These are three important body systems. The respiratory system absorbs oxygen, vital to keeping cells alive. This oxygen is inhaled into the alveoli, the air sacs found in the lungs. Here, there are capillaries(tiny blood vessels) in close contact with the alveoli. There is an exchange of oxygen for carbon dioxide and water, wastes that are exhaled. The circulatory system is important because it transports materials to and from the cells. When food is ingested, it is far too complex to be able to be transported to the cells in the circulatory system. It must first be broken down into endproducts. The purpose of the digestive system is to take complex proteins, carbohydrates and lipids and hydrolyze them to their smallest components--amino acids, glucose and fatty acids and glycerol, respectively. Once digested, these nutrients enter tiny hairs called villi, lining the small intestine. Inside, there are capillaries and a lacteal(part of the lymphatic system). The glucose and amino acids enter the capillaries and the circulatory system transports these nutrients to the cells. The fatty acids and glycerol enter the lacteal for transport through the body via the lymphatic system. In the neck, the lymph returns to a vein and becomes part of the circulating blood. The circulatory system transports respiratory gases and digested nutrients to the body's cells.
Thank you soo mch this helped a lot