Homeostasis is a characteristic found in systems that survive: the obvious example is mammalian temperature, but many other things are also finely balanced.
Effective control in living things relies on feedback systems, where a shortage of an item triggers its production, and an excess stops production in some way.
Animals have a variety of control systems: nerves carry fast messages, hormones are slow and wide-reaching, pheromones carry signals between individuals.
There are two kinds of signalling methods within animals like us: target-specific messages are sent by nerves and slower general messages are sent by hormones.
Many hormone systems are driven by secretions from the pituitary gland, and if indirect influences are included, most hormone systems are pituitary-driven.
An important male hormone is testosterone and an important female hormone is estrogen, but other hormone is present in small amounts in the other sex.
The key hormone in blood sugar balance is insulin, which is produced as and when it is needed, in cells in the pancreas called the islets of Langerhans.
Gonadotrophin is the name given to a group of proteins: human chorionic gonadotrophin is produced by the placenta and in the urine, is a pregnancy indicator.
Around 170, Galen discovered how nerves operate when he cut into the laryngeal nerve of a pig, after which it continued to struggle, but stopped squealing.
Nerves communicate at a synapse, where chemicals like glycine and acetylcholine carry a signal from one nerve to another, being destroyed soon afterwards.
The operation of the nervous impulse can be described as electrical signals, but the operation of the nervous system involves changes in membranes.