Anaphylaxis

Anaphylaxia is an allergic condition in which the cardiac output and arterial pressure often fall drastically causing anaphylactic shock. Such a reaction is detrimental to the circulatory system in several important ways.

First, if the antigen - antibody reaction takes place in direct contact with the vascular walls or cardiac musculature, damage to these tissues presumably can result directly.

Second, cells damaged anywhere in the body by the antigen - antibody reaction release several highly toxic substances into the blood. Among these is histamine and histamine like substances, released mainly from the circulating basophils and the mast cells outside the capillaries.

The histamine in turn causes, firstly an increase in vascular capacity because of venous dilation, secondly dilation of the arterioles with resultant greatly reduced arterial pressure, and thirdly greatly increased capillary permeability with rapid loss of fluid into the tissue spaces. Often, persons experiencing this reaction die of circulatory shock with in a few minutes unless treated with norepinephrine a sympathomimetic drug to oppose the effects of the histamine. Also released from the cells is a  slow-reacting substance called anaphylaxis, which sometimes causes spasm of the smooth muscle of the bronchioles, eliciting an asthma like attack sometimes causing death by suffocation.