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NancyMEDSCI203 > Lecture 22: Ischaemia And Infarction > Flashcards

Lecture 22: Ischaemia And Infarction Flashcards

0
Q

What is hypoxia?

A

One of many consequences of ischaemia

A deficiency of oxygen which causes cell injury by reducing aerobic respiration

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1
Q

What is ischaemia?

A

Inadequate local blood supply to a tissue

I,e, an insufficient quantity of blood

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2
Q

What is anoxia?

A

The complete lack of oxygen

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3
Q

In addition to causing tissue hypoxia. What does ischaemia also cause?

A

Reduced transfer of metabolic substances e.g. Glucose into tissues and metabolic substances like glucose into cells and catabolites like H+ out of tissues

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4
Q

What is infarction?

A

Necrosis

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5
Q

What is necrosis?

A

Cell murder

Non programmed cell death of tissue due to ischaemia

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6
Q

What are the possible causes of ischaemia

A 
External occlusion of vessels
Internal occlusion of vessels
Spasm of vessel
 Capillary blockage
Shock
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7
Q

What is an example of external occlusion of vessels?

A

Tumour, compression (bedsores)

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8
Q

What is an example of internal occlusion of vessels

A

Atherosclerosis, thrombosis or embolism

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9
Q

What is an example of spasm of vessels

A

E.g. Due to cold, frost bite not actually due to cells freezing but due to soasms

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10
Q

What is an example of capillary blockage

A

Sickle cell anaemia, cerebral malaria

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11
Q

What is shock

A

Circulatory failure with low arterial blood pressure which causes impaired perfusion of tissues

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12
Q

Why do different cell types have different susceptibilities to ischaemia

A

Highly differentiated cells (e.g. In brain, heart, kidneys) depend on aerobic respiration to make ATP

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13
Q

What is the susceptibility of different cell types in decreasing order of sensitivity to ischaemia?

A 
Neurons
Renal proximal tubular epithelium
Myocardium
Skeletal muscle
Fibroblasts and macrophages
Neutrophils
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14
Q

Describe the susceptibility of neurons to ischaemia

A

Very sensitive
Irreversibly damaged by only 3 minutes of anoxia
Neurons in brain require almost continuous supply of blood

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15
Q

Describe the sensitivity of renal proximal tubular epithelium

A

Sensitive

Renal ion reabsorption is rapidly impaired

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16
Q

Describe the sensitivity of myocardium to ischaemia

A

Sensitive
Irreversible after 20mins of anoxia
Functional impairment (with risk of dysrhythmia within 1minute)

17
Q

Describe the sensitivity of skeletal muscle to ischaemia

A

Less sensitive to ischaemia ,

Capable of anoxia work

Exercise causes ischaemia. Muscles undergo anaerobic respiration producing lactic acid

18
Q

Describe fibroblast and macrophage sensitivity to ischaemia

A

Insensitive.

19
Q

Describe the sensitivity of neutrophils to ischaemia

A

Neutrophils are weird

Their resistance to cell death is enhanced by hypoxia
Tis s allows them to function in damaged or infected tissues which are often hypoxic

20
Q

What does the outcome of vessel occlusion depend on?

A

Types of cells present in the tissue supplied by occluded vessel

Anatomy of blood supply to organ

Size of occluded vessel

Speed of onset

Duration of occlusion

Metabolic demands of tissue

General adequacy if circulatory system

21
Q

How does anatomy of blood supply affect the outcome of vessel occlusion?

A 
Collateral circulation (more than one vessel supplying the organ  )
Will reduce the susceptibility of the organ to ischaemia

Organs supplied by multiple vessels are relatively resistant to ischaarmia

22
Q

How does the size of the occluded vessel affects the tissue susceptibility to ischaemia?

A

The larger the vessel blocked, the greater the volume of ischaemic tissue,

Tissues and organs more susceptible to ischaemia if its a large vessel which supplies it is blocked

23
Q

How does the duration of the occlusion affect the organs susceptibility to ischaemia?

A

Cells may survive short periods of occlusion better than long periods of occlusion

Even if they survive a period of occlusion they may be killed by damage which occurs when blood flow is restored (reperfusion injury)

24
Q

How do the metabolic demands of the tissue at the time of ischaemia affect the tissues susceptibility to ischaemia?

A

An ischaemic tissue under pressure has more severe ischaemia than a tissue at rest

25
Q

How does the general adequacy of the circulatory affect organs susceptibility to ischaemia.

A

If body has coexisting heart failure or anaemia the outcome of the blockage is worsened

As heart can’t pump as much or not as much Hb to bring oxygen to tissues have a disproportional large effect.

26
Q

What are the range of outcomes of ischaemia on tissue in order of decreasing damage

A

Infarction- necrosis of most/all cells in a tissue due to overwhelming injury

Apoptosis - isolated cells. (Strange because this requires energy which is limited in infarction)

Reversible damage - to isolated cells

Adaptation - fatty change, atrophy and shut down. Like changing from aerobic to anaerobic respiration

Functional defect - due to suboptimal tissue perfusion e.g, myocardial dysrhythmia, renal insufficiency

No effect

27
Q

When does infarction occur

A

When perfusion of tissue is so severely ducked that most cells within the tissue are killed

28
Q

In practice, what do most infarctions result from ?

A

Thrombotic or embolism events

29
Q

What are the two types of infarction?

A

Red infarcts

White infarcts

30
Q

Where does red infarction occur?

A

In tissues with dual blood supply like lungs

Or tissues where blood flow is reestablished after previous arterial occlusion

31
Q

Where does white infarction occur?

A

Slid tissues supplied by single artery

These are often wedged shaped

The apex of the wedge is at the point of occlusion and the base is at the organ surface

32
Q

What is coagulative necrosis?

A

Dominant appearance after infarction in many solid organs

33
Q

What other kind of necrosis may develop in the brain?

A

Liquefactive necrosis

34
Q

What develops in the viable margins of infarcts?

A

Acute inflammation

35
Q

How soon does acute inflammation develop?

A

Within 24 hours usually

36
Q

What does acute inflammation involve?

A

The recruitment of neutrophils

After 1-3 days macrophages and some lymphocytes start to enter margins of infarcts tissue

Fibroblasts and ECs are recruited (organisation) which repair infarcts tissue by granulation tissue formation

Granulation tissue over the following weeks is remodels into no function fibrous scar

Some tissues like the liver attempt regeneration of original tissue instead of forming fibrous scar

37
Q

What is organisation

A

The recruitment of fibroblasts and endothelial cells

38
Q

What is ischaemic heart disease usually caused by?

A

Atherosclerotic narrowing of coronary arteries
Tsk s leads to reduced blood flow to heart muscle

Leading to several clinical syndromes

39
Q

What are the clinical syndromes of ischaemic heart disease in order of increasing severity?

A

Angina pectoris

Chronic ischaemic heart disease

Myocardial infarction

NancyMEDSCI203 (12 decks)

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