Figure 8.28, page 176, shows the pressure changes in the left atrium, left ventricle and aorta throughout two cardiac cycles. Make a copy of this diagram.

Figure 8.28

a. i. How long does one heart beat (one cardiac cycle) last?

ii What is the heart rate represented on this graph, in beats per minute?

b. The contraction of muscles in the ventricle wall causes the pressure inside the ventricle to rise. When the muscles relax, the pressure drops again. On your copy of the diagram, mark the following periods:

i. The time when the ventricle is contracting (ventricular systole)

ii. The time when the ventricle is relaxing (ventricular diastole).

c. The contraction of muscles in the wall of the atrium raises the pressure inside it. This pressure is also raised when blood flows into the atrium from the veins, while the atrial walls are relaxed. On your copy of the diagram, mark the following periods:

i. The time when the atrium is contracting (atrial systole)

ii. The time when the atrium is relaxing (atrial diastole).

d. The atrioventricular valves open when the pressure of the blood in the atria is greater than that in the ventricles. They snap shut when the pressure of the blood in the ventricles is greater than that in the atria. On your diagram, mark the points at which these valves will open and close.

e. The opening and closing of the semilunar valves in the aorta depends in a similar way on the relative pressures in the aorta and ventricles. On your diagram, mark the points at which these valves will open and close.

f. The right ventricle has much less muscle in its walls than the left ventricle, and only develops about one-quarter of the pressure developed on the left side of the heart. On your diagram, draw a line to represent the probable pressure inside the right ventricle over the 1.3 seconds shown.

Transcribed Image Text:

16 14 - aortic pressure 12 left ventricular pressure left atrial pressure 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 Time /s 6. 2. Pressure/kPa