1. The Structures of the Human Heart
The human heart has four chambers: two ventricles, each of which is a muscular chamber that squeezes blood out of the heart and into the blood vessels, and two atria, each of which is a muscular chamber that drains and then squeezes blood into the ventricles. The two atria reside at the top of the heart; the two ventricles are at the bottom. And, the heart is divided into left and right halves, so there is a left atrium and left ventricle, as well as a right atrium and right ventricle. The reason that the heart is divided into halves is because of the two-circuit circulatory system. The right side of the heart can pump blood to the lungs, while the left side of the heart pumps blood to the rest of the body. Blood goes in both directions on each and every pump.
The Functions of the Human Heart
Right-Hand Side of the Heart
The right-hand side of the heart receives de-oxygenated blood from the body tissues (from the upper- and lower-body via the superior vena cava and the inferior vena cava, respectively) into the right atrium. This de-oxygenated blood passes through the tricuspid valve into the right ventricle. This blood is then pumped under higher pressure from the right ventricle to the lungs via the pulmonary artery. Left-Hand Side of the Heart
The left-hand side of the heart receives oxygenated blood from the lungs (via the pulmonary veins) into the left atrium. This oxygenated blood then passes through the bicuspid valve into the left ventricle. It is then pumped to the aorta under greater pressure (as explained below). This higher pressure ensures that the oxygenated blood leaving the heart via the aorta is effectively delivered to other parts of the body via the vascular system of blood vessels (incl. arteries, arterioles, and capillaries). 2. How blood flow through the heart
The right and left sides of the heart work together
Blood enters the heart through two large veins, the inferior and superior vena cava, emptying oxygen-poor blood from the body into the right atrium. Left Side
The pulmonary vein empties oxygen-rich blood, from the lungs into the left atrium.
Blood flows from your right atrium into your right ventricle through the open tricuspid valve. When the ventricles are full, the tricuspid valve shuts. This prevents blood from flowing backward into the atria while the ventricles contract (squeeze). Left Side
Blood flows from your left atrium into your left ventricle through the open mitral valve. When the ventricles are full, the mitral valve shuts. This prevents blood from flowing backward into the atria while the ventricles contract (squeeze). Ventricular contraction
Oxygen and carbon dioxide travels to and from tiny air sacs in the lungs, through the walls of the capillaries, into the blood. Right Side
Blood leaves the heart through the pulmonic valve, into the pulmonary artery and to the lungs. Left Side
Blood leaves the heart through the aortic valve, into the aorta and to the body. This pattern is repeated, causing blood to flow continuously to the heart, lungs and body. 3. The Conduction System of the Heart
The conducting system of the heart consists of cardiac muscle cells and conducting fibers (not nervous tissue) that are specialized for initiating impulses and conducting them rapidly through the heart. They initiate the normal cardiac cycle and coordinate the contractions of cardiac chambers. Both atria contract together, as do the ventricles, but atrial contraction occurs first. The conducting system provides the heart its automatic rhythmic beat. For the heart to pump efficiently and the systemic and pulmonary circulations to operate in synchrony, the events in the cardiac cycle must be coordinated. 4. Cardiac Cycle
The cardiac cycle is the sequence of events that occurs when the heart beats. There are two phases of the cardiac cycle. In the diastole phase, the heart ventricles are...
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