Fox Chapters 13 and 14 (a figure from chapter 12)
In multicellular metazoan, need a vascular system (in terestrial plants
above mosses, xylem and phloem)
Circulation : Cardiovascular system
Anatomy of the heart
(Review, Introductory Biology)
Chambers of heart
Birds and mammals have 4 chambers
Note that right is drawn on left as if looking into the chest of a supine
subject (as I first mentioned when I lectured on Loewi's discovery of vagus
Here is the circuit: LA - LV - Arteries (aorta, etc.) (blood pressure taken
here) - Arterioles (regulate blood flow to muscles, brain, digestion, kidneys
and skin) - Capillaries (near, exchange, WBC's) - venules - veins (no pressure,
valves)- RA - RV - Pulmonary arteries - Lung capillaries - Pulmonary veins
Heart valves and sounds
pulmonary valve (semilunar) feeds pulmonary arteries
aortic valve (also semilunar) feeds aorta
These valves snap shut from arterial back pressure at the end of systole
to make second heart sound- "dub"
Superior and inferior vena cava feed right atrium -> ventricle via tricuspid
Pulmonary veins feed left atrium -> ventricle via bicuspid (atrioventricular)
Tricuspid & bicuspid snap shut at start of ventricular contraction to
make first heart sound- "lub."
If there is backslosh through valves, this is called a heart murmur.
artery is like hose
blood flow to emptying into vascular bed: regulation by smooth muscle of
capillary is one layer of endothelial cells (fenestrated or continuous)
(Review, Introductory biology)
- blood spreads out as it goes from arteries -> arterioles -> capillaries
and hence moves slower. Pressure goes down during movement arteries ->
arterioles -> capillaries (bottom).
Blood moves slowly and with very little pressure in veins. Movement in veins
is mostly passive with a series of valves and where contraction of skeletal
Lymphatic circulation helps to percolate interstitial fluid back to circulation
Shunts (arteriovenous anastomoses) help to regulate circulation through
peripheral vascular beds.
Cardiac cycle and blood pressure
Diastole (between heart beats), systole is during ventricular contraction,
hence terms systolic and diastolic blood pressure.
Ventricle fills during diastole.
Ventricle empties during systole.
Ventricular pressure builds during systole.
Relates ventricular pressure to arterial pressure.
Pulmonary pressure is lower than systemic.
Buildup of ventricular pressure opens valve and blood moves to aorta.
As ventricle relaxes, back pressure from artery snaps valve shut.
The greater the ventricular filling, the greater the cardiac output.
This is good! -- recall that the tension length relationship for striated
muscle had a peak, but, if the muscle got too long, less force could be
This figure also shows that the sympathetic nervous system moves this curve
Measuring blood pressure
It is arterial blood pressure that is usually measured.
close off artery, when it opens (systolic pressure), blood flow is turbulent
and noisy (Korotkoff sounds), when it is always open (diastolic pressure),
blood flow is no longer noisy
Blood pressure is measured in arteries
High blood pressure is called the "silent killer."
hypertension 45 million Americans - salt intake is still debated, >140/95
high 140/70 normal
high diastolic is especially bad
Explained by Wiggers diagram, if diastolic b.p. is high, then it takes higher
ventricular pressure before valve opens and blood actually moves.
Regulation of blood pressure
Blood pressure is regulated by sensory receptors in aortic arch and carotid
Goes to medulla oblongata of brain theh out to sympathetic and parasympathetic
There are also brain influences that come down via hypothalamus.
Heart muscle cells branch and come together and are joiined at intercalated
discs with gap junctions that spread the electrical signal from cell to
cardiac muscle - automatic (explained below)
a picture from our histology course of heart muscle cells joined at intercalated
(like Figure 12.32)
Electrical activity of heart cells
Electrical - SA (sinoatrial) node (or electrical pacemaker) - spread - automatic.
Sympathetic nervous system speeds it up, parasympathetic nervous system
slows it down.
AV (atrioventricular node) is eventually stimulated.
If it were not, it is also automatic but slower and would generate a heart
beat in the venticals.
Bundle of His, bundle branches, and Purkinje fibers get ventricular depolarization
to happen almost synchronously.
Pacemaker cells have depolarization during diastole because of slow Ca2+
Pacemake potential-HCN=hyperpolarization cyclic nucleotide (beta-1 adrenergic
Spike is from Fast Ca2+ channels and Na+ channels
Repolarization uses K+ channels.
Ventricular myocardial cells have long action potentials involving the specific
Einthoven's triangle to show possible placement of EKG (ECG = electrocardiogram)
Because a lot of cells in heart work together, and because extracellular
fluid has high conductivity, electrical activity can be recorded non-invasively.
P is atrial depolarization.
QRS is ventricular depolarization.
T is ventricular repolarization.
This figure relates EKG to pressure and sounds
Normally artery has
tunica interna (endothelium and elastic layer )
A layer of fat with cholesterol between media and externa
ulceration lining lumen
atherosclerosis - hardening of the arteries - plaques
atheroma with macrophages
Cholesterol is a problem
Myocardial cells not regenerate (by mitosis in the adult). This is why heart
attack is so damaging. The same is true for the nerves in the central nervous
system where similar damage is called stroke.
Coronary arteries clog -> myocardial infarction - coronary thrombosis
- ischemia (too little blood flow for oxygen delivery)
Angina, chest pain, and referred pain
Platelet aggregation - thrombus (local), embolism (from elsewhere) cause
tissue plasmogen activator (TPA) dissolve clots
streptokinase thru catheter dissolve clot
aspirin inhibits clotting, coumaden is a strong anticoagulant
catheter with balloon angioplasty insert stent
fibrillation - CPR (keep brain alive, needs O2)
In CPR (cardiopulmonary resuscitation) chest pressure keeps blood flowing
a little and rescue breathing keeps blood oxygenated
1 million Americans die/yr reducing since 1971
bypass operations, replace coronary artery with vessel from somewhere else
in the body, there are 100,000-200,000/yr operations - 30% may be unnecessary
"heart attack" - myocardial infarction
heart muscle is aerobic
anaerobic metabolism would build up lactic acid and cause pain (angina pectoris)
nitroglycerine relaxes smooth muscle (Viagra and other ED medications would
heart muscle damage by necrosis (as opposed to apoptosis - programmed cell
can be detected in S-T of ECG
uncoordinated contraction of heart muscle - fibrillation
in atria fibrillation is not so important becaus atrial beat only addis
a little bit to ventricular filling
in ventricles, it is fatal and hence the importance of defibrillators
re-entry of excitation as electrical signal takes long route around scar
tissue after heart attack can contribute to poor ventricular coordination
Risk facrors for heart attack
(1) High blood pressure (the silent killer) -- Wiggers diagram --heart has
to work harder to open semilunar valves.
(2) prior heart attack
(5) family history - a dominant allele in hypercholesterolemia (and other
(6) LDL-low density lipoprotein - made in liver - low LDL receptors help
liver take up cholesterol
LDL receptors take out cholesterol which otherwise deposits
HDL may lower deposition - excercise good for this
(7) clotting, especially clumping of platelets) inhibited by aspirin (and
coumadin) - hence term "coronary thrombosis" (in coronary artery)
(1) exercise - increase HDL (endothelial cells do not take up)
(2) antioxidants (oxidized LDLs in endothelial cells are bad)
alcohol in moderation (but people who die of cirrhosis rarely have atherosclerosis)
statins (box on p. 412):
(a) block rate limiting step in cholesterol synthesis in liver
(b) secondarily increase LDL receptors
S. Cohen J Leor Rebuilding broken hearts, Scientific American, November
infarct kills cardiomyocytes
noncontractile fibrous cells replace
adjacent healthy myocytes may die
ventricle wall becomes thinner, distends, might rupture
tissue engineering - must have scaffold for cells and blood supply
3-D sponge-like frame made alginate (from algae) frozen
progress so far- can prevent further damage
add controlled release microspheres of growth factors to help angiogenesis
Pacemakers (keep the beat) [working knowledge] M Fischetti, Scientific American,
wires run in through vein
tips have steroid reservoir to block early inflammation
that keeps contacts healthy
ICD - Implantable cardioverter defibrillator
Exam questions from 2004 - 2011 that relate to this outline:
Ventricles fill during most of ventricular diastole. Toward the end of ventricular
diastole, there is a small increase in the filling curve that had otherwise
pretty much reached asymptote. What is the cause of this small final amount
of ventricular filling?
the atrial beat
For your BME senior project, you invented a device that will read out pressure
in the left ventricle as a function of time noninvasively. When you present
this at the senior legacy symposium, your sophomore physiology professor
comes up and says "Great, but an ordinary cuff on your arm would give
you additional important information missing from your readout." What
the diastolic blood pressure (in the arteries)
Within the intercalated disk. there are specializations (called what?) that
allow the action potential to be transmitted from one myocardial cell to
"The T wave represents the repolarization of the ventricles."
Why was there no equivalent wave representing the repolarization of the
it was hidden under QRS
CPR does not restart a heart in ventricular fibrillation. Then why would
it save the victim's life before emergency medical personnel arrived with
keeps a little oxygenated blood going to the brain
Backslosh through leaky heart valves. Answer either (1) What is the term
for this that makes reference to heart sounds? or (2) What bacterial disease
might lead to this?
heart murmur, rheumatic fever
After the atrio-ventricular valves snap shut but before the semilunars open,
the ventricles contract and build up pressure. What happens to the volume
of blood in the ventricles during this period?
it stays the same
There are many layers in an artery. Only one of these layers of cells is
present in a capillary. What is this type of cell called?
There is a family of curves for different amounts of sympathetic nerve stimulation
where stroke volume in ml is plotted as a function of ventricular end-diastolic
volume in ml. Answer either (1) What is this called? (2) In what way does
this distinguish the properties of cardiac vs striated muscle as a function
of length? or (3) What effect does sympathetic stimulation have on these
Frank-Starling law, cardiac muscle does not get weakker as a function of
length, it moves them up and to the left
Parasympathetic and sympathetic portions of the autonomic nervous system
affect heart rate, acting on the SA (and AV) nodes. What additional direct
affect does the sympathetic nervous system have on the heart?
sympathetic NS increases myocardial contractility
What would have to happen to the shape of the action potential of a ventricular
myocardial cell to compensate for the increased heart rate that accompanies
the long duration action potential would get shorter
If, for some reason, the signal that should have originated in the SA node
were not transmitted appropriately, the heart would still beat. What would
drive this heart beat?
the automaticity of the AV node
HCN channels. Answer either (1) What is the cyclic nucleotide referred to
by "CN?" or (2) What do we call the unusual electrophysiology
mediated by the HCN channel?
cAMP, pacemaker potential or diastolic depolarization
"Here, quick, chew this aspirin and drink it down." If this stopped
a heart attack in progress, how would it do that?
"Action potentials that originate in the SA node pass from one atrial
myocardial cell to another and usually usually trigger the AV node before
it would have fired automatically." Say why spreading from one myocardial
cell to the next is not a full explanation of action potential spread in
bundle of His, bundle branches, and Purkinje fibers get the action potential
to the apex first
Name one of the 4 risk factors for heart attack that ranks higher than family
high blood pressure, prior heart attack, smoking, diabetes
For the atrial beat, answer either (1) Why does it contribute only minimally
to ventricular filling? Or (2) What would keep the blood from flowing backward
into the veins coming into the atria?
1 blood goes from atria to ventricles even before the beat, 2 nothing except
those valves that are in veins
The first few moments of ventricular contraction fail to move blood into
the arteries. Why?
isovolumetric contraction is because semilunars remain closed until ventricular
pressure is higher than afterial pressure
You feel chest pain so you take nitroglycerine. How did this save you from
a heart attack?
relaxation of smooth muscle in coronary arteries would alleviate the block
(that likely resulted from a thrombus or an embolism in an artery already
partially occluded from atherosclerosis)
Why do the textbook artists color the pulmonary arteries blue?
they carry blood low in oxygen and high in carbon dioxide
Why can you hear the brachial artery below the blood pressure cuff when
the cuff pressure is between the systolic and diastolic levels?
Korotkoff sounds are when blood flow is turbulent from partly closed artery
In the atria, all that was needed to propagate the electrical signal was
the connections from one myocardial cell to the next. For the ventricles,
why was it important to have the added feature for propagation (bundle of
His and bundle branches)?
to start the contraction at the "apex" (bottom), to send the action
Three "leads" describe 3 different ways both wrists might be fed
in for measuring the ECG. Why might different people have differences in
how the ECG looks with the 3 leads?
orientation of heart (axis) can differ, abnormalities like murmurs might
create an asymetry in heart muscle
What would the sympathetic nervous system do to the shape of a myocardial
cell's action potential?
shorten that prolonged spike
A person drops over and has no pulse. To keep him or her alive until medical
equipment and personnel arrive, (answer either) (1) What is the name of
the procedure you would perform? Or (2) How would this keep the victim alive?
CPR, it keeps the brain alive
"Re-entry of excitation:" After recovering from a heart attack,
why might some myocardial cells be excitable (no longer refractory), and
be triggered to fire, before the appropriate time (that appropriate time
being the time synchronized from the SA and AV nodes)?
a pathway of myocardial cells around the scar might be long
Why was a reminder of the process of receptor-mediated endocytosis by clathrin-coated
pits relevant in the context of heart attacks?
LDL is removed by that process
Approximately what is the pressure in the left ventricle when the semilunar
valve (to the aorta) opens?
At that moment it should equal diastolic pressure
Opening up the arteriovenous anastomoses would do what to blood flow in
the capillary loops in the dermis?
It would bypass (therefore decrease) blood flow in the capillary loops of
The parasympathetic output to the heart affects both the SA and the AV nodes.
What affect in addition to these two does the sympathetic output to he heart
It affects contractility in the myocardium in addition to affecting rate
via the nodes
How would the sympathetic nervous system affect the shape of a series of
action potentials recorded from a cell in the SA node?
Diastolic depolarization (pacemaker potential) would reach threshold faster
(and the rate would go up)
Why is the expression "referred pain" sometimes applied to the
pain experienced during a heart attack?
Pain from viscera and heart is projected onto the somatosensory map, thus
for the heart, classic symptoms of shooting pain in left shoulder and neck
especially in men
When, in the heart cycle, do the bicuspid and tricusid valves snap shut?
at the beginning of ventricular contraction
What kind of blood vessels have the highest TOTAL cross sectional area?
What does the last Korotkoff sound signify?
the diastolic (arterial) blood pressure
What are the cells that line blood vessels including capillaries called?
Why is the wall of the ventricle thicker than the wall of the right ventricle?
systemic circulation is higher pressure than pulmonary
What is Einthoven's triangle?
Hook-ups for diagnostic EKG Leads I, II, and III on 2 wrists and left ankle
Long QT Syndrome, diagnosed by a lot of time between the QRS and the T,
affects a channel (for what ion?) involved in the repolarization of ventricular
Cells in what areas depolarize automatically during diastole?
Although the electrical signal would pass from one myocardial cell to the
next, specialized fibers hurry it to much of the ventricular muscle synchronously.
What are these fibers?
bundle of His, bundle branches, Purkinje fibers
Why would you die of if there were too much time between heart failure and
defibrillation without CPR (cardio-pulmonary resussitation)?
brain would die without O2 (and glucose)
The time between the QRS and the T represents the duration for what specific
ventricular myocardial cell
For a normal person, slow Ca2+ channels would control heart rate in which
specific part of the heart?
In good health, what part of the body clears LDL (and HDL) from the blood
How does nitroglycerine help to relieve angina pectoris?
relax artery smooth muscle
What is the likely mechanism that antioxidants might prevent heart attacks?
oxidized LDL is bad
Why isn't an atrial beat needed for most of the venous return to go to the
ventricles during diatole?
tricuspid and bicuspid valves are open
What does the endothelium line?
If you took statins, what substance would decreased?
How do gap junctions contribute to heart function?
get action potential from one cell to another
Since there is not much blood pressure left, what is needed to help blood
flow along in veins?
Taking blood pressure, you inflate the cuff to 180 mm Hg, then lower it.
You hear nothing until the systolic pressure is reached. After the diastolic
pressure is passed, you hear
nothing. Why do you get sounds only between systolic and diastolic pressures?
What causes the second heart sound at the end of systole?
semilunars snap shut
How does aspirin help to prevent heart attacks?
inhibits platelet aggregation
Where does the vena cava (superior and inferior) empty into?
At the moment the semilunar valves open, what is the blood pressure in the
same as arterial diastolic
What is the function of an arteriovenous anastomosis?
shunt blood from peripheral vascular bed
What is the endothelium?
cell lining of blood vessels
What is a heart murmur?
a leaky valve
Compare the duration of the isovolumetric portion of the ventricular contraction
for someone with high diastolic blood pressure with that for a normal person.
the ventricle would contract further before forcing open the valves to arteries
(for high b.p.)
What regulates the precapillary sphincter?
the sympathetic nervous system
"CN" in "HCN channels" stands for "cyclic nucleotide."
What do cyclic nucleotides have to do with pacemaker cells?
adrenergic receptor affects cAMP level
Explain the interval between the QRT complex and the T wave in terms of
the shape of the myocardial action potential.
that is a long action potential, QRS is depolarization, T is repolarization
How could you get a heart beat if there were no trigger from the SA node?
Eventually the AV node would kick in
At the moment of the last Korotkoff sound, what does the pressure dial show?
What are baroreceptors in the carotid sinus used for?
In addition to increasing contractility, what does sympathetic input to
the heart do?
regulate heart rate
What is ischemia?
interuption of blood flow and hence oxygen supply
What does a defibrillator do to save your life?
starts heart again, makes it so SA node triggers heart
What does a high HDL/LDL ratio in your blood test results imply?
less risk for coronary artery problems
As opposed to apoptosis, what is the damage to cardiomyocytes in a heart
What is it called when you have pain in parts of your body, like your left
arm, in a heart attack?
What is a thrombus and why is it potentially damaging?
a blood clot that clogs the artery
What event occurs at the end of the isovolumetric contraction of the left
Aortic semilunar valve opens
Why do veins need to have valves to ensure forward blood flow while arteries
there is no blood pressure driving the blood
In what way does the Frank-Starling law differ from the striated muscle's
FS-More stretch (ventricular filling) more contraction, striated weaker
when muscle is long
Why is the first part of the ventricular contraction isovolumic?
Bicuspid and tricuspid are closed, semilunars do not open until ventricular
pressure > arterial
Heart cells die by cell damage, rather than by programmed cell death (apoptosis).
What is the term used for this kind of damage?
A blood test shows that a patient has a high HDL to LDL ratio. What does
these are good numbers re artery health
In an arteriole, what would a precapillary sphincter do under the influence
of the autonomic nervous system?
open or close to regulate blood flow to the capillary bed
What valves close right at the start of ventricular contraction?
tricuspid and bicuspid (atrioventricular)
Hyperpolarization cyclic nucleotide (HCN) channels are important in pacemaker
cells. Name the relevant and famous cyclic nucleotide, the one controlled
by beta-1 adrenergic receptors.
In atria, the action potentials are passed from one myocardial cell to the
next. Why are there additional fibers (bundle of His, bundle branches, and
Purkinje fibers) for ventricles?
to speed the action potentials to the base
Parasympathetic fibers slow the SA and AV nodes below their rate of automaticity.
What nerve is this?
vagus, 10th cranial
Above the systolic pressure and below the diastolic pressure, you hear nothing.
Why are there Korotkoff sounds between systolic and diastolic pressure?
blood flow is turbulent
What does the Wiggers diagram tell us about the opening of the aortic semilunar
valve when the diastolic blood pressure is high?
ventricular pressure would have to be higher to push open the valve
Give an approximate value for the blood pressure in the ventricles during
What symptom would be noticed if the heart muscle were to attempt anaerobic
What do aspirin, coumaden and the rat poison WARFarin have in common?
they inhibit coagulation
Valves between where and where snap shut at the beginning of ventricular
atria and ventricles
For part of the heart cycle, ventricular and arterial pressures are equal.
How do these two pressures relate the rest of the time?
in diastole, ventricular is lower than arterial
What holds shut the aortic and pulmonary semilunar valves during the beginning
of ventricular contraction?
In addition to the automatic tissues (predominantly SA & AV nodes) to
what does the sympathetic nervous system connect and why?
heart muscle to increase contractility
Electrically, what do pacemaker cells during diastole?
How come the electrocardiogram can reach as far as the wrists and ankles
virtually no extracellular resistance
What would happen to the time between Q and T waves with sympathetic activation?
What is the difference between a thrombus and an embolism?
thrombus clot forms locally, embolism dislodged from elsewhere and arrives
at trouble spot
Why would a large area of damage in the heart lead to re-entry of excitation?
the distance from cell to cell to cell would have the spike arriving after
the refractory period is over
What type of cell is used for continuous and fenestrated capillaries?
What is it that may shunt blood from arteriole to venule to bypass capillary
bed in the skin?
In what way is heart muscle different from striated muscle with respect
to strength as a function of length?
Frank Starling law has it that fuller (more stretched) ventricle has higher
contractility, while striated muscle tension drops off
As cuff pressure is being released, between the systolic blood pressure
and the diastolic pressure, your figure indicated that you get "sounds
at every systole." Why?
turbulent blood flow
How would nitroglycerine help if you felt a heart attack coming on?
relax smooth muscle in artery
Describe referred pain as it refers to heart attack.
projected to neck, arms
What is it that makes the bicuspid and tricuspid valves close to make the
first heart sound ("lub")?
pressure in the ventricles closes these atrio-ventricular valves
Why might a person pass out if (s)he stands without moving for a long time?
muscular contraction contributes to venous return, hence venous pooling
What part of the nervous system would regulate the precapillary sphincter?
During ventricular systole, just when the pressure forces the aortic semilunar
valve open, what is the arterial blood pressure?
equal to the diastolic pressure right then
About what fraction of ventricular filling is from the beat of the atria?
a very small amount, the figure shows about 10 out of 80 ml
What happens to the brachial artery when the blood pressure cuff is first
it is completely closed
Suppose your SA node failed to fire. You would probably still have a heartbeat
(how?) and it might be reasonably adequate (why?).
AV node would fire, see q 10, most of the ventricular filling does not rely
What happens to the electrical potential of a cell in the sinoatrial (SA)
node during diastole?
there is diastolic depolarization in these pacemaker cells until threshold
How do we get recordings from 3 different "leads" in Eindhoven's
triangle starting with a positive electrode connected to one wrist, a negative
electrode connected to the other, and ground connected to an ankle?
The three so-called "leads" are gotten by swapping (2 at a time)
connections to the 3 locations
Before paramedics arrive with the defibrillator, why is cardiopulmonary
CPR delivers enough oxygenated blood to the brain to keep it alive
"The bad news is that your cholesterol is high. The good news is that
your ratio is good." What would be a good ratio (when the cholesterol
level is broken down into its components)?
If HDL/LDL is high
At the peak of systole, how does the pressure in the right ventricle compare
with the pressure in the left ventricle?
Way lower pressure in pulmonary circulation
Both branches of the autonomic nervous system (sympathetic and parasympathetic)
connect to both nodes of the heart(SA and AV). In addition, the sympathetic
nervous system also makes additional connections to the heart (to where?
Or for what purpose?).
to muscle to increase strength of contraction
What would happen to the Q-T interval during strenuous exercise?
What is the function of an arteriovenous anastomosis?
Shunt blood to bypass capillaries in skin to prevent heat loss
What is the status of bicuspid and tricuspid valves during diastole?
open and blood gushes from atria to ventricles
"Fenestrated endothelium." Explain either (1) fenestrated or (2)
windows (holes) in layer that lines blood vessels (capillaries
How would nitroglycerine give you relief?
relax smooth muscle, coronary arteries more patent to relieve angina
Why does blood flow more slowly in capillaries than in arteries?
there is a greater cross sectional area
Why do the atria contribute only minimally to the ventricular filling during
because blood flows to ventricles during diastole b/c A-V valves are open
Even before ventricular pressure overcomes arterial diastolic pressure,
increasing ventricular pressure does (what?) to (what valves?).
snaps shut A-V valves
What did pumping the blood pressure cuff up to 140 mmHg do? (Assume you
have a subject with fairly normal blood pressure.)
close brachial artery
"The heart is an electrical syncitium" because of what specialization?
What is the channel critical for diastolic depolarization (pacemaker potentials)?
HCN hyperpolarization cyclic nucleotide
Why would you prescribe an inhibitor of angiotensin converting enzyme to
decrease blood pressure
What is the difference between plaque and a thrombus in arterial occlusion?
plaque builds up in artery wall b/c of cholesterol, thrombus is blood clot
What would have to be wrong with a patient to warrant shocking the chest
with paddles and why would that help?
ventricular fibrillation, i.e., heart electrical activity flat lines
What is the status of the semilunar valves during diastole?
How does the nervous system regulate precapillary sphincters?
sympathetic nervous system causes vasoconstriction or hyperemia
What do the carotid sinus and aortic arch have to do with the regulation
of the heart?
Pressure receptors feed to brain to regulate heart output
Myocardial cells are electrically connected via gap junctions. Why, then,
was it useful to have bundle of His, bundle branches, and Purkinje fibers?
gets action potential to heart apex so that ventricular contraction ejects
What do aspirin, rat poison and the heart have to do with each other?
aspirin and WARFarin would inhibit clots (thrombus or embolism) in coronary
Referring to the Wiggers diagram, why would high diastolic blood pressure
be especially hard on the heart?
higher ventricular pressure would be required to force open semilunar valves
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