Gas Exchange

• When you think about how the cardiovascular system works with other body systems, you probably think of the respiratory system. This is because the circulatory system has a direct path through the lungs. When blood returns from the body to the heart, it is depleted of oxygen. It has to pick up oxygen in the lungs before it can return to circulation.
  
  The deoxygenated blood first enters the right atrium of the heart then fills the right ventricle. From the right ventricle it is pumped to the lungs via the pulmonary artery. The pulmonary artery passes the blood through the lungs via capillaries surrounding thin membrane sacs called alveoli. The blood and alveoli exchange oxygen and carbon dioxide.
  
  The newly oxygenated blood travels back into the heart by way of the pulmonary veins. The pulmonary veins deliver the blood into the left atrium, which empties into the left ventricle. The left ventricle pumps the blood into circulation throughout the rest of the body.
  
  

Delivery System

• The cardiovascular system is the most significant conduit in the body for delivering molecules to and for other body systems. We have already seen how oxygen is carried by the cardiovascular system, but hormones, nutrients, electrolytes and antibodies are also important molecules that depend on the bloodstream for delivery. To explain how these are linked together, follow a peanut butter sandwich as it travels through your body.
  
  Your mouth starts to break down the sandwich, and the carbohydrates from the bread are absorbed into the bloodstream. Breakdown and absorption continue in the stomach and end with the absorption of the proteins in the small intestine. The blood is now carrying high amounts of carbohydrates, or sugars. This signals the endocrine system, specifically the pancreas, to secrete d insulin into the bloodstream. The insulin facilitates the uptake of sugar into the body's cells. The sugar is used for energy and converted into ATP. ATP is the body's energy currency and enables muscles contraction, neuron firing and cellular respiration.
  
  Sometimes, antibodies that are carried in the bloodstream inaccurately identify the insulin producing cells of the pancreas as foreign cells. The antibodies target the pancreatic cells for destruction. This leads to low insulin levels and Type I diabetes. If the sugar in the bloodstream is not absorbed by the cells, serious effects including acidosis, occur . Acidosis is a condition that leads to a blood pH level that is too acidic to sustain life. Normally, the immune system does not attack self-identified cells. However, the cardiovascular system simply acts as a vehicle to deliver the immune system cells and not as a mediator of their functions.
  
  

Regulation

• An acid-base imbalance in the body can often be regulated by different factors absorbed into the bloodstream. Depending on diet and health, there can also be too much salt or too much water.
  
  The kidneys form urine to carry wastes and excess fluid out of the body so that the cardiovascular system is not harmed by vast changes in pressure. Too much salt initiates water absorption into the blood vessels. This increases the blood volume and thus the pressure inside the vessels causing extra stress on the vessel walls. Too much stress can damage the elasticity of the blood vessels and disrupt the functioning of the cardiovascular system as a whole.
  
  A decreased blood volume, on the other hand, results in poor oxygenation of body tissues and can lead to shock and death. The cardiovascular system depends on the urinary system to correct and maintain these imbalances.
  
  

Conclusion

• We have examined how it partners with the digestive system to deliver nutrients to cells and how the cardiovascular system acts as a conduit for the endocrine system. We have touched on how the cardiovascular system depends on the urinary system to help maintain the right balance of water and electrolytes. But, the cardiovascular system also depends on several systems in order to function properly.
  
  For example, the cardiovascular system depends on the musculoskeletal system for new red blood cells generated in the bone marrow to bind and carry oxygen. It depends on the action of the muscles to pump blood in the veins back to the heart. And finally, the cardiovascular system relies on the lymphatic system to rid plasma--the liquid portion of blood--of infections and debris. Without these supports, the cardiovascular system could not carry out its primary functions.