THE HUMAN CIRCULATORY SYSTEM FUNCTINS
Human Circulatory System Small organisms don’t have a bloodstream, but instead rely on the simple diffusion of materials for transport around their cells. This is OK for single cells, but it would take days for molecules to diffuse through a large animal, so most animals have a circulatory system with a pump to transport materials quickly around their bodies. This is an example of a mass flow system , which means the transport of substances in the flow of a fluid (as opposed to diffusion, which is the random motion of molecules in a stationary fluid). The transport of materials in the xylem and phloem of plants is an other example of mass flow. Mass flow systems work together with the specialized exchange systems (such as lungs, gills and leaves), which we saw in module 1. Humans have a double circulatory system with a 4-chambered heart. In humans the right side of the heart pumps blood to the lungs only and is called the pulmonary circulation , while the left side of the h...