HGH is secreted by the pituitary gland (high glucose blocks it) which also stimulates the hypothalamus to secrete more DHEA .
The liver takes HGH and turns it into IGF-1 (insulin growth like factor), and will release that (if exogenous glucose/carbohydrate intake is low enough?) rather than the pancreas releasing insulin when you eat something and you do not exceed a certain carbohydrate threshold e.g. 20-50 grams.
Pituitary-Hypothalamus-Adrenal-Axis (also known as HPA-Axis):
HGH also works with the components that make up adrenaline to tell the body to release lipid droplets from adipose cells (your burning/oxidizing body fat along with dietary fat which mostly happens when you sleep REM-delta).
For example if you eat only a little bit of protein, it instructs the alpha cells on the pancrease and stomach lumen to release glucagon rather than insulin (pancreatic beta cells) which then instructs the muscle, liver and adipose cells to release glycogen into the blood stream for the organs that are glucose dependent.
Also beware if you try to take HGH as a supplement; your pituitary gland will stop secreting it and you will dependent on a exogenous or external sources? Not only that you will mess up your entire endocrine system doing so and gain weight in the process or gain back the weight you lost by trying to high dose it with HGH?