Feedback loops How does homeostasis happen The body

Feedback loops

How does homeostasis happen? • The body has complex feedback control systems (homeostatic mechanisms) to maintain homeostasis/keep the internal environment constant. • Feedback control systems depend on different body systems / organs working together. • Feedback systems can be positive (increases the magnitude of change) or negative (decreases the magnitude of change). Negative feedback is the most common type of feedback loop in organisms. Negative and Positive feedback loops

Differences between Positive and Negative Feedback • Negative feedback promotes stability • Positive feedback promotes the opposite

Negative feedback • Negative feedback is a response to a stimulus that opposes the original change. • This means that when there is a change in the system, corrective measures are set off to reverse the change and get the system back to a "normal" range. You could think of it as a thermostat on your home heating system. When the room temperature drops, the sensors turn on the heating and the room temperature increases, when the room temperature reaches a certain level, the heating system is turned off again. • All systems have these increases and decreases; an efficient system minimizes these fluctuations.

• Homeostatic systems cannot prevent any change in the internal environment. • What happens is that conditions fluctuate above and below the set point. • This is because there must be a delay between the detection of a change and the response that corrects it. • The longer the delay, the greater the departure from the set point and the stronger the corrective response, leading to “overshoot”.

Positive feedback • Positive feedback is described as a self-amplifying cycle in which one change, leads to even more significant changes in the same direction. • Positive feedback is not a corrective mechanism activated by the body when it strays from the set point, but rather, it is a way for the body to produce significant changes in a relatively short period of time.

Positive feedback • E. g. a woman in labour. • The baby's head pushes on the cervix, sending signals to the brain, which then produces oxytocin, which stimulates contractions, which then push the baby's head even more tightly against the cervix, and the loop then repeats and becomes more and more intense until the baby has been born.

Positive feedback mechanisms

Homeostasis involves Feedback • Detection of change away ‘normal’ e. g. CO 2 levels during exercise Increased rate of CO 2 excretion Increased breathing rate Normal blood CO 2 (set point) Increased muscular activity CO 2 levels in blood rise

Explaining this Feedback loop • The higher blood CO 2 levels rises ABOVE normal, the greater the stimulation of breathing muscles – more CO 2 is excreted • This is an example of a NEGATIVE FEEDBACK • CO 2 levels fluctuate above and below normal and the rate of breathing adjusts to suit

Principles of homeostasis • Organisms need to maintain a cellular environment that is optimal for cell function. • Homeostatic control systems have three functional components: Ø A receptor – to detect change Ø A control centre Ø An effector – to direct the Ø appropriate response

Components of a Homeostatic System Communication system Stimulus Receptor Effector Response • The body must be able to detect a change – Stimulus is detected by a receptor • One or more effector(s) bring about a response – Receptors linked to effectors by a communication system

Examples of components in a negative feedback loop