ischaemia, infarction and the results

Question 1

define ischaemia

Answer 1

an inadequate rate of blood flow to an organ. inadequate quantity not quality.

Question 2

define infarction

Answer 2

necrosis due to ischaemia. a localised area = infarct

Question 3

5 causes of ischaemia

Answer 3

1 - external occlusion (tumours, compression (bed sores))
2 - internal stenosis or occlusion, athero, thrombosis, embolism
3 - spasm of vessel ie cold in frost bite
4 - capillary blockage eg sickle cell, cerebral malaria
5 - shock

Question 4

define shock

Answer 4

circulatory failure with low ABP, causing impaired perfusion of tissues.

Question 5

4 causes of shock

Answer 5

1- cardiogenic - MI, arrythmia, outflow obstruction (pulmonary embolism), external compression.
2 - hypovolaemic - haemorrhage, severe burns
3 - septic - gram positive and negative bacteria
4 - anaphylactic - generalised type 1 hypersensitivity.

Question 6

3 generic metabolic consequences of ischaemia

Answer 6

1 - hypoxia
2 - poor nutrient supply
3 - failure to remove waste products so may alter pH and electrolyt balance.

Question 7

5 cells types in decreasing order of sensitivity to ischaemia

Answer 7

1 - neurons - very sensitive, irreversibly damaged by only 3 minutes of anoxia
2 - renal proximal tubular epithelium - sensitive, rapid impairment of ion reabsorption.
3 - myocardium - irreversible damage after 20 mins anoxia, but functional impairment (risk of dysrhythmia) in 1 minute.
4 - skeletal muscle - capable of anoxic work
5 - fibroblasts and macrophages - insensitive.

Question 8

what affects an organ’s susceptability to ischaemia

Answer 8

largley the anatomy of the blood supply to it.
1 - collateral circulation may reduce susceptability. - venous circulation, some arterial systems (gut), can develop collateral if slow and progressive stenosis (coronary)

2 - organs with dual blood supply - 2nd may suffice. lungs = pulmonary and bronchial arteries and alveolar air. liver = hepatic portal vein and hepatic artery. brain = circle of willis

3 - single vessel = functional end arteries. very susceptible eg kidney, spleen.

Question 9

8 factors affecting outcome from ischaemia

Answer 9

1 - anatomy of blood supply
2 - size of block (vessel size)
3 - degree of block (stenosis or occlusion)
4 - speed of onset (develop collateral)
5 -persistence of block - some thrombi are unstable
6 - vulnerability of the tissue
7 - demand of the tissue - inadequate on exertion (heart angina, leg in intermittent claudication)
8 - general inadequacy of the circulatory system ie coexisting anaemia, heart failure, shock etc

Question 10

5 effects of ischaemia

Answer 10

1 - nothing
2 - functional defects (dysrhythmia, renal insufficiency)
3 - reversible cell damage (cell swelling, fatty change in myocardium (subendocardial zone) and hepatocytes (centrilobular region).
4 - infarction
5 - ischaemic reperfusion injury

Question 11

microscopic appearances in infarction

Answer 11

1 - ischaemic coagulative necrosis
2 - acute inflammation at the viable margins
3 - some regeneration or organisation.

Question 12

describe the changes in ischaemic coagulative necrosis

Answer 12

1 - visable 4-12 hours afterwards. earlier biochemical damage (eg enzyme leak)
2 - cytoplasm increase eosinophilia due to protein denaturation and loss of RNA.
3 - nuclei can undergo - karyolysis (pale), pyknosis (shrunken), karyorhexis (fragmentation)
4 - tissue architecture preserved for several days.

Question 13

describe acute inflammation in infarction

Answer 13

developes at the viable margins within 24hrs.

Question 14

describe tissue regen or organisation in infarction

Answer 14

liver may attempt regeneration but usually the infarct is organised. 3-5 days macrophages appear, granulation tissue develops. 6-8 weeks replaced by nonfunctional scar.

Question 15

7 changes in the macroscopic appearance in infarction

Answer 15

1 - acute anoxia may - capillary dilation or haemorrhage hence poorly defined and red early on.
2 - pale infarcts
3 - red infarcts
4 - cone shaped/wedge shaped
5 - fibrinous exudate , red margins
6 - septic infarct and abscess
7 - liquefactive necrosis

Question 16

describe pale infarcts

Answer 16

in soft tissue where infarct goes pale and rapidly demarcates in 24hrs. heart, kidney, spleen.

Question 17

describe red infarcts

Answer 17

due to haemorrhage
arterial occlusion - in spongy tissue such as lung, tissue with collateral blood supply (gut), congested tissues.

venous occlusion

Question 18

infarct shapes?

Answer 18

determines by blood supply. usually cone shaped with apex at point of occlusion and base at organ surface. = wedge shaped in 2 dimensions.

Question 19

margins and exudate of infarcts

Answer 19

in early stages the margins of pale infarct can be red due to acute inflam and granulation tissue. may be a fibrinous exudate on the organ surface. eventually replaced by grey scar tissue.

Question 20

secondary infection after necrosis

Answer 20

in some tissue ie lung. leads to a septic infarct and possibly and abscess.

Question 21

brain infarct

Answer 21

undergoes liquefactive necrosis. necrotic cells are digested quickly, form a liquid containing cyst, surrounded by reactive glial cells.

Question 22

define ischaemic reperfusion injury

Answer 22

when blood flow is restored to ischaemic cells that havent died and reversible injury becomes irreversible.

Question 23

mechanisms of reperfusion injury

Answer 23

1 - generation fo fresh mdiators of cell injury - free radicals, calcium overload.

2 - initiation of acute inflammation by delivery of neutrophils and complement.

Question 24

4 examples of infarction

Answer 24

1 - myocardial infarction
2 - cerebral infarction
3 - pulmonary infarction
4 - renal infarction

Question 25

8 effects of myocardial infarction

Answer 25

1 - dysrhythmia
2 - sudden death
3 - cardiogenic shock
4 - rupture of the infarct
5 - mural thrombosis on the endocardium
6 - scarring 
7 - adaptation to reduced CO - hypertrophy
8 - cardiac failure

Question 26

common cause of cerebral infarction

Answer 26

common carotid thrombus or plaque that forms an embolus.

shock - common in the elderly

Question 27

cause of pulmonary infarct

Answer 27

pelvic or leg vein thromboembolism

Question 28

effect of pulmonary infarct

Answer 28

1 - silent
2 - impaired lung function
3 - pressure overload on right heart and right sided heart failure
4 - infection - septic infarct, abscess, pneumonia
5 - shock

Question 29

cause of renal infarction

Answer 29

thromboemboli from the heart or elsewhere. kidneys recieve 25% of CO through one vessel so are at risk.

Question 30

effects of renal infarct

Answer 30

small infarcts are often silent

- large - haematuria, renal failure.