Which of the following is part of the main content of the thoracic cavity?

The thoracic cavity primarily contains structures that are crucial for respiratory and circulatory functions. Among these, the heart and the great vessels, such as the aorta and the pulmonary arteries and veins, play a central role in transporting blood throughout the body. The thoracic cavity also houses the lungs, which are vital for gas exchange, but in the context of this question, the heart and the great vessels directly relate to the circulatory system's function and are relevant components of this cavity.

In contrast, the liver and gallbladder are located in the abdominal cavity, which is distinct from the thoracic cavity. Similarly, the stomach and intestines also reside in the abdominal cavity, while the kidneys and adrenal glands are located in the posterior abdominal cavity. Understanding the anatomical divisions of the human body is essential, as each cavity contains specific organs and structures that serve unique physiological roles.