Unit 1.7 Ischemia, Infarction, Shock Flashcards
a deprivation of adequate blood supply to a given tissue
ischemia
a localized area of necrosis produced by either blockage of the arterial blood supply or venous drainage of a part
infarction
Not sharply demarcated. Looks like severe peripheral passive hyperemia. Red to dark red to almost black. Swollen
Venous Infarct
What’s the biggest gross difference between a venous and arterial infarct?
arterial infarcts are sharply demarcated while venous infarcts are not
Why are old infarcts pale in color?
red infarcts gradually become pale due to lysis of RBCs
Why are healed infarcts pale and depressed?
because they are composed of fibrous CT (scar tissue)
Three main things that can cause an infarct:
thrombus, edema, external pressure/constriction
Effect and significance of infarction depends on (6):
- degree of collateral circulation provided
- gen. status of circulation
- vulnerability of tissue to ischemia
- invasion of saprophytes –> gangrene –> toxemia
- septic vs. bland
- extent of involvement
Why is it important to ischemia and infarction?
usually occur over a short period of time and cause severe debilitation or even sudden death
An arterial infarct will often be what shape?
wedge-shaped
A venous infarct will strongly resemble:
peripheral passive congestion
When infarcts heal, the dead tissue is replaced by:
fibrous connective tissue
What’s the name for wall-to-wall hemorrhage?
“transmural” hemorrhage
pulmonary infarct will always be:
red and hemorrhagic
Why is an infarct in the GI always bad?
b/c the dead tissue is immediately attacked by bacteria that readily break through the mucosal barrier
occurs when infarcted tissue is invaded by saprophytic bacteria
gangrene
compromises the supply not only of oxygen, but also metabolic substrates (glucose)
ischemia
Why are ischemic tissues injured more rapidly and severely than hypoxic tissues?
loss of supply of oxygen AND metabolic substrates
List the 4 causes of ischemia:
pressure, vascular constriction, thrombi, thromboemboli
Ischemia typically leads to:
infarction with coagulative necrosis
What do most infarcts result from?
thrombotic or embolic events in arteries
Although venous thrombosis may cause infarction, it usually results in:
venous obstruction and congestions
When are infarcts caused by venous thrombosis more likely?
in organs with single venous outflow (i.e. testis, ovaries)
Describe a typical infarct lesion:
- Sharp line of demarcation between normal and necrotic tissue
- Early on, the line of demarcation is surrounded by a zone of hyperemia
What colors are infarcts in tissues with dual circulation (i.e. liver, kidneys)?
red, dark purple
What colors are infarcts in solid organs? Why?
pale; frequently start out red due to back flow of blood and leakage of blood from injured vessels, but they rapidly become pale as RBC’s and tissue proteins break down
Venous infarcts are caused by:
obstructed veins (starts as passive congestion)
Necrosis in a venous infarct occurs:
secondary to hypoxia
Why do the infarction of arteries have sharp lines of demarcation?
delineate the vascular field of that particular artery (often wedge shaped)
What is the earliest change in response to ischemia/necrosis?
cell swelling and disintegration of mitochondria
