Reptile hearts are highly adapted to work efficiently with very variable metabolic demands . Birds and mammals have 4-chambered hearts . The advantages of 4-chambered hearts are that oxygenated and deoxygenated blood do not mix, gas exchange is maximized by diffusion of gases at the lungs, and the systemic and pulmonary circuits can work at different pressures . The cardiovascular system transports TO all the cells of the body oxygen from the lungs and nutrients and water from the intestinal tract. The cardiovascular system helps the body eliminate metabolic wastes, heat, and carbon dioxide .
Blood flows from an area where there is higher pressure to an area where there is lower pressure.
The beating of the heart creates the high pressure that allows blood to flow throughout the vasculature and back to the heart. Hydrostatic pressure is the pressure of the liquid related to the height of a liquid-filled column. Hydrostatic pressure is also the pressure of the blood in the vasculature at any point in the system. The heart generates pressure by its contracting muscle transferring pressure to the blood within. Vasoconstriction is usually accomplished by contraction of the vascular smooth muscle cells around the vessel.