Final answer:
The body initiates the growth of new blood vessels, through a process called angiogenesis, in response to low oxygen levels in tissues. This is part of the body's way to improve oxygen delivery and is primarily triggered by the release of factors like VEGF.
Step-by-step explanation:
The body knows to grow new blood vessels primarily in response to low oxygen levels in tissues, which is not directly related to glucose levels, growth hormone, or activation of the parasympathetic nervous system as might initially be thought.
The process of forming new blood vessels is called angiogenesis, and this can be triggered by various factors, including low oxygen concentrations (or hypoxia) in tissues, which stimulates the release of factors like vascular endothelial growth factor (VEGF). VEGF then stimulates the growth of new blood vessels to improve oxygen delivery to the tissues.
Increased blood glucose levels primarily trigger the release of insulin to facilitate the cellular uptake of glucose and is not involved in the direct stimulation of blood vessel growth. Hormones like insulin and the nervous system can influence metabolic processes and may have indirect impacts, but they aren't the primary drivers of angiogenesis.