Conditions of the internal environment must be kept within narrow limits
Stimulus-response model
Receptor -> control centre -> effector -> response
Receptor
An organ that detects an environmental stimulus/ something that receives
If there is a change in the internal environment (stimulus) it is often detected by a cell or organ (receptor)
Control centre
Communicates with receptor and effector
Effector
Produces a response
Internal environment
The environment of (fluid surroundings) the cells within a multicellular organism, e.g. blood plasma, tissue fluid
Negative feedback
A stimulus-response system in which the response produced by the effector reverses the direction of, or counteracts, the stimulus, creating equilibrium
Intercellular
Between cells
Extracellular
Outside of cells
Homeostasis
The maintenance of a constant/stable internal environment, despite changes in the external environment
If the environment changes the body must regulate and maintain a stable internal environment
Control system
Works through receptors & effectors
Body transmitters (nerves and hormones) send messages
Types of receptors
Thermoreceptors (detects changes in temperature)
Nociceptors (detects painful stimuli)
Baroreceptors (detects changes in pressure)
Chemoreceptors (detects changes in chemical concentration)
Photoreceptors (detects changes in light)
Negative feedback loop
1. The change (stimulus) is detected by a receptor
2. The receptor sends out a signal to the control centre (modulator, usually the hypothalamus or pituitary gland)
3. The control centre sends a signal to an appropriate effector
4. The effector responds to the signal and the original state is restored
