Frogs have a well-developed circulatory system that connects to all of the other body systems because there are arteries to circulate blood away from the heart to all the body organs, and veins to carry blood back to the three chambered heart. Lungs will provide oxygen to capillaries which are tiny blood vessels in the lungs. These in turn, help circulate that oxygen around the body. There are also capillaries under the thin moist skin to absorb additional oxygen from the environment. A tube within a tube digestive system along with digestive glands, allows for the breakdown of food and when it reaches the small intestine, it is absorbed into the circulating blood to be transported. A common cloaca, or exit chamber allows undigested food materials, urine, and sperm or eggs, to exit the body, depending on which body system needs to use it at the time. A complex nervous system including a brain, spinal cord and many nerves helps to connect all the body systems together and coordinate activity. Voluntary muscles allow frogs to hop around and reflex actions help to keep it alive. These are just some examples of how the frog's organ-- systems are interconnected.