Asthma Causes Part 2

-

Causes Of Asthma

The main component of bronchial asthma is Airflow obstruction

This airflow obstruction is due to 3 factors:

A-Contraction of the airway smooth muscle(Bronchoconstriction)

Smooth muscle tissue is a type of muscle tissue found in blood vessels, digestive tract, some sphincters and bronchioles. This type of muscle tissue is innervated by the autonomic nervous system thus it is involuntary acting.

In a normal individual, bronchial smooth muscle tissues relax causing dilatation of the airways when more oxygen supply is needed as in fight or flight, they contract causing bronchoconstriction when there is no demand for more oxygen as during rest and sleep.

In an asthmatic, there is an exaggerated bronchoconstriction and airway narrowing on exposure to allergens. This is due to hyperresponsiveness of their airways ( This was discussed in the previous article).

B-Increased secretion of the epithelial glands

Airways are lined by epithelial cells and epithelial glands that secrete mucus which moistens and protects the airways and serves as a barrier that prevents infection and tissue injury.

In a normal individual, mucus is secreted in moderate amounts that are easily cleared and don’t cause any respiratory distress.

In an asthmatic, there is hypersecretion of thick mucus that can form a mucus plug which can cause airway obstruction.

C-Inflammatory oedema and vasodilatation

Steps of an asthmatic response of the airways:

Early Asthmatic Response (EAR)*:

In asthmatics, inhalation of an allergen causes an early response characterized by smooth muscle contraction and increased mucus production. This response in 15 minutes, reaches its peak in about 30 minutes and resolves within 90-180 minutes.

What happens is that when an asthmatic inhales an allergen, it binds to specific antibodies on the surface of Mast cells. These are a type of cells of the immune system that plays a key role in the inflammatory response. Mast cells contain granules rich in an inflammatory mediator called histamine.

When an allergen binds to specific antibodies on the surface of mast cells , it causes Degranulation of the granules and release of histamine from the mast cells. This histamine is the cause of the smooth muscle contraction and increased mucus production in the EAR*.

Note:- There are other inflammatory mediators released from mast cells namely prostaglandin D2 and leukotriene C4 but histamine is the main inflammatory mediator in the causes of asthma.

Remember:Causes of asthma

Asthmatic Inhales Allergen – Then

Allergen Binds to Abs On the surface Of mast cells – Then

Mast cells release Histamine and other mediators – Then

Histamine causes Smooth muscle contraction and increased mucus production.

Late Asthmatic Response*:

The EAR* is followed by a partial recovery period over the next 1 to 2 hours and then by a further progressive deterioration of respiratory function that reaches its maximum between 6 to 12 hours. A full recovery occurs by 24 to 48 hours.

During the LAR*, there is a striking infiltration of the airways by inflammatory cells namely eosinophils, lymphocytes, monocytes, macrophages and neutrophils.


LAR* is considered to be the primary mechanism responsible for Bronchial HyperResponsiveness(BHR*).

The BHR* is an exaggerated bronchoconstriction of smooth muscles and airway narrowing after inhalation of allergens (as we mentioned in the 1st article, allergens are normally harmless stimuli to normal individuals. They only cause bronchial asthma in patients with hyperresponsive airways(asthmatics).

Remember:

In EAR*, Contraction of the bronchial smooth muscles(bronchoconstriction) is the important factor of airway obstruction.

In LAR*, inflammatory oedema and Vasodilatation are the important factors of airway obstruction.

To Sum up – Causes of Asthma:

An asthmatic with BHR* inhales an allergen – Then

After 15 minutes EAR* starts reaching its maximum in 30 min (smooth muscle contraction and increased mucus)This is due to release of histamine mainly, prostaglandin D2 and leukotriene C4 – 

Then

After 90-180 min EAR* resolves (Partial recovery period) – Then

After 6-12 hours LAR* starts(Progressive deterioration of respiratory function)

This is due recruitment of inflammatory cells (eosinophils,basophils, neutrophils,etc) by Prostaglandin D2 and leukotriene C4 (Inflammatory Oedema and vasodilatation) – Then

After 24 to 48 hours – Full Recovery - By Dr.Karim

Comments

Post a Comment

Popular posts from this blog

Basic Procedure of Nebulization

-
Image
Bronchial asthma is a life-threatening respiratory problem that does not exempt anyone. This condition can affect both men and women, young and old. As a matter of fact, it has been enlisted by the World Health Organization as one of the top leading cause of mortality and morbidity cases across the globe. In line with this, several therapeutic regimens and preventive measures were designed to control the number of cases. Among these favorable treatment procedures is the use of nebulization (a dispenser that turns a liquid into a fine mist). This procedure is also used as a primary treatment for other respiratory problems that involve thick and tenacious sputum. So, what is nebulization and how it is used properly? Learning the Basic Keys of Nebulization Nebulization is classified as a dependent nursing care because it requires a doctor’s order to administer medicine for asthmatic patients. However, nurses can educate the folks of the patient (parents or adults) on...
Read more

Medication Side Effects

-
A substance that has a physiological effect when ingested or otherwise introduced into the body, in particular a medicine with intended results (like for asthma treatment), may cause a number of unwanted side effects. These effects can occur when you start a new asthma medication, decrease or increase the dose of a asthma medication, or when you stop using a asthma medication. A side effect that happens in 1% or more of people taking a specific medication is considered by medical researchers to be caused by that particular medication. Examples of common medicine side effects include nausea, vomiting, fatigue, dizziness, dry mouth, headache, itching, and muscle aches and pains. Some side effects may be severe and require medical attention, while others may be mild and of little concern. Severe or annoying side effects are one of the main reasons why people stop taking their medications. If you are having worrisome side effects, your doctor may want to change your dose, try a di...
Read more

Asthma Medicines

-
Asthma Controller Medicines Asthma controller medicines assists in preventing asthma symptoms when taken daily as prescribed. These preventive asthma medicines include several different types. Each works in it’s special ways, and some are more suitable for certain levels of asthma severity. Check out the more suitable one below:- Inhaled Steroids Inhaled steroids, also known as inhaled corticosteroids or ICS for short, have become the main medicine type in asthma treatment for persistent asthma in children and adults. They are more safe in terms of side effects, effective and make a significant difference in the quality of life for people who have asthma. Asthma Leukotriene Modifiers Asthma Leukotriene modifiers are asthma controller medications that are sometimes used in combination with, or instead of, inhaled steroids for people whose asthma is moderate to severe. They are also called Asthma Leukotriene Antagonists. Asthma Long-Acting Beta Agonists Asthma Long Actin...
Read more