68 Singular form: atrium. Signals start at the top of the heart and move down to the bottom. Every minute of our life we breathe from five to six litres of air. ONLINE RESOURCES Main cardiovascular diseases carbon dioxide: anidride carbonica chamber: camera to drain: drenare fist: pugno lung: polmone to propel: spingere avanti sac: alveolo (polmonare) waste: scorie THE CARDIOVASCULAR AND RESPIRATORY SYSTEMS The cardiovascular system The cardiovascular system transports food, oxygen, water, and other fundamental substances to tissue and carries away waste products. It is made up of three parts: the blood, which is the fluid in which materials are carried to and from tissue. It is a connective tissue made of cells which move freely in its liquid portion, known as plasma; the heart, which is the driving force that propels blood. It is a hollow organ about the size of a fist which works as a muscular pump that sends the blood around the body; the blood vessels, the routes by which the blood travels to, through, and from tissue back to heart. They can be classified into three groups: arteries, which carry blood from ventricles (pumping chambers of the heart) to the capillaries in organs and tissue; veins, which drain capillaries in the tissues and organs, and return the blood to the heart; capillaries, which allow exchanges between the blood and body cells and between the blood and air in lung tissue. Anatomy of the heart The human heart is a four-chambered muscular organ whose structure resembles that of a building, with walls, rooms, doors, and an electrical system. It includes: the pericardium: a cover composed of three layers: endocardium, myocardium, and pericardium; four chambers: the upper ones being the left and right atria , and the lower ones being the left and right ventricles; four valves: they open and close to allow blood to flow through. They are: the tricuspid valve, between the right atrium and the right ventricle; the pulmonary valve, between the right ventricle and the pulmonary artery; the mitral valve, between the left atrium and the left ventricle; the aortic valve, between the left ventricle and the aorta; an electrical conduction system: it controls the rhythm and pace of the heartbeat . The respiratory system The fundamental functions of the respiratory system are to provide oxygen, which is needed to obtain energy from food, to transfer energy to tissue cells, and to remove carbon dioxide. The respiratory system is an intricate arrangement of spaces and passageways that conduct air into the lungs. These spaces include: the nasal cavity, the pharynx, the larynx, the trachea, the lungs, with their tubes and sacs. Ventilation is the movement of air into and out of the lungs, as in breathing. The two phases of ventilation are: inhalation, the act of drawing air into the lungs; exhalation, the act of expelling air from the lungs. 136 SCIENCE AND PHYSICS