Smooth muscle is primarily found in which areas of the body?

Smooth muscle is essential for involuntary movements within the body, primarily functioning in the walls of internal organs and blood vessels. Its structure allows for changes in the diameter of blood vessels, facilitating blood flow regulation and digestion by contracting and relaxing in response to various stimuli. This type of muscle is non-striated and controlled by the autonomic nervous system, distinguishing it from skeletal muscle, which is striated and voluntary.

In contrast to the other options, bones are composed of dense connective tissue and do not contain smooth muscle. The walls of the heart contain cardiac muscle, which is distinct from both smooth and skeletal muscle. Moreover, while skin and hair follicles contain various cell types, smooth muscle is not a primary component of these structures. Thus, the presence of smooth muscle is prominently associated with the walls of internal organs and blood vessels, making this the correct choice.