Infarction and Ischaemia Flashcards
What is infarction
Death of tissue within living body due to ISCHAEMIA
What are three characteristics of an infarct in the first 6 hours
- ECG changes
- No visible change histologically
- EM shows swollen mitochondria
What are three characteristics of an infarct after the first 24 hours
- Pallor visible
- Inflammatory reaction at age of ischaemia site
- Striations disappear from cardiac myocytes
What are three characteristics of an infarct during the first few weeks
- Dead myocytes removed by macrophages
2. Replacement by fibrous tissue
What is the characteristic of an infarct months after it took place
Fibrous scar
At what stage of an infarct is the tissue at the site weakest
When macrophages and polymorphs clear dead tissue
why people with a myocardial infarction can die 10 days after due to rupture of healing process
Is the scarred area where the infarction took place functional?
Nope - still protrudes into the lumen and can cause more problems for the patient in the future
What problem can arise from a scarred area of a myocardial infarction
Aneurysms as scar can be stretched at high pressure but can’t recoil
Define Gangrene
When whole areas of a limb or region of a gut have their arterial supply cut off and tissues die in bulk
Define dry gangrene
Tissue dies, mummifies and healing occurs above it
dead area drops off
What condition does dry gangrene take place in
Diabetes
Define wet gangrene
Bacterial infection supervenes and patient dies from sepsis
What mechanism other than dry and wet can cause gangrene
Torsion
What is a torsion
Twist on a mesentery, ovary or testes occluding venous return
Organ swells and oedema compresses drainage further
Arteries continue to pump blood into organ causing an infarction
How can capillary ischaemia take place
- Capillaries damaged so severely that area supplied becomes ischaemic
- Blocked by parasites
- Balance of thrombotic and thrombolytic mechanism is disturbed
why does susceptibility to ischaemia change in different parts of th body
Less susceptibility - another artery can take over the job and still supply area + low tissue needs
More susceptibility - Only one artery is supplying the area
+ high tissue metabolic needs (retinal artery leads to blindness)
What are watershed areas
Tissue at interface between adjacent territories of two arteries (no collateral circulation to provide blood from alternative vessels)
Examples of watershed areas
Splenic flexure of colon (between superior and inferior mesenteric) + regions of cerebral hemispheres
+ myocardium
What cells are most exposed to infarction and why?
Cereal neurones because they have a large metabolic requirement + Cardiac myocytes
Define shock
Profound circulatory failure resulting in life-threatening hypo perfusion of vital organs. Compensatory mechanisms maintain BP until they fail. Ends in hypotension
What can shock be classified as
Cardiogenic: due to myocardial infarction
Hypocolaemic: due to reduction in effective circulating blood volume
What are compensatory mechanisms
These increase peripheral vascular resistance to maintain BP supplying vital organs
What is the consequence of mechanisms failing
Vulnerable to ischaemic injury
What can shock result in
- Irreversible neuronal injury
- Renal failure due to acute tubular necrosis
- Acute pancreatitis
