1.1 - Intro to Pathology Flashcards
What is pathology
- Branch of medicine concerned with diseae and understanding the process of disease
- Explains why patients experience symptoms
- Guides treatments
What is disease
- pathological condition of a body part, an organ, or a system characterised by an identifiable group of signs + symptoms
- Consequence of failed homeostatis
- Consequent morphological and function disturbances
Different pathology disciplines
- chemical pathology aka clinical biochemistry is biochemical investigation of endocrine diseases eg thyroid disease, inborn errors of metabolism, diabetes etc
- haematology ie blood clotting factors, blood transfusions
- cellular pathology aka histopathology. Subdivided into neuropathology, forensic + paediatric pathology
- immunology eg auto-immunity and immunodeficiency
- medical microbiology disease caused by microbes + virology. Including advice on antibiotic usage
What is cellular pathology + cytopathology study
cellular pathology examines organs, tissues and cells for diagnosis and to guide treatment, often cancer work + conducting autopsies
cytopathology is study of disaggregated cells rather than tissue
Histology vs cytology
histology
- Whole piece of tissue (inc cells, stroma + extracellular matrix)
- Eg biopsies, cancer resection, excised skin lesions
- Often therapeutic + diagnostic
- Can assess architecture around cells
- Can differentiate invasive from in situ disease
- Provides info about completeness of excision
- Grading and staging
- Better for immunohistochemical and molecular testing
cytology
- Just cells + groups of cells (architecture may be lost)
- Fine needle aspirates of breast, thyroid, lymph nodes etc + cervical smears + urine
- Faster + cheaper
- Non-invasive and safe
- Good for cells in fluid
- May need to still take histology for more investigations
- Higher error rates
- Only really used for confirming/excluding cancer, rather than diagnosis
What can histopathologists determine from pathology investigations
- Type of cancer
- Grade of cancer (ie how differentiated is it → how aggressive is disease process)
- Completeness of excision
- Stage of cancer
- Likely efficiency of further treatments
How is staging of cancer done? TNM
- Looks for tumor, nodes and metastasis
- Determines what the patient has next ie treatments, discharged etc
What is tissue autolysis
- Self digestion of tissues begins when the blood supply is cut off
- Destroys cells + tissues architecture
- Can block biochemical process of autolysis with fixatives
Fixation + what does it do
- Fixatives hold tissue in suspended animation
- Usually use formalin (formaldehyde in water)
- Penetrates tissue at 1mm/hr
- Inactivate tissue enzymes + denature proteins
- Prevent bacterial growth
- Harden tissue
- for larger specimens ☞ need to slice into so that it has a larger SA
How are specimens processed (broadly, detail on separate cards)
- Specimen taken eg aspiration or biopsy
- Fixation to prevent autolysis + cell damage
- Trimming (cutting up sample)
- Embedding (hardening agent eg paraffin wax)
- Blocking
- Microtomy
- Staining (ie with H+E)
- Mounting (preserving + protecting slice of tissue)
- Microscopy
- Make diagnosis
How is embedding done
- In order to cut thin sections, tissue needs to be hardened
- Done by surrounding with paraffin wax
- Have to remove water from tissue → dehydration of tissue using alcohol in a vacuum
- Then replace alcohol with xylene (can mix with wax)
- Then replace xylene with molten paraffin wax which can penetrate the cells
☞ can also be done by processors
What is the process of blocking
- Tissue taken out of the cassettes by hand
- Put into metal blocks
- These are filled with molten paraffin wax
- Wax is allowed to harden
- Metal tray removed
- Can then cut using microtomy
Process of microtomy
- Need to cut very thin slices from the block
- Very thin = need to see on microscope
- 3-4 microns thin
- Cut using microtome
- The thin wax sections are floated on a water bath to separate them
- Picked up on microscope slide
Staining
- Colouring the tissue so that it can be see under a microscope
- Usually done with H+E
- haematoxylin stains nuclei purple
- eosin stains cytoplasm + connective tissue pink
- Other stains can be used to demonstrate different substances/structures and micro-organisms
Process of mounting + microscopy
- Preserving + protecting the slice of tissue
- Mounting medium applied to the slide
- Coverslip placed on top
- Slides looked at by pathologist
- Diagnosis made
What is immunohistochemistry
- Demonstrates substances in-/on cells by labelling them with specific antibodies
- Any substance that is antigenic can be identified ie contractile protein actin (smooth muscle cells), cadherins, hormone receptors, Her2 receptors + microorganisms etc
- Usually antibody is joined to enzyme (eg peroxidase) that catalyses colour-producing reaction
- Can use cytokeratins (family of intracellular fibrous proteins that are present in all epithelia) ☞ act as markers for epithelial differentiation
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What is immunohistochemistry
- Demonstrates substances in-/on cells by labelling them with specific antibodies
- Any substance that is antigenic can be identified ie contractile protein actin (smooth muscle cells), cadherins, hormone receptors, Her2 receptors + microorganisms etc
- Usually antibody is joined to enzyme (eg peroxidase) that catalyses colour-producing reaction
- Can use cytokeratins (family of intracellular fibrous proteins that are present in all epithelia) ☞ act as markers for epithelial differentiation
What is molecular pathology
- Studies how diseases are caused by alterations in normal cellular biology
- Can be due to altered DNA, RNA or protein
- Ie sequencing of DNA from tumour can show if mutation is present in a particular gene
- mRNA ‘signatures’ can predict how a tumor is likely to behave
what are frozen sections and how are they used (process on separate card)
- urgent histopathology (ie while patient still on operating table)
- not as good quality as paraffin sections
- takes about 10-15 mins from receiving specimen to making diagnosis
- aim is to establish the presence + nature of a lesion (and therefore influence the course of the operation)
- accuracy is 96% so risk of misinterpretation
process of frozen sections
- sample received from operating theatre
- specimen cut to reveal lesion
- cut lesion sample is rapidly frozen
- microtomy to make thin slice
- examined under microscope to make diagnosis
- diagnosis reported back to surgeon
what information does histology/cytology reports contain
- clinical details (ie prev diagnosis etc)
- macroscopic (appearance when cut up)
- microscopic (appearance under microscope)
- conclusion (used to help guide diagnosis)
what clinical details need to be included on histology/cytology request form
- age
- gender
- past medical history
- symptoms + signs
- risk factors (ie smoking history)
- endoscopic findings (if relevant)
- clinical teams thoughts and diagnoses
