E1.3 Regulation of gas content in blood

Question 1

Cardiac cycle: Atrial systole

Answer 1

Both atria contract → Remaining blood is pumped into the ventricles through the tricuspid valve and bicuspid valve

Pressure of atria > Pressure of ventricles (Reason: 1)
→ The remaining blood is pumped from the atria to the ventricles

Pressure of ventricles < Pressure of aorta/pulmonary artery (Reason: 2)
→ Blood tends to flow from the aorta/pulmonary artery to the ventricles, but this is prevented by the closed semilunar valves

Question 2

Cardiac cycle: Ventricular systole 1

Answer 2

Pressure of ventricles > Pressure of atria
→ (Reason: 2) Blood flows from the atria to the ventricles
Tricuspid valves and bicuspid valves are forced to close when the pressure of ventricles is just higher than that of atria
→ prevent the backflow of blood into the atria

The first heartbeat sound is produced when:
the pressure of ventricles is just higher than that of atria (Graph: I1)
Which forces the tricuspid and bicuspid valves to close
to prevent the backflow of blood into the atria.

Question 3

Cardiac cycle: Ventricular systole 2

Answer 3

The ventricles continue to contract (at maximum intensity of ventricular contraction, ventricular pressure exceeds aortic pressure)
Ventricular pressure exceeds aortic pressure (Reason: 1)
The semilunar valves are forced to open when the ventricular pressure just exceeds aortic pressure
Blood is pumped from the ventricles to the aorta and the pulmonary artery

Question 4

Diastole 1

Answer 4

Both atria and ventricles relax
Pressure of ventricles < pressure in aorta/pulmonary artery
→ (Reason: 1) Ventricles relax
Blood tends to flow from the aorta/pulmonary artery to the ventricles.
The semilunar valves are forced to close when the pressure of ventricles is just lower than that in the aorta/pulmonary artery

The second heart sound is produced when the pressure of ventricles is just lower than that in the aorta/pulmonary artery, which forces the semilular valves to close to prevent the backflow of blood into the ventricles

** Blood from the vena cava and the pulmonary veins flow into the atria

Question 5

Diastole 2

Answer 5

Atria pressure increases and exceeds the ventricular pressure
→ (Reason: 2) Blood accumulates in the atria
Tricuspid and bicuspid valves are opened when the atria pressure just exceeds ventricular pressure [Note: BEFORE atria contracts)
Blood starts to flow into the ventricles
NOTE: No muscle contraction
Valves do NOT open due to muscle contraction