Introduction to PP Flashcards
What is pathology
Branch of medicine concerned with disease and understanding the process of disease
Have an overview of the different branches of pathology
Chemical pathology (clinical biochemistry)
Biochemical investigations of disease eg. Endocrinology, diabetes, lipidology, thyroid disease, inborn errors of metabolism
Haematology
Diseases of the blood, blood clotting, blood transfusion and bone marrow transplantation
Immunology
Diseases of the immune system eg. Allergy, autoimmunity and immunodeficiency
Medical microbiology
Disease-causing microbes including advice on antibiotic usage
Cellular pathology (histopathology and cytopathology)
Examine organs, tissues and cells for diagnosis and to guide treatment, often cancer work
Conduct autopsies
Neuropathology, forensic pathology, paediatric pathology
Differentiate between cytology and histology
Histology - study of macroscopic and microscopic tissue samples - viewing microscopic slides prepared from tissue sections
Eg. Core biopsies, excised skin lesions, endoscopic biopsies, cancer resection specimens
Often therapeutic as well as diagnostic
Differentiate between invasive from in situ disease
Identify behaviour of cancer or how it will differentiate, and completeness of excision
Cytology - study of specimens consisting of disaggregated cells rather than tissue - study of cells scraped or sucked out of an organ or lesion, or extracted from a body fluid such as urine
Eg. Fine needle aspirates of breast, thyroid, salivary glands, lung; effusions, cervical smears, sputum, urine
Faster and cheaper
Minimally invasive and very safe
Often used as preliminary test before other investigations or more tissue taken for histology
Higher inadequate and error rates
Identify if cancer or not and not for diagnosis
What information can be obtained from microscopic examinations
Before major surgery to remove a lesion, a microscopic diagnosis is required
Guides the type and extent of surgery
If it is cancer, histopathologists can also find what type of cancer, grade of cancer, stage of cancer, completeness of excision and if margins are involved which ones, likely efficacy of further treatments
State the process involved in producing microscopy slides
Fixation Cut-up (trimming) Embedding using processors Blocking Microtomy Staining Mounting Microscopy
Describe what happens in fixation
Tissue autolysis (self-digestion)
After cutting off blood supply, tissue begins to self digest and decay
Stop this process with fixatives (preserves tissue)
Inactivates tissue enzymes and denature proteins
Prevent bacterial growth
Harden the tissue to cut a very thin slice
Fixation - hold tissue ‘suspended animation’
Usually use formalin
Describe what happens in cut-up
Pathologist needs to cut samples out of tissue and place into cassette
About the size of a stamp so they can be adequately infiltrated by chemicals
May need to take 30 or more in complicated cases
Cassettes have holes in and placed in racks in formalin
Describe what happens in embedding in processors
Getting the tissue hard to able to slice thin sections - use paraffin wax
Have to remove the water from the tissue first
Dehydration using alcohol in a vacuum so that water is drawn out of the cells
Then replace alcohol with xylene which can mix with wax
Then replace xylene with molten paraffin wax
Describe what happens in blocking
Tissue taken out of cassettes by hand and put into metal blocks
These are filled with molten paraffin wax and body of cassette is placed on top
Wax is allowed to harden and the metal tray is removed
Describe what happens in microtomy
Very thin sections are cut from the block using microtome
Thin wax sections are floated on a water bath and picked up on a microscope slide
Place into water bath to eliminate wrinkles in tissue and allow tissue to stick onto slide
Describe what happens in staining
Usually with H&E
Haematoxylin stains nuclei purple
Eosin stains cytoplasm and connective tissue pink
Describe what happens in mounting
Preserving and protecting the slice of tissue
Mounting medium is applied to the slide, coverslip is put on top
Mounting medium dries and hardens, preserving the tissue and attaching the coverslip
What is immunohistochemistry
Immunohistochemistry - demonstrates the presence in or on cells of specific substances, usually proteins, by labelling them with antibodies
Usually the antibodies are joined to an enzyme (e.g., peroxidase) that catalyses a colour-producing reaction (most commonly brown)
Define molecular pathology
Studies how diseases are caused by alterations in normal cellular molecular biology
What is frozen section and when are they used
Urgent histopathology - bypass the processes of formalin fixation and embedding in paraffin wax and instead involve rapidly freezing a small piece of fresh tissue on a cryostat
Piece of tissue can then be sliced thinly, stained, mounted and passed to a pathologist for microscopy
Takes about 10 minutes from receiving specimen in lab to giving a result
Not routinely used as morphology not as good as in paraffin sections
Accuracy is in the order of 96% -misinterpretation or absence of diagnostic tissue in frozen section
Aim to establish presence and nature of a lesion and influence the course of the operation
