Homeostasis: the inner balance

In short: Homeostasis means that a living being keeps important internal values such as temperature, blood sugar or water content within a narrow range despite a changing environment. Without this stability, cells and enzymes could not work reliably.

In more detail: Control usually works through feedback loops with negative feedback: if a value drifts, the body starts countermeasures that bring it back to the set point. The nervous and hormonal systems work closely together in this.

In detail

• Parts of a feedback loop: Sensors measure a value, a control centre compares it with the set point, and effector organs such as muscles or glands correct the deviation.
• Negative feedback: The counter-reaction reduces the deviation, much like a thermostat that switches off the heating as soon as it is warm enough.
• Body temperature: In humans it is around 37 °C; in heat, sweating and widened skin blood vessels help, in cold, shivering and narrowed vessels. An important control centre is the hypothalamus in the brain.
• Blood sugar: When the sugar level rises after a meal, the pancreas releases insulin; when it falls, the hormone glucagon ensures that stored sugar is released.
• Water balance: The kidneys control how much water and salt are excreted; when water is short, less and more concentrated urine is produced, and thirst arises.
• Acid-base balance: The pH of the blood is kept very precisely in a slightly alkaline range, supported by buffers in the blood, breathing and the kidneys.
• Positive feedback as the exception: Sometimes a process deliberately reinforces itself, for example contractions during childbirth or blood clotting, until a goal is reached.
• When regulation fails: Diseases such as diabetes show what happens when a feedback loop no longer works properly; with fever, by contrast, the body deliberately raises the set point (hormone-und-stoffwechsel, enzyme-grundlagen, blutgerinnung-wie-sie-funktioniert).