Importance of homeostasis

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What you need to know

• Homeostasis means regulating your internal conditions to keep them at the optimum for enzyme action and all cell functions.
• Enzymes catalyse (speed up) most cell reactions, work fastest at an optimum temperature and pH, and need a specific active-site shape.
• Have a goSam is confidently wrong again: "Enzymes work equally well at any temperature, so nothing needs regulating." What have they missed?

  Each enzyme works fastest at an optimum temperature (and an optimum pH).

  Away from the optimum, enzymes work less well, so the body has a reason to hold its conditions steady.

• Human internal body temperature is kept within a very small range around 37 °C.
• Below the optimum, enzymes collide with their substrates less often, so reactions slow down.
• At higher temperatures the active site changes shape, so the enzyme catalyses less well and can denature.
• Have a goFinish the sentence: when it is too cold, reactions slow because of fewer ____; when it is too hot, catalysis falls because the ____ changes shape.

  Collisions between enzymes and substrates; the active site.

  Cold and heat hurt enzymes in two different ways, so neither direction can be ignored.

• A significant, sustained rise above 37 °C is hyperthermia; a significant, sustained fall is hypothermia. Both can lead to death if untreated.
• Water balance is the concentration of water and mineral ions in the blood, which the brain monitors and adjusts.
• We lose water by urination, sweating and exhaling. Losing more than we take in is dehydration; severe cases can lead to death.
• Have a goA hiker sweats and breathes out water all afternoon but drinks very little. Is more water leaving than entering, and what is the result called?

  Yes: more is lost than taken in, so she becomes dehydrated.

  Dehydration is defined by losing more water than we take in, and it can lead to death if severe.

• Control systems have receptors that detect changes, a coordination centre that processes them, and effectors (muscles or glands) that respond.
• Antagonistic effectors work against each other: sweating cools and shivering warms; insulin lowers blood glucose and glucagon raises it.

The big picture

Homeostasis is the regulation of the body's internal conditions to keep them at the optimum for enzyme action and all cell functions. Receptors detect a change, a coordination centre processes the information, and effectors bring about a response that restores the optimum. Some effectors are antagonistic: they work against each other.

⚠ Watch out

Thinking only overheating is dangerous. Both directions harm enzyme action, and a significant, sustained fall (hypothermia) or rise (hyperthermia) can lead to death if untreated.

Memory hook

Detect, decide, do. Receptors detect, the coordination centre decides (processes), effectors do. Lose any one and the condition drifts.

Check yourself

Without scrolling up: name the three parts of a homeostatic control loop in order, then say what happens to a condition if the second part is missing.