Observations & Reflections

Thoughts from the operating room, the laboratory, and the spaces in between — on medicine, science, and the human condition. Short entries; occasionally a figure or a link worth sharing.

2025 Thyroid / Guidelines

TI-RADS & thyroid cancer guidelines

2025 Thyroid Surgery

RLN reconstruction & monitoring

2025 Medullary Thyroid Cancer

Surgical approaches in medullary thyroid cancer

2025 Parathyroid Surgery

Parathyroid intraoperative visualization & imaging

2025 Adrenal Surgery

Bilateral adrenalectomy for congenital adrenal hyperplasia

2025 Adrenal Surgery

Adrenergic receptors & alpha-blocker comparison

Adrenergic receptor subtypes, locations, and pharmacology:

Adrenergic Receptor Location Effects of Receptor Agonism Receptor Agonists Receptor Antagonists
Alpha-1 (α1)Vascular smooth muscle, eyes, bladder, prostateVasoconstriction, pupil dilation (mydriasis), bladder contraction, increased peripheral resistancePhenylephrine, NorepinephrinePrazosin, Doxazosin, Terazosin
Alpha-2 (α2)Presynaptic nerve terminals, pancreas, plateletsDecreased norepinephrine release, decreased insulin release, platelet aggregationClonidine, MethyldopaYohimbine, Phentolamine
Beta-1 (β1)Heart (SA node, AV node), kidneysIncreased heart rate, increased contractility, increased renin releaseDobutamine, Isoproterenol, EpinephrineMetoprolol, Atenolol, Bisoprolol
Beta-2 (β2)Bronchial smooth muscle, skeletal muscle vessels, liver, uterusBronchodilation, vasodilation, glycogenolysis, uterine relaxationAlbuterol, Terbutaline, SalmeterolPropranolol, Labetalol
Beta-3 (β3)Adipose tissue, bladderLipolysis, bladder relaxation (detrusor muscle)MirabegronN/A

Alpha-blocker comparison for preoperative pheochromocytoma preparation:

Feature Doxazosin Phenoxybenzamine
ClassSelective α1-adrenergic antagonistNon-selective irreversible α1 and α2 adrenergic antagonist
Receptor SelectivitySelective for α1 receptorsNon-selective (blocks both α1 and α2 receptors)
Mechanism of ActionBlocks α1 receptors, leading to vasodilation and decreased blood pressureIrreversibly blocks α1 and α2 receptors, leading to prolonged vasodilation and decreased blood pressure
Duration of ActionIntermediate (12–24 hours)Long-lasting (24–48 hours or more due to irreversible binding)
Half-Life~22 hours24 hours, but effects can last longer due to irreversible binding
Onset of Action1–2 hoursSlower onset, hours to days
Clinical EffectsDecreases blood pressure via vasodilation, less reflex tachycardiaProlonged and sustained blood pressure control, higher reflex tachycardia due to α2 blockade
Side EffectsDizziness, hypotension, mild reflex tachycardiaOrthostatic hypotension, tachycardia, nasal congestion, fatigue