Bronchodilation

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Bronchodilation is the dilation of the airways of the lungs, brought about by relaxation of the smooth musle that makes up the walls of the Bronchi and Bronchioles [1]. Bronchodilation increases the diameter of the airways, thus decreasing resistance and increasing air flow to the alveoli [2].

Bronchodilation may be brought about via activation ofβ2-adrenoreceptors, by a β2 agonsist [3]. Examples include long-acting drugs such as Salmeterol, which have an effect for 8-12 hours, and may be used regularly in long-term treatment alongside other medications such as glucocorticoids, and short-acting drugs such as Salbutamol, which have effect for 3-5 hours [4].

Asthma is a disease of the airways, involving various different triggers leading to bronchoconstriction in the airways [5]. This is treated by β2 adrenoreceptor agonists, which reverse the contraction of smooth muscle cells. Salbutamol and Clenbuterol are examples of selective β2 agonists which work in this way.

As the smooth muscle of the lungs has no direct innervation by the sympathetic nervous system [6], bronchodilation and bronchoconstriction must be controlled through the β adrenoreceptors which themselves control the smooth muscle cells.

References

  1. Rang HP, Dale MM, Ritter JM, Flower JR (2007) Rang & Dale's Pharmacology, 6th Edition, Chapter 11 Page 176. Philadelphia: Elsevier.
  2. Mendonça NT et al, (2011), Airway resistance at maximum inhalation as a marker of asthma and airway hyperresponsiveness, Respiratory Research 12(96). Available through PubMed.
  3. Taylor M, Reide P, (2001) Mosby's Crash Course: Pharmacology, 2nd Edition, Chapter 5 Page 110. Maryland Heights, Missouri: Mosby
  4. Rang HP, Dale MM, Ritter JM, Flower JR (2007) Rang & Dale's Pharmacology, 6th Edition, Chapter 23 Page 361. Philadelphia: Elsevier
  5. Taylor M, Reide P, (2001) Mosby's Crash Course: Pharmacology, 2nd Edition, Chapter 5 Page 109. Maryland Heights, Missouri: Mosby
  6. Taylor M, Reide P, (2001) Mosby's Crash Course: Pharmacology, 2nd Edition, Chapter 5 Page 110. Maryland Heights, Missouri: Mosby
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