithelium for protection- uses?
- Prevents dehydration, chemical, mechanical etc. damage
- Covering of inter/outer surfaces
- Multi-layered for strength – i.e. stratified
- Replicative to replace sloughed / damaged cells
- Tight seals between cells
- Specialisations such as keratinisation for oesophagus, skin, vagina etc. (squamous) Bladder and urinary tract (transitional)
Epithelium for absorption- uses?
- Epithelial lining of gut specialised for absorption e.g. glucose, ions and water
- Relies on cell polarity
- Brush border for increasing surface area and hence more area for absorption
Epithelium for surface movement- uses?
Cilia move in co-ordination to provide unidirectional movement. Found in airways (mucus), testis (sperm) and fallopian tube (ova).
Epithelium for gas exchange- uses?
Single layer of squamous cells that line blood vessels (endothelium) – minimal distance for gaseous diffusion.
Functions of endothelium in the epithelium:
- Produce prostacyclin (avoids blood clots)
- Control vascular cell growth
- Modulate smooth muscle activity
- Trigger blood coagulation
- Regulate the traffic of inflammatory cells
Epithelium for surface lubrication- uses?
- Mesothelium is simple (unilayer) epithelium known as serosa
- Lines all body cavities
- Potential spaces contain protein rich fluid (serous)
- Lubrication of surfaces that move against each other
Epithelium for secretion- uses?
• Function varies
• Isolated epithelial cells (e.g. goblet cells)
• Organised multicellular glandular structures:
-Ducts open onto epithelial surfaces = exocrine glands
-Glands without ducts secreting into blood stream = endocrine glands
Mechanisms of exocrine secretion- merocrine
– Protein product in intra-cellular vesicle
– Vesicle membrane fuses with cell membrane
– Protein product released by exocytosis
– Fused plasma membrane recycled by endocytosis (the taking in of matter by a living cell by invagination of its membrane to form a vacuole)
– E.g. Pancreatic enzymes in exocrine pancreas
Mechanisms of exocrine secretion- apocrine
– Protein product in vesicle
– Approaches apical membrane
– Apical membrane pinches off with loss of some apical membrane
Mechanisms of exocrine secretion- holocrine
– Secretory product accumulates in cytoplasm
– Cell disintegrates to release product
– Sebum in sebaceous glands
Disorders of epithelial function- Epidermolysis bullosa
- Blistering skin disorder
- Inherited
- Gene mutation of adhesion molecules that stick the epithelium to the basement membrane
- Abnormal anchoring of epidermis to dermis
- Blisters
Disorders of epithelial function- CF
- Mutations in CFTR gene
- Defective chloride channel on apical surface of epithelial cells
- Lungs but also exocrine glands e.g. pancreas
- Less water in mucous-thickens
- Builds up-cannot expel
- Infection
