The nervous, endocrine, muscular, and integumentary systems are involved in regulating body temperature. The details of thermoregulation are discussed in chapter 26, but here we briefly consider the role of the skin. The dermis contains naked nerve endings called thermoreceptors, some of which respond when the skin temperature rises above normal and others when it falls below normal. They transmit signals to a region called the hypothalamus in the base of the brain. To warm the body, the hypothalamus sends signals that constrict the cutaneous arteries, reducing blood flow near the body surface and retaining heat deeper in the body. To cool the body, hypothalamic signaling is inhibited and the cutaneous arteries are allowed to dilate. This increases blood flow through the skin and allows more heat to radiate away from the body. If this is inadequate to restore normal temperature, the hypothalamus also stimulates sweating. When sweat evaporates, it carries heat away from the body.
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This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.