Which surface of the heart is dominated by the left ventricle?

The correct answer is inferior.The heart is an organ of the cardiovascular system that functions to receive and pump blood around the body to where it is needed.

It consists of two sets of chambers, atria, and ventricles. The atria sit on top of the ventricles which are located more inferiorly and are much larger in size.

Diagram of the human heart
Diagram of the human heart

Ventricles have much thicker walls and are larger than atria since they have to contract more forcefully to push blood up into the arteries against gravity. They are also sending the blood further to various parts of the body.

Blood carried by the veins enters the left and right atria which contract to push this blood into the lower chambers, the ventricles.

Once the ventricles are full of blood they contract to force blood into the arteries leaving the heart. Valves separate the atria from ventricles and ventricles from arteries.  These valves ensure that blood flow is only in one direction.

When atria and ventricles contract it is called systole, while when blood flows into atria and no contraction is occurring, it is known as diastole.

The electrical activity of the heart can be measured using an ECG which shows the systolic and diastolic parts of the cardiac cycle.

The sounds of the heart that are heard through a stethoscope are the sounds of the various valves snapping shut, and this can be used to assess heart function.

Heart anatomy

The heart is a muscular pump that consists of four chambers that are all separate from each other and divided by muscular septa and valves formed from connective tissue.

The surface of the heart contains various grooves in which blood vessels, coronary arteries are found. These arteries ensure that the heart tissue receives oxygen and nutrients.

Heart muscle is known as myocardium and it is histologically unique among the types of muscle tissue found in the human body. This is because it has intercalated discs present in the cells to help coordinate and synchronize muscle contraction and hence, the heartbeat.

The atria are the two chambers that are located in a superior position, while the ventricles are the two chambers that are located in an inferior position.

Atria receive and fill with blood that enters via the veins of the body. The ventricles are responsible for pumping blood into the arteries that leave the heart.

Atrioventricular valves are found between each atrium and each ventricle, and semilunar valves are found between the ventricles and arteries. These valves help keep the blood in the right place and flowing in the correct direction.

Heart function

Blood enters the left and right atrium through the veins. Once the atria are completely full the muscular walls contract to force the remainder of the blood down through the atrioventricular (AV) valves and into the larger heart chambers, the ventricles.

Once all the blood has moved into the ventricles, the AV valves snap closed. The ventricular myocardium then contracts with great force to push the blood up and into the arteries that are leaving the ventricles.

Once the blood has moved out of the ventricles completely, the semilunar valves snap shut to stop blood falling down and back into the ventricles.

The semilunar valve between the aorta and left ventricle is the aortic valve, while that between the pulmonary artery and right ventricle is known as the pulmonary valve.

The ventricles have to push blood against the force of gravity and into arteries which is why they are larger and more muscular chambers than the atria.

Pulmonary and systemic circulations

There are two blood circulations that occur simultaneously through the heart. In the pulmonary circulation, blood circulates between the lungs and the heart. Oxygenated blood flows from the lungs via the pulmonary veins into the left atrium.

The blood then moves into the left ventricle which contracts to force the blood into the aorta. This is the largest artery of the body which transports oxygenated blood to all of the tissues of the body.

The right atrium of the heart receives deoxygenated blood that enters by means of the inferior vena cava and superior vena cava. These are two large veins that drain into the atrium.

The muscle of the right atrium then contracts to squirt the blood into the right ventricle. This lower chamber then contracts to push blood into the pulmonary arteries.

These arteries carry the blood to the lungs so that carbon dioxide can be removed and breathed out.

Since the right ventricle only pumps blood to the lungs the walls do not need to be as thick as those of the left ventricle. Remember the left ventricle has to pump blood much further to all the rest of the body cells.

The cardiac cycle

The cardiac cycle can be divided into two parts, a time of contraction of chambers, known as systole and a time of relaxation of chambers, known as diastole.

Diastole is the time during which the atria fill with blood that enters by means of veins. First both the atria contract and then both the ventricles contract once filled with blood.

The first contraction, of the atria, can be seen by a small peak on an ECG, at the P wave, while the larger contraction of the ventricles is seen in the QRS complex.

The muscles contract in response to stimuli received from the nervous system. Thus, the nervous system has to be functioning correctly in order for the cardiac cycle to occur.

A doctor can thus detect how your heart is working by looking at an ECG which measures the electrical activity, and hence the ability of the heart chambers to contract.

Heart function can also be indirectly measured since the valves can be heard using a stethoscope. The first sound of the heartbeat, the “lub” is actually the noise made by the AV valves snapping shut. The second sound, the “dub” is then the sound of the semilunar valves closing.

References

  1. Editors of Encyclopedia Britannica (2019). Heart. Retrieved from Encyclopedia Britannica.
  2. JG Betts, et al. (2017). Human Anatomy and Physiology. Houston: USA, Rice University.
  3. MF Oliver, BE Mathews, ME Rogers (2019). Circulatory system. Retrieved from Encyclopedia Britannica
  4. RL Dorit, WF Walker, RD Barnes (1991). Zoology. Philadelphia: USA, Saunders College Publishing.
  5. C Rye, R Wise, V Jurukovski, J DeSaix, J Choi, and Y Avissar (2017). Biology. Rice University.

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