Introduction To Pathology & Cell Injury Flashcards
What does diagnostic pathology involve?
Studying the structural and function alterations in cells and tissues in order to arrive at a diagnosis
What are the main branches of pathology?
Medical microbiology -virology Chemical pathology Haematology Immunology Cellular pathology (histopathology and cytopathology) -neuropathology -forensic pathology -paediatric pathology
What is the difference between histopathology and cytology?
Histology involves viewing microscopic slides prepared from tissue sections
Cytology is the study of cells scraped from or sucked out of an organ or lesion or extracted from a body fluid such as urine
Does cytology or histology have higher inadequate and error rates?
Therefore cytology is generally used for what?
Cytology
Used to confirm/exclude cancer or dysplasia rather than to diagnose other conditions
What are the advantages of histology over cytology?
The architecture as well as the cellular atypia re assessed which allows differentiation in situ and allows you to make comment on the completeness of excision
Can grade and stage more completely
Better for immunohistochemical and molecular testing
What 9 stages are involved from taking a pathological specimen to the report?
1) Fixation
2) Trimming
3) Embedding
4) Blocking
5) Microtomy
6) Staining
7) Mounting
8) Microscopy
What is immunohistochemistry?
Demonstrating the presence in or on cells of specific substances, usually proteins, by labelling them with antibodies
Give examples of 5 antigenic substances that can be demonstrated by immunohistochemistry
Contractile protein actin Cytokeratins Microorganisms Hormone receptors Her2 receptor
What is molecular pathology?
The study of how diseases are caused by alterations in normal cellular molecular biology
(Can be due to altered DNA, RNA or protein, most often DNA)
What do frozen sections allow that processes of formalin fixation and embedding do not?
Very quick (10 minutes) retrieval of results for a specific piece of tissue to establish the presence and nature of the lesion whilst the patient is still on the operating table
Are frozen sections or routine paraffin wax embedded sections easier to interpret?
Paraffin wax embedded sections as the cell morphology is easier to interpret
Name 7 things that can cause damage to cells
1) Hypoxia
2) Physical agents e.g. Direct trauma, extremes of temperature, electric currents, radiation
3) Chemical agents and drugs e.g. Glucose or salt in hypertonic solutions, oxygen in high concentrations, poisons, alcohol, illicit drugs, therapeutic drugs
4) Microorganisms
5) Immune mechanisms
6) Dietary insufficiency and deficiencies and dietary excess
7) Genetic abnormalities e.g. Errors of metabolism
How can causes of hypoxia be classified?
Hypoxaemic
Anaemic
Ischaemic
Histiocytic
What is the purpose of fixation?
To block the biochemical process of AUTOLYSIS by used fixatives: inactivate tissue enzymes, denature proteins, prevent bacterial growth, harden tissue
What substance is used to fix tissue samples?
Formalin (formaldehyde in water)
What happens during embedding of tissue?
Dehydration of tissue using alcohol in a vacuum, then the alcohol is replaced with XYLENE and then replace the xylene with paraffin wax
How thick are the sections of tissue cut by the microtome?
3-4 microns
What is used to stain the tissue?
What colour does it stain the cell?
Haemotoxylin and Eosin (H and E)
Stains the nuclei PURPLE and
cytoplasm/connective tissue PINK
Name 7 causes of cell injury
Hypoxia, toxins, physical agents, radiation, micro-organisms, immune mechanisms, dietary insufficiency/ dietary excess
What are the four main types of hypoxia?
Hypoxaemic hypoxia
Anaemic hypoxia
Ischaemic hypoxia
Histiocytic hypoxia
What are some of the effects of short term hypoxia?
Cell swelling and blebbing
Increased glycolysis
Inability to synthesise proteins- fat deposition (e.g. Fatty Liver)
What are the consequences of prolonged hypoxia
Decreased levels of ATP
Decreased phospholipids
Digestion of membrane and cytoskeletal proteins
Damage to nuclear chromatin
What are the three most biologically relevant Reactive Oxygen Species (ROS)?
OH. (Hydroxyl free radical)
O2- (Superoxide)
H2O2 (Hydrogen Peroxide)
How do ROS cause damage to cells?
Lipid peroxidation damages the cell membrane by producing more free radicals
Oxidises proteins, carbohydrates and DNA–> mutagenic–>carcinogenic
The anti-oxidant system is made up of what to help protect against ROS?
ACE vitamins which donate electrons
Metal carrier and storage proteins which sequester iron and copper
Enzymes
What are some causes of ROS production?
Radiation Normal oxidative reactions Oxidative burst Drugs/chemicals Contact with unbound metals
What are the four essential cell components that are the principal targets of cell injury?
- Cell membranes
- Nucleus
- Proteins
- Mitochondria
!!Describe the stages of hypoxic cell injury:
- Cell is deprived of oxygen
- Mitocondrial ATP production stops
- ATP-driven membrane ionic pumps run down
- Sodium and water seep into the cell
- Cell swells and the PM is stretched
- Glycolysis enables cell to limp on for a while
- Heat shock stress response
- pH drops as lactic acid accumulates
- Calcium enters the cell
- Calcium activates phospholipases, proteases, ATPases and endonucleases
- ERand organelles swell
- Enzymes leak out of lysosomes and attack cell contents
- Cell membranes damaged and start to bled
- Cell dies
During hypoxic cell injury, calcium activates phospholipases, proteases, ATPases and endonucleases, how do they damage the cell?
Phospholipases- break down cell membrane
Proteases- damage cytoskeleton and cell membrane
ATPases- further loss of ATP
Endonucleases- clumping of nuclear chromatin
What are heat shock proteins?
Give an example
Proteins that are released after any form of injury to protect the cell and maintain protein viability
Ubiquitin
What is ischaemia-reperfusion injury?
When ischaemic tissue is reperfused with blood, it can sometimes cause more damage due to increased production of free radicals, increased neutrophils causing more inflammation and delivery of complement proteins
How do injured cells appear under the microscope?
Pale
Swollen
Blebbing
How do dead cells appear under the microscope?
Pink cytoplasm with varying degrees of change to the nucleus
(Karyo)Pyknosis is what?
How does this look under the microscope
The irreversible condensation of chromatin of cells undergoing apoptosis/necrosis
Pink cytoplasm, nucleus very dark and shrunken
What is karyorrehxis?
How does this look under the microscope?
The irreversible rupture and fragmentation of the nucleus of cells undergoing apoptosis/necrosis
Pink cytoplasm, nucleus broken up into bits
How would you describe the process by which cells lose their nucleus completely as a result of apoptosis/necrosis?
Karyolysis
Due to DNAses and RNAases
What is oncosis?
Cell death with swelling: spectrum on changes that occur in injured cells PRIOR to cell death in injured cells
What is apoptosis?
Cell death with shrinkage: death of a single cell or a cluster of cells due to an INTERNALLY PROGRAMMED and CONTROLLED ACTIVATION of CELL DEATH
What is necrosis?
Is it a type of cell death?
In a living organism the MORPHOLOGICAL changes that occur after a cell has been dead some time
NO this is not a type of cell death, it just describes the visible features of cell death
What are the two main types of necrosis?
What other two also exisit?
Coagulative necrosis
Liquifactive necrosis
Others: Caseous necrosis and fat necrosis
What is the difference between coagulative and liquifactive necrosis, which tissues do each of these occur in, how do they present microscopically?
Coagulative: seen in ischaemia of solid organs, denaturation of proteins e.g. heart, the cell architecture is preserved- get ghost outline of cells
Liquifactive: seen in ischaemia of loose tissues, enzymatic release and digestion of tissues e.g.brain, lungs, can’t really see anything- no cell architecture, may be lots of neutrophils present
What is caseous necrosis?
Where is this most commonly seen?
“Cheese-like” necrosis that contains structureless debris
Some broken down cells, no ghost cells
In TB infected lungs
What is fat necrosis?
What does it look like?
Necrosis due to enzyme leakage which break down fats to produce fatty acids which then react with calcium to form calcium salts (hard lump)
How do apoptotic cells appear under the microscope?
Shrunken and intensely eosinophillic
Chromatin condensation
Cytoplasmic BUDDING, not blebbing as seen in oncosis
What are the three key phases of apoptosis?
Initiation
Execution
Degradation
What is “gangrene”?
What are the two types of gangrene and how do they differ?
Necrosis visible to the naked eye
Dry gangrene: visible necrosis that has been modified by exposure to air (coagulative necrosis)
Wet gangrene: visible necrosis that has been modified by infection (liquifactive necrosis) e.g. gas gangrene
Define the term “infarct”
An area of necrotic tissue which is a result of loss of arterial blood supply
What is an “infarction” ?
Necrosis caused by a reduction in arterial blood flow by thrombus, embolus, testicular torsion for e.g.
What three factors contribute to the outcome of an infarction?
The alternative blood supply
Speed of ischaemia
The tissue that is involved
The oxygen content of the blood
Give the different colours that can be used to describe infarcts and the tissues that they may occur in
White infarct: In solid organs after occlusion of an end artery e.g. heart
Red infarct: In loose tissues with collateral blood supply allowing haemorrhage into the dead tissue
What are the principle toxic molecules that are released from cells when they are injured?
Potassium
Enzymes
Myoglobin
What is calcification of tissues?
How can this be divided into two groups?
The abnormal deposition of calcium salts within tissues
Dystrophic- in an area of dying tissue e.g. atherosclerotic plaque, ageing, damaged heart valves due to a local change or disturbance in tissue
Metastatic - wide-spread due to disturbances in calcium metabolism
