Histamine

Histamines are chemicals released by cells of the immune system during the inflammatory response, which is one of the body’s defenses against infection. For instance, the inflammatory response helps neutralize bacteria that enter the body when the skin is accidentally cut with a knife. In addition, the sneezing, runny nose, and itchy eyes of allergies are actually small-scale inflammatory responses initiated by allergens such as dust, mold, and pollen. Histamines play a prominent role in both kinds of reactions.

Histamines are contained within two types of immune cells, basophils and mast cells. Basophils are free-floating immune cells, while mast cells are fixed in one place. When basophils and mast cells are activated by other immune cells—such as in response to invasion of the body by bacteria—they release histamines into body tissues.

Once histamines are released, they exert a variety of effects. Histamines dilate blood vessels, stimulate gland secretion, and prompt the release of proteins from cells. These effects, in turn, help the body rid itself of foreign invaders. The dilation of blood vessels increases the circulation of blood to the injured area, washing away harmful bacteria. The release of proteins from cells attracts other immune cells to the area, such as macrophages, which engulf and destroy bacterial invaders. In response to these activities within the body, the injured area becomes red, swollen, and painful. These symptoms of inflammation signal that the body’s inflammatory response is activated.

Histamines also play a role in allergic responses. Instead of responding to bacterial or viral invaders, mast cells and basophils bind to allergens and then release histamines and a special kind of antibody called IgE. Histamines released from mast cells in the nasal passages, lungs, and throat in response to allergens prompt inflammatory responses in these organs, leading to allergic symptoms, such as a running nose, coughing, sneezing, and watery eyes.

An effective way to control allergic symptoms is to disable the histamines with antihistamines which prevent the allergen from exerting their effects on the tissues. Antihistamines are the active ingredients in many allergy medications, and work by binding to the released histamines, effectively inactivating them. Until recently, antihistamines had an inconvenient side effect: they caused drowsiness. Newer antihistamines do not cause drowsiness, and most people can tolerate these antihistamines without side effects.

Histamine

Histamines are chemicals released by cells of the immune system during the inflammatory response, which is one of the body's defenses against infection . For instance, the inflammatory response helps neutralize bacteria that enter the body when the skin is accidentally cut with a knife. In addition, the sneezing, runny nose, and itchy eyes of allergies are actually "small-scale" inflammatory responses initiated by allergens such as dust, mold , and pollen. Histamines play a prominent role in both kinds of reactions.

Histamines are contained within two types of immune cells, basophils and mast cells. Basophils are free-floating immune cells, while mast cells are fixed in one place. When basophils and mast cells are activated by other immune cells—such as in response to invasion of the body by bacteria—they release histamines into body tissues.

Once histamines are released into the tissues, they exert a variety of effects. Histamines dilate blood vessels, stimulate gland secretion, and prompt the release of proteins from cells. These effects, in turn, help the body rid itself of foreign invaders. The dilation of blood vessels increases the circulation of blood to the injured area, washing away harmful bacteria. The release of proteins from cells attracts other immune cells to the area, such as macrophages, which engulf and destroy bacterial invaders. In response to these activities within the body, the injured area becomes red, swollen, and painful. These symptoms of inflammation signal that the body's inflammatory response is activated.

Histamines also play a role in allergic responses. Instead of responding to bacterial or viral invaders, mast cells and basophils bind to allergens and then release histamines and a special kind of antibody called IgE. Histamines released from mast cells in the nasal passages, lungs, and throat in response to allergens prompt inflammatory responses in these organs, leading to allergic symptoms, such as a running nose, coughing, sneezing, and watery eyes.

An effective way to control allergic symptoms is to disable the histamines with antihistamines which prevent the allergen from exerting their effects on the tissues. Antihistamines are the active ingredients in many allergy medications, and work by binding to the released histamines, effectively inactivating them. Until recently, anti-histamines had an inconvenient side effect: they caused drowsiness in a small percentage of the population. Newer antihistamines do not cause drowsiness, and most people can tolerate these antihistamines without side effects.

Histamine

Histamine is a hormone that is chemically similar to the hormones serotonine, epinephrine, and norepinephrine. A hormone is generally defined as a chemical produced by a certain cell or tissue that causes a specific biological change or activity to occur in another cell or tissue located elsewhere in the body. Specifically, histamine plays a role in localized immune responses and in allergic reactions.

A select population of cells located in the brain manufactures histamine. After being made, the hormone is stored in a number of cells (e.g., mast cells, basophils, enterochromaffin cells).

Normally, there is a low level of histamine circulating in the body. However, the release of histamine can be triggered by an event such as a mosquito bite. Histamine causes the inconvenient redness, swelling and itching associated with the bite. For those with severe allergies , the sudden and more generalized release of histamine can be fatal (e.g., anaphylactic shock).

Mast cell histamine has an important role in the reaction of the immune system to the presence of a compound to which the body has developed an allergy. When released from mast cells in a reaction to a material to which the immune system is allergic, the hormone causes blood vessels to increase in diameter (e.g., vasodilation) and to become more permeable to the passage of fluid across the vessel wall. These effects are apparent as a runny nose, sneezing, and watery eyes. Other symptoms can include itching, burning and swelling in the skin, headaches, plugged sinuses, stomach cramps, and diarrhea. Histamine can also be released into the lungs, where it causes the air passages to become constricted rather than dilated. This response occurs in an attempt to keep the offending allergenic particles from being inhaled. Unfortunately, this also makes breathing difficult. An example of such an effect of histamine occurs in asthma.

Histamine has also been shown to function as a neuro-transmitter (a chemical that facilitates the transmission of impulses from one neural cell to an adjacent neural cell).

In cases of an extreme allergic reaction, adrenaline is administered to eliminate histamine from the body. For minor allergic reactions, symptoms can sometimes be lessened by the use of antihistamines that block the binding of histamine to a receptor molecule.

See also Immune system

his·ta·mine / ˈhistəˌmēn; -ˌmin/ • n. Biochem. a heterocyclic amine, C₅H₉N₃, that is released by cells in response to injury and in allergic and inflammatory reactions, causing contraction of smooth muscle and dilation of capillaries.DERIVATIVES: his·ta·min·ic / ˌhistəˈminik/ adj.

histamine (hist-ă-meen) n. a compound derived from the amino acid histidine, found in nearly all tissues of the body. Histamine causes dilation of blood vessels and contraction of smooth muscle; it is an important mediator of inflammation and is released in large amounts after skin damage, producing flushing, a flare, and a weal. Histamine is also released in anaphylactic reactions. See also anaphylaxis, antihistamine.