L2: Ischaemia, infarction and gangrene Flashcards
What is the definition of ischemia?
Decrease of blood supply to a part of tissue due to occlusion of its artery.
What are the types of ischemia?
- Sudden (acute) ischemia: Thrombosis Embolism Arterial spasm Surgical ligature Twisting of the organ’s pedicle
- Gradual (chronic) ischemia: Pressure on the artery by tumor or enlarged L.N.
What do the effects of vascular occlusion depend on?
The effects of vascular occlusion range from no or minimal effect to death of a tissue or person depending on:
•Nature of the vascular supply (end artery or dual blood supply).
- Rate of vascular occlusion. “Acute or chronic”
- Vulnerability of tissue to hypoxia: Neurons (3 to 4 minutes), Myocardial cells (20 to 30 minutes).
- Oxygen content of the blood.
What is the definition of infarction?
It is an area of coagulative necrosis (liquefactive in the brain) due to inadequate blood supply to the affected area.
What is an example of ischemic necrosis?
Infarct
What are types of infarction?
Red (hemorrhagic) infarct
Pale (anemic) infarct:
Where does red hemorrhagic infarct occur?
- loose tissues (allow the collection of blood in the infarcted area)
- Vascular organs such as lung and intestine (dual blood supply)
- Previously congested tissue. “Nutmeg liver”
- Reperfusion of previously ischemic tissue
- Occlusion of a vein
Where does pale anemic infarct occur?
- Occurs in solid and less vascular organs like the kidneys, spleen, and heart
- arterial occlusion
- end arterial supply
What type of infarct could occur in the brain and spleen?
Infarction of the brain and spleen may be pale or red.
What is N/E of infarction?
• Size of infarct area is related to
➢size of the obstructed artery
➢susceptibility of the tissue to ischemia.
• Wedge-shaped (pyramidal) the arteries have
a fan-like distribution, The base is directed towards the surface of the organ and the apex is deep.
• Subcapsular:
raised when recent (due to edema), depressed when healed (due to fibrosis)
- Surrounded by a red zone of hyperemia (inflammation)
- Firm (soft in the brain)
- Sero-fibrinous inflammation of overlying serosa.
What is M/E of infarction?
Area of coagulative necrosis (liquefactive in the brain) surrounded by a zone of acute inflammation (Hyperemia).
What is the fate of infarction?
• Small infarct:
Necrotic tissue is removed by macrophages, Granulation tissue fills the defect followed by fibrosis.
• Large infarct:
- surrounded by a fibrous capsule
- dystrophic calcification.
• In the brain (due to high lipid content): it leaves a cyst surrounded by glial tissue.
What is the definition of gangrene?
A type of necrosis most often affects the lower extremities or bowel and it is secondary to vascular occlusion. And it is associated with a saprophytic bacterial infection.
What are the types of gangrene?
Dry and wet
Where does dry gangrene start and what causes it?
Begins in the distal part of a limb due to ischemia.
What is the rate of spread of dry gangrene?
Slow until it reaches a point where the blood supply is adequate to keep the tissue viable.
In Which type of gangrene is the line of separation formed between the gangrenous part and the viable part?
Dry Gangrene
What is the rate of development of wet gangrene and what causes it?
Develops rapidly due to blockage of venous and arterial blood flow (from thrombosis or embolism).
What are the characteristics of the affected parts with wet gangrene?
The affected part is stuffed with blood which favors the rapid growth of putrefactive bacteria.
What is the characteristic thing for wet gangrene?
The toxic products formed by bacteria are absorbed causing profound systemic manifestations of septicemia, and finally death.
What are examples of wet gangrene?
- Diabetic foot: High sugar content in the necrotic tissue which favors the growth of bacteria.
- Bedsores: Bed-ridden patient due to pressure on sites like the sacrum, buttocks, and heels
Compare between dry and wet gangrene according to:
Sites Cause Progression Line of demarcation Gangrenous part Putrefaction and bad odor Toxemia
“SCG PP LT”
A- Extremities e.g. lower limb
A- Internal organs e.g. intestine, lung.
Extremities in crush injury and diabetes.
B- Gradual arterial obstruction
B- Sudden arterial and venous obstruction.
C- Slowly Present
C- Rapid Absent
D- Black, Dry, and mummified
D- Swollen, edematous with ulcerated skin.
E- Minimal due to lack of fluids Mild
E- Maximal
F- Mild
F- Severe and marked
What is the definition of gas gangrene?
A special form of wet gangrene is caused by gas-forming clostridia (gram-positive anaerobic bacteria).
How do gas-forming Clostridia enter the tissues?
through open contaminated wounds, especially in the muscles, or as a complication of operation on the colon which normally contains clostridia.
What do Gas forming Clostridia produce?
- It produces various toxins which produce necrosis and edema locally.
- Also absorbed producing profound systemic manifestations.
