Final answer:
The endothelium and related cell types are part of the cardiovascular system, which is responsible for transporting materials throughout the body. This system includes the heart, blood, and blood vessels. Its main function is to maintain homeostasis by transporting substances such as oxygen, nutrients, and waste products.
Step-by-step explanation:
The endothelium and related cell types are part of the cardiovascular system. The cardiovascular system, also known as the circulatory system, includes the heart, blood, and three types of blood vessels: arteries, veins, and capillaries. The main function of the cardiovascular system is to transport materials such as hormones, oxygen, cellular waste, and nutrients throughout the body to maintain homeostasis.