AP BIOLOGY

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THE CELL

CELL COMMUNICATION

Question [CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]
As humans, we have receptors for two kinds of beta adrenergic compounds such as catecholamines. Cardiac muscle cells have beta 1 receptors that promote increased heart rate. Some drugs that slow heart rate are called beta blockers. Smooth muscle cells, however, have beta 2 receptors which mediate muscle relaxation . Blockers of these effects are sometimes used to treat asthma. The use of beta 2 antagonist drugs may be useful in asthma because
A
they may increase constriction of the skeletal muscle of the chest wall.
B
they may dilate the bronchioles by relaxing their smooth muscle.
Explanation: 

Detailed explanation-1: -Beta-1 receptors are located in the heart. When beta-1 receptors are stimulated they increase the heart rate and increase the heart’s strength of contraction or contractility. The beta-2 receptors are located in the bronchioles of the lungs and the arteries of the skeletal muscles.

Detailed explanation-2: -Stimulation of the beta-2 receptor results in activation of the associated G-protein, Gs, which dissociates to release a protein subunit, free Gs-alpha. Gs-alpha in turn activates adenylyl cyclase, resulting in a rise in intracellular cyclic adenosine monophosphate (AMP) levels.

Detailed explanation-3: -beta(1)-and beta(2)-adrenergic receptors are G protein-coupled receptors expressed throughout the body and serve as receptors for the catecholamines epinephrine and norepinephrine. They are targets for therapeutive agonists and/or antagonists in treatment of heart failure and asthma.

Detailed explanation-4: -Targeted activation of the beta-1 receptor in the heart increases sinoatrial (SA) nodal, atrioventricular (AV) nodal, and ventricular muscular firing, thus increasing heart rate and contractility. With these two increased values, the stroke volume and cardiac output will also increase.

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