Sympathetic Nervous System Quiz

α2 receptors are located on the presynaptic nerve endings of sympathetic neurons. They control the release of norepinephrine by inhibiting further output when stimulated. This acts as a local mechanism to regulate norepinephrine release.

When a sympathetic adrenergic nerve is stimulated, a portion of the released norepinephrine binds to α2 receptors on the presynaptic membrane, leading to feedback inhibition, which reduces further release of norepinephrine.

α2 receptors are also found on presynaptic parasympathetic neurons, where they play a role in regulating the release of acetylcholine.

β-adrenoceptors are a different type of receptor compared to α-receptors. They respond strongly to isoproterenol, a drug known to stimulate β-adrenoceptors.

β1 receptors have near equal affinity for both epinephrine and norepinephrine, while β2 receptors have a higher affinity for epinephrine. This means tissues with more β2 receptors, like skeletal muscle vasculature, are more responsive to epinephrine.

A chemical that binds to and activates adrenergic receptors, triggering various physiological responses. These receptors are found throughout the body, influencing functions like heart rate, blood pressure, breathing, and blood sugar levels.

A type of adrenergic receptor that is activated by agonists like epinephrine and norepinephrine. These receptors are involved in constricting blood vessels, raising blood pressure, and stimulating certain glands.

A type of adrenergic receptor that is activated by agonists like epinephrine and norepinephrine. These receptors are involved in dilating airways, increasing heart rate, and regulating blood sugar levels.

A naturally occurring hormone produced by the adrenal medulla. It acts as a potent agonist for both alpha and beta receptors, stimulating the 'fight or flight' response.

A type of adrenergic receptor that is activated by epinephrine and norepinephrine. These receptors primarily regulate blood pressure and are involved in constricting blood vessels.

A type of adrenergic receptor that is activated by epinephrine and norepinephrine. These receptors are involved in inhibiting the release of neurotransmitters in the brain, and are important in regulating blood pressure.

A type of adrenergic receptor that is activated by epinephrine and norepinephrine. These receptors primarily influence heart rate, contractility, and blood pressure.

A type of adrenergic receptor that is activated by epinephrine and norepinephrine. These receptors primarily regulate airway dilation, blood flow in the lungs, and relaxation of uterine muscles.

A class of adrenergic agonists that directly bind to and activate adrenergic receptors. These include drugs like epinephrine, norepinephrine, and isoproterenol.

A class of adrenergic agonists that work indirectly by causing the release of neurotransmitters like norepinephrine. These include drugs like amphetamine and methamphetamine.

Epinephrine, also known as adrenaline, is a hormone and medication that plays a vital role in the body's response to stress. It is primarily produced by the adrenal glands, acting as a powerful stimulant on the sympathetic nervous system.

Epinephrine increases blood glucose levels by stimulating the liver to release stored glucose (glycogenolysis), promoting the release of glucagon, reducing insulin secretion, and decreasing glucose uptake by tissues.

Epinephrine's vasoconstriction effects help maintain blood pressure and reduce bleeding. It can also help improve blood flow to the heart and brain.

Epinephrine is essential for maintaining airway patency and reversing bronchospasm, primarily by stimulating β2-adrenergic receptors.

Epinephrine's rapid metabolism and short duration of action require different routes of administration depending on the situation. Oral administration is ineffective due to rapid breakdown.

Norepinephrine (NE), primarily acting on α1-, α2- and β1-adrenergic receptors, is the neurotransmitter in the sympathetic nervous system, playing a crucial role in regulating cardiovascular function. It has a negligible effect on β2-adrenergic receptors.

Epinephrine is a primary treatment for anaphylactic shock, bronchospasm, and is used in cardiac resuscitation. It can also prolong the duration of local anesthetics and aid in controlling epistaxis and capillary bleeding.

Serious side effects of Epinephrine include cerebral hemorrhage and cardiac arrhythmias. It's contraindicated in patients with cardiovascular conditions like hypertension, angina, cardiac arrhythmias, and congestive heart failure.

Norepinephrine has a direct stimulating effect on the heart (β1) and constricts all blood vessels (α1), leading to increased blood pressure (systolic, diastolic, and pulse).

Norepinephrine's vasoconstriction outweighs its β2 vasodilation effect on skeletal muscle blood vessels, resulting in overall vasoconstriction.

Norepinephrine's increase in blood pressure triggers the baroreceptor reflex, causing increased vagal activity and a reflex bradycardia (slowing of the heart rate).

Norepinephrine's weak β2 activity limits its effectiveness in treating bronchospasm or anaphylaxis, conditions where β2 stimulation is crucial.

Norepinephrine is used to treat shock by increasing vascular resistance and blood pressure. It can also be used to raise blood pressure in hypotensive states.

Isoproterenol is a non-selective β-receptor agonist, stimulating both β1 and β2 receptors.

Isoproterenol's β1 activity increases heart rate, contractility, and cardiac output, while its β2 activity dilates skeletal muscle arterioles, decreasing peripheral resistance.

Isoproterenol is a potent bronchodilator, making it useful in treating bronchospasm.

Phenoxybenzamine blocks α1 receptors, preventing vasoconstriction and decreasing peripheral resistance. This leads to reflex tachycardia, but blocking presynaptic α2 receptors on sympathetic nerve terminals increases norepinephrine release, further raising heart rate and cardiac output.

Phenoxybenzamine is used for short-term management of some hypertensive crises, particularly those associated with phaeochromocytoma. However, it's not preferred for long-term hypertension management due to the risk of cardiac issues.

Phentolamine is an imidazoline derivative that competitively blocks both α1 and α2 adrenergic receptors. It also affects 5-HT receptors and K+ channels, and can cause histamine release from mast cells.

Phentolamine is given intravenously, has a rapid onset, but short duration.

Phentolamine can cause adverse effects like tachycardia, palpitations, arrhythmias, and may even precipitate angina or myocardial infarction.

Prazosin is a potent and selective α1-adrenergic receptor blocker given orally, with effects on blood vessels, but minimal impact on heart rate.

Unlike nonselective α-blockers, selective α1-blockers like prazosin, terazosin, and doxazosin produce minimal or no tachycardia.

The first dose of prazosin can cause significant orthostatic hypotension and syncopal attacks due to rapid blood pressure drop. It's important to start with a small dose and give it at bedtime to minimize the risk.

Nadolol and propranolol are nonselective beta-blockers used to manage portal hypertension in patients with cirrhosis. They reduce the risk of variceal hemorrhage.

Cardioselective beta-blockers preferentially block β1 receptors, minimizing unwanted bronchoconstriction seen with nonselective agents in asthma patients.

Cardioselective beta-blockers like acebutolol, atenolol, and metoprolol lower blood pressure in hypertension and increase exercise tolerance in angina.

Esmolol, a cardioselective beta-blocker, has a very short half-life and is primarily used intravenously to control blood pressure or heart rhythm during critical situations.

Cardioselective beta-blockers have fewer effects on pulmonary function, peripheral resistance, and carbohydrate metabolism compared to nonselective beta-blockers.

Labetalol is a beta-blocker that also blocks α1 receptors, having both beta and alpha blocking actions.

Labetalol is used orally for essential hypertension and intravenously for hypertensive emergencies. It is also safe during pregnancy.

Labetalol can cause postural hypotension and hepatotoxicity as significant side effects.