Hemorrhage is the escape of all the constituents of the blood through the walls of the heart or of the blood-vessels. It is divided into three classes, according to the vessel from which it escapes, as arterial, venous, or capillary.
It may occur by rhexis, in which case there is a demonstrable defect of the vessel wall, or by diapedesis, when there is no discoverable lesion. The latter form occurs only from veins and capillaries. The method of escape of the corpuscles is not clear, but is generally supposed to take place through the stigmata of the lining endothelium. Hemorrhage by rhexis may be primary or immediate and secondary or recurrent; the first following immediately upon laceration of the vessel wall, the second occurring some time after the original injury.
Fig. 2. - Multiple Capillary Hemorrhages in the Cerebrum. X 270 (Dürck).
1, Cerebral substance; 2, engorged capillaries; 3, small artery with hemorrhagic infiltration of its walls; 4, hemorrhage by diapedesis in the tissues around a small artery; 5, smaller hemorrhagic foci without any connection with any blood-vessel visible in the section.
Hemorrhages may also be designated by special terms according to the area involved. Petechia are minute, circumscribed hemorrhages. Ecchymoses are of moderate extent; are what are commonly known as bruises. Extravasations, suffusions, and sugillations are conditions in which extensive areas are implicated. A hematoma is a collection of blood within a solid tissue. A hemorrhagic infarct is a circumscribed hemorrhage within tissues, the result of the obstruction of an end-artery.
A hemorrhage may also have a special name according to its locality. Cerebral apoplexy is a hemorrhage brought about by a rupture of one of the arteries of the brain. According to the cavity in which it collects there may be a hemothorax, hemopericardium, etc. According to its method of escape from the body it may be known as epistaxis, bleeding from the nose; hemoptysis, from the lungs; hematuria, from the urinary tract, etc.