What is homeostasis? Can you use a couple of examples to explain the difference between positive vs negative feedback?

DEFINITION   Homeostasis = the maintenance of a constant internal environment Every process in the body that occurs in everyday life, such as keeping the heart beating, changing from sleep to wakefullness, talking, exercising, and eating, as well as some events that may only occur as a one-off in the life of an organism (for example pregnancy and giving birth in females, or fighting a nasty disease) are due to many, many biochemical/physiological processes. These ususally involve proteins, enzymes and other similar substances. For all these processes to work in order for the organism to survive, we need to keep the environment in which they are being carried out as uniform and stable as possible. (just like needing peace and quiet for revision/study and enough sleep and food to be a good learner!) This is the basis of homeostatic mechansisms. These tend to be part of the subconscious control of your body (for example, when your body temperature starts to rise if you are hot or exercising, you don't make the active decision to start sweating, or control when that process begins- it just does). Mainly controlled and regulated via hormones (endocrine system) and the nervous system. Utilises FEEDBACK LOOPS to control when different processes in the body need to 'turn on' or 'turn off'. This is where positive and negative feedback comes into the picture. NEGATIVE FEEDBACK = is the more common type of feedback loop. This feedback, as the name implies, involves 'switching off' a process or response, once it has served its purpose and returned a certain parameter back to normal levels. **Examples: Control of blood glucose (sugar) levels- very important, especially for the function of the brain and nervous system, that blood glucose levels remain within strict parameters. If blood glucose rises above the set point --> more insulin is released --> this hormone acts to bring glucose from the bloodstream into cells for use/storage of energy --> so blood glucose levels decrease back to normal --> INSULIN SECRETION IS REDUCED Oxygen to tissues - important for cells to be able to aerobically respire. If volume of oxygen delivered to cells (via haemoglobin in the blood) DECREASES too much during exercise--> the brain is alerted --> quicker breathing rate --> more gas exchange in lungs and then cells around the body --> more oxygen delivered to cells --> BREATHING RATE SLOWS POSITIVE FEEDBACK = less commonly observed in the body, although just as important. If a certain parameter increases above the set point, positive feedback actually causes that parameter to CONTINUE to increase - accentuating the effect of the causative process/response. **Examples: During birth (labour) - signals from the foetus and changing hormone levels when the baby is ready to be born --> increased contractions of the womb (uterus) muscles --> dilation and start of labour --> this is DETECTED --> increased hormone levels further --> more contraction and dilation --> --> --> --> (this cycle continues to increase, until the dilation of the womb plus the contractions are sufficient to expel the baby from the body).