The Circulatory System: An Overview
Without rest, the heart pumps blood across the body every second of the day. The cardiovascular system works with the other 10 body systems to keep the human body running. This article will provide an overview of the cardiovascular systems and its many functions.
The cardiovascular system is responsible for the transportation of blood across the body as well as some temperature regulation. Since humans are warm-blooded creatures, they are required to maintain a body temperature within a very narrow range. To maintain their body temperature, warm blood is pumped from the center of the body to the surface, where the outside environment cools it. On hot days, external blood vessels are dilated. This causes more heat to be released to the environment, which keeps the body cool. On cooler days, blood vessels are constricted. This causes less heat to be released to the environment, and this helps conserve body heat. These phenomena are known as vasodilation and vasoconstriction respectively.
The cardiovascular system’s components include the heart, blood vessels, and blood. The average human has 1.2–1.5 gallons of blood in their body. Blood is a mixture of plasma; red blood cells; white blood cells; platelets; and dissolved nutrients, wastes, and gases. Plasma is a liquid mostly made of water. It is the fluid that carries blood cells, nutrients, and hormones. It also supplies cells with fluids needed to maintain a proper fluid balance. Red blood cells are cells without a nucleus who make use of a molecule known as hemoglobin to transfer oxygen from the lungs to capillaries. Hemoglobin also carries CO2 from capillaries to the lungs for it to be inhaled for hemoglobin to be made, a diet with sufficient iron should be consumed. Red blood cells are made in the red bone marrow. White blood cells serve to fight infections in the body. They are made in the bone marrow and by the lymphatic system. They pass through blood vessels to engulf and ingest infectious agents in tissue and later dispose of this waste. Platelets help to seal damaged blood vessels by forming blood clots. These clumps of platelets help prevent excessive blood loss. Platelets are also made in the bone marrow. Blood also carries hormones and nutrients to regions of the body that need them.
Blood is carried around the body by three types of blood vessels: Arteries, Veins, and Capillaries. With the pulmonary artery as an exception, arteries carry oxygenated blood away from the heart and spread it to all areas of the body. The pulmonary artery carries deoxygenated blood from the heart from the lungs for it to get oxygenated. Arteries are muscular and elastic since they must handle the force of blood being pumped around the body. The Aorta is the largest artery in the body and it receives blood directly from the heart. The Aorta branches into smaller arteries that branch into arterioles, which finally empty into capillaries. With the pulmonary vein as an exception, veins carry deoxygenated blood to the heart from other parts of the body. The pulmonary vein carries oxygenated blood from the lungs back to the heart. Veins are thin and less muscular than arteries but have valves which ensure that blood only travels to the heart instead of in the opposite direction. Venules empty into veins which and empty into either the Inferior or Superior Vena Cava, which happen to be the thickest veins. Arterioles and Venules connect in capillary beds. Capillaries are the connector blood vessels between arterioles and venules. They have one cell thick walls, and this allows substances to leave and enter the bloodstream. At capillary beds, nutrients and O2 are deposited into tissue while waste and CO2 is collected from the tissues and filtered out of the blood by the kidney.
The heart is a muscular organ that pumps blood across the body. It is composed of cardiac muscle and pumps blood out of arteries at high enough pressures to reach every part of the body. When fully developed, it is approximately the size of an adult fist. It is located between the lungs in the chest. The heart has 3 layers: the endocardium, myocardium, and pericardium. The pericardium is a sac that surrounds the heart. The myocardium is the thick cardiac muscle that pumps blood. The endocardium is the smooth layer that lines the inside of the heart. The heart also has 4 chambers: The Right and Left Ventricles, and the Right and Left Atria. Atria receive blood from the body and transfer it to the ventricles, who pump blood away from the heart. There are valves between each atrium and ventricle as well as ventricles and arteries. These prevent the backflow of blood. The pumping of blood causes these valves to shut, which produces the “Lub Dub” sound heard while listening to the heart. The heart also has its electrical system, which means it can continue to pump blood without receiving signals from the brain. An EKG test measures the electrical activity of the heart. The average adult heart beats from 60–80 times in a minute, but this range is generally lower in athletic individuals.
Two types of circulation occur: pulmonary and systemic circulation. Pulmonary circulation refers to the flow of blood from the heart to the lungs and vice versa, while systemic circulation refers to the flow of blood from the heart to the body and vice versa. The path of blood as it is pumped through the body is as follows: deoxygenated blood is collected from the body via veins and is deposited into the Right atrium of the heart through the Inferior and Superior Vena Cava. The right atrium pumps the blood through the tricuspid valve and into the right ventricle. The right ventricle pumps blood through the pulmonary valve and into the pulmonary artery, which carries it to the lungs. The lungs oxygenate the blood, which is then returned to the heart using the pulmonary veins. The pulmonary veins empty into the left atrium, which pumps the blood through the mitral valve and into the left ventricle. The left ventricle pumps the blood through the aortic valve and into the aorta at high pressures. The aorta spreads the blood throughout the body, where the oxygen is deposited. The deoxygenated blood returns to the right atrium and the cycle continues.
As individual ages, their cardiovascular health starts to deteriorate. Changes include decreased elasticity of the arteries, decreased heart valve efficiency, decreased contractility of cardiac muscle, and decreased cardiac output. There is also an increased narrowing of the arteries due to the buildup of plaque. To prevent/lessen these effects, an individual can take part in many preventative measures, including practicing good nutrition, getting sufficient exercise, not smoking, and getting routine blood pressure checkups.
The cardiovascular system also has many diseases, including Anemia, Aneurysms, Angina Pectoris, Arteriosclerosis, Atherosclerosis, Congestive Heart Failure, Hypertension, Inflammation of the layers of the heart, Leukemia, Septicemia, Thrombosis, and Varicose Veins. More information on each of these diseases will be posted in separate articles, so be on the lookout for those!
In conclusion, the cardiovascular system is responsible for transporting nutrients and waste across the body as well as regulating body temperature. Look out for my next article on the skeletal system which will be posted soon!
References:
Mitchell, Dakota, and Lee Haroun. Introduction to health care. Clifton Park, NY: Delmar, Cengage Learning, 2012. Print.
Zimmermann, K. A. (2019, July 4). Circulatory System: Facts, Function & Diseases. Retrieved from https://www.livescience.com/22486-circulatory-system.html.
