1.2 Examining Cells & Tissues Flashcards
State the meaning of the term tissue.
A group or layer of cells specialised to form a specific function.
How many nanometres are in a millimetre?
1,000,000
1mm = 1000 um (micro metres) = 1000000 (nanometres)
Provide an example of each of the 4 types of tissue.
Epithelial: cells lining inner surfaces of organs, vessels and cavities. E.g. skin.
Nervous: neurons and neurolgia (supporting cells) bundled into fibres called fascicles –> further bundled to nerves.
Muscle: skeletal, cardiac and smooth. Allows for movement.
Connective: connect tissues together, providing support, protection and transport. E.g. blood, lymph, bone and cartilage.
Explain the value of histology in diagnosis.
Allows samples to be viewed and prepared.
- Issue procurement.
- Fixation.
- Embedding.
- samle dehydrated with increasing % alcohol.
- solvent added (e.g. xylene), which allows paraffin wax (embedding medium) to infiltrate the tissue.
- left to solidify overnight.
- solvents strip out fats.
- yields formalin-fixed paraffin-embedded sample (FFPE). - Cutting into thin sections.
- microtome used to cut. - Staining.
- Microscope examination.
Freezing can be used:
1. Tissue procurement.
2. Freezing.
3. Sliced with cryotome (like microtome).
- Used during surgery to rapidly see if any cancer is left.
Describe the common biopsy techniques giving examples of tissues which can be sampled by each method.
Surgical Removal
- removal of tissue or entire organs.
- either through direct excision or endoscope.
- e.g. polycistic kidneys.
Scraping Methods
- curettage.
- skin, uterus
Needle
- fine needle aspiration: lumps
- venepuncture: taking blood
- pipelle: uterus lining
- trephine: bone marrow (large bore needle into back).
Transvascular
- wire catheter into a blood vessel, then travels to target site.
- e.g. heart, lungs, liver.
Patient Collection
- e.g. stool, urine, hair etc.
Explain why tissues need to be fixed and state which fixatives are commonly used.
After biopsy, fixation is needed to prevent tissues degrading.
Sample submerged in solution isotonic to intracellular fluid.
Solution contains formalin (formaldehyde) which forms cross links between proteins.
Describe how tissue processing can lead to the formation of shrinkage and other artefacts.
Frozen preparation of samples are prone to artefacts:
- ice formation.
- folds.
- dust.
- air bubbles.
Discuss the value of histological staining and state the components of tissue stained by routine stains, such as Haematoxylin and Eosin (H&E).
Most stains aren’t water soluble, so solvent (xylene) added to disolve the parafin.
Haematoxylin & Eosin (H&E) used:
- haematoxylin (blue) is basic, binding to acidic structures. E.g. DNA.
- Eosin (pink) is acidic, binding to basic structures. E.g. cytoplasm.
Masson’s trichrome:
- used to examine muscle tissue and connective tissue.
- black to nucleus, red to cytoplasm/RBCs/muscle fibres, blue to collagen.
Periodic Acid-Schniff Stain
- visualise anything with sugar attached, turning magenta.
- helps to identify cancers, fungal infections and kidney diseases.
Discuss the value of specialist methods, such as immunohistochemistry and immunofluorescence.
Immunohistochemistry: labelled antibodies that bind to specific antigens.
- either chromogenic - enzyme attached that produces a coloured product.
- or immunofluoresent where the label is a flurophore.
Outline the advantages conferred by phase contrast, dark field, fluorescence and confocal light microscopy.
Dark field: illuminates unstained samples, so they appear brightly lit against a dark background. Useful for examining cell surface structures.
Phase contrast: enhances image for transparent/colourless speciments, without the need for stains. Useful for looking at live samples.
Fluorescence: Fluorophore added via stain or antibodies. High intensity light source applied, which makes the sample glow. Used to detect specific components of living/fixed cells.
Confocal: type of fluorescent microscopy. Used to view thick speciments, with multiple images taken at different depths. Investigatges eye disease.
Explain why electron microscopes are capable of finer resolution than light microscopes.
Use electron beam instead of photons (visible light).
much smaller limit of resolution.
Hence finer resolution.
Scanning or transmission electron microscopes.
Define the term “limit of resolution”.
smallest distance by which two objects can be separated and still be distingushed as two separate objects.
