This as quickly review the important points of

This lesson delves into something known as type I hypersensitivity reactions. You’ll find out how everything from mast cells, basophils, and IgE to histamine, bee stings, and peanut allergies all play a role in this process.

Hypersensitivity Reactions

Your immune system is definitely there for a good reason.

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It helps protect you against some nasty things. However, every now and then something goes wrong. It’s not a perfect system by any means. If it were, it would be infallible, and we would have no reason for this lesson.

However, sometimes our immune system produces excessive and even fatal reactions to everything from allergens to pathogens to even our own body’s cells or receptors. These types of reactions are called ‘hypersensitivity reactions,’ and we’ll be focusing in on one major type in this lesson.

Type I Hypersensitivity

The first type of hypersensitivity reaction is called, unsurprisingly, type I hypersensitivity. This is appropriately called ‘immediate hypersensitivity’ because your body’s response to an antigen occurs immediately, or within minutes of exposure to it. This is the most common type of hypersensitivity reaction, and therefore, I’m more than sure you can come up with several examples of substances or events that can cause you a combination of:

  • Redness
  • Swelling or congestion
  • Pain
  • Itching

For example, some things that can cause these signs include:

  • Bee stings
  • Drug allergies to things like penicillin
  • Food allergies to things like peanuts or milk
  • Pollen, which may cause allergic asthma
  • Atopy, or a genetic predisposition to allergies

The Pathophysiology of Type I Hypersensitivity

In essence, if it causes a fast onset allergic reaction to something your body encounters, it’s a type I hypersensitivity reaction.The way all of the things I mentioned above work is mainly thanks to an antibody called IgE, which is the primary class of antibody involved in type I hypersensitivity reactions.Once your body is exposed to an allergen, it makes IgE antibodies specific for that allergen.

However, in people hypersensitive to an allergen, the level of IgE specific to the allergen is sometimes thousands of times higher than in people not allergic to the same compound.These antibodies then use their Fc, or tail portion, to attach to the surface of white blood cells, called mast cells and basophils, which are the primary cells involved in type I hypersensitivity reactions.Only when you are re-exposed to the same allergen does the allergen actually cause you issues, as it binds to the arms of the Y-shaped antibody IgE located on the surface of the mast cells and basophils.This action then causes a sequence of events that leads to the release of many different compounds involved in inflammation, notably histamine, which is the principal compound involved in type I hypersensitivity reactions. Histamine and other molecules released from mast cells and basophils then cause everything from the swelling, redness, and itching to the difficulty breathing, congestion, and pain people experience during an allergic reaction.

Anaphylactic Shock

In the worst-case scenario, anaphylaxis may occur. This is a severe and potentially deadly allergic reaction.

If too many basophils and mast cells are activated by an allergen all over the body all at once, the substances they release may cause serious problems, including:

  • Difficulty breathing
  • Low blood pressure
  • Arrhythmias of the heart
  • Swelling of the eyes and tongue

Emergency treatments for this vary depending on what is happening in each individual person, but it may be treated with serious medications that counter the effects of histamine release, such as epinephrine.

Lesson Summary

Since the type I hypersensitivity reactions occur pretty quickly, we should just as quickly review the important points of this specific subset of reactions.Type I hypersensitivity is appropriately called ‘immediate hypersensitivity’ because your body’s response to an antigen occurs immediately, or within minutes of exposure to it.

The primary class of antibody involved in type I hypersensitivity reactions is called IgE. The primary cells involved in type I hypersensitivity reactions are mast cells and basophils, whereas the principal compound involved in type I hypersensitivity reactions is histamine.In the worst case scenario, anaphylaxis may occur. This is a severe and potentially deadly allergic reaction that occurs when too many mast cells and basophils release all of their compounds, such as histamines, all over the body at the same time.

Learning Outcomes

You will have the ability to do the following after watching this video lesson:

  • Describe how type I hypersensitivity reactions occur
  • List the symptoms and common causes of type I hypersensitivity
  • Identify how IgE, mast cells, basophils and histamine are involved in type I hypersensitivity
  • Explain how anaphylaxis occurs and list the signs of it
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