Cardiac Cycle

Question 1

How does the CVS transport oxygen around the body?

What is Convection?

Answer 1

• By Convection
• The mass movement of a fluid caused by a pressure difference.

The heart creates the pressure, the arteries can alter the blood flow, the capillaries allow for solute/fluid exchange, and the veins act as a reservoir for the blood.

Question 2

Describe the phases that occur in the Action Potentials of the SA node

LOOK AT DIAGRAM!

Answer 2

The SAN has Pacemaker potentials, also called Funny channels (If)

Phase 4: Funny channels activate the HYPERPOLARISATION Na+ channels = SLOW Na influx = SLOW Depolarisation

Phase 0: Depolarisation activates VGCCs = Ca2+ influx = Full Depolarisation

Phase 3: Activation of VG K channels = K+ efflux = Repolarisation

Question 3

Describe the phases that occur in the Action Potentials of the AVN node

LOOK AT DIAGRAM!

Answer 3

Phase 4 - Resting Phase:
Na-K ATPase pump moves Na+ out and K+ in. But membrane is impermeable to Na+, and permeable to K+, creation the resting potential (RMJ).

Phase 0 - Rapid Depolarisation:
VG Na channels activate = Na+ influx = SLOW opening of VGCC’s - this causes depolarisation to be very fast.

Phase 1 - Early Repolarisation:
VG Na channels close.

Phase 2 - Plateau:
VGCCs are FULLY open = Ca2+ influx. Also, the VG K+ channels open SLOWLY. The plateau phase is important as there’s CICR, so no more AP firing can occur - Refractory period.

Phase 3 - Rapid Repolarisation:
VGCCs close and K channels open FULLY = K+ efflux.

Question 4

Describe the electrical conduction through the heart

Where does ventricular contraction begin?

Answer 4

• From the SAN, it spreads across both atria and is delayed at the AVN - delay allows full ventricle filling. It then travels along the Bundle of His in IV septum, and then along the Purkinje fibres of the ventricular walls.
• At heart apex.

Question 5

How is pressure generated in the heart?

Why is there a BP during systole and diastole?

Answer 5

• The electrical activity is converted into myocardial contraction to create pressure changes within the chambers - cause the movement of blood through the heart.
• So blood flow occurs in both parts of the heartbeat.

Question 6

What occurs during Systole and Diastole, in terms of pressure changes, valves, and types of contraction/relaxation?

LOOK AT DIAGRAMS FOR CHANGES IN LEFT VENTRICULAR PRESSURE AND VOLUME.

Answer 6

1. At start of Diastole, the blood moves into atria and passively moves into the ventricles since the Atrial pressure > Ventricular pressure. Both AV valves are open.
2. At start of Systole, there’s ISOVOLUMETRIC contraction (occurs with all valves closed) = ↑↑↑Ventricular pressure. Ventricular pressure > Atrial pressure, so AV valves close.
3. At end of Systole, Ejection occurs once Ventricular pressure > Arterial pressures = Semi-lunar valves open and blood flows into aorta and pulmonary artery (blood enters atria during this).
4. At end of Diastole, there’s ISOVOLUMETRIC relaxation. Once Arterial pressure > Ventricular pressure = Semi-lunar valves close and ventricles
   relax in order to passively receive blood from the atria again.

Question 7

What is SV, EDV, ESV?

How is SV worked out?

Describe the LV pressure-volume loop curve

LOOK AT DIAGRAM!

Answer 7

• SV (Stroke volume): amount of blood ejected in every heartbeat.
  EDV - End diastolic volume
  ESV - End systolic volume
• SV = EDV - ESV
• Indicates Stroke Work, which is the amount of energy being used during every heart beat. It’s the area under the curve. The bigger the curve/area, the more energy being used.

Question 8

Describe the graph for right atrial pressure changes

What are the X and Y drops seen as in the neck veins?

What is the clinical significance of changes in Jugular venous pressure?

What causes ↑RA pressure and how?

LOOK AT DIAGRAMS!

Answer 8

• A wave during end of diastole, then an X descent during ventricular systole, then a small V wave before the start of diastole, which has a Y descent.
• A pulsatile collapse.
• ↑Pressure in right atrium = ↑JVP height
• e.g. RS heart failure, Pulmonary Hypertension. ↓Ejection from RV = ↑Blood left in RV after systole = Atria pumps against a greater pressure.

Question 9

What causes a heart sound?

What are the 4 different heart sounds? What causes them?

Answer 9

• Turbulent blood flow through the valves as they’re closing.
• S1 - “Lubb”:
  Closure of tricuspid and mitral valves at start of ventricular systole

S2 - “Dupp”:
Closure of aortic and pulmonary valves at start of ventricular diastole

S3 - Occasional:
Turbulent flow of blood into ventricles near end of the first 1/3 of diastole

S4 - Pathological in adults:
Forceful atrial contraction against a stiff ventricle