Part 24: Beta-Blockers and Sympatholytics Flashcards
at a cellular level, cardiac contraction and the movement of blood between the chambers of the heart and eventually out into circulation is achieved by what is known as _____
excitation-contraction coupling
AP are generated by the ____ node and propogated by the _____ system in the heart
SA; electrical conduction
once an AP reaches the cardiac muscle cells in the atria and ventricles, the membrane depolarization causes ____ channels to open, which causes more depolarization and the openinf od ____ channels
Na; Ca
the influx of Ca interacts with receptors on the _____ to cause _____ to be released. This process is called _____
SR; stored Ca; calcium induced Ca release
the large concentration of Ca in the cytoplasm of the cardiac myoscytes interacts with _____ to cause cardiac muscle contraction
contractile fibers (myofilaments)
what happens when all of the heart cells contract together?
the whole heart contracts and pumps blood out of the chambers in a coordinated way
t/f the larger the amount of intracellular Ca, the larger the cardiac contraction
t
when the sympatholytic nervous system is activated, the release of _____ activates B1 adrenergic receptors in the heart
catecholamines (NE and Epi)
B1 receptors are G____ coupled and their activation leads to increased concentrations of ____ and ____
S; cAMP and PKA
what is the effect of Ca and contraction of heart cells when activated by B1?
increased intracellular Ca through the channels, resulting in a forceful cardiac contraction
sympathetic activation causes the SA node to fire AP _____(faster or slower)
faster
sympathetic activation makes the heart pump ____ and ___ (harder and faster or weaker and slower)? Does this increase of decrease cardiac output?
faster and harder ; increased cardiac output and increased BP
what are 3 ways to target the sympathetic activation of the heart?
- centrally target the sympathetic nervous system in the brain
- target the B adrenergic receptors
- target the Ca channels
what is the MOA of clonidine?
centrally acting antihypertensive agent that acts as an agonist at Alpha 2 adrenergic receptors in the brain to reduce sympthetic input to the heart
the alpha 2 receptor is primarily expressed on ____ neurons and acts as a ____ receptor
presynaptic ; auto
stimulation of the alpha 2 receptor by an endogenous NT like NE or Epi regulates the release of _____ and regulates the propogation of _____ between neurons and ultimately modulates the sympathetic effects in target tissues
additional NT; signals
clonidine stimulates Alpha 2 receptors in the ____ neurons, particulary in the _____, activating G___ coupled signalling cascade
central; medulla; i
when clonidine activates the Gi signalling cascade, it ____(raises/lowers) the amount of NE being released from the central neurons, which ____ (increases/decreases) sympathetic tone
lowers; decreases
what does a decrease in sympathetic tone do bronchodilation, vasoconstriction, and cardiac output?
less bronchiodilation, less vasoconstriction, reduced CO
clonidine acts in the ____, which is the part of the brain responsible for regulating cardiac function
medulla
t/f clondine may act on off target alpha 2 receptors (not in the medulla) and this can cause off target effects
t
what are the most commonly observed side effects of clonidine?
headache, hypotension, dizziness, fatigue, nausea and othe rcentral nervous effects
the actions of clonidine on the CNS may be beneficial for patients with ____
ADHD
how is it belived that clonidine may help with ADHD?
modulating NE release from adrenergic neurons may help to restore some balance between neuronal circuits in teh prefrontal cortex to help with attention
