Homeostasis is the maintenance of a stable, internal environment within the body. Several mechanisms control homeostasis, including the nervous system and the endocrine system. Receptors sense stimuli and impulses travel to the brain or spinal cord, where a response is sent to an effector. This can be a muscle or a gland, which carries out the response. Disease can disturb homeostasis in the body. Prolonged stress can also disturb the body's equilibrium. It causes the body's central nervous system to respond. The hypothalmus secretes various hormones during stress which have an effect on the pituitary gland, beginning the stress response pathway. The tiny pituitary gland, located at the base of the brain, releases adrenocorticotropic hormone, which affects the adrenal glands. These are located above the kidneys and release cortisol. This major stress hormone is a steroid hormone, that causes an increase in blood sugar, suppresses the immune system, decreases bone formation and aids in metabolism of nutrients. The amygdala processes emotions related to stressful situations. The hippocampus which has to do with memory formation influences how we process our reactions to stress and chronic stress can damage this area. The spinal nerve cord transfers stress response impulses from the brain to the effectors of the body. Peripheral nerves cause a fight or flight response--having an effect on muscles, heart rate, blood sugar, respiration, etc. Chronic stress can lead to pain, irregular heartbeat, weakened immune system, ulcers, weight loss, shortness of breath, elevated blood pressure, bone loss, which can all have a negative effect on homeostasis.