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Pathway of a Red Blood Cell
Transcript of Pathway of a Red Blood Cell
The Journey Riley Donaldson
Biology 12 Red blood cells travel through the circulatory system in order to deliver blood to various organs and tissues in the body. Red blood cells are mature blood cells that contain hemoglobin which allows them to carry oxygen throughout the body. The left index finger also known as the ring finger is where our story begins. Within the capillary bed of this finger is a lone deoxygenated red blood cell which has a great journey ahead of it. In order to return oxygenated, it must make its journey back to the lungs and heart. Along its path it will travel through various veins and arteries to make its way back to where it came from. The journey begins in the capillary bed of the finger. The capillary bed is a concentration of capillaries which supply blood to tissues and organs. The capillary beds mark the terminus of circulation where the blood loops back to become reoxygenated. The capillaries are the smallest unit in the circulatory system and connects with arterioles and venules. Blood which exits the capillary beds is deoxygenated. The blood flow is the slowest in the capillaries to allow for the exchange of gases and nutrients. When the red blood cells exit the capillaries they enter the venules. From the venules they will enter the larger veins. Many venules join together to form a single vein. The blood is still deoxygenated. The deoxygenated blood rises from the finger through to digital vein. The deoxygenated blood then enters the radial veins. These veins run through the back of the hand and into the forearm. They join with the ulnar veins to form the brachial veins. Both the ulnar and radial veins are formed by numerous venules. As these veins merge with others and continue towards the heart, they widen. The blood also slowly speeds as it progresses towards the heart away from the finger. The brachial vein carries the deoxygenated blood up the arm from the elbow to the shoulder blade. It is classified as a deep vein which runs deep in the arm. It is known as the lower part of the much larger axillary vein. It combines with the basilic vein which runs along the back of the forearm. As the blood travels through the veins in the arm it passes through many valves which prevent it from back flowing and keep it going along its path. The deoxygenated blood then flows through the subclavian vein. After flowing through the subclavian vein the blood enters the heart through the superior vena cava. The subclavian vein is large in diameter which means the blood pressure is also very low. The blood will be under its lowest pressure when it enters the heart via the superior vena cava. The deoxygenated blood enters the heart through the superior vena cava. The superior vena cava has thin walls and the blood is under low pressure. From the superior vena cava, the blood enters the right atrium. The right atrium has thin walls due to the low pressure of the chamber and the ease of pumping to low pressure areas. The deoxygenated blood then flows through the tricuspid valve which prevents it from flowing back to the right atrium. The blood then enters the right ventricle where it is then pumped into the pulmonary artery through the semi lunar valve once the pressure in the ventricle becomes higher than that of the artery. The walls of the right ventricle are thicker than those of the right atrium due to the resistance of blood flow to the lungs. In order to overcome this resistance, thick muscle is required. The deoxygenated blood then exits the heart through the pulmonary arteries which lead to the left and right lungs. The pulmonary arteries are under less pressure than the pulmonary veins because they are larger and carry deoxygenated blood. When the deoxygenated blood reaches the lungs, its gases are dissolved into the alveoli where they pass through its membrane into the capillaries. In the capillaries, the red blood cells bind to oxygen molecules which makes them oxygenated. Once oxygenated, the blood travels through the pulmonary veins back to the heart. The pulmonary veins are the only veins in the body to carry oxygenated blood since the blood must return to the heart and veins always lead back to the heart. The oxygenated blood travels back to the heart via the pulmonary veins. It re-enters the heart in the left atrium. The left atrium is noticeably thicker than the right because the blood it receives is oxygenated and pumped throughout the body which requires higher pressure and energy which creates thicker muscle. The oxygenated blood then enters the left ventricle through the bicuspid valve. Similarly to the tricuspid valve, the bicuspid valve prevents the back flow of blood into the left atrium. The only difference is that it has 2 flaps instead of 3. The final stop in the heart is the left ventricle. The left ventricle receives the oxygenated blood and pumps it into the aorta where it is distributed to the rest of the body. The pressure within the left ventricle is very high due to it relaxing and contracting quite rapidly in order to force the blood out of the heart. As a result, its walls are much thicker than those of the right ventricle. The oxygenated blood exits the heart into the aorta through the aortic valve. The aortic valve opens to allow blood to exit the heart when the pressure in the left ventricle rises above the pressure in the aorta. The oxygenated blood follows from aorta to the upper body. Once in the aortic arch, the blood skips by the first two arteries and branches into the third artery which leads to the left arm. The aorta is the largest artery in the body and distributes oxygenated blood throughout the body. Since it is the body's main distributor, the blood is under high pressure and has a rapid velocity compared to other arteries though it does not flow at a consistent rate. The subclavian artery rises from the aortic arch and supplies the oxygenated blood to the left arm. The blood passes from the subclavian artery and then enters the brachial artery. The brachial artery passes down the inside of the arm where the oxygenated blood is passed on to the radial artery. The blood continues to flow at a rapid and inconsistent velocity. As the blood flows away from the heart, the pressure at which the blood is under continues to decrease slowly in the arteries. The radial artery receives the oxygenated blood and transports it to the wrist and hand. The pressure in the radial artery is weaker than many other arteries. The blood then branches off from the radial artery to the digital artery of the left index finger. As the blood branches off into the smaller arteries in the finger, the velocity of the blood lessens. The oxygenated blood branches off of the digital arteries into the arteriole which leads to the capillary. The arterioles also control blood pressure and can either slow or speed up the blood depending on which chemical or electrical messages it receives. In our case the blood slows down before it enters the capillaries. The journey ends where it began, in the capillary bed of the left finger. Blood received from the arteriole enters the many capillaries where the exchange of gases, nutrients and wastes take place. Due to their size, the oxygen and nutrients pass through the capillaries due to a process known as diffusion. Once these substances are delivered, the blood becomes deoxygenated once again and begins the process over again. This process will take on average 20 seconds to occur.