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.
Endocrine glands produce hormones that can be used inside the body. The endocrine transmits the hormonal messages to cells by secreting them into the blood and extracellular fluid. A receptor is needed in order to receive the message transmitted. The target points may be cells, tissues or organs.