Beta2 adrenergic receptors are not found on: September 2010
**Core Concept:** Beta2 adrenergic receptors are a specific type of adrenergic receptors that are found on smooth muscles, cardiac myocytes, and airway epithelial cells. They respond to short-acting beta-agonists like salbutamol and are involved in bronchodilation, increased cardiac output, and glucose release.
**Why the Correct Answer is Right:** Beta2 adrenergic receptors are not found on skeletal muscles because they are specific to smooth muscles and cardiac myocytes. Skeletal muscles express alpha-adrenergic receptors, which respond to epinephrine and norepinephrine. The correct answer, C, represents this concept by mentioning the specific tissue type where beta2 receptors are not present.
**Why Each Wrong Option is Incorrect:**
A. Beta2 receptors are found on the heart, specifically cardiac myocytes, thus making this option incorrect.
B. Beta2 receptors are involved in bronchodilation, which is a beneficial response to beta-agonists, so this option is incorrect because it contradicts the receptor's function.
D. Beta2 receptors are expressed in airway epithelial cells, which are involved in asthma treatment with beta-agonists, making this option incorrect as well.
**Clinical Pearl:** Understanding the distribution of beta2 receptors is crucial for selecting appropriate medications in the management of respiratory and cardiovascular disorders. Short-acting beta2 agonists like salbutamol are used for acute asthma treatment due to their selective effect on airway smooth muscles and epithelial cells, while long-acting beta2 agonists like salmeterol are used for chronic asthma treatment as they have a longer duration of action and fewer systemic effects.