U01.04.006 Types of infarcts

Infarcts are areas of tissue death due to a lack of blood supply, which can occur in different organs and tissues. Infarcts are classified into two main types: red infarcts and pale infarcts, depending on the blood supply and the mechanism of injury.

Red Infarcts

Occurrence:
- Red infarcts occur in tissues with multiple blood supplies such as the liver, lungs, intestines, and testes.
- They are also associated with venous occlusion and reperfusion, such as after angioplasty.
Mechanism:
- The tissue in red infarcts becomes congested with blood due to the dual or collateral circulation.
- Reperfusion injury, which occurs after restoring blood flow, can further damage the tissue through the generation of free radicals.
Key Points to Remember:
- Commonly seen in organs with dual blood supply.
- Free radicals play a significant role in tissue damage during reperfusion.

Pale Infarcts

Occurrence:
- Pale infarcts occur in solid organs with a single (endarterial) blood supply, such as the heart and kidneys.
Mechanism:
- The tissue in pale infarcts does not receive adequate blood supply, leading to ischemia and subsequent tissue death.
Key Points to Remember:
- Occurs in organs with a single blood supply.
- Typically seen in heart and kidney infarcts.

Free Radical Injury

Mechanism of Damage:

Free radicals damage cells through:
- Membrane lipid peroxidation: This leads to the disruption of cell membranes.
- Protein modification: Alters protein structure and function.
- DNA breakage: Causes mutations and cellular dysfunction.

Initiation Factors:

Radiation Exposure: Seen in cancer therapy.
Drug Metabolism: Phase I reactions in the liver.
Redox Reactions: Occur during normal metabolic processes.
Nitric Oxide Production: Particularly during inflammation.
Transition Metals: Such as iron and copper.
Oxidative Burst: From white blood cells like neutrophils and macrophages.

Elimination of Free Radicals:

Scavenging Enzymes:
- Catalase
- Superoxide dismutase
- Glutathione peroxidase
Spontaneous Decay
Antioxidants:
- Vitamins A, C, and E
Metal Carrier Proteins:
- Transferrin (binds iron)
- Ceruloplasmin (binds copper)

Table: Examples of Free Radical Injury

Condition	Description
Oxygen Toxicity	Retinopathy of prematurity, bronchopulmonary dysplasia, reperfusion injury
Drug/Chemical Toxicity	Acetaminophen overdose (hepatotoxicity), carbon tetrachloride toxicity (fatty liver, centrilobular necrosis)
Metal Storage Diseases	Hemochromatosis (iron overload), Wilson disease (copper overload)

Table: Examples of Free Radical Injury

Key Points to Remember:

Free radicals are highly reactive molecules that can cause extensive cellular damage.
Scavenging systems like enzymes and antioxidants are crucial in mitigating free radical damage.
Conditions associated with free radical injury include oxygen toxicity, drug toxicity, and metal storage diseases.

USMLE Step 1 Review Series

Curriculum

U01.04.006 Types of infarcts

Red Infarcts

Pale Infarcts

Free Radical Injury

Table: Examples of Free Radical Injury

Key Points to Remember:

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