In a hypersensitivity reaction, what produces edema?
The Correct Answer and Explanation is :
In a hypersensitivity reaction, edema is primarily produced by the increased permeability of blood vessels. This occurs due to the action of inflammatory mediators such as histamine, prostaglandins, and leukotrienes. These mediators are released during an allergic response, leading to the dilation of blood vessels and allowing fluid to leak into the surrounding tissues, which results in swelling or edema.
Explanation:
Hypersensitivity reactions are immune responses that occur when the body reacts excessively to a harmless substance, such as pollen, food proteins, or insect venom. There are four types of hypersensitivity reactions, and the process of edema production is particularly prominent in Type I hypersensitivity (also known as immediate or allergic hypersensitivity).
In Type I hypersensitivity, the process begins when an allergen (e.g., pollen or dust mites) is encountered by an individual who is sensitized to it. This means their immune system has already produced IgE antibodies in response to the allergen. Upon subsequent exposure to the allergen, these IgE antibodies bind to mast cells and basophils, which are immune cells involved in allergic responses.
When the allergen binds to IgE on these cells, it triggers the release of various inflammatory mediators, including histamine. Histamine, a key mediator, causes vasodilation (widening of blood vessels) and increases the permeability of the blood vessel walls. As a result, plasma proteins and fluid leak out of the blood vessels and accumulate in the surrounding tissues, leading to edema.
The swelling is most evident in areas such as the skin (resulting in hives or urticaria) or in mucosal tissues like the nose or lungs, leading to symptoms such as runny nose, wheezing, or even anaphylaxis in severe cases.
In summary, edema in hypersensitivity reactions is caused by the release of histamine and other mediators that increase blood vessel permeability, allowing fluid to escape into the tissues, causing swelling.