Adrenergic Agonist Patho and Receptors Flashcards
The sympathetic outflow is also called ___
the thoracolumbar outflow
The sympathetic, or thoracolumbar, outflow arises from ____.
segments T1–L2 or segments T1–L3
Most sympathetic preganglionic neurons synapse with ____
postganglionic fibers in the paravertebral ganglia
Sympathetic cardiac accelerator fibers arise from ___.
T1–T4
The stellate ganglion is formed by ___.
the inferior cervical and first thoracic ganglia
The effects of the sympathetic nervous system on the body’s physiology are designed to ____.
facilitate the fight-or-flight response
The sympathetic nervous system is anatomically and functionally more ____.
systemic in its effects when compared to the PNS
A massive sympathetic response would lead to ____
tachycardia, dry mouth, bronchodilation and diaphoresis.
Effects of the Sympathetic Nervous System on organs in the body system
Eye - The pupil dilation (mydriasis)
Heart - Increased heart rate
Secretions - Decreased salivary and bronchial secretions
Smooth Muscle - Bronchodilation, and decreased motility and tone of the stomach and intestines and relaxation of the bladder (detrusor muscle)
Pancreas – Increased blood glucose
What are the main endogenous neurotransmitters for adrenergic receptors?
Norepinephrine and epinephrine
The major subtypes of adrenergic receptors are ___.
alpha-1, alpha-2, beta-1, and beta-2
Preganglionic SNS fibers are ____.
short, myelinated and release Acetylcholine
Postganglionic SNS fibers are ____.
long, unmyelinated, have nicotinic receptors at the ganglia and release either NE or Ach onto target adrenergic receptors
The adrenal medulla is directly stimulated by ___.
a preganglionic SNS fiber to release NE and Epi into systemic circulation
What is a ganglia?
a group of cell bodies in the periphery, and in the SNS, sympathetic ganglia are where many preganglionic dendrites synapse on postganglionic cell bodies
The preganglionic SNS fibers exit the spinal cord through ____.
the ventral nerve root
All preganglionic SNS fibers pass through the ___.
white ramus (myelinated) in route to the paravertebral ganglia
Where do some preganglionic SNS fibers synapse in?
the paravertebral ganglia
Where do the postganglionic SNS fibers pass through?
the grey ramus (unmyelinated), and travel to effector organ
some preganglionic fibers ascend or descend in the ___.
paravertebral ganglia before synapsing with postganglionic neurons
some preganglionic neurons pass through the paravertebral ganglia without _____.
synapsing; these fibers synapse with postganglionic neurons in peripheral ganglia
In addition to the collateral ganglion, another example of a peripheral ganglia is ____.
the stellate ganglion
A stellate ganglion block is ___.
an injection of medication into these nerves that can help relieve pain in the head, neck, upper arm and upper chest.
A stellate ganglion block is also an unintentional consequence of ___.
a brachial plexus block
Horner’s syndrome is common side effect of ____.
a stellate ganglion block
Signs and symptoms of Horner’s Syndrome
Ipsilateral miosis, ptosis, enophthalmos, flushing, increased skin temperature, anhydrosis, and nasal congestion (stuffiness)
Very Homely PAM: Vasodilation, Horner, Ptosis, Anhydrosis, Miosis
Ipsilateral miosis = lazy eye
Enophthalmos = posterior displacement of the eye
Anhydrosis = inability to sweat normally.
In the adrenal medulla, norepinephrine is converted to ___.
epinephrine, the catecholamine pool is comprised 20% NE and 80% epinephrine.
Describe the steps of the synthesis of norepinephrine
- Tyrosine transported into nerve terminal from bloodstream.
- Tyrosine converted to dopa.
- Dopa converted to dopamine.
- Dopamine transported into presynaptic vesicle.
- Dopamine converted to norepinephrine.
- Norepinephrine stored in presynaptic vesicles
Describe the steps of the release of norepinephrine
- An action potential travels along the axon of sympathetic postganglionic neuron.
- Depolarization opens voltage-gated Ca+ channels.
- Ca+ diffuses through channels into nerve terminal down electrochemical gradient
- Ca+ unites with calmodulin, and this second messenger system initiates a series of reactions leading to exocytosis.
- Norepinephrine spills into the synaptic cleft.
First, norepinephrine combines with adrenergic receptors of postsynaptic membrane. Then what happens?
2.Norepinephrine-receptor complex causes:
- ion channels to open, or
- activation of adenylate cyclase and subsequent intracellular production of cAMP
3.The cell responds in a characteristic way to the opening of ion channels or the activation of adenylate cyclase (second messengers have tissue-specific actions).
•Ex: cAMP relaxes vascular smooth muscle but stimulates contraction of the myocardium
Termination of norepinephrine
Diffusion of norepinephrine away from receptors is the first step in the termination of action of norepinephrine.
- Norepinephrine is actively transported back into the presynaptic nerve terminal; most (80%) of the released norepinephrine is returned to the nerve terminal by this reuptake mechanism.
- Small amounts of norepinephrine are metabolized in the synaptic cleft by monoamine oxidase (MAO); MAO is found on the surface of mitochondria; some MAO leaks from the nerve terminal into the synaptic cleft.
- Small amounts of norepinephrine diffuse into the bloodstream; once in the vascular compartment, norepinephrine is metabolized by catechol-O-methyl transferase (COMT).
Indirect-acting sympathomimetics work in part by ___.
displacing norepinephrine from sympathetic nerve terminals.
Ephedrine is the most frequently used indirect-acting sympathomimetic. Ephedrine also stimulates adrenergic receptors directly, so it also is a direct-acting agent.
What agents should be avoided in the patient taking an MAO inhibitor?
indirect-acting sympathomimetic agents (ephedrine) and meperidine; meperidine, like ephedrine, triggers the release of norepinephrine. When either ephedrine or meperidine is administered to a patient taking an MAO inhibitor, the release of excess amounts of norepinephrine may cause a hypertensive crisis. This hypertension is generally worse with meperidine.
α1 (alpha 1) receptors are ___
postsynaptic adrenoceptors located in smooth muscle throughout the body (in the eyes, lungs, blood vessels, uterus, gut, and genitourinary system)
α1(alpha 1) agonists are associated with ___.
mydriasis, bronchoconstriction, vasoconstriction, uterine contraction, constriction of GI/GU sphincters and inhibits insulin secretion.
mydriasis = pupils dilate
The most important cardiovascular effect of α1 stimulation is ___.
vasoconstriction, which increases peripheral vascular resistance, left ventricular afterload, and arterial blood pressure.
α2 (alpha 2) receptors are located primarily on ___.
the presynaptic nerve terminals, in addition to tissues on postsynaptic membranes in the brainstem and in peripheral tissues
stimulation of alpha-2 receptors on sympathetic postganglionic, presynaptic nerves produces ____.
inhibition of norepinephrine synthesis and release
this is a negative feedback system.
stimulation of postsynaptic alpha-2 receptors in the brainstem causes ____.
sedation and inhibits outflow of the sympathetic nervous system, which leads to peripheral vasodilation and lower blood pressure
stimulation of alpha-2 receptors in the substantia gelatinosa of the spinal cord promotes ____.
analgesia
Where are beta 1 receptors located?
heart and kidney
Stimulation of beta 1 receptors is __ and produces ___.
excitatory and produces positive chronotropic (increased heart rate), dromotropic (increased conduction), inotropic (increased contractility) effects and increase renin release
β2 (Beta 2) Receptors are primarily ___ and located ____.
primarily postsynaptic adrenoceptors located in smooth muscle and gland cells; but are also located in ventricular myocytes.
β2 (Beta 2) stimulation causes ___.
smooth muscle relaxation, resulting in bronchodilation, vasodilation, and relaxation of the uterus (tocolysis), bladder, and gut.
Glycogenolysis, lipolysis, gluconeogenesis, and insulin release are stimulated by ____.
β2-receptor activation.
β3 (Beta 3) Receptors are found in ___.
adipose tissue and play a role in lipolysis and thermogenesis in brown fat.
Stimulation of alpha 1 receptor on the pupil causes ___.
mydriasis (pupil dilates)
Stimulation of beta 1 receptor on the SA Node causes ___.
increased heart rate
Stimulation of beta 1 receptor on the AV Node causes ___.
increased conduction speed
Stimulation of beta 1 receptor on muscle fibers causes ___.
increased contractility
Stimulation of alpha 1 receptor on most arterial systemic vessels causes ___.
vasocontriction (increased SVR)
Stimulation of beta 2 receptor on artieral skeletal muscle vessels causes ___.
vasodilation (decreased SVR)
Stimulation of alpha 1 receptor on veins causes ___.
vasocontriction (increased preload)
Stimulation of beta 2 receptor on the bronchiolar muscle of the lung causes ___.
bronchodilation
Stimulation of beta 2 receptor on the secretory glands of the lung causes ___.
increased secretions
Stimulation of alpha 1 receptor on the spleen causes ___.
release of RBCs
Stimulation of beta 1 receptor on the kideny causes ___.
increased renin release
Stimulation of alpha 1 receptor on the kidney causes ___.
decreased renin release
Stimulation of beta 2 receptor on the liver causes ___.
Glycogenolysis & Gluconeogenesis
Stimulation of beta 2 receptor on the gallbladder causes ___.
relaxation
Stimulation of alpha 1 receptor on the stomach and intestines causes ___.
relaxation
Stimulation of beta 2 receptor on the urinary bladder wall causes ___.
relaxation
Stimulation of beta 2 receptor on the pancreas causes ___.
increased insulin secretion
Stimulation of alpha 2 receptor on the pancreas causes ___.
decreased insulin secretion
Stimulation of alpha 1 receptor on adipose tissue causes ___.
increased glucagon secretion
Stimulation of beta 1 receptor on adipose tissue causes ___.
Lipolysis
Stimulation of beta 2 receptor on the uterus causes ___.
relaxation
Stimulation of alpha 1 receptor on the uterus causes ___.
contraction
Stimulation of beta 2 receptor on the the sodium potassium pump causes ___.
the stimulation of the Na-K pump which causes decreased plasma potassium
Dopamine (DA) receptors are ____.
a group of adrenergic receptors that are activated by dopamine; these receptors are classified as D1 and D2 receptors.
Activation of D1 receptors ____.
mediates vasodilation in the kidney, intestine, and heart.
D2 receptors are believed to play a role in ____.
antiemetic action