Pathophysiology of Ischemia and Infarction

Question 1

define ischemia

Answer 1

relative lack of blood supply to tissue/organ leading to inadequate o2 supply to meet needs of tissue/organ leading to hypoxia

Question 2

what is stagnant hypoxia?

Answer 2

when there is normal inspiration of o2 but abnormal delivery that can be local or systemic

Question 3

give two examples of stagnant hypoxia

Answer 3

shock

occlusion of a vessel

Question 4

what is cytotoxic hypoxia?

Answer 4

when the inspiration of o2 is normal but it is abnormal at tissue level

Question 5

give some examples of factors effecting oxygen supply

Answer 5

inspired o2
pulmonary function
blood constituents
blood flow
integrity of vasculature
tissue mechanisms

Question 6

what factors affect oxygen demand?

Answer 6

the tissue itself, different tissues have different requirements and the activity of the tissue above a baseline value

Question 7

name some supply issue that lead to ischemic heart disease

Answer 7

> coronary artery atheroma
> cardiac failure
> pulmonary function
> anaemia
> previous MI

Question 8

what will be the clinical consequence of a stable atheroma in a coronary artery?

Answer 8

a stable angina

Question 9

what is the clinical consequence of a complicated atheroma in a coronary artery?

Answer 9

an unstable angina

Question 10

what is the clinical consequence of an ulcerated plaque?

Answer 10

there can be thrombosis and ischemia and infarction

Question 11

what is the clinical consequence of an atheroma in an aorta?

Answer 11

aneurysm

Question 12

what would the effects be from an atheroma that creates a decrease in blood flow from 4 to 2?

Answer 12

it would cause a decrease in flow by 16 fold leading to a decrease in o2 leading to ischemia and infarction

Question 13

describe the biochemical effects of ischemia

Answer 13

there is anaerobic metabolism which leads to cell death due to a build up of lactic acid

Question 14

what are the cellular effects of ischemia?

Answer 14

different tissues have variable o2 requirements and are variably susceptible to ischemia

Question 15

what could the outcome of ischemia be?

Answer 15

there could be no clinical effects
there could be resolution (or therapeutic intervention)
It could lead to infarction

Question 16

define infarction

Answer 16

ischemia necrosis within a tissue/organ in living body produced by occlusion of either the arterial blood supply or venous drainage

Question 17

what is the aetiology of infarction?

Answer 17

cessation of blood flow

Question 18

give some causes of infarction

Answer 18

> thrombosis
embolism
strangulation
trauma

Question 19

give some factors on which the scale of damage of infarction depends

Answer 19

> time period
tissue/organ
pattern of blood supply
previous disease

Question 20

where does colliquitive necrosis take place?

Answer 20

the brain

Question 21

where does coagulative necrosis take place?

Answer 21

the heart and lungs

Question 22

how quickly is the onset of atp depletion from the beginning of anaerobic metabolism in ischemia of the heart?

Answer 22

seconds

Question 23

how long does it take the myocardial cells to lose contractibility from the onset of ischemia?

Answer 23

less than 2 minutes

Question 24

how long does it take for myocyte necrosis to begin in an MI?

Answer 24

20-40 minutes

Question 25

what happens if an infarction has gone on for over an hour?

Answer 25

there is injury to the microvasculature

Question 26

what might you see down an electron microscope 12 hours after an infarction?

Answer 26

swollen mitochondria

Question 27

what tissue will have a pale infarct?

Answer 27

myocardium
spleen
liver

Question 28

what is the colour of lung and liver infarct?

Answer 28

red

Question 29

what are the microscopic changes of an infarct in 24-48 hours?

Answer 29

there is acute inflammation and loss of specialised cell features

Question 30

what will happen to pale infarct if it continues for 72 hours?

Answer 30

it becomes red around the periphery

Question 31

after 72 hours what will infarction look like microscopically?

Answer 31

chronic inflammation
macrophages remove debris
granulation tissue
fibrosis

Question 32

what replaces the area of tissue damage in an infarction?

Answer 32

a scar

Question 33

describe the reparative process in myocardial infarction

Answer 33

cell death > acute inflammation > macrophage phagocytosis of dead cells > granulation tissue > collagen deposition > scar formation

Question 34

describe the effects of a myocardial infarction at 4-12 hours

Answer 34

> early coagulation necrosis
oedema
haemorrhage

Question 35

describe the effects of a MI at 12-24 hours

Answer 35

> ongoing coagulation necrosis
myocyte changes
early neutraphilic infiltrate

Question 36

what are the effects of a MI at 1-3 days?

Answer 36

> coagulation necrosis
loss of nuclei and striations
brisk neutrophilic infiltrate

Question 37

what are the effects of a MI at 3-7 days?

Answer 37

> disintegration of dead myofibres
dying neutrophils
early phagocytosis

Question 38

what are the effects of a myocardial infarction at 7-10 days?

Answer 38

> well developed phagocytosis

> granulation tissue at margins

Question 39

what are the effects on a MI at 10-14 days?

Answer 39

> well established granulation tissue with new blood vessels

> collagen deposition

Question 40

what will an MI look like at 2-8weeks?

Answer 40

> increased collagen deposition

> decreased cellularity

Question 41

describe a MI at more than 2 months?

Answer 41

dense collagenous scar

Question 42

what is a transmural infarction?

Answer 42

ischemic necrosis affecting the thickness of the myocardium

Question 43

what is a subendocardial infarction?

Answer 43

ischemic necrosis mostly limited to a zone of myocardium under the endocardial lining of the heart