The cardiorespiratory system is composed of two parts: the cardiovascular system and the respiratory system.
The cardiovascular system consists of a pump, the heart; a system of channels, blood vessels and the capillaries; and a fluid medium, the blood. The cardiovascular system has five main functions. It delivers essential oxygen and nutrients to all of our cells, and helps in the removal of carbon dioxide, and other waste products of metabolism. The carbon dioxide is removed to the lungs, and other waste products are removed to the kidneys and gastrointestinal tract. It transports hormones from the glands where they are made, to the organs where they operate. It helps to maintain body temperature and pH, through constriction and dilatation of peripheral blood vessels, and the buffering abilities of blood. And finally, it helps to prevent infection (through the white cells in blood) and dehydration (by assisting with thermoregulation).
The cardiovascular system consists of a pump, the heart; a system of channels, blood vessels and the capillaries; and a fluid medium, the blood. The cardiovascular system has five main functions. It delivers essential oxygen and nutrients to all of our cells, and helps in the removal of carbon dioxide, and other waste products of metabolism. The carbon dioxide is removed to the lungs, and other waste products are removed to the kidneys and gastrointestinal tract. It transports hormones from the glands where they are made, to the organs where they operate. It helps to maintain body temperature and pH, through constriction and dilatation of peripheral blood vessels, and the buffering abilities of blood. And finally, it helps to prevent infection (through the white cells in blood) and dehydration (by assisting with thermoregulation).
The respiratory system consists of the nose and mouth, pharynx and larynx, trachea, bronchi and lungs contained in large sacs, the pleura, which allow smooth movement of the lungs, and assisted by the diaphragm and intercostal muscles. During an inhalation, the diaphragm and intercostal muscles contract, enlarging the chest cavity and expanding the lungs. As the lungs expand, air is pulled in through the mouth or nose, travelling into the trachea via the pharynx and larynx. The trachea splits into the right and left main bronchus, which form the main passageway of air into each of the lungs. Within the lungs, the bronchi split into a series of smaller branching bronchioles, eventually terminating in small sacs known as alveolae, where gas exchange between the air and blood occurs. The main function of the respiratory system is to inhale oxygen into the body and exhale carbon dioxide, a waste product of metabolism.
The blood vessels start with the largest artery, the aorta, taking oxygenated blood away from the heart. The aorta divides into a series of smaller arteries delivering oxygen and nutrient rich blood to all the end organs of the body. Arteries have a relatively thick, muscular wall because they are receiving blood under relatively high pressure. Each artery divides into a smaller series of blood vessels, the arterioles. In every organ of the body, the arterioles split into a network of tiny capillaries, with a single cell layer as their wall, where oxygen and nutrients are delivered to the organs, and waste products of metabolism are removed. The capillaries coalesce to form small venules, which then take deoxygenated blood and waste away from the end organs. These venules unite to form larger veins, which deliver the blood back to the right side of the heart. Because veins are not under as much pressure as arteries, their walls are thinner. However, many veins do have to work against gravity to deliver blood back to the heart. For this reason, veins have a series of valves in their walls, which prevent blood from pooling in the limbs. This is further assisted by the contraction of muscles, which act like a pump, assisting the blood back to the heart.
The heart is a four-chamber pump. It receives CO2 rich, deoxygenated blood from the body’s organs via the largest veins – the superior and inferior vena cava – into the right atrium. This blood is then pumped through the tricuspid valve into the right ventricle. From there, the blood pumps, under relatively low pressure, through the pulmonary valve into the pulmonary artery. The pressure here needs to be low, so that the lungs are not damaged by the force of the heart’s contraction. The pulmonary artery then delivers deoxygenated blood to the lungs. It is the only artery in the body which carries deoxygenated blood.
The blood from the pulmonary arteries, like in all other organs, travels through a series of vessels with ever decreasing diameters until it reaches the pulmonary capillaries. The two systems unite in the lungs where the pulmonary capillaries and alveolae meet. Here, gas exchange is made relatively simple, because both the alveolae and the capillaries are thin-walled. The alveolae replenish the blood with oxygen from an inhalation of air, and remove the carbon dioxide from the returning blood. Haemoglobin, a protein found in red blood cells helps move oxygen from the alveolae to the blood, and then carries the oxygen until it is removed at the end-organs. The lungs then blow off this carbon dioxide with an exhalation, when the diaphragm and intercostals relax, reducing the chest cavity and “squeezing” the lungs.
Meanwhile, the now oxygen-rich blood returns via venules to the pulmonary veins. There are two pulmonary veins for each lung, returning the oxygenated blood to the left atrium of the heart. This blood is then pumped through the mitral valve of the left atrium to the left ventricle of the heart. The left ventricle has a significantly thicker wall than the right ventricle because it has to pump blood around the whole of the body. With a forceful contraction, and with the blood under significantly higher pressure than the right side, the left ventricle pumps blood into the aorta, via the aortic valve, and from there blood is pumped all around the body, delivering oxygen rich blood to every organ.