Your cells are finicky. They’d be those people in the office who never stop fiddling with the AC temperature. They are selective about what they eat, how much they eat, and when they eat it. Divert them away from their preferred way of being and their annoyance will be very apparent. Your cells, the tissues they form, the organs formed of those tissues, and the systems the organs comprise are constantly tweaking their surroundings to keep them optimum and stable for optimal performance. They are, in a sense, changing the AC temperature to meet their dynamic needs. This constant effort to maintain a stable and optimum internal environment is called homeostasis. In this video, we’ll look at how your body goes about maintaining homeostasis through negative and positive feedback loops, as well as examples of key homeostatic mechanisms in the body. All life must maintain homeostasis. Biomolecules that make up your cells function within a specific optimum range of conditions. Some important factors are pH, temperature, electrolyte balance, and glucose balance. The nervous system and the endocrine system are two key players in homeostasis. They detect when a change has occurred and release signals through neurons or hormones, respectively, to return the body to homeostasis. The kidneys, filtering blood to remove excess water and electrolytes, are also important homeostatic regulators. The body uses two mechanisms to maintain homeostasis—negative feedback and positive feedback. Negative feedback is like a tug of war, involving a push and pull to maintain homeostasis. Negative feedback works like this: change occurs, a sensor will sense it, and relay the information to a central hub. That central hub will signal a response to counteract the change. Consider glucose levels in the blood, which are maintained within a stable range through negative feedback loops. After a meal, your blood glucose levels increase beyond a certain range. The pancreas senses this as the blood flows through it. Chemical receptors—little proteins jutting out from cells—on the pancreas bind to these glucose molecules. This triggers the pancreas to produce and secrete the hormone insulin into the bloodstream. One of insulin’s functions is to tell other cells in the body to take up the sugar and either use or store it. As the cells increase their uptake of glucose, its level will decrease in the blood. Temperature is also maintained through negative feedback loops. Temperature is regulated by the hypothalamus, a critical region in your brain. Temperature-sensing neurons located all over the body send the hypothalamus information about temperature. If it is hot, the hypothalamus sends signals to cool us down. This includes signals to the blood vessels to either expand or vasodilate. This allows more blood to reach the skin, where heat can escape. We also begin sweating, which cools us down through evaporation. If it is too cold, the hypothalamus sends signals to warm us. This includes signals to the blood vessels to narrow or vasoconstrict. Narrow blood vessels mean less blood will reach the skin, so we lose less heat. Erector pili, small muscles attached to hair follicles in the skin, will contract to cause goosebumps, which serve to trap a layer of air between the hairs. We may also begin to shiver, which generates a lot of heat from muscle activity. Humans and other mammals maintain a constant internal temperature through a range of physiological changes. This is why we’re called warm-blooded, or more correctly, endotherms. Animals like reptiles and amphibians rely on external environments to regulate their body temperature, which is why we often see lizards and snakes sunbathing. Negative feedback also controls blood pH, blood pressure, and the levels of hormones such as adrenaline and cortisol. Positive feedback is all about more, more, more, amplifying the signal beyond a normal range. Positive feedback usually operates for short bursts. Two examples of this are childbirth and blood clotting. During labor, the posterior pituitary gland in the brain secretes the hormone oxytocin to induce labor pains. Oxytocin levels continue to increase to strengthen the contractions, far beyond optimum ranges. The increasing intensity of the subsequent contractions helps push the baby out of the uterus. Once the birth occurs, the levels of oxytocin decrease. If this was a negative feedback loop, oxytocin secretions would cease when the muscle contractions reached an optimal range. In blood clotting, the cells of the injured blood vessel and immune cells release chemicals that attract platelets and activate other molecules to form the clot. These stimulating chemicals keep the blood clotting process going at a rapid rate, allowing the clot to seal the wound before too much blood is lost. If homeostasis is thrown off balance, then disease occurs in the body. For example, sustained high glucose levels in the blood can lead to diabetes mellitus, a disease that affects the cells' glucose metabolism. So, the next time you scowl at your finicky coworker as they change the AC dial for the tenth time, remember that your cells are constantly doing a similar thing to keep you alive!