Pathology Flashcards
What is the important nemonic for pathology?
V -vascular I - infection /inflammation N -neoplasia =new D -drugs/ toxins I - iatrogenic = diseased caused by medical means C - congenital / developmental A - autoimmune T - trauma E - endocrine / metabolic
What causes acute inflammation?
Injury
Vascular changes
Cellular changes
How long do mediators last?
Only as long as the stimulus exists
How long do neutrophils last outside blood vessels?
Only a few hours
What are the stages of inflammation?
Resolution
Suppuration
Repair, organisation and fibrosis
Chronic inflammation
What is the progression of inflammation dependant on?
The site of the injury
The type of injury
The duration of injury
What is required for resolution from injury?
Minimal cell death
Tissue has the capacity to repair
Good vascular supply
Injurious agent easily removed
What is suppuration?
The formation of pus in inflammatory response.
Pus contains living, dying and dead cells and if it’s collected may be termed an abscess
A walled off space filled with pus may be called an empyema
What is repair, organisation and fibrosis to do with?
Scarring
When is organisation/ repair not good?
If an injury produces lots of necrosis
If an injury produces lots of fibrin that isn’t easily cleared
If it has a poor blood supply
If it’s a particular tissue type
What happens when damage goes beyond the basement membrane?
Healing by organisation and repair is favoured over resolution
This requires a scaffold for resolution to occur around
Erosions/ abrasions = injury with the basement membrane intact
What is a common response of the mucosa when injury is severe and it can’t be easily rebuilt?
Granulation tissue formation.
The defect is slowly infiltrated by capillaries and then myofibroblasts which deposit collagen and smooth muscle cell leaving it looking very red.
The tissue is replaced by scar tissue which is not particularly functional and can lead to loss of function.
What is scarring and fibrosis in the liver?
Cirrhosis
Results in liver failure and vascular disturbances
Describe chronic inflammation.
It isn’t related to time or severity and can occur without preceding acute inflammation.
Favoured if there is suppuration, persistency of injury, infectious agents, or autoimmune injuries.
Characterised by lymphocytes and macrophages.
What are granulomas?
Aggregate epithelial hystocytes
(Collection of inflammatory cells)
Can be caused by foreign bodies, endogenous substances (keratin, bone, crystals) and exogenous substances (talc, asbestos, suture material, oil)
Can also be caused by specific infections (worms, parasites, syphilis, mycobacterium- TB)
What occurs with tuberculosis granulomas?
Caseous necrosis
How does hypoxia cause cell injury and then acute inflammation?
No oxygen = no ATP > Na/K ATPase fails > increases potassium > swelling > calcium pump fails > increased intracellular calcium > stimulates a number of things which make it worse (ATPases, phosphlipase, proteases, endonucleas, mitochondrial permeability)
How do phospholipases make cell injury worse in hypoxia?
They cause membrane damage
How do proteases make cell injury worse in hypoxia?
They cause membrane and cytoskeleton damage
How do endonucleases make cell injury worse in hypoxia?
They damage DNA and break it down
What does mitochondrial permeability do that worsens cell injury in hypoxia?
Released pro death factors
What is the window of time in which clot busting drugs can be used to prevent cell death?
20 minutes, after 30 mins the cells will certainly die
What can be seen in the first 20 minutes of myocardial infarction?
Nothing to see
Changes on an ECG
At autopsy there would be no macroscopic changes
There would also be no changes under a microscope
What happens to cells in the first 20 mins hypoxia?
Cells shrink (pyknotic), becomes red, nucleus shrinks and becomes dark, marginal contraction bands appear
What happens to cells 24 hours after hypoxia?
Cell contents leak
Complement cascade initates
Acute inflammation
Vascular changes (vasodilation, slowing of flow, margination, rolling, pavementing, diapedesis, chemists is, phagocytosis)
When is the risk of cardiac rupture greatest?
3-7 days
At this point the wall of the heart is weakest. Necrosis and neutrophils may be all that’s is holding it together if the full thickness is affected.
What happens 48 hours after hypoxia?
-as time progresses, neutrophils fade away and are gradually replaced by macrophages
Definite changes can be seen at autopsy -macrophages have a yellow appearance
Macrophages can also be seen down the microscope
What restitution happens after myocardial infarction?
- gradual process
- progressive scarring
- macrophages fade away and are replaced by fibroblasts
What do fibroblasts do?
Gradually lay down collagen
Occurs progressively after 2 weeks
Complete at 6 weeks (if an MI occurred more than 6 weeks ago it can’t be dated)
What is scarring after an MI a problem?
(Depends in amount of damage)
Scar tissue has replaced an area of muscle so the muscle can’t pump as well > weak heart
Nerve bundles may also be damaged and so the pace of the heart isn’t kept properly
What are the adaptive responses to stress?
Hypertrophy (more work)
Hyperplasia (more work)
Atrophy (less work) -reduction in size, physiological or pathological
Metaplasia (different work)
These only work to a point and then stress is too much (cell death)
Describe necrosis.
Requires no energy
Not normal, always pathological
Three types - coagulative, liquefactive and caseous
What is coagulative necrosis ?
Necrosis which preserves cell outlines
Dead cells are consumed by various enzymatic processes and cells
Occurs when the micro environment is too toxic for proteolysis
Common types
Seen in cardiac muscle (myocardial infarction)
What is liquefactive necrosis ?
Involved a liquid viscous mass where no cell structure remains
Pus formed
Associated with localised bacterial and fungal infections
Necrosis within the brain
What is caseous necrosis?
(Cheesy necrosis)
Associated with TB
Microscopic
Granulomatous inflammation with central necrosis
To test - ask for culture, PCR and a ziehl neelson stain
Describe apoptosis.
Programmed cell death in response to specific signals
Requires energy
Can be physiological, part of normal growth
Involved in removal of self reactive lymphocytes
Hormone dependant involution (how tissues that grow as a result of hormonal changes are removed after the hormone is removed)
Can also be pathological-in response to injury, radiation, chemotherapy, graft vs bone disease etc
All mechanisms rely on activating caspases (intrinsic or extrinsic)
Describe the extrinsic pathway.
Death receptor initiates pathway
Cell membrane receptors with “death domain”
Death receptors - tumour necrosis factor (TNF) and fas
Fas is involved in recognition of self (preventing autoimmune disease)
TNF - induces apoptosis in association with inflammatory conditions
Describe the intrinsic pathway
Mitochondrial pathway
Growth signals promote anti-apoptotic molecules in mitochondrial membrane
When these are removed they are replaced by Bax and Bak which increase the permeability of mitochondria
This results in the release of proteins that stimulate caspases and cytochrome C
What does p53 do?
Asses DNA damage, halts cells cycle and if DNA cannot be repaired then p53 stimulated caspases and induced apoptosis
What is the morphology of apoptosis?
Cells shrink
Chromatin condensed
Cytoplasmic blend are formed by breakdown of the cytoplasm
Macrophages hoover everything up
What are the signs of cellular aging?
Oxidative stress - free radical damage
Accumulation of metabolism by products
Lipofuscin
How do we slow aging?
Low calories reduced IGF signalling which silences specific genes
what is hyperplasia?
increase in cell number in response to an external stimuli. it will regress onwithdrwl of stimulus and usually increases organ volume. can be physiological or pathological.
what is hypertrophy?
increase in cell size not number.
often occurs with hyperplasia or can be in isolation. response to mechanical stress.
what is atrophy?
reduction in cell size which can be physiological or pathological.
what happens in response to stress?
we produce more growth factors or growth factor receptors
what are the 3 categories of growth receptor?
1- receptors with intrinsic tyrosine kinase activity
2- 7 transmembrane G protein coupled receptors
3- receptors without intrinsic tyrosine kinase activity
what are the stages of the cell cycle?
G1, S, G2, M
what are cyclins and CDKs?
each step in the cell cycle is controlled by a series of cyclin dependant kinases that activate each other and other enzymes. each CDK is activated by a specific cyclin and these vary in concentration throughout the cell cycle.
cyclins D, E, A and B (D= highest conc., B= lowest conc.)
what happens in G1?
the cell gets bigger with increased protein synthesis and CDK4 is activated by cyclin D.
CDK4 phosphorylates the Rb (retinoblastoma protein)
describe the Rb protein.
- important in normal cell growth and malignancy
- is bound to E2F normally, which prevents the beginning of cell division
- when phosphorylated by CDK4, Rb can,t bind to E2F and therefore cell division occurs.
describe the S phase
E2F initiates DNA replication and increases the levels of cyclin A which goes on to activate CDK2. CDK2 also promotes DNA replication.
Describe G2 phase
second growth phase where the cell gets bigger and there is more protein synthesis.
the main checkpoint occurs at the end of G2 and is checked by p53.
what does p53 do?
checks cell for mistakes and if they are found the cell cycle is paused and a repair attempt is made. if the repair is successful it will progress, if not it will undergo apoptosis. (via BAX pathway)
what are telomeres?
capped ends of chromosomes that provide protection and stop degradation. consists of TTAGGG repeats and with every division the number of repeats gets smaller
stem cells can switch them off
what examples of hyperplasia?
-breast tissue at puberty
-endometrial lining of uterus in pregnancy
can occur after loss of tissue e.g liver
what are examples of pathological hyperplasia?
- hormonally induced - excess oestrogen
- hormonally induced prostatic hyperplasia - enlarged prostate
- as a result of infection
- hyperplastic tissue is at risk of development of cancer.
when does hypertrophy become pathological?
when the heart can no longer function, may result in heart failure.