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Hyperemia vs Congestion
Hyperemia: active process. Vasodilation of small muscular arteries and arterioles to fill increased physiological need.
Congestion: Passive process. Venous obstruction past area of congestion resulting in decreased outflow of blood and increase in deoxygenated blood to tissue. Pathological
Effects of vascular congestion
Edema
Hemorrhage
Long term - parenchymal loss and replacement by fibrosis (parenchyma die first because have high metabolic need)
Two most common types of vascular congestion
Pulmonary congestion
Hepatic congestion
Increased lung capillary pressure due to heart failure leads to pulmonary edema and small hemorrhages.
Chronic changes are:
1. Thickened, fibrotic lobular septa with loss of lung parenchyma
2. Hemosiderin macrophages ("heart failure cells") in alveoli. Hemosiderin is a heme breakdown product following hemorrhage that is taken up by macrophages.
Chronic liver congestion
Gross appearance is "nutmeg liver"
Punctate areas of necrosis surrounding viable liver.
Liver has arterial and portal blood supply which enter hepatic lobule via portal tract. Both flow through hepatic sinusoids drain to central vein.
Zone furthest from portal tract and closest to central vein (Zone 3) is nutrient and oxygen poor, and most susceptible to ischemic injury. In chronic liver congestion, slowed flow due to congestion = ischemic injury, necrosis of hepatocytes, and fibrosis leading to cirrhosis.
Increased extracellular fluid (transudate) that is low in plasma proteins.
Collects in interstitium (called tissue edema) and serosal cavities (effusion)
Can be localized (due to venous obstruction) or systemic (due to increased osmotic pressure)
Ascites
Effusion in peritoneal cavity
Systemic edema
Anasarca
Types of edema
Cutaneous, localized
Dependent - most common in elderly, secondary to heart failure
Pulmonary - secondary to heart failure
Cerebral
Ascites - liver failure
Pleural/pericardial effusions
Starling equation
Jv = Kf [(Pc-Pi)-(PIc-PIi)]
Fluid movement is equal to different in hydrostatic pressure minus difference in osmotic pressure.
Osmotic pressure increases over capillary bed, hydrostatic pressure decreases.
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