The International Union for the Conservation of Nature (IUCN) lists 9 species of spider monkey, which can be found in rain forests from southern Mexico through Brazil. The IUCN lists 3 spider-monkey species as Critically Endangered; 5 species of spider monkey are listed as Endangered, and 1 species is Vulnerable.
The foundations of the endocrine system are hormones and glands. A gland is a group of cells that produces and secretes hormones. Hormones are the body's chemical messengers. They send and relay messages between different systems. Many different hormones move through the bloodstream.
The parasympathetic nervous system (PNS) controls homeostasis and the body at rest and is responsible for the body's rest and digest function. The sympathetic nervous system (SNS) controls the body's responses to a perceived threat and is responsible for the fight or flight response.