Which structure is responsible for temperature regulation by releasing water and other substances onto the skin surface?

The structure responsible for temperature regulation by releasing water and other substances onto the skin surface is the sweat gland. Sweat glands play a crucial role in thermoregulation, primarily through the process of perspiration. When body temperature rises, whether due to external heat or physical exertion, sweat glands secrete moisture onto the surface of the skin. As this sweat evaporates, it helps cool the body down.

The composition of sweat is primarily water, but it also contains electrolytes such as sodium and chloride, along with small amounts of other substances. This secretion not only helps with temperature control but also plays a role in maintaining skin hydration and supporting skin barrier function.

In contrast, while sebaceous glands produce oil (sebum) that lubricates the skin and hair, they do not contribute to temperature regulation directly. Endocrine glands release hormones into the bloodstream and do not have a direct role in regulating temperature through sweat. Apocrine glands, which are primarily associated with scent and are activated during stress, do not play a primary role in temperature regulation but instead secrete a thicker fluid that can contribute to body odor. Thus, sweat glands are the key players in maintaining the body's optimal temperature through the evaporation of sweat.