Lectures 14-15 Flashcards
What are myocardial autorhythmic cells?
can generate their own APs without external input | ensures heart is beating
What is pacemaker potential?
unstable membrane potential starting at -60mV | no resting membrane potential
What is the cardiac action potential?
the pacemaker potential | no resting membrane potential, always fluctuating
What causes autorhythmic cells to be auto-rhythmic?
HCN channels
What does HCN channel stand for?
Hyperpolarization-activated Cyclic Nucleotide-gated channels
What are HCN channels?
(only in heart) | permeable to Na+/K+ and similar to those voltage-gated channels | 6-segments, S4 = charged | 2nd messengers bind to HCN = modulate activity, activate cAMP
What activates HCN channels?
hyperpolarization
How does HCN get activated via hyperpolarization?
when intracellular charge becomes negative »_space;> activates and opens HCN »_space;> allows influx of Na+ »_space;> depolarization = AP
What are 2 cyclic nucleotides?
cAMP and cGMP
What are the funny currents (If)?
the current generated by HCN
What ion drives cardiac AP?
calcium (mostly) (na+ = just depolarizes)
What membrane potential is needed to activate HCN channels?
-40mV or below
What will an HCN blocker drug cause?
inhibits heart cells to propagate another pacemaker potential
What are the 3 main areas where auto-rhythmic cells are found within the heart? Order them from fastest to slowest and indicate intrinsic capacity.
sinoatrial (SA) node = 1s | atrioventricular (AV) node = 2s | Purkinje fibers = 3s
Which node initiates the autorhythmic activity and dictates the heartbeat?
SA node
What do the AV node and Purkinje fibers act as? How?
fail-safe systems | will generate pacemaker potential if SA node fails
What happens if the SA node doesn’t work?
AV node generates rhythm but at a slower pace than SA node bc intrinsic capacity = 2s
How do the AV node and Purkinje fibers beat at the pace of the SA node if they have their own rhythm?
all are connected and because SA is faster and first, it will send its AP down to the other 2 = make them beat with SA
What autorhythmic cells surround the ventricles?
AV bundle (bundle of His)
When does one need a pacemaker?
if ventricular pace is too slow
Why does the conduction of AP slow down as it moves through the AV node (AV delay)? What is the purpose for this?
the delay is that AV node passes the signal through the Purkinje fibers 1st before contracting ventricles | allows the ventricles to fill with blood
What would happen to the conduction if the AV node malfunctioned and could no longer depolarize?
SA and PF = not connected »_space;> SA fires every 1s = atrium contracts every second === PF fires every 3s = ventricles contract every 3s »_space;> ventricles are getting filled 3x more due to atrial contraction per 1 ventricular contraction
Which group of autorhythmic cells contracts the atria?
SA node
What will the individual experience due to AV node malfunction?
dizziness due to O2 not being delivered at the appropriate time
What does fibrillation mean?
loss of coordination of myocardial cells | disconnect = causes fibrillation
What are the 2 types of fibrillation?
atrial and ventricular
What is atrial fibrillation? What is the treatment?
asymptomatic can lead to stroke | Tx: blood thinners
What is ventricular fibrillation? What is the treatment?
ventricles not contracting in unison = cannot pump blood to body = life-threatening | Tx: defibrillators (jump start heart) and pacemakers
What is bradycardia?
slow heart rate (under 60bpm)
What is tachycardia?
fast heart rate (over 100bpm)
What is angina pectoris?
chest pain due to lack of blood flow to the heart
What is arrhythmia?
irregular heart rate
How does parasympathetic stimulation affect the heart?
hyperpolarizes membrane potential | slows depolarization === slows heart rate
How does sympathetic stimulation affect the heart?
depolarizes membrane potential = speed up pacemaker potential = speed up heart rate
What is another term for epinephrine?
adrenaline
What nerve innervates the heart?
vagus nerve
What is the term that is used in ECG denoting where the 3 leads/electrodes are connected on the body?
Einthoven’s triangle = right and left arms, left leg
What does the P-wave represent?
depolarization of atria
What does the QRS complex present?
depolarization of ventricles (ventricles onctract = big force = large part of graph) | small atrial repolarization
What does the T-wave represent?
repolarization of ventricle
What are the 3 things to look for in an ECG?
heart rate | rhythm is regular | all waves and segment present
What does the ECG measure?
the overall change in voltage that the heart is giving out
What is the 3rd-degree block in an abnormal ECG?
complete disconnect of the SA and AV nodes from the PF | regular 1s P-waves = SA works fine | QRS complex not following P-waves = happening at PF rhythm pace due to disconnect
What is atrial fibrillation in an abnormal ECG?
no P-waves | QRS complex = noisy and weird | irregular rhythm
What is happening in the heart during atrial fibrillation?
atria not contracting uniformly = blood not flowing into ventricles = cannot pump blood efficiently
What is happening in the heart during a 3rd-degree block?
SA node works fine | PF contracts ventricles at own rhythm = every 3 seconds
What is ventricular fibrillation in an abnormal ECG?
just a bunch of squiggly waves
What is happening in the heart during ventricular fibrillation?
ventricles = no depolarization = no contraction = can’t pump blood to body
What is a second-degree block on an abnormal ECG?
Some P-waves are irregular and some match up with the PQRST-set
What is happening in the heart during a second-degree block?
PF not always firing in sync with SA and AV | heart skips a beat
What is the 1st-degree block?
big delay between P-wave and QRS-T bc Sa not functioning effectively = heart rate is slower
How is using a 12-lead ECG beneficial?
gives more info | can indicate heart tissue damage and heart attacks
Which ANS response (parasympathetic or sympathetic) has a greater influence on the heart?
parasympathetic - constantly slowing it down
What receptors are activated in the parasympathetic pathway of the heart?
M2 muscarinic receptors
What kind of nerve is the vagus nerve in relation to the heart?
pre-ganglionic
What type of neurotransmitter system does the sympathetic pathway use to act on the heart?
cholinergic system
Where are epinephrine and norepinephrine released from?
Epi = adrenal gland | sympathetic post-ganglionic neurons
Which neurotransmitter (NE or Epi) better binds to beta-1 receptors?
Epi due to structure
What is phospholamban?
regulatory protein activated by cAMP
What is systole?
contraction of heart muscle | top number
What are the 2 types of systole?
atrial and ventricular
What is diastole?
heart muscle relaxes, expands due to passive filling of blood | bottom number
What is the Frank-Starling Law?
relationship between the stretch of heart muscle and the force generated when the heart muscle contracts | force generated will push certain amount of blood
What is the end-diastolic volume (EDV)?
volume of blood in the filled chamber as ventricle is relaxing = stretch determines sarcomere length
What is stroke volume?
indication of force of contraction
What is the end-diastolic volume determined by?
venous return
What are 3 ways that contribute to venous return?
skeletal muscle pump | respiratory pump | sympathetic innervation of veins
What is the skeletal pump?
constriction of veins due to contraction of skeletal muscles that return blood to the heart
What is inotropic effect?
refers to the force of contraction
What are inotropic agents? Example of one.
any chemical that affects contractility and its influence is inotropic effect | NE and epi
What is a positive inotropic effect?
increase force of contraction | NE and epi
What is a negative inotropic effect?
decrease force of contraction
What is ejection fraction?
how much volume is being ejected with that one contraction (stroke volume / EDV)
What is cardiac output?
output of blood from the heart affected by stroke volume and heart rate
What is stroke volume determined by?
force of contraction in ventricles
What 2 things influence the force of ventricular contraction?
contractility | EDV
What is end diastolic volume vary with?
venous return
What is the respiratory pump?
changes in abdominal pressure during breathing
What happens as vessels get narrower and narrower?
will decrease on how much blood can go through = increase in pressure
Why do arteries have a high amount of elastic tissue and smooth muscles?
to withstand great pressure changes
What is the purpose of having less fibrous tissue encapsulating the blood vessels?
increase diffusion of O2 and nutrients as fibrous tissue inhibits this
What is the purpose of endothelium on blood vessels?
lines the vessels
What is vasoconstriction? Affect from NE?
increase of NE = narrowing of vessel diameter
What is vasodilation? Affect from NE?
decrease of NE = widening of vessel diameter
What is the function of capillary beds and what feature allows this function?
site of O2 and nutrient exchange | porous
What are the 2 types of capillaries?
continuous and fenestral
What are continuous capillaries?
continuous with other vessels | leaky junctions = openings where nutrients and O2 can pass
What are fenestrated capillaries?
highly porous | for demanding tissues
What is transcytosis?
transport of things from one side to another through vesicles | vesicles can form channel-like openings
How can BP be artificially controlled?
block beta 1 receptors
What are fenestrations?
breaking of endothelial cells allowing nutrients and materials to flow through cells
What is blood flow opposed by?
resistance of the system
What is needed in order for blood to flow?
pressure gradient from high to low
What are the 3 factors that affect resistance in blood flow?
radius and length of blood vessels | viscosity of blood
What is the primary determinant of the velocity of blood flow?
the shape of the cross-sectional area of vessels (some are round and others are flat)
What branch of the ANS controls most vascular smooth muscle?
sympathetic
What type of receptors are on vessels for the ANS input?
alpha-adrenergic receptors
