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Congestion. Hyperemia and Congestion. Hyperemia means increased blood volume in a particular tissue or organ, due to dilatation of the microcirculation resulting from either increased blood flow (inflow) or impaired venous drainage (outflow). It may be active or passive.
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Hyperemia and Congestion • Hyperemiameans increased blood volume in a particular tissue or organ, due to dilatation of the microcirculation resulting from either increased blood flow (inflow) or impaired venous drainage (outflow). • It may be active or passive.
Active hyperemia (hyperemia): It occurs when arterial and arteriolar dilatation produces an increased flow of blood into the capillary beds with opening of inactive capillaries. Causes: might be Physiological e.g. muscular exercise. Pathological .e.g., acute inflammation.
Passive hyperemia (congestion) It results from impaired venous drainage (return), and it leads to accumulation of blood on the venous side of the circulation with blue-red colouration of the affected part (as the blood is deoxygenated). Congestion is almost always pathologic.
Congestion is subclassified according to its distribution: Localized Generalized (systemic) Each is further subclassified according to the onset and duration: Acute and Chronic congestion
Acute local congestion: Sudden complete venous obstruction occurs due to: ligature of a vein, thrombosis of a vein, and mechanical pressure caused by strangulated hernia, volvulus, and intussusception. Effects: if there is collateral circulation no harm will occur, but if there is poor collateral circulation, local venous congestion, edema and cyanosis will occur.
Chronic local congestion: There is gradual incomplete venous obstruction caused by: venous compression by a tumour, enlarged lymph node, liver cirrhosis & bilharzial hepatic fibrosis (portal venous congestion). Effects: the veins, venules, and capillaries proximal to the obstruction become dilated and congested resulting in edema. Also it will lead to gradual opening of the collateral anastomotic veins.
Systemic or generalized venous congestion It is a condition where all the veins of the body are distended and engorged with blood. It is due to affection of a central organ as the heart or the lung. Acute generalized venous congestion: occurs as a terminal condition in acute heart failure. Chronic generalized venous congestion: might be due to mitral stenosis (in the heart) or emphysema, or extensive fibrosis caused by tuberculosis of the lung with resulting obstruction in the pulmonary circulation.
Effects: In both right and left ventricles decompensation, there will be systemic venous congestion affecting all the organs. Left ventricular failure will affect only the pulmonary circulation. Right ventricular failure will affect the entire body sparing the lung.
General effects of venous congestion: Hypoxia,due to reduction in oxygenation of the blood as a result of stasis. Cyanosis, due to slow blood flow and increase in the blood volume with an increased amount of reduced hemoglobin in the distended venules leading to generalized blue colouration. Edema, due to overfilling of venules causing increased hydrostatic pressure. venous congestion of the kidney causing retention of water and electrolytes. Edema starts in dependent parts where the venous pressure is greatest especially around the ankles, and then spreads upwards.
Chronic venous congestion of the lungs • Grossly, the lungs are voluminous in early stages, it is dark red and wet (edematous), later on in advanced stages, it is firm, brown and indurated ("brown induration of the lungs").
Microscopically, the interalveolar capillaries are dilated and congested. hemorrhages intra alveolar hemorrhages hemorrhages in the interalveolar septa. NB The breakdown of RBCs gives hemosiderin pigment which is engulfed by macrophages with the formation of hemosiderin-laden macrophages "heart failure cells".
Ac. Pul. Congestion Chr. Pul. Congestion with heart failure cells
Chronic venous congestion of the liver • Grossly, • In early stages : moderately enlarged with tense capsule and smooth surface. • The cut surface is mottled in appearance with dark red areas of congestion alternating with yellow fatty areas simulating nutmeg. It is known as "nutmeg liver". • In long standing conditions, the size of the liver is slightly reduced due to fibrosis and development of “cirrhosis".
The red areas represent the congested and necrotic central zones of the lobules. The pale areas are the periportal areas
Microscopically, The central vein and sinusoids of the centrilobular regions are distended with blood. The hepatocytes in the central regions are atrophic secondary to chronic hypoxia, ultimately they undergo necrosis. The hepatocytes in the mid zones of the lobules suffer from less severe hypoxia and develop fatty change. Hepatocytes in the peripheral zones of the lobules are normal or show cellular swelling.
Microscopically, the nutmeg pattern results from congestion around the central veins, as seen here. This is usually due to a "right sided" heart failure.
