Which of the following is not considered an organ system in the human body?

The option indicating "Circulatory and respiratory" as not being considered an organ system is correct because these two systems are actually distinct and recognized organ systems within the human body.

The circulatory system is responsible for the transportation of blood, nutrients, gases, and waste products throughout the body via the heart, blood vessels, and blood. On the other hand, the respiratory system is involved in the exchange of gases—specifically oxygen and carbon dioxide—between the body and the environment through structures such as the lungs and trachea.

Properly identifying organ systems is crucial for understanding human anatomy and physiology, as each system plays a vital role in maintaining homeostasis and ensuring the body's overall function. By listing "Circulatory and respiratory" together, the option incorrectly implies that they are a single system, which does not align with scientific classifications. Thus, the separation and individual recognition of these organ systems affirm that the correct answer is that "Circulatory and respiratory" are not a singular organ system.