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Histamine: Definition, Effects & Role

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  • 0:01 What Is Histamine?
  • 1:13 Role of Histamine
  • 3:10 Effects of Histamine
  • 5:15 The Role of Antihistamines
  • 6:06 Lesson Summary
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Lesson Transcript
Instructor: Wendy McDougal

Wendy has taught high school Biology and has a master's degree in education.

Histamine is a chemical produced and stored within the body. It is a part of our immune response and is released during an allergic reaction. Learn more about this substance and quiz yourself at the end.

What is Histamine?

Do you suffer from allergies? Perhaps you are familiar with the symptoms of hay fever that arise every spring. You may experience sneezing, itching, watery eyes and low energy when spring is in full bloom. Or maybe you have an animal allergy and every time a cat rubs against you, you break out in a rash. Whatever your symptoms may be, they are caused by histamine, a chemical released by the body as an allergic response. In this lesson, we'll take a closer look at this substance and gain an understanding of its purpose in the body.

As previously mentioned, histamine is a chemical stored within our body. It is produced by cells known as mast cells. Histamine is a protein molecule with the chemical formula C5H9N3. It serves as an important part of our body's immune response. When we come into contact with an allergen, such as pollen or animal dander, histamine is released by the body to the site of contact. The intention of this response is to help the body deal with the irritation caused by the allergen. Strangely enough, the histamine released actually causes allergic symptoms. In addition, in cases of severe allergy, the release of histamine can be deadly.

Role of Histamine

In order to better understand the role of histamine, let's explore an allergic reaction in more detail. Imagine walking through a field of tall grass during the month of June. For those of you who experience allergies, I hardly need to describe the sneezing fit you are about to have. Your nose will start running, and your eyes and throat immediately becomes itchy, but why? And what, exactly, does this have to do with histamine?

In this particular scenario, pollen has entered your body through your nose and mouth. Often when there is a foreign object inside your body, your immune system is triggered. This is because most often foreign invaders are bacteria or viruses. Since your body is programmed to fight infection and to maintain a healthy internal environment, it must act when there is an intruder. In this case, it is microscopic grains of pollen that are now the enemy, and your body wants to rid itself of this pest. And so a signal is sent out for the release of histamine.

Histamine now acts as a messenger, traveling to the site of irritation to activate a particular response in that area. Chemically, histamine works in the body by binding with special receptors on protein molecules in various parts of the body. When bound to the receptor, a particular effect is produced, such as inflammation or increased mucous production. The allergic reaction a person experiences depends on the amount of histamine released. This varies from individual to individual.

There are four types of receptor sites within the body. One of the most important is known as H1. This receptor is involved in allergic reactions. But this is not the only role of histamine in the body. Histamine also binds to H1 receptors in order to help regulate your internal clock. The binding of histamine to H1 receptors makes you feel more alert. In addition, the binding of histamine to other types of receptors affect gastric acid secretion as well as some neurological effects.

Effects of Histamine

When the histamine arrives at the site of irritation, it causes several important effects. One is the dilating, or widening, of small blood vessels in that area. This is known as an inflammatory response, or swelling. Swelling increases the flow of blood to the area. Have you ever been stung by a bee? Usually the skin gets red and puffy right around the site of the sting. This is due to the histamine triggering the blood vessels to dilate. Although it can be uncomfortable, inflammation is part of the body's natural healing process. By allowing for faster blood flow to the area, white blood cells can be delivered at a faster rate. Hives and rashes are other examples of the inflammatory response.

Histamine also causes constriction of smooth muscle. If you have asthma, histamine is partially to blame. When irritants are inhaled into the lungs, histamine is released to that area, and the smooth muscles around the bronchi of the lungs contract. This makes breathing difficult and can produce an asthma attack.

Now, it may seem counterintuitive that histamine is released as part of an immune response but actually produces allergic symptoms. There is a purpose to this process. Let's consider common allergic symptoms, such as sneezing and a runny nose. A sneeze is a powerful tool used by your body to blast out unwanted intruders. What better way to attempt to expel pollen from your nasal cavity?

Additionally, when your nose begins running like a faucet, it is simply the histamine telling your body to produce more mucous. The mucous is your body's way of attempting to clean the allergens out of your nose. This can be yet another annoying symptom caused by the well-intended histamine.

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