Question

question 13
1 pts
which of the following is not true of ventricles?
they are the pumping chambers of the heart.
the myocardium of the ventricles is thicker than that of the atria.
the myocardium of the left ventricle is thicker than that of the right ventricle.
all of the above are true of the ventricles.
question 14
1 pts
starlings law of the heart states that, within limits, the longer, or more stretched, the heart fibers are at the beginning of the contraction, the
weaker the contraction.
slower the heart rate.
faster the heart rate.
stronger the contraction.
question 15
1 pts
cardiac output is determined by
stroke volume and blood pressure.
heart rate and blood pressure.
stroke volume and heart rate.
stroke volume and peripheral resistance.

Explanation:

Question 13

• Ventricles are the pumping chambers of the heart. The myocardium (heart muscle) of ventricles is thicker than that of atria because ventricles need to pump blood with more force (atria just fill ventricles). The left ventricle's myocardium is thicker than the right ventricle's as the left ventricle pumps blood to the whole body (higher pressure requirement) while the right ventricle pumps to the lungs. So all the first three statements are true.

Starling's law of the heart (Frank - Starling law) states that, within physiological limits, the more the heart muscle (cardiac muscle fibers) is stretched (pre - load, related to end - diastolic volume), the stronger the contraction. This is because up to a point, increased stretch allows for better interaction between actin and myosin filaments in the muscle fibers. It has no direct relation to heart rate in the context of this law (heart rate is regulated by the sino - atrial node, autonomic nervous system etc.).

Cardiac output ($CO$) is defined as the volume of blood pumped by the heart per minute. The formula is $CO=\text{Stroke Volume (SV)}\times\text{Heart Rate (HR)}$, where stroke volume is the volume of blood pumped per beat and heart rate is the number of beats per minute. Blood pressure is related to cardiac output (through the formula $BP = CO\times\text{Peripheral Resistance}$), but it is not a direct determinant. Peripheral resistance is a factor in blood pressure calculation, not in the basic definition of cardiac output.

Answer:

All of the above are true of the ventricles.

Question 14