Cardiac 1 Flashcards
Themes
- Bulk transport and Diffusion (O2 & C02 transport)
- Heart & Blood vessels together as an integrated system
- Anatomy
- Electrical & Mechanical events
- Heart is a “smart pump” (Frank Starling & Pressure/Volume)
- Regulation of blood flow
- Cardiovascular function curves
- Diseases
The Mammalian Heart is a Dual Pump
- Pulmonary (right heart)
- Systemic (left heart)
-Red indicates oxygenated blood, blue indicates deoxygenated blood (it is actually dull red)
Overview of blood movement through the heart and body
- The blood coming out of the right side of the heart is deoxygenated, because it’s collecting blood from the body
- The right side of the heart pushes that blood out to the pulmonary circulation, which brings it to the capillaries in the heart, where CO2 is removed and oxygen is added
- The oxygenated blood comes back to the left side of the heart, enters the atrium, then the the ventricle, and is pumped out through the aorta and feeds the whole systemic circulatory system
What are the large veins that collect the blood in the pulmonary system called?
Vena cava
Default is to talk in systemic
If you say venous or arterial blood, this indicates systemic circulation. If you want to indicate that it’s pulmonary, you have to put pulmonary in front of it
Definition of artery
Takes blood away from the heart at high pressure
Definition of vein
Takes blood toward the heart and typically has a lower pressure
Blood pressure info (add or wait for lectures on circulation?)
Where is the highest source of pressure in the circulatory system?
In the large arteries (averages at around 100 mmHg)
What is the pressure in the large veins?
Around 0
What is the driving force for pressure?
The pressure gradient
Diagram of pulmonary and systemic circulation
More detailed diagram of pulmonary and systemic
- Parallel pathways
There’s __ liters of blood per minute coming out of the aorta and going through the pulmonary arteries
5
Why do we need less pressure for pulmonary circulation?
Because it doesn’t fight gravity (and the lungs are close to the heart)
The walls of the left ventricle are ___ than the walls of the right ventricle
Thicker
Diagram of heart
What is the left AV valve also called?
Bicuspid valve and mitral valve
Just call it the left AV valve
What is the right AV valve called?
Tricuspid valve
Just call it the right AV valve
Movement of blood through left side of the heart
- The blood comes into and pools in the left atrium from the lungs, oxygenated
- The ventricle relaxes, and allows the blood to flow down through the left AV valve (when the ventricle squeezes, the valve slams shut because of the pressure, but when the pressure in the ventricle is low, the valve is open)
- When the ventricle starts squeezing and the pressure goes up really high, the AV valve closes to prevent backflow
- The pressure rises until the pressure in the ventricle exceeds the pressure in the aorta and then the aortic valve opens to allow blood to exit
- When the ventricle relaxes again, the pressure in the ventricle drops, and when the pressure in the ventricle drops below the pressure in the aorta, the aortic valve closes to prevent blood from going from the aorta back into the ventricle
Movement of blood through right side of the heart
- Right atrium is filled with blood coming back from the body at low pressure
- The right AV valve opens to let it flow into the ventricle
- When the right ventricle squeezes, pressure goes up, AV valve closes
- Pressure continues to go up, and the pulmonary semilunar valve opens and blood goes out through the pulmonary arteries
What opens and closes valves in the heart?
Pressure gradients
What is responsible for the filling of the ventricle?
- Most of the filling is caused by the relaxing of the ventricle, causing a drop in pressure, opening the valve, causing the blood to be dumped into the ventricle
- At the very end, right before the filling is done, the atria give a little squeeze and tops off the volume in the ventricle
What is the purpose of the papillary muscles and tendons that insert on the ventricular face of the AV valve?
- They do not open the valve - this would be counterproductive
- The wave of depolarization that sweeps through the ventricular muscle cells and causes the ventricle to squeeze and start increasing pressure also activates the papillary muscles and pull on the inner surface of the AV valve
- They pull on it to prevent the valve from being blown out into the atrium due to the high pressure in the ventricle
- So the papillary muscles help the valve that isn’t mechanically strong enough to resist all the pressure in the ventricles
- Without this, there would be regurgitation of blood
- There are some on the right side of the heart as well
Right AV valve
- Has 3 ‘leaves’ to it
- Also called tricuspid valve
Systole and diastole
- Systole- muscle contracting
- Diastole- muscle relaxing
- Atrial first, ventricular second
Synchronization of the left and right atria and ventricles
- The atria and ventricles are synchronized- they squeeze at the same time
- Partly because everything is electrically-coupled
Transverse and frontal sections of the heart
- a) ventricles are squeezing
When is the aortic valve open and closed?
- Open when the ventricle is contracting (systole)
- Closed when the ventricle is relaxed (diastole)
What do valves look like in people with heart murmurs?
What makes the thud noise during the heartbeat?
The closing of the valves
Lub: AV valve slams shut
Dub: aortic valve slams shut
When do you hear other sounds during a heartbeat?
If the valve does not open or close properly
What is laminar flow?
When blood goes through a valve smoothly (no turbulence)
What is turbulent flow?
When there is a leaky valve, there is turbulent backflow, which causes noise (murmur)
Normal closed valve
No noise because there is no flow
Normal open valve
Laminar flow, quiet
Stenotic valve
- Narrowed valve
- Turbulent flow causes a murmur
Insufficient valve
- Leaky valve because it doesn’t close properly
- You would hear sound after the first heart sound, which is the closing of the left AV valve
How would the sound be different if there was aortic insufficiency (aortic valve wasn’t closing properly)?
You would hear the regurgitation noise after the second sound (aortic valve closing)
Sequence of contractions: atria, then ventricles from apex to arteries
- Muscles of atria and ventricles form 2 units
- Start of contraction
- Direction of atrial contraction
- Delay between atria and ventricles
- Direction of ventricular contraction
- Delay between contractions
Most of the cells in the heart are ___ cells that ___
Muscle
Contract
(there’s also connective tissue, etc.)
There’s a small percentage of cells in the heart that are ___ cells, within which there are ___ cells (that kind of act like axons)
Pacemaker
Conductive
How is the heartbeat generated?
It has its own intrinsic pace due to the pacemaker cells, e.g. those in the SA node
Do the pacemaker cells rest?
- No, they are always depolarizing, repolarizing, and ramping up to threshold and depolarizing and repolarizing again
- They are also electrically coupled to each other
What are the fastest pacemaker cells of the heart?
The cells of the SA node
What would happen if you cut sympathetic and parasympathetic innervation of the heart?
- The heartbeat would be around 120 BPM
- The dynamic range of heartbeats can go from very low to 300 BPM (e.g for a little baby) (200/220 for adults)
- Parasympathetic slows down the heartbeat and sympathetic speeds it up
Resting heart rate of people who get heart transplants
They lose nervous innervation, so their resting heart rate is somewhere in the 120s, and will adjust as they regain nervous innervation of the heart
What would happen if you sprinkled acetylcholine on pacemaker cells?
They would slow down
What would happen if you sprinkled norepinephrine on pacemaker cells?
They would speed up
Electrical coupling of heart cells
The pacemaker cells are electrically coupled to muscle cells and each muscle cell is electrically coupled to its neighbor
Intercalated discs
- Squiggly lines on diagram
- There are pores that ions can travel through very quickly to transfer current between cells and cause simultaneous contraction (syncytium)
- Once the pacemaker cells reach the threshold and fire, it’s an instantaneous reaction of the excitability spreading of the excitability spreading throughout the heart, which triggers contraction within a very short window of time.
Why do the atria pause before the ventricles contract?
To let blood flow into the ventricles
Are the atria and ventricles directly electrically coupled to each other?
No
- The AV node is electrically coupled to the other cells in the atrium. When it gets depolarized, it pauses the signal (responsible for the pause), and then passes the depolarization to the ventricles
Diagram of spread of electrical activity through the heart
- The yellow arrows show the spread of electrical activity
- It spreads to both atria within a few milliseconds
- When the atria depolarize, just like skeletal muscle, calcium levels go up, cross-bridges form, and they generate force and shorten
How are muscle cells wrapped around the atria and ventricles?
- You can think of them as being wrapped around the surface of a balloon
- When the muscle cells shorten, they decrease the radius and volume of the balloon and squeeze it
Where does the AV node pass current to?
- It conducts the current down the septum of the heart to the apex, through the bundles of His and Purkinje fibers (long cells that are kind of like axons) and swings up the lateral sides of the heart towards the atria
What is the P wave of the EKG?
The spread of electrical activity through the atria
What is the QRS complex?
The depolarization of the ventricles
What is the pause after the QRS complex?
Pause when the ventricles are in systole, pushing blood out
What is the T wave?
Repolarization of the ventricle
When is the repolarization of the atria in an EKG?
In the QRS complex, but gets buried by the depolarization of the ventricles
What is happening between S and T in an EKG?
The ventricle is in systole
Diagram of heart with conducting system
Is the pause at the AV node modifiable?
Yes, as heart rate increases and decreases
What does the AV node determine? (in terms of the EKG)
The distance between atrial and ventricular depolarization (P to Q)
How are action potentials in cardiac muscle different from those in skeletal muscle?
- A ventricle may contract for about 100 ms, so the squeeze has to be held
- If you squeeze and hold, there has to be a signal to maintain calcium levels high
- In skeletal muscle, the only way you can do that is by having a neuron synapse onto that muscle cell and fire high-frequency action potentials for 100 ms (one AP would be gone in 20 ms)
- Cardiac muscles maintain a plateau of depolarization, which allows calcium levels to stay high and cross-bridge formation to continuously occur
- This is enabled by having other ion channels playing a role e.g. calcium channels, and closing of potassium channels to delay repolarization
More info on opening and closing of potassium channels?
How will something that increases sodium or calcium concentration affect membrane potential?
It will bring it up
How will something that increases potassium concentration affect membrane potential?
It will bring it down
More detail on ion permeability during the cardiac cycle
- During the rising phase, sodium permeability goes up
- Sodium permeability goes down immediately because sodium channels inactivate
- Permeability of calcium goes up and the permeability of potassium goes down (the change in voltage triggers the open and closed state of calcium and potassium channels)
- What ends the plateau? Closing calcium channels and opening potassium channels causes repolarization, which leads to relaxation.
- This is because when the membrane repolarizes, calcium is no longer released intracellularly and it is pumped back into the SR.
Where does the calcium come from? (in cardiac muscle)
- Some from the SR
- Some from the calcium channels that remain open during the plateau
Pacemaker potential
- The pacemaker cell is never at rest
- It repolarizes down to a negative value, ramps up to threshold, and when it reaches threshold, the voltage-gated channels open and it causes a very slow action potential that repolarizes again
- At a negative value, the permeability to potassium is higher than the permeability to calcium and sodium
- When the membrane potential is more positive, the membrane is more permeable to sodium and calcium and less to potassium
Relative membrane permeability to ions during action potential of pacemaker cells
- At hyperpolarization, the lowest membrane potential, potassium is highest, then sodium (Pf), then calcium is the lowest)
- As potassium channels close, depolarization occurs, Pf (funny) sodium channels open and then shut
- The funny sodium channels open the most when the membrane is very negative. As the membrane depolarizes, the voltage-gated sodium channels close (these are not like the voltage-gated sodium channels that give you an action potential- when you depolarize those, they open even more)
- The transient calcium channels open, which continues to cause depolarization, and then you get to threshold
- Threshold is the L-type calcium channels- they open, stay open for a while, and then close, causing the very sluggish action potential that takes 150 ms
- Once you fire the action potential, the potassium channels open again (sluggishly), to end the depolarizatoin by bringing the mV back down to a negative value
Diagram showing overview of ion permeability
Clarification of pacemaker potential and timing between action potentials (11:13)
What determines the timing between the action potential?
- How far away from threshold we start
- The slope of the ramp up to threshold
L-type calcium channels
- They give the action potential in pacemaker cells
- They also give the elongated plateau in the heart muscle cells
- They take a long time to open but once they do, they stay open for a long time
How is pacemaker permeability modulated?
Overview:
- Sodium and calcium in during the ramp-up phase
- After threshold is reached, calcium in through L-type
- Potassium out to give repolarization
- Sympathetic stimulation increases funny sodium, so the ramping phase is steeper, and also increases calcium channels, so the latter part increases as well –> faster heart rate
- Also doesn’t hyperpolarize as much
- Parasympathetic increases potassium permeability and decreases calcium permeability, slowing it down
What two factors affect the pacemaker potential - the rate at which the heart beats?
- The slope of the pacemaker potential- how quickly it ramps up to threshold
- How far away from threshold it starts (if it’s more hyperpolarized, it takes longer to reach threshold)
EKG and associated ventricular action potential
- Depolarization occurs during the QRS complex
- There’s a plateau phase in between the ST segment
- Then repolarization occurs during the T wave
- Anytime there’s a change in membrane potential, there will be a change in currents flowing in the extracellular fluid that’s picked up with the EKG
Graph showing membrane potential and tension
Between the beginning of depolarization and the beginning of generating tension is the excitation contraction coupling (opening up voltage-gated calcium channels, releasing calcium from the SR, troponin etc.)
EKGs are ___ recording
Extracellular
Field potentials (many cells at once)
Extracellular currents and EKG explanation (13:25)
EKG diagram
Depolarization in atria vs. ventricle
- The atria depolarization pretty much at the same time
- The ventricular muscle cells are more complicated -this is why the QRS complex looks the way it does
Do all cells depolarize/repolarize at the same time?
No, they’re not all synchronized
What affects the speed of depolarization of a cell?
- Where the cell is in the heart
- This has to do with the pathway of the current from the SA node through the rest of the heart
What is Q in the EKG?
The current going up the septum
What is R in the EKG?
All of the depolarization wave spreading throughout the ventricles
What is S in the EKG?
Some segments of the upper ventricles depolarize at the very end
The first cells to depolarize in the septum are the ___ cells to repolarize
Last
Repolarization occurs in the opposite direction
The last cells to depolarize are the first to repolarize
Cardiac cycle diagram
In the ventricles, blood pushes from ___ to ___
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