Control loops

In the human body there are a lot of control loops which, for example, ensure that hormone levels are adjusted and regulated according to circumstances. A typical such control circuit is that for the thyroid hormone thyroxine.

The higher the concentration of TSH, a hormone of the anterior pituitary gland, the more thyroxine the thyroid gland secretes.

TSH is produced the more TRF, a hormone of the hypothalamus, is present.

However, the more thyroxine there is in the blood, the less of this TRF is produced.

Since all 3 hormones are broken down by the liver, a constant hormone level is maintained.

This can be simulated in a semantic model.

The dependence of the hormones on each other can be formulated, for example, by the following sentence:

Hormone1increase is proportional to hormone2

In this way 2 sentences are to be formed.

A special case is the increase of the TRF. The thyroxine is said to have an inhibitory effect on TRF production. Now one cannot set TRF-increase is proportional to 1/thyroxine, because for thyroxine=0 an infinitely large increase would follow. In order to limit this, one therefore demands

TRFZu is proportional to 1/(a+thyroxine), where a is a suitably chosen constant that determines the maximum TRF production.

The standard phrases

Hormone increases to increase hormone levels or

Hormone decreases to decrease hormone

need not be explained separately.

On the other hand, the reduction of hormones by breakdown in the liver depends on the hormone level, so that the corresponding sentence would probably read as follows

Hormone decrease is proportional to hormone.

The model is now complete. If the initial values are suitable, you can now follow in a graph how the thyroxine level is adjusted to a constant value.

Now select this long-term adjusted level as the starting value and you will see the fine adjustment of the hormone level in the graph.