Cvs 2 - Part 1 Flashcards
Where are Alpha 1 receptors found
blood vessels (smooth muscles)
Where are alpha 2 receptors found
heart, pancreas, and kidneys; mostly insignificant
What do alpha 2 receptors do to the heart
causes a converse effect on the heart causing relaxation;
Where are beta 1 receptors found
Heart
What happens when beta 1 receptors are stimulated
if these receptors are stimulated, heart rate and contraction of the cardiac muscle is increased (vice versa)
Where are beta 2 receptors found
Bronchial musculature (lungs and airways);
What happens when beta 2 receptors are stimulated
if these receptors are stimulated the airways open up and breathing becomes less labored (eases the burden of breathing; especially witnessed in cases of Bronchial Asthma)
• What is the first major beta-blocker?
Propranolol; non-selective beta-blocker
When can propranolol be dangerous
And what does it do?
can potentially be dangerous in patients with Asthma due to its blocking of ALL beta receptors
What types of conditions is propranolol used in
used in over 1,000 conditions mainly related to increased heart rate
Who discovered propranolol
What did he win?
Scottish scientist James W. Black; won the Nobel prize in Medicine for this in 1988
• Denervation Atrophy
– interruption of the nerve connection to an organ or part
Auto-rhythmicity –
• generating rhythmic action potential independent of the nervous system;
• Cardiac Cell Membrane – what kind of unique channels does. It have
has unique channels called fast sodium channels
Cardiac tissue has what two characteristics
is self excitable and exhibits auto-rhythmicity
How are cardiac tissue cells joined
special junctions that are called intercalated discs. Intercalated discs are gap-junctions
What are gap junctions
neighboring cells are connected to each other via junctions that are shaped like bridges or tunnel
What is happening to the cells in a region of the heart when one cell is relaxed or excited
All cells same level of excitation or relaxation due to the presence of these gap junctions
What happens to 2% of the heart. What does that 2% become?
• 2% of the cardiac tissue has undergone functional specialization and has transformed into the “conducting system of the heart”
What happens If the heart wiring is cut the enter process of excitation is compromised
When does this usually happen?
satellite entities attempt to dictate their own aberrant rhythm, hence arrhythmias result. This most often happens in the setting of a myocardial infarction (portion of the heart dies forever after a heart attack).
• Each and every part of the conducting system of the heart is
auto-rhythmic in nature.
• The most common setting where one will see issues with auto-rhythmicity is
After a myocardial infarction
• Absolute Refractory period –
time period in which the cardiac tissue will not get excited at all. It is already in a state of some activity and does not want to be disturbed.
• Time frame of the absolute refractive period?
250 milliseconds.
• Relative Refractory period –
the time period in which the cardiac tissue will not get excited with a stimulant that is not potent. A very potent stimulant may excite it.
What is the range of the resting membrane potential (rmp)?
Range value is from -20 to -200 millivolts in the cells of the human body
• What is the major mechanism that helps create the RMP?
Sodium Potassium Activated Pump
• RMP in the conducting system of the heart is how many millivolts
-60
Depolarization
• – the phase in which the membrane potential moves from negativity to positivity.
• What is the mechanism of depolarization?
Positively charged ions move to the inside of the cell and make the membrane potential less negative
What is phase 1 of depolarization
o Phase 1: Fast sodium channels open up. Sodium moves to the inside and the membrane potential proceeds to become less negative. This phase continues up to-40 millivolts. Threshold potential is achieved at -40 millivolts.
What is phase 2 of depolarization
o Phase 2: Calcium channels open up and calcium moves to the inside. The membrane potential then very quickly proceeds towards zero. It then overshoots zero. At the zenith of Phase 2 the conducting system of the heart fires (action potential is generated and excites the cardiac muscles in its vicinity).
What is phase 3 of depolarization
o Phase 3: Phase of Repolarization – attempt is made to regain the RMP. Involves the opening of the potassium channels whereby efflux of the potassium ions is witnessed. As the positively charged potassium ions are discharged from the cells the membrane potential proceeds towards negativity. This process will continue unabated until the RMP is restored.
What is phase 4 of depolarization
o Phase 4: Not present in all regions of the heart. Involves the continuum of the phase 3 overshooting the RMP. In this phase the membrane potential becomes more negative than the RMP. It allows the cell to correct the electrolytic imbalance that had occurred due to the earlier events of depolarization, repolarization, etc.
Quick RECAP OF THE MEMBRANE POTENTIAL PHASES:
o Phase 1: Influx of Sodium ions
o Phase 2: Influx of Calcium ions
o Phase 3: Efflux of Potassium ions
o Phase 4 (if present): Efflux of Potassium ions (it is the continuum of Phase 3)
• Antiarrhythmic agents –
used to suppress abnormal rhythms of the heart
• Type 1 antiarrhythmic agents block
Phase 1, the fast sodium channel (Influx of Sodium ions)
• Type 2 antiarrhythmic agents are
Beta-blockers that block Beta 1 receptors of the heart
• Type 3 antiarrhythmic agents block
Phase 3, the potassium channel (Efflux of potassium ions)
• Type 4 antiarrhythmic agents block the
Calcium slow-channel; fairly ineffective on the heart (Effective in the smooth muscle in the Tunica media of arteries and arterioles)
• Type 5 antiarrhythmic agents
act by other diverse and unknown mechanisms
• Why are type 1A, 1B, and 1C all causing the same effect?
They all block phase 1, the fast sodium channel.
• what are the 4 Adrenergic receptors
alpha 1, alpha 2, beta 1, beta 2
Name an auto rhythmic organ
the heart is auto-rhythmic
Function of fast sodium channels
sodium perpetually enters the cardiac cells and depolarization happens every 0.8 seconds
