This video easily explains the function of the endocrine system. It tells you the six major types of glands that secrete hormones. Hormones are secreted into the capillaries that run through each major endocrine gland. It shows red blood cells moving through the capillaries. You can not see the hormones running through them though because they are in the solution in the blood plasma. Hormones can travel freely through the capillary walls and only influence specific target cells. Target cells have specific chemical receptors that can be on the surface or inside of the cell.