Biology 3.4 Demonstrate understanding of how an animal maintains a stable internal environment

Homeostasis “The tendency of an organism or a cell to regulate its internal conditions, usually by a system of feedback controls, so as to stabilize health and functioning, regardless of the outside changing conditions” ?

Why? Cells only function within a narrow range of conditions such as: – pH – Osmotic pressure – Temperature These conditions must be kept relatively the same, despite internal activity and changes in the external environment The body must be constantly working using various organs / systems / physiological processes to achieve a stable equilibrium

How? Feedback control systems control the internal environment and involve: – Input: a stimulus (internal or external, eg temp change) – Receptors / sensors: detect stimulus (nerves, organs) – Controllers: signal a response, (brain, esp hypothalamus) – Effectors: action the response, (glands / muscles / organs) – Output: the response / action of effector Feedback means that the level of output will affect input and thus the system is cyclical.

Where’s the hypothalamus?

Negative Feedback High output inhibits further output (system receives high input which halts output) For example: – Its cold in the room – Thermostat detects cold temperature, turns on heater (output) – The room gets hot – Thermostat detects hot temperature, turns off heater (output): this is negative feedback – Room gets cold…

Biology 3.4 Requirements… Comprehensive understanding of a control system that regulates ONE of these: – Body temperature – Blood pressure – Osmotic balance – Blood glucose levels – Levels & balance of respiratory gases in tissues

When good control systems go bad… Efficiency of control systems decreases with aging…results in: – Unstable internal environment – Disorders Hypothermia, hyperthermia…. Death

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