Digestion  begins in the mouth with chewing and ends in the small intestine.  As food passes through the GI tract, it miâ¦xes with digestive  juices, causing large molecules of food to break down into smaller  molecules.
Tracing the flow of blood through the heart isn't as simple as it may seem. The heart is a complex organ, using four chambers, four valves and multiple blood vessels to provide blood to the body. The flow through the heart is equally complex, with blood moving through the heart, then the lungs, before returning again to the heart.
In the heart, there are valves to prevent back flow of blood. First there are the atrioventricular valves to prevent back flow back into the atria. Second there are the pulmonary valve and the semilunar valve to prevent back flow into the ventricle.