This system shows a variety of two state transitions. The most basic feeding two states are stop and go. In animal studies, damage to the medial hypothalamus produces animals who are irritable, eat too much, and become obese. Damage to the lateral go-system results in animals who eat little and tend to starve. The hypothalamus is also the brain link to the body's hormonal network, regulating the pituitary gland, which in turn regulates the endocrine glands.
Hormones are the blood-born molecules that regulate our metabolic and reproductive functions.
The ingestion, digestion, and metabolism of food is one the chief concerns of the endocrine system. There are numerous opportunities for this regulatory system to fail. Often appetite and weight regulation is unstable for short periods of weeks but produces dramatic, lasting changes in size and shape.