A very simple thing you can learn that will enhance your understanding of common family medicine medications is the four types of adrenergic receptors. By understanding what happens when these receptors are stimulated or blocked, we can understand what happens when we give medications that act on these receptors.
alpha-1
- Smooth muscle contraction
- Blood vessels – vasoconstriction
- Iris dilator muscle – mydriasis (side note recall that there are two muscles that control pupil size iris dilator which receives sympathetic stimulation to dilate the pupil, and iris sphincter which receives parasympathetic stimulation to constrict the pupil)
- Ureter, bladder – contraction of of bladder and ureters
- Medication example: oxymetazoline
- Selective alpha-1 agonist, and partial alpha-2 agonist
- Used for nasal decongestion by vasoconstriction of nasal vessels which decreases exudates from post-capillary venules
- Used for rosacea by causing topical vasoconstriction and easing erythema and flushing
alpha-2
- Decreased sympathetic outflow
beta-1
- Increases heart rate and contractility
- Medication example: metoprolol, bisoprolol
- Beta-1 selective beta-blockers are useful for asthmatics because it won’t cause their bronchioles to close up
beta-2
- Dilates bronchioles in lungs
- Vasodilation
- Causes tremors