Chapter 4: Infarction

Question 1

What is an infarct?

Answer 1

An infarct is an area of ischemic necrosis caused by occlu- sion of the vascular supply to the affected tissue

Question 2

Which organs are mostly affected by infarction?

Answer 2

The brain and heart

Question 3

What process underlies the vast majority of infarctions?

Answer 3

Arterial thrombosis or arterial embolism

Question 4

Venous thrombosis can cause infarction. How does this occur?

Answer 4

Often in organs with a single efferent vein (testis/ovary), cause usually bypass channels restore the arterial bloodflow

Question 5

An infarct may be red or white. What does red mean?

Answer 5

hemorrhagic

Question 6

An infarct may be red or white. What does white mean?

Answer 6

anemic

Question 7

How do red infarcts occur?

Answer 7

1) as a result of venous occlu- sions (such as in ovarian torsion); (2) in loose tissues (e.g., lung) where blood can collect in infarcted zones; (3) in tissues with dual circulations such as lung and small intestine, where partial, albeit inadequate perfusion by collateral arterial supplies is typical; (4) in previously congested tissues (as a consequence of sluggish venous outflow); and (5) when flow is reestablished after infarction has occurred (e.g., after angioplasty of an arterial obstruction).

Question 8

How do white infarcts occur?

Answer 8

White infarcts occur with arterial occlusions in solid organs with end-arterial circulations (e.g., heart, spleen, and kidney), and where tissue density limits the seepage of blood from adjoining patent vascular beds (Fig. 4.17B). Infarcts tend to be wedge- shaped, with the occluded vessel at the apex and the organ periphery forming the base (Fig. 4.17); when the base is a serosal surface, there is often an overlying fibrinous exudate

Question 9

Fill in: In most tissues, the main histologic finding associated with infarcts is …. An inflammatory response begins to develop along the margins of infarcts within a few hours and usually is well defined within 1 to 2 days

Answer 9

ischemic coagulative necrosis

Question 10

In the brain, not ischemic coagulative necrosis occurs, but another type of necrosis. Which?

Answer 10

Liquefactive necrosis

Question 11

Fill in: …. occur when infected cardiac valve vegetations embolize, or when microbes seed necrotic tissue. In these cases the infarct is converted into an abscess, with a correspondingly greater inflammatory response and healing by organization and fibrosis

Answer 11

Septic infarctis

Question 12

The effects of vascular occlusion range from inconsequential to tissue necrosis leading to organ dysfunction and sometimes death. By which three variables are the range of outcomes influenced?

Answer 12

• Anatomy of the vascular supply
• Rate of occlusion
• Tissue vulnerability to hypoxia

Question 13

Explain anatomy of vascular supply (a variable that influences an infarct)?

Answer 13

The presence or absence of an alternative blood supply is the most important factor in determining whether occlusion of an individual vessel causes damage

Question 14

Which organs are more susceptible to the anatomy of vascular supply (with regard to infarction)?

Answer 14

The lung, the liver, the hand and forearm are resistant to infarction (because of dual supply).

The kidney and spleen have end-arterial circulations

Question 15

How does the rate of occlusion influence infarct development?

Answer 15

slowly developing occlusions are less likely to cause infarction because they allow Tim for the development of collateral blood supplies

Question 16

Which organs/tissues are more vulnerable to hypoxia (that influences infarct development)

Answer 16

Neurons undergo irreversible damage when deprived of their blood supply for only 3 to 4 minutes. Myocardial cells, although hardier than neurons, still die after only 20 to 30 minutes of ischemia. By contrast, fibroblasts within myocardium remain viable after many hours of ischemia.