The cardiovascular system is a closed structure consisting of the heart and blood vessels. Primary functions of the cardiovascular system include transporting nutrients to bodily cells, removing waste products and maintaining a stable environment within the body during exercise and at rest. During periods when the cardiovascular system must work harder, it is designed to continue to meet the nutrient demands of cells.
Heart
The heart is a hollow four-chambered organ that pumps blood through vessels to the lungs and to the rest of the body. An adult heart is about the size of a fist, according to "Anthony's Textbook of Anatomy and Physiology." Two atria (right and left atrium) and two ventricles (right and left ventricles) comprise the four chambers of the heart. The atria are situated at the top part of the heart and the ventricles are in the lower section. Blood is supplied to the heart by the left and right coronary arteries.
Heart Valves and Blood Flow
The right atrium (RA) collects blood from the body, and the right ventricle (RV) pumps blood to the lungs, according to "Human Anatomy and Physiology" by Dr. Marieb and Dr. Hoehm. Blood is collected from the lungs by the left atrium (LA) and pumped to the rest of the body by the left ventricle (LV). The heart has valves to keep blood flowing in one direction. AV valves separate the atria from the ventricles, the tricuspid valve controls blood flow from the RA and RV, and the bicuspid (or mitral) valve maintains blood flow between the LA and LV. Two other valves exist in the heart--the pulmonary valve separates the RV and the pulmonary artery leading to the lungs. An aortic valve sits between the LV and the aorta, which directs blood to the body.
Heart Beat
The electrical impulse that starts heart contractions begins at the sinoatrial (SA) node, or intrinsic pacemaker. From the SA node, the electrical impulse spreads through the two atria until it reaches the atrioventricular (AV) node, which is situated between the two ventricles. At the AV node, a delay of the electrical impulse occurs to allow the two atria to contract and fill the two ventricles with blood. The electrical impulse moves through a branch of cells called the AV bundle, or bundle of His. A network of cells called the Purkinje fibers then rapidly conducts the impulse to the ventricles, which allows the ventricles to contract at about the same time.
Blood Vessels
The blood vessels deliver blood to the body and return the blood back to the heart, as noted in "Human Anatomy and Physiology" by Dr. Marieb and Dr. Hoehm. Arteries carry blood from the heart to the body. The arteries leaving the heart are large and they branch into smaller arteries and vessels called arterioles. Arterioles branch into microscopic capillaries, which exchange blood with the body's tissues. Capillaries on the artery side are connected to the capillaries of the venous side. The venous capillaries converge into venules, which merge into veins. Large veins bring blood to the heart. Some veins, such as those in the legs, have valves that help blood flow to the heart and prevent blood from flowing backwards.
References
- "Anthony's Textbook of Anatomy and Physiology;" Gary Thibodeau and Kevin Patton; 1999.
- "Human Anatomy and Physiology;" Elaine Marieb and Katja Hoehm; 2007.
