Welcome aboard the SS William Harvey! As you well know the human body is a complex system of intricate cells that work together to maintain a perfect and efficient environment on which an individual can thrive. Two systems in the human body that work together to ensure that a human individual remains healthy are the circulatory and the cardiopulmonary systems. Working in conjunction with each other, these systems help with the transportation of gasses, nutrients, and hormones to different organs within the human body. While the intricate mazes that make up the different systems in the human body may confuse some individuals, finding one's way from the femoral vein in the circulatory system to the lungs is not as complicated as it sounds.
Join us as we embark on this Fantastic Voyage through the human body as we visit and discover new cells and organs of the human body. We currently find ourselves in the right femoral vein of a healthy female body. We were injected into this site with the sole purpose of finding our way to the right lung. But first, we must find our way to the right lung from our current position.
In the femoral vein you will note that we are surrounded by deoxygenated blood, which means that we must find our way to the lungs so that our surrounding blood can get oxygenated and continue to supply oxygen to various organs of the body. As we travel via the femoral vein to the heart, you will notice that we are surrounded by three types of blood cells: erythrocytes -- aka red blood cells, leukocytes -- aka white blood cells, and thrombocytes -- aka platelets (Cotterill, 2000). In order to move anywhere within the circulatory system, we must wait for the human heart to pull and push us to various parts of the body with every heartbeat. On average, the human heart will beat an average of 60 to 80 beats per minute (Gregory, n.d.). As we begin to move through the femoral vein up towards the heart, we will find ourselves begin to merge with the right external iliac vein. The right external iliac vein is charged with transporting deoxygenated blood from the legs back up to the heart. The right external iliac vein is located behind the inguinal ligament in the lower region of the abdomen (Inner Body, 2011). If you look out the window, you will notice that we are rapidly approaching a much bigger tunnel. This is the inferior vena cava. As we begin to merge into this large vein, we must remember that we are not the ones travelling into the inferior vena cava and that blood from the left side of the body also converges here. The inferior vena cava is a large vein that ascends an individual's abdomen up towards the heart (Inner Body, 2011). While we are here, please notice how blood from the hepatic veins, lumbar veins, gonadal veins, renal veins, and phrenic veins converge into one large blood pool that will be collectively transported to the heart. With every heartbeat, we find ourselves one step closer to the heart and one step closer to our target, the right lung. Before you know it, we find ourselves in the superior vena cava and must wait only seconds before we are pulled into the heart.
The heart is a unique organ and is solely responsible for making sure that blood is moved throughout the body through various channels called arteries, veins, and capillaries. The heart has two different pumps that are made up of an atrium and a ventricle. Each pump is responsible for pumping blood to different parts of the body. The left side of the heart is responsible for pumping blood to various parts of the body, while the right side of the heart is responsible for pumping blood to the lungs (Gregory, n.d.). To get into the heart itself, we must pass through the right atrium where blood from the inferior and superior vena cava is collected. Take a look at the right atrium's structure. The right atrium has "relatively thin walls and receives blood returning [to the heart] through the veins" (Inner Body, 2011). As quickly as the heart involuntarily pumps once again, we will pass through the tricuspid valve that will close up behind us so that no blood accidentally flows back into the right atrium and into the right ventricle. The right ventricle, like the left ventricle, work together by forcing blood out of the heart into different arteries that will take blood various parts of the body (Inner Body, 2011). Specifically, the right ventricle works to make sure that blood is pumped to the lungs. Additionally, the right ventricle, as opposed to the left ventricle, has a much thinner wall because it does not need to exert as much force as the left ventricle to pump blood to the lungs as they are closer to the heart than the left ventricle's bloody tunnels.
As we are forced out of the heart we find ourselves in the right pulmonary artery. This artery is much thicker and longer than the artery that leads to the left lung. Pretty soon, and with the assistance of the heart's pumping action, we find ourselves on our way to the lungs. The right pulmonary artery transverses the upper chest and travels below the aortic arch before it reaches the hilum of the right lung. This right pulmonary artery leads directly into the right lung and helps to keep the lung healthy by providing it with a steady supply of blood. The right pulmonary artery is unique because it is one of the few arteries in the human body that does not transport oxygenated blood, but rather takes blood to be oxygenated. From this point, we will begin the final leg of our fantastic voyage moving towards the lower lobe of the right lung towards alveoli where carbon dioxide is released from the body through gas exchange.
***News Alert*** We have just been informed that bacteria are attempting to attack the right lung and that we will find ourselves in the midst of combat! In order for an attack to commence, airway epithelial cells will signal white blood cells, also called neutrophils, "to move from the bloodstream into the lungs and airway to fight potential infection" (New Research Shows How Lungs Fight Bacteria and Prevent Infection, 2009). In order for these white blood cells to be called into action, epithelial proteases must be activated; "the opening of these junctions is initiated by a change in calcium levels" (New Research Shows How Lungs Fight Bacteria and Prevent Infection, 2009). Once neutrophils have been released, they stick to "bacteria or fungi, rendering it immovable or useless, or they may release chemicals that kill bacteria. They may also be on catch, destroy and eat missions in which they fight infections to the death" (How Does the Body Fight Infections?, n.d.). The release of white blood cells to the infected area can either be detrimental or beneficial to the combat of bacteria in a specific site of the body. For instance, "too many white blood cells can lead to excessive inflammation, interfering with breathing and damaging the airways" (New Research Shows How Lungs Fight Bacteria and Prevent Infection, 2009). Because of this, it is important to figure out how to control how many white blood cells are released to combat bacteria, especially in the lungs. Additionally, phagocytes may also be released into the lungs, which will create "environments inhospitable for infection" (How Does The Human Body Fight Infections?, n.d.).
On the other hand, it has also been found that friendly bacteria help to fend off viral infections in the lungs. Studies have shown "that mice treated with neomycin antibiotics…