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Physiology > Cardiovasvular Physiology 2 > Flashcards

Cardiovasvular Physiology 2 Flashcards

1
Q

Describe the conduction system of the heart

A

The SA node is the primary pacemaker of the heart, which means that it normally dominates the control of the heart

  • Only if it fails one of the other components of the conduction system takes over (AV node). For this reason they are called auxiliary pacemakers.
  • SA node pacemakers have the fastest action potential firing rate of any cardiac muscle cells. (70/min). AV node acts as a subsidiary pacemaker (40/min)
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2
Q

What is the pathway of the Cardiac pacemaker current?

A
  1. Sinus node
  2. Atrioventricular node
  3. Bundle of His
  4. Split into bundles, bundles of His then go down bundle branches
  5. Purkinje fibers
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3
Q

Give the sequence of depolarization of the cardiac muscle

A
  1. AP generation in the SA node
  2. Right/left atrium depolarization leads to contraction
  3. AV node depolarization (delay as ventricles are being filled!)
  4. Bundle of His (same as AV bundle)
  5. Septum depolarization
  6. Apes depolarization
  7. Atria repolarization begins —> atria relaxation(atria relaxed while ventricles contract)
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4
Q

Summarize what happens at different 0arts of the heart

A
  1. SA node depolarizes
  2. Electrical activity goes rapidly to AV node via internodal pathways
  3. Depolarization spreads more slowly across atria. Conduction slows through AV node
  4. Depolarization wave spreads upwards from apex
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5
Q

When does contractions occur?

A

AFTER depolarization

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6
Q

What is peacemaking?

A

Peacemaking is the function of some unique ion channels expressed in pacemaker cell and the electrical connectivity of the cardiac muscle via ‘gap junctions’

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7
Q

Why does the heart have automaticity?

A

Action potentials are generated automatically by pacemakers

Gap junctions give electrical connectivity through out the heart, causing rgphythmic contraction

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8
Q

What is the resting membrane potent of the pacemaker?

A

Don’t have a pacemaker potential

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9
Q

What are the electrophysiology properties of cardiac pacemakers?

A

(A) the pacemaker potential gradually becomes less negative until it reaches threshold, triggering an action potential

(B) ion movements during an action potential and pace maker

(C) States of various ion channels

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10
Q

What is the pace maker potential?

A

The pacemaker potential is vital electrical property that infers rhythmically

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11
Q

Explain pacemaker depolarization

A
  1. During pacemaker potential(it is negative) there is net sodium ions in and calcium channels or Ca ions as potential becomes more positive and approaches threshold.-slowing down potassium efflux (IF-channels)(phase 4)
  2. Calcium brings it to threshold
  3. IF channels close, calcium channels open at threshold and fast calcium channels open(steep portion of curve)(phase 0)
  4. At peak, potassium channels open and K+ efflux occurs and calcium ions channels close(phase 3)

The heart primes itself because of this mechanism

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12
Q

Describe the contribution of ionic channels to the pacemaker potenti

A

Pacemaker potential is the sum of increased inward currents and decreased outward current:

IF channels: Non selective cation current that depolarizes and is activated by hyperpolarization

ICa2+ channels: Increased inward Ca2+ current depolarizes

Ik+ channels: Decreased outward K+ current depolarizes

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13
Q

What is the resting cardiac muscle potential?

A

-90 mV

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14
Q

Summarize ‘Driven’ Cardiac Action Potential

A
  • resting membrane potential
  • Sodium ion channels open and membrane potential rises to +20 mV(straight line upwards)
  • Ca+ channels open; fast K+ channels close (here it plateaus but then mV curves down)(the dip before is because of decreased potassium(phase 1)
  • Ca+ channels close; slow K+ channels open
  • resting membrane potential
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15
Q

What are the 5 phases of Cardiac action potentials ?

A

Phase 0- Na+ channels open

Phase 1- Na+ channels close

Phase 2- Ca2+ channels open; fast K+ channels close

Phase 3- Ca2+ channels close; slow K+ channels open

Phase 4- Resting potential

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16
Q

Describe refractory period of cardiac muscle

A

Cardiac muscle fiber: the refractory period lasts almost as long as the entire muscle twitch

-Long refractory period in a cardiac muscle prevents tetanus

No summation, no tetanus

It is a pump-A.P. Needs to be timed for maximal blood transport

17
Q

Describe refractory period in skeletal muscles

A

Fast twitch fiber: the refractory period (yellow) 8s very short compared with the amount of time required for the development of tension

-skeletal muscles that are stimulated repeatedly will exhibit summation and tetanus

18
Q

Describe heart action potential duration

A

Cardiac action potential has a long duration (250 msec) (Neural action potential 1-2 msec duration)

Refractory period is also long

Action potential is almost as long as the contraction it causes

This leads to summation of contractions is impossible in the heart
-Ensures that a second action potential cannot be generated until after the muscle has relaxed

19
Q

Briefly describe the excitation skeletal muscle cell

A

Troponin holds tropomyosin in position to block myosin-binding sites on actin(Relaxation)

Ca2+ binds to troponin, which changes the shape of the troponin-tropomyosin complex and uncovers the myosin- binding sites on actin(Contraction)

20
Q

Describe excitation contraction coupling of cardiac muscles

A
  1. Action potential enters from adjacent cell
  2. Voltage-gated Ca2+ channels open. Ca2+ enters cell
  3. Ca2+ induces Ca2+ release through reading receptor channels (RyR)
  4. Local release causes Ca2+ spark
  5. Summed Ca2+ sparks create a Ca2+ signal
  6. Ca2+ ions bind to troponin to initiate contraction
  7. Relaxation occurs when Ca2+ unbind from troponin
  8. Ca2+ is pumped back into the sarcoplasmic reticulum for storage
  9. Ca2+ is exchanged with Na+
  10. Na+ gradient is maintained by the Na+-K+-ATPase
21
Q

What are the differences of cardiac and skeletal muscles?

A

Some differences:

  • Action potent arrives from current generated by pacemakers
  • Step 3: cardiac muscle has Ca2+ induced Ca2+ release
  • Step 9: Cardiac muscle had additional Ca2+ removal via Na+/Ca+ exchanger

Cardiac myocyte contractions can be graded depending on Ca2+ influx from E.C.F. In skeletal muscles it is all or none response

22
Q

What are the properties of cardiac muscles?

A
  • Strength of contraction in a cardiac muscle is graded, in which the fiber can vary the force it can generate
  • This ability is dependent on the amount of Ca2+ available -more calcium available, more bind8bg of actin-myosin, more forceful contraction
  • Force generated depends on the number of active crossbridges
  • In skeletal muscle it is all or none response
23
Q

What is the difference between EKG and ECG?

A

Same thing son

24
Q

What is a distant ECG?

A
  • The ECG is a distant extracellular recording of the electrical activity of the heart
  • The electrodes are so far apart that we can treat the heart as a ‘dipole’ (battery)
  • As the heart goes through a cardiac cycle currents change direction. Therefore, the dipole rotates and turns on and off
  • That is a simplistic way of thinking of why the ECG looks the way it does
25
Q

How does and an EKG work?

A

Electrodes are attached to the skin surface

-A lead consists of two electrodes, one positive and negative

If you have a lead in the same direction of current, it will have max deflection

If lead and current then it will cancel out

An electro potential difference must exist(must have a negative and positive poor )must have a positive and negative pole and have a difference between them- current moves from negative to positive poles

26
Q

What are the general points of ECGs?

A
  • electrocardiogram or ECG is recording of the electrical activity of the heart
  • It is a timely sequence of depolarizations and repolarizations in the heart. Because the atrium depolarizes before the ventricle the ECG shows the atrial signal before the ventricular signal
  • The strength of the signal generated at any given time is determined by the number of muscle fibers depolarizing or repolarizing simultaneously at this moment.
  • Because the ventricle is much bigger than the atrium, more muscle fibers de/repolarizes simultaneously, the signal it generates is stronger than the atrial signal
27
Q

What does the strength of ECG depend on?

A

The strength of the signal recorded in an ECG depends on two factors:

  • the strength of the signal generated by the atrium or ventricle.
  • The method of recording the signal, e.g. the placement of the electrodes

ECGs show only electrical events , not mechanical events

-Under pathological conditions it is possible that a heart depolarizes and repolarizes without beating, that is without any muscle contraction

28
Q

What are the leads of an EKG?

A

The standard EKG done has 12 leads

  • 3 limbs leads
  • 3 augmented leads
  • 6 chest leads

Back, front, etc all provide different views

This provides a 3 dimensional view of the electrical activity of the heart

In the emergency room- if there is only one lead, you’re seeing the parallel lead to the general direction. This is Lead 2

29
Q

Whaat are the uses of EKG?

A
  • rate
  • rythym(may be third beat does feel the same for example)
  • conduction velocity (the speed)
  • muscle mass
  • injury to myocardium
  • electrolyte abnormalities
30
Q

Describe the ECG and Einthoven method

A

Connecting three leads to both arms and one leg provides best results, because of an equilateral triangle with the heart close to its centre and same distance to the leads

The right leg is connected to a ground lead to prevent electrical interferences

Lead 1 attaches the right arm(negative pole) and left arm is positive

Lead 2 attaches right arm(negative pole) and left leg (positive pole)

Lead three attaches left arm(negative pole) and left leg(positive pole)

31
Q

Which is the most parallel lead?

A

Lead 2

32
Q

What are chest leads particularly useful for?

A

MIs

Physiology (36 decks)

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