This patient-friendly animation describes the main role of insulin in the human body. When food is ingested, it travels along the digestive tract where it is broken down into its component nutrients in order to be absorbed into the bloodstream. One such nutrient is glucose, a simple sugar. Glucose gets absorbed by the stomach and intestines and then enters the bloodstream. It travels through the circulation to all body cells. Once absorbed into the bloodstream, glucose circulates causing the blood sugar level to rise. An increased level of blood sugar sends a signal to the pancreatic beta cells, which respond by secreting the hormone insulin into the circulation. Insulin is necessary for glucose to reach and be used by several important target tissues throughout the body. These include the liver, muscle, and adipose tissue. Insulin is necessary to keep blood glucose levels stable in the body. Circulating insulin binds to specific insulin receptors located on the cell membrane of tissue cells throughout the body. Upon binding, a signal is sent to the nucleus of the cell, instructing it to transport glucose channels to the cell surface. These channels allow glucose to enter the cell. Glucose enters the cell through a process called facilitated diffusion.