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Circulation!!
Quick Outline
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Glossary
Blood Flow
Heart Sounds
Heart Rate and how it changes
Blood Pressure and how it changes
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Terms (of Endearment?)
The Heart
Its Electricity
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Vena Cava
Right Atrium
Right AV Valve
Right Ventricle
Pulmonary Valve
Pulmonary Artery
Pulmonary Vein
Left Atrium
Left AV Valve
Left Ventricle
Aortic Valve
Aorta
Arterioles
And Controls
Intercalated Disks
•Sympathetic
Desmosomes
•Excites the Heart
Gap Junctions
•Uses NE
SA Node
AV Node
•Acts on SA node
and arterioles
Bundle of His
Left and Right Bundle •Parasympathetic
Branches
•Relaxes the Heart
• Terminal Purkinje Fibers
•Uses Ach
•Acts on SA node
Basics of Flow
ZOOM!!
RA
RV
LA
LV
So we have Vena CavaRARV
Pulmonary ArteryLung
Pulmonary VeinLALVAorta
Body Arterioles
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Heart Sounds
• Lub: the closing of the AV Valve
– This happens just after the ventricles start contracting.
(Contraction increases the pressure in the ventricle
above the pressure in the atria, causing the valves to
close.)
• Dub: the closing of the Pulmonary and Aortic
Valves
– This happens just after blood is finished ejecting from
the ventricle. (The ventricle relaxes, decreasing its
pressure below the pressure in the pulmonary artery
or the aorta, so the pulmonary or aortic valves close.)
Valves close passively as a result of a pressure
difference on each side of the valve.
Electrical Statement
• Electrical Synapses:
– Faster than Chemical
– Can transmit information in either direction
– Travel through gap junctions—don’t diffuse through synapses
•Gap Junctions Look Like:
•Desmosomes Look Like:
Cell 1
Cell 1
Cell 2
Gap Junction
Cell 2
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Conduction
SA Node
Depolarization of
R and L atria
AV Node
Bundle of His
Left and Right
Bundle Branches
Terminal Purkinje
Fibers
It’s Got Rhythm
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Each part of the heart has inherent rhythm,
but some parts are faster than others
• The SA Node is the fastest--so it paces the heart
• Its Action Potential Looks
like
• Ion Channels:
– F Channels
• Permeable to Na+ and K+ at
membrane voltages below 40mV
– V-gated Ca++ channels
– K+ channels
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Sympathetic Stimulation and
SA Node Action Potentials
Recall that this occurs when norepinephrine binds to betaadrenergic receptors on the SA Node
Thank you to U. Rochester for this image
Actions of Parasympathetic
Stimulation on SA Node Action
Potentials
Recall that this happens when acetylcholine binds to
muscarinic acetylcholine receptors on the SA Node
Again, props to U. Rochester for the image
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Ventricular Muscle Cell Action
Potential
Key:
1st Fast increase in membrane
potential due to V-gated Na+
channels
2nd The Na+ channels close, and Vgated Ca++ channels and K+
channels open. The K channels
are acting to decrease the
membrane voltage and the
Ca++ are acting to increase it.
Result? Plateau.
3rd The v-gated Ca++ close.
4th Resting membrane voltage is
set by the high permeability of
K+.
Equations to Scribble in the
Margins
• CO=HR x SV
• BP= CO x TPR
• Blood pressure can be changed by changes in CO or in
TPR. You saw how CO could be changed 2-3 slides
ago. Altering heart rateChange in COChange in BP.
• So an increase in sympathetic stimulation increases the amount of
NE bound to _-adrenergic receptors in the SA node, which
increases the HR, which increases the CO and the BP.
• An increases in parasympathetic stimulation increases the amount
of ACh bound to muscarinic ACh receptors, which decreases the
HR, which decreases the CO and the BP.
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But what about TPR? What
changes it?
– TPR is influenced by the resistance to flow in
the arterioles, which is controlled the
arterioles’ radii, which are controlled by the
contraction or relaxation of the smooth
muscle around the arteriole.
– Arterioles have SNS innervation but not
PSNS
• When norepinephrine binds to _-adrenergic receptors
on the smooth muscle cells, the smooth muscle
contracts, which decreases the radius of the arteriole.
This causes an increase in TPR, and because BP=CO x
TPR, it lead to an increase in BP.
• When less norepinephrine binds, the smooth muscle
relaxes, which causes an increase in the radius of the
arteriole. This leads to a decrease in TPR, and
because BP=CO x TPR, it leads to a decrease in BP.
Baroreceptors
• Baroreceptors serve as the sensor in the
blood pressure negative feedback loop.
They are located in the carotid artery and
have mechanosensitive neurons that sense
blood pressure. They send action
potentials into the brain stem, where the
comparator is. The brain then changes the
relative amount of sympathetic and
parasympathetic amounts of innervation if
necessary.
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Baroreceptors
• If baroreceptors are cut, then the axon terminal
(in the brain stem) and the peripheral terminal
(in the carotid artery) are not communicating.
• If the barorecptor is cut and then the axon stump
(which is still connected to the brain stem) is
stimulated at a high rate, the brain stem is
“sensing” high blood pressure. So it will take
action to decrease the blood pressure.
• Meanwhile, the peripheral terminals will sense a
decrease in BP, but won’t be able to get this
information to the brain stem.
Ok
take a deep breath
It’s time for
respiration
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