The cardiac pressure-volume cycle & ions and action potentials Flashcards
What is the name of the circle of arteries on the underside of the base of the brain AND what is its physiological function?
- The Circle of Willis
- It provides redundancies in arterial blood supply to the brain, vouchsafing consistent perfusion to all regions (and protection from ischaemia) in cases where one major artery supplying the brain was temporarily blocked or narrowed
Name TWO plasma secretions of the kidney that are central to the RAAS.
- Angiotensin converting enzyme
- Renin
Name THREE aspects of the circulation of large skeletal muscles that make it a “special circulation”.
- Can use up to 80% of cardiac output during exercise
- Arterial supply vasodilates in response to sympathetic stimulation
- Muscle pump contributes directly to venous return.
Name TWO aspects of the circulation of the brain that make it a “special circulation”.
- Auto-regulation (constancy of flow and pressure)
- Circle of Willis
Name FOUR aspects of the special circulation of the skin that make it well-suited for thermo-regulation.
- Can regulate blood perfusion by up to 100-fold
- Arterio-venous anastomoses allow for thermal exchange without the resistance of a capillary bed
- Sweat glands turn fluid ultrafiltrate from plasma into a rapid heat loss system.
Name THREE reactions of the special circulation of the skin that make its inflammatory response to trauma unique.
- Red reaction
- Flare
- Wheal.
Draw a ventricular action potential. Include axes, units, and approximate values.

List the heart valves, and for each one state the type of valve it is, and the regions it separates.
- Tricuspid Valve: AV valve, Right Atrium from Right Ventricle
- Pulmonic Valve: semilunar, Right ventricle from Pulmonary Arteries
•
•
- Mitral (bicuspid) Valve: AV valve, Left Atrium from left Ventricle
- Aortic Valve: semilunar, left ventricle from aorta
Name the valve sounds and when they can appear in the cardiac cycle.
•S1: First heart sound (lub)
–When Mitral & Tricuspid Close
–during systole
–
•S2: Second heart sound (dub)
–When Aortic & pulmonic valves Close
–during diastole
–Diastole is longer than systole
Align an ECG in time directly underneath a ventricular action potential
QRS complex lines up with depolarisation of ventricular AP
T wave lines up with repolarisation of ventricular AP

Draw a nodal action potential. Include axes, units, and approximate values.
Nodal AP is in red

Align an ECG in time directly underneath a nodal action potential
P wave lines up with depolarisation of SA Node

List the phases of the ventricular action potential and state for each what channel is responsible for conducting that current.
0 Depolarisation: Na+ gates open in response to wave of excitation from pacemaker
1 Transient Outward Current: tiny amount of K+ leaves cell, this leads to a small amount of repolarisation
2 Plateau phase: Inflow of Ca2+ just about balances outflow of K+
3 Rapid repolarisation phase: Membrane potential falls as K+ leaves cell
4 Back to resting potential
List the phases of the cardiac nodal action potential and state for each what channel is responsible for conducting that current.
0 Depolarisation: Ca2+ channels open in response to automaticity
3 Rapid repolarisation phase: Membrane potential falls as K+ leaves cell
4 Pacemaker potential
Name 3 types of potassium channel that are important in cardiac rhythmic activity AND for each name its primary function.
- Delayed rectifier: repolarises the action potential
- Inward rectifier: clamps voltage near resting potential (in non-nodal myocytes). Also contributes to late repolarisation of AP
- Ach-activated K+ channel: slows down heart rate in response to vagal stimulation by decreasing the pacemaker potential’s slope upward.
- Could also mention:
- K(ATP) channels
What is tetany, and why does it not occur in cardiac muscle?
Tetany is a state of maximal contraction in a skeletal muscle cell in which a high stimulation frequency is too rapid for recovery and relaxation, so the contractions effectively become continuous and stronger than possible with a single twitch. It occurs because calcium builds up in the cytosol due to the lack of time to pump it back into the SR. This does not happen in cardiac muscle because an extended contraction without relaxation would effectively stop the beating of that cell and prevent relaxation/diastole.
What is the pacemaker potential and how does it come about?
The pacemaker potential is the upward drift in voltage that occurs between action potentials, which occurs in myocytes of SA node, AV node, and conduction system only. Also called: diastolic potential. It occurs instead of the resting potential (because these cells lack the inward rectifier K+ channels that would clamp the cell to the resting potential). The slope of PP determines the automatic rate of firing of the cell.
Draw a graph of the pressure volume loop of a cardiac cycle of the left ventricle (ie graph pressure vs volume). Label the axes (including units and approximate values), and label each phase of the cardiac cycle. Draw arrows where each set of valves open and close.
4-1: Filling
1-2: isovol contr
2-3: ejection
3-4: isovol relax
AV valves
Open at 4
Close at 1
Semilunar valves
Open at 2
Close at 3
Under what circumstances would you expect a systolic murmur? Or a diastolic murmur?
Systolic murmur: semilunar insufficiency/stenosis, AV valve regurgitation
Diastolic murmur: semilunar regurgitation, AV valve insufficiency/stenosis
What is the molecular basis of cardiac muscle contraction?
This is the sliding filament model (explained in detail in module 102) where thick filaments pull on thin filaments from two opposing z-lines, thus shortening the sarcomere. The thick filaments are mostly made up of myosin (a “motor protein”) and the thin filaments are structurally based on actin. The thin filaments also have on them the regulatory proteins tropomyosin and troponin, which are essential in converting the calcium signal in the cytoplasm into contraction.
In the Wiggers plot above:
Identify systole and diastole
Identify the four phases of the cardiac pressure cycle.
Identify when each pair of valves opens and closes.
Draw an ECG that aligns in time with the pressure plots.

IVC is defined as the time between when the mitral valve closes and the aortic valve opens. During this time the “contraction” of the left ventricle generates increasing pressure but without changing volume (ie there is force generation without extensive contraction in size because the blood fluid is not compressible, and the aortic valve has not yet opened). You can tell when the mitral valve is closed because the atrial pressure (red at bottom) and the ventricular pressure (black) are identical. When the mitral valve closes, the ventricular pressure become independent of the atrial pressure. Likewise, you can tell when the aortic valve is open because the aortic pressure (red, upper) and the ventricular pressure (black) become identical. When the aortic valve closes (as the ventricle starts to relax), the aortic pressure and the ventricular pressure split apart. At the end of IVR the mitral valve opens and the ventricle and the atrium have identical pressures.
Given the normal ventricular pressure-volume (grey), explain what type of valve dysfunction is shown in red (at X) and explain the mechanism for why the valve changes result in the pressure-volume changes?

This aortic valve stenosis.
There is high afterload because the valve creates resistance during systole that obstructs blood from leaving. No change in preload
The high afterload manifests as very high pressure during ejection, and high volumes during isovolumic relaxation (because the stenotic valve interferes with ejection
Given the normal ventricular pressure-volume (grey), explain what type of valve dysfunction is shown in red (at X) and explain the mechanism for why the valve changes result in the pressure-volume changes?

This is mitral stenosis.
The stenotic mitral valve interferes with filling (and thus reduces preload), so volume during isovolumic contraction is low..
Because preload is so much lower, afterload is lowered (because the ventricle generates so much less pressure) due to reduced Starling forces.
The lower afterload manifests as a low isovlumic relaxation. It also results in the lack of a corner because the previous systole did not pump so much blood, so there is less systemic back pressure on the aortic valve
Given the normal ventricular pressure-volume (grey), explain what type of valve dysfunction is shown in red (at X) and explain why its pressure-volume relationship is round rather than square-ish?

This is aortic regurgitation.
The preload is much higher than normal (ie the right edge of the red curve is shifted leftward).
Preload is higher in all regurgitating valve anomalies. In aortic regurgitation, during diastole the aortic valve allows fluid to back-flow into the left ventricle, added to the fluid coming from the left atrium.
Both regurgitating valve pathologies have rounded PV curves (ie they do not have corners, or IVC and IVR phases). The straight lines of IVC and IVR occur when both valves are closed and the left ventricle is a sealed unit. In regurgitating valves, there is never a time when both valves are completely closed – one valve is always leaking

