Transport System

The first thing I think should be addressed regarding the circulatory system is the blood, since it's basically what delivers most things we need throughout our body. Blood is made of 45% solids (which would be cells) and 55% fluids (which would be plasma); among these fluids are dissolved waste products, proteins, water, hormones, antibodies, and nutrients. It's important to mention that platelets are also in the blood, which are cell fragments with no nucleus and is involved in clotting. There are also two types of blood cells, the red blood cell and the white blood cell. The red blood cell is erythrocyte and is responsible for transporting oxygen and carbon dioxide to and from tissues. The white blood cell is leukocyte and is responsible for counteracting foreign substances and disease.

The second "member" of the circulatory system that should be mentioned is the heart which is the muscular organ that pumps the blood through the system by contraction and dilation. The heart has four chambers, two atria, and two ventricles. The right side of the heart (right atrium and right ventricle) is responsible for pumping and controlling the oxygenated blood while the left side (left atrium and left ventricle) is responsible for deoxygenated blood.

Blood vessels are also an important component to call attention to in the circulatory system. The blood vessels are divided into three types: arteries, veins, and capillaries. There are structural and functional differences between the these three vessels. Arteries have a thick elastic wall that helps withstand the high pressure, an outer fibrous coat to prevent from rupturing under high pressures, a small lumen compared to the wall thickness to maintain high pressure, layer of smooth muscle - which allows them to contract. It is important to note that the only large lumen (as an artery) is near the heart, used to conduct a large volume of blood. Veins, on the other hand always have a large lumen in relation to the diameter to facilitate blood flow, it has a thin wall, more collagen and fewer elastic fibres than arteries because the pressure is low. It also have very little muscle since its not needed for constriction, and the valves are used to prevent back flow between pulses. Capillaries, in my perspective, is the smallest form of blood vessel since it has no muscle and elastic tissue once the pressure is very low and the endothelial layer on the cell is thick to allow permeability, diffusion of chemicals, or tissue fluid. Furthermore, the diameter is small, which leads exchanged to occur, there are pores to allow rapid diffusion, and there are no valves since the pressure is very low.

I think that the lab done in class was very helpful for us to understand the heart. When I started to learn the events that occur within the heart that causes the blood to move throughout the whole body, I got kind of stuck. This happened mostly in part because of the names and the constant opening and closing of something. But after seeing the heart and actually seeing the venrticles, atrium, arteries, etc. I became more familiar with the process and the relation between all parts. Firstly, the blood is collected in the atria and it is pumped into the ventricles. Then, the opened atrio-ventricular valves allow the flow from the atria to the ventricles (right atrium ⇒ right ventricle + left atrium ⇒ left ventricle). The closed semi-lunar valves (which I see as the "end points" of the pulmonary artery and the aorta) prevent the backflow from the arteries to the ventricles. Next, the blood is pumped from the ventricles to the arteries and the opened semi-lunar valves allow this flow. The now closed atrio-ventricular valves prevent backflow to the atria. The pressure is then generated by the heart, causing the blood to move through the body; the pumping of the blood occurs from the beginning of one heart beat, which is initiated by the SAN (sino atrial node).

This now leads me to the mechanisms that control the heartbeat. The heartbeat is the myogenic which is the muscle contraction of the heart. Then, the SAN (mentioned above) generates an electrical impulse on its own with a regular frequency, known as pacemaker. This impulse is spread to both atria, causing the two to contract in unison. The AVN (atrio ventricular node) picks this impulse that was spread in the right atrium septum and conduces it to the ventricles through fibers, causing the heart to contract and "relax" - the heart beat.

I've explained basic functions and concepts present in the transport system, and now the basic process of the blood flow throughout the whole body will be outlined. To begin with the right atrium receives blood from the body through the vena cava, the blood then passes through the right atrioventricular valve, which is closed when contracted, keeping the blood from re-entering the atrium. Following, the blood goes into the right ventricle (the wall of the right ventricle is thinner than the left ventricle and it only pumps blood to the lungs). Then, the blood goes to the right semilunar valve (beginning of artery) and it closes to prevent the blood from flowing back to the ventricle. The blood goes into the pulmonary artery, which takes the deoxygenated blood to the lungs. Once it is taken, the blood goes to both the left and right lungs. In the lungs, the capillaries that are present are in close contact with the alveoli so the blood can release CO2 and pick up O2. The alveoli (even though it's more relevant in the respiratory system) has a large surface area (because it's round), has a short diffusion distance from the blood, has a dense capillary network, and has a moist solution of gases - all of which facilitate the exchange of CO2 and O2. Next, from the lungs, the pulmonary vein carries the now oxygenated blood back to the heart, which is received from the left atrium. The blood then passes through the left atrioventricular valve and enters the left ventricle (the wall of the left ventricle is is thicker than the right ventricle and it pumps blood to the whole body). After this, the blood passes through the left semilunar valve which is at the start of the aorta. The aorta is the main and largest artery of the body; from the artery, the coronary artery branches off, which supplies blood to the heart muscle so it can pump. If the coronary artery is blocked, it can cause parts of the heart to die if they don't get the nutrients and oxygen. At last, the aorta also branches off into arteries that distributes blood tho the whole body, marking this as the last step in the transport system as the process begins all over again.


Below is a short video that I found on circulation. I chose this brief video because it's easy to understand and underlines the basic process of circulation.


Below is the concept map I did for the transport system. It's pretty big but contains important aspects to be studied.