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98 Cards in this Set
- Front
- Back
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Where do sympathetic nerve tracts originate?
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-Hypothalamus
-Brainstem (medulla) |
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Where do sympathetic nerve tracts descend?
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Spinal cord
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Where do sympathetic preganglionic nerve fibers exit the spinal cord?
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-T1-12
-L1-2 |
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What kind of output is sympathetic outflow from the central nervous system?
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Thoracolumbar output
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What kind of structures do most sympathetic preganglionic nerves pass to and where are they located?
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-Ganglia
-Adjacent to vertebral column (paravertebral ganglia, sympathetic chains) or in abdomen |
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Where do sympathetic preganglionic nerves synapse with postganglionic sympathetic nerves? What is the neurotransmitter?
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-Ganglia
-Acetylcholine |
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Where do postganglionic sympathetic nerves travel to and what does their sympathetic discharge do?
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-Target tissues
-Modify target cell function |
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Where do some sympathetic preganglionic nerves travel to (not to ganglia to synapse with postganglionic nerves)?
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Directly innervate adrenal medulla
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What occurs when sympathetic preganglionic nerves innervate the adrenal medulla?
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Release of ACh from preganglionic nerves causes adrenal medulla chromatin cells to release epinephrine and norepinephrine into the blood
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What is the neurotransmitter released from sympathetic preganglionic nerves?
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Acetylcholine
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What kind of receptors are on sympathetic postganglionic nerves?
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Nicotinic receptors
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What is the neurotransmitter released from sympathetic postganglionic nerves?
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Norepinephrine
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What kind of receptors bind NE on target tissues?
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Adrenergic receptors
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Describe neurotransmission at the sympathetic postganglionic nerve terminal (to synaptic cleft):
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-Action potential arrives at nerve terminal and depolarization occurs
-Voltage-gated channels open, and calcium diffuses into nerve terminal -NE-containing vesicles empty NE into synaptic cleft |
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Describe neurotransmission at the sympathetic postganglionic nerve terminal (synaptic cleft):
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-NE diffuses across synaptic cleft and binds to adrenergic receptors on postsynaptic membrane (i.e. target cell membrane)
-NE also binds to autoreceptors on presynaptic nerve membrane |
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Describe neurotransmission at the synaptic postganglionic nerve terminal (neurotransmitter reuptake):
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-Released NE is taken back up by presynaptic nerve ending
-80% restored in synaptic vesicles -Remaining NE metabolized by monoamine oxidase (MAO) in nerve terminal (must be replaced by new NE) |
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How is circulating epinephrine and NE metabolized?
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By the enzyme, catechol-O-methyl transferase (in the blood and liver)
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What are the 4 adrenergic receptors? Are they pre- or post-?
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-alpha 1 (post)
-alpha 2 (pre- autoreceptors, post) -beta 1 (post) -beta 2 (post) |
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What does alpha-1 adrenergic stimulation cause?
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-Arteriolar vasoconstriction: increased peripheral vascular resistance and blood pressure
-Venous constriction: increased venous return, stroke volume, cardiac output, and blood pressure |
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What does beta-1 adrenergic stimulation cause?
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-Heart rate increases: increased cardiac output and blood pressure
-Increased myocardial contractility: increased stroke volume, cardiac output, and blood pressure |
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What does beta-2 adrenergic stimulation cause?
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-"Epinephrine effect"
-Vasodilation of skeletal muscle arterioles (increase skeletal muscle blood flow) |
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What receptors does norepinephrine NOT affect?
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Beta-2 ("epi effect")
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What is an agonist?
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A compound (endogenous or exogenous) that interacts with a receptor and produces a biological or pharmacological effect
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What are sympathomimetics?
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Adrenergic agonist drugs that mimic the actions of the SNS
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What are the 3 classes of drugs?
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-Naturally occurring (endogenous) catecholamines)
-Synthetic (exogenous) catecholamines -Synthetic noncatecholamines |
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What are the 2 mechanisms of action of sympathomimetic drugs?
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-Direct acting
-Indirect acting |
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How do direct acting drugs work?
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Activate adrenergic receptors directly
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How do indirect acting drugs work?
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-Promote NE release from sympathetic postganglionic nerve terminals
-Drugs enter the nerve terminal and displace NE into the synaptic cleft -Have some direct actions as well |
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What drugs are alpha-1 adrenergic agonists?
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-phenylephrine
-methoxamine |
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Phenylephrine is a ____ agent. What does this mean?
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-Pressor
-Causes vasoconstriction and increased SVR |
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What is a potential side effect of phenylephrine?
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Reflex bradycardia (causing a decrease in cardiac output)
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What is phenylephrine used for?
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-Treating intraoperative hypotension (i.e. spinal block)
-Decongestant |
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What does methoxamine do?
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Potent pressor agent
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What do nonselective beta adrenergic agonists do?
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Activate both beta-1 and beta-2 adrenergic receptors
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What drug is a nonselective beta adrenergic agonist?
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Isoproterenol
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What drug is the most potent sympathomimetic at beta receptors (more potent than epinephrine)?
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Isoproterenol
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What are the beta-1 effects of isoproterenol?
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-Positive inotrope (increase contractility)
-Positive chronotrope (increase heart rate) |
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What are the beta-2 effects of isoproterenol?
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-Bronchodilation
-Reduces SVR and diastolic BP (due to effect on skeletal muscle arterioles) |
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What drug is a selective beta-1 adrenergic agonist?
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Dobutamine
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What is the effect of dobutamine?
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-Positive inotropic agent (increase CO by increasing contractility)
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What is dobutamine's effect on the sinoatrial node?
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Modest or no effect (less potent than isoproterenol)
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Is there any beta-2 action with dobutamine?
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-There may be slight reduction in SVR (beta-2, skeletal muscle arterioles)
-Dobutamine is SELECTIVE for beta-1, not SPECIFIC |
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What is the most common use for selective beta-2 adrenergic agonists?
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Bronchodilation (treatment of bronchial asthma)
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What are some of the beta-2 adrenergic agonist drugs?
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-Terbutaline
-Albuterol -Metaproterenol -Isoetharine -Ritodrine |
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What is ritodrine used for?
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-To inhibit contractions of premature labor
-"Tocolytic" |
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Do beta-2 adrenergic agonists have any beta-1 effects?
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-Some beta-1 agonist activity
-SELECTIVE, not SPECIFIC -Increased doses = increased beta-1 effects (increased heart rate) |
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What drugs have both alpha- and beta- agonist activity?
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-Epinephrine
-Norepinephrine -Ephedrine -Dopamine |
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What receptors does epinephrine activate?
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-Potent activator of alpha adrenegic receptors
-Activates both beta-1 and beta-2 adrenergic receptors |
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What are the uses of epinephrine?
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-Positie inotropic agent
-Pressor agent (doesn't always increase MAP) -Bronchodilator -Coadministration with local anesthetic to cause vasoconstriction (alpha-1) to prolong anesthetic action (decrease absorption) |
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What receptors does norepinephrine activate?
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-Very potent activator of alpha adrenergic receptors
-Activates beta-1 receptors (similar to epinephrine) |
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What receptor does norepinephrine have no effect on?
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Beta-2
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What is the action/use of norepinephrine?
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Potent pressor agent (causes intense peripheral vasoconstriction)
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How does ephedrine work?
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Primarily an indirect acting sympathomimetic
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Where does ephedrine primarily work?
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On the heart to increase cardiac output and heart rate
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Is ephedrine a pressor agent?
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A mild pressor agent (commonly used in anesthesia to treat hypotension)
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What kind of catecholamine is dopamine and where is it found?
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-Endogenous catecholamine
-Found in sympathetic nerve terminals and is secreted by the adrenal medulla |
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What is the precursor of norepinephrine?
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Dopamine
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Dopamine: low dose (1-2)
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-Stimulate dopamine D1 receptors in the kidney
-Renal vasodilation -Increased renal blood flow -Diuresis |
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Dopamine: intermediate dose (2-10)
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-Activate beta-1 adrenergic receptors
-Increase myocardial contractility -Increase heart rate -Increase cardiac output |
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Dopamine: high dose (>10)
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-Activate alpha adrenergic receptors
-Peripheral vasoconstriction |
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What are alpha-2 adrenergic agonists referred to as?
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Sympatholytics
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What is the mechanism of action of alpha-2 adrenergic agonists?
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-Reduce sympathetic outflow from the brainstem
-Reduce NE release from adrenergic nerve terminals (presynaptic alpha-2 autoreceptors) |
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What drugs are alpha-2 adrenergic agonists?
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-Clonidine
-Dexmedetomidine |
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What kind of agent is clonidine?
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Antihypertensive
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What are the uses of clonidine?
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-Sedation, anxiolysis
-Decreased anesthetic/analgesic requirements -Decreased circulating catecholamines -Decreased postoperative shivering |
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What drug has higher affinity for alpha-2 receptors? Clonidine or dexmedetomidine?
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Dexmedetomidine
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What are the uses of dexmedetomidine?
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-Sedation
-Reduces anesthetic/analgesic requirements -Reduces perioperative sympathetic activity |
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What is an antagonist?
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An agent that binds to a receptor, does not exert a biological effect, and blocks the effects of receptor agonists
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What drugs are alpha adrenergic antagonists?
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-Phenoxybenzamine
-Phentolamine -Prazocin |
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Is phenoxybenzamine selective or nonselective?
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Nonselective (blocks both alpha-1 and alpha-2 receptors)
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Onset and duration of phenoxybenzamine?
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-IRREVERSIBLE
-Prolonged blockade |
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Uses of phenoxybenzamine:
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-Preoperative control of blood pressure in patients with a pheochromocytoma
-Reversal of intense peripheral vasoconstriction (hemorrhagic shock or Reynaud's syndrome) |
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Is phentolamine selective or nonselective?
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Nonselective
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Onset and duration of phentolamine?
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-Reversible
-Short lived blockade |
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Uses of phentolamine:
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Treat acute intraopertive hypertension (manipulation of a pheochromocytoma)
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Is prazocin selective or nonselective?
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-Selective
-Alpha-1 antagonist |
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Onset and duration of prazocin?
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Reversible blockade
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Uses of prazocin:
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-Treatment of essential hypertension
-Reduction of peripheral vascular resistance in patients with heart failure -Preoperative preparation of patients with a pheochromocytoma |
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What are the adverse effects of alpha-2 adrenergic antagonists?
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-Orthostatic hypotension (due to alpha-1 blockade, no venoconstriction)
-Reflex tachycardia (baroreceptor reflex, exaggerated by blocking alpha-2 receptors and no NE release) |
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Are nonselective beta adrenergic antagonists reversible or irreversible?
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Reversible
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What is the prototype beta adrenergic antagonist all others are compared to?
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Propranolol
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Uses of propranolol:
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-Treat essential hypertension (decrease HR/CO to decrease BP)
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What drugs are used to control ventricular rate during supraventricular tachycardia?
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-Propranolol
-Esmolol |
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What drug is used for beta blockade in patients with thyrotoxicosis and pheochromocytoma?
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Propranolol
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What is the mechanism of action of selective beta-1 adrenergic antagonists?
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-Block cardiac beta-1 receptors
-Little or no effect on beta-2 receptors in other tissues (i.e. lungs, skeletal muscle arterioles) |
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What drugs are selective beta-1 adrenergic antagonists?
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-Metoprolol
-Atenolol -Esmolol |
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Onset and duration of esmolol?
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-Rapid onset
-Very short acting |
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Uses of esmolol:
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-Treatment of intraoperative hypertension
-Blunting of cardiovascular reflex response to intubation -Treatment of intraopertive supraventricular tachycardia |
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What are the general effects of beta adrenergic antagonists?
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-Reduce heart rate
-Reduce myocardial contractility |
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What is a potential side effect of nonselective beta adrenergic antagonists?
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Can increase airway resistance and peripheral vascular resistance (due to beta-2 effects)
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What drugs should you avoid using in patients with COPD or peripheral vascular disease?
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Nonselective beta adrenergic antagonists (due to beta-2 effects)
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What are the clinical uses of beta adrenergic antagonists?
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-Treatment of essential hypertension
-Treatment of acute blood pressure or heart rate increases (in surgery) -Management of angina pectoris -Antidysrhythmic (SVT) |
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How do beta adrenergic antagonists treat angina pectoris?
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Reduce myocardial oxygen requirements secondary to decreased heart rate and cardiac output
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What is the mechanism of action of labetalol?
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Competitively blocks both beta and alpha-1 receptors
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What is the ratio of receptors for labetalol?
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-7:1
-beta:alpha |
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Labetalol: What does alpha-1 blockade cause?
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-Arteriolar vasodilation (decrease in peripheral vascular resistance)
-Venodilation (decreased venous return and cardiac output) |
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Labetalol: What does beta-1 blockade cause?
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Prevents reflex tachycardia that might otherwise occur in response to alpha adrenergic blockade
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Uses of labetalol:
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-Essential hypertension (rare)
-Hypertensive episodes or controlled hypotension (in anesthesia/surgery) |
