Monday, 1 July 2013


I could probably think of a title, but something needs to be done about all that, so that's what you're getting instead.  In the meantime:

Click to tweet: .  Homoeostasis or homeostasis is where a system maintains itself in a stable state, an important concept in cybernetics as well as biology.  Two simple examples of homeostatic mechanisms, both of which work by feedback, are a thermostat (as developed by Andrew Ure) and a governor on a steam engine.  A bimetallic strip thermostat carries a current which is interrupted when the strip warms and therefore expands at different rates, bending the strip away, whereas a governor opens and closes according to the pressure of the steam passing through it, maintaining a constant pressure inside a boiler.

When someone stands, they are attempting to maintain balance in a similar way.  This balance extends in other ways to the internal environment.  For instance, water is mediated by the concentration of body fluids leading to the production of anti-diuretic hormone by the pituitary, which increases the absorption of water by the kidneys until the level is up again.  Thirst also increases.  If kidneys are damaged or the pituitary doesn't secrete enough ADH (vasopressin), fluid will be rapidly lost to the body in a process known as diabetes insipidus, which can easily be fatal.

Temperature control is somewhat related to the osmoregulation mentioned above.  Here, there is a combination of behavioural and plain physiological processes.  Heat leads to sweating, vasodilation of peripheral blood vessels allowing excess heat to radiate and the removal of clothing.  Cold reduces sweating, induces shivering, vasoconstricts peripheral blood vessels intermittently and induces people to behave in such a way as to increase their temperature.  These can fail, leading to hypothermia, frostbite and Raynaud's syndrome on the one hand and heatstroke on the other.

Health is very often a stable state and illness an unstable one.  Therefore, healing is about shifting someone from that unstable state back into a state which is self-sustaining.

This is two things (at least).  One is that it's on the AQA IGCSE Biology syllabus, although of course rather few people are likely to be following it right now.  The other is that it links to the whole "herbalism as cybernetics" thing i keep meaning to cover.  It sounds a bit weird to make that equation, and of course as an equation it's far more bedeutungsvoll (if that's a word) than it is sinvoll, but it's there in spades.

Incidentally, it's very irritating having a 16:9 ratio to deal with all the time.  You have to get really far from the camera for your whole body to be visible and framing's a real struggle.

Tomorrow will be a toss-up between phytoestrogens and the Turing test.  Actually, no it won't:  it'll be about the former - a personal account.