vascular system
1. A specialized network of vessels for the circulation of fluids throughout the body tissues of an animal. All animals, apart from simple invertebrate groups, possess a blood vascular system, which enables the passage of respiratory gases, nutrients, excretory products, and other metabolites into and out of the cells. In vertebrates it consists of a muscular heart, which pumps blood through major blood vessels (arteries) into increasingly finer branches until in the capillaries it is in intimate contact with tissues. It then returns to the heart via another network of vessels (the veins). This circulation also enables a stable internal environment for tissue function (see homeostasis), the transmission of chemical messengers (hormones) around the body, and a means of defending the body against pathogens and damage via the immune system. A water vascular system is characteristic of the Echinodermata.

2. The system of vascular tissue in plants.

vascular system See VASCULAR BUNDLE and VASCULAR TISSUE.