The cardiovascular system is sometimes called the blood-vascular, or simply the circulatory, system. It consists of the heart, which is a muscular pumping device, and a closed system of vessels called arteries, veins, and capillaries. As the name implies, blood contained in the circulatory system is pumped by the heart around a closed circle or circuit of vessels as it passes again and again through the various "circulations" of the body.
As in the adult, survival of the developing embryo depends on the circulation of blood to maintain homeostasis and a favorable cellular environment. In response to this need, the cardiovascular system makes its appearance early in development and reaches a functional state long before any other major organ system. Incredible as it seems, the primitive heart begins to beat regularly early in the fourth week following fertilization.
The vital role of the cardiovascular system in maintaining homeostasis depends on the continuous and controlled movement of blood through the thousands of miles of capillaries that permeate every tissue and reach every cell in the body. It is in the microscopic capillaries that blood performs its ultimate transport function. Nutrients and other essential materials pass from capillary blood into fluids surrounding the cells as waste products are removed.
Numerous control mechanisms help to regulate and integrate the diverse functions and component parts of the cardiovascular system in order to supply blood to specific body areas according to need. These mechanisms ensure a constant internal environment surrounding each body cell regardless of differing demands for nutrients or production of waste products.
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What are heart valves?
The heart consists of four chambers, two atria (upper chambers) and two ventricles (lower chambers). There is a valve through which blood passes before leaving each chamber of the heart. The valves prevent the backward flow of blood. These valves are actual flaps that are located on each end of the two ventricles (lower chambers of the heart). They act as one-way inlets of blood on one side of a ventricle and one-way outlets of blood on the other side of a ventricle. Normal valves have three flaps, except the mitral valve, which has two flaps. The four heart valves include the following:
- tricuspid valve: located between the right atrium and the right ventricle
- pulmonary valve: located between the right ventricle and the pulmonary artery
- mitral valve: located between the left atrium and the left ventricle
- aortic valve: located between the left ventricle and the aorta
How do the heart valves function?
As the heart muscle contracts and relaxes, the valves open and shut, letting blood flow into the ventricles and atria at alternate times. The following is a step-by-step illustration of how the valves function normally in the left ventricle:
After the left ventricle contracts, the aortic valve closes and the mitral valve opens, to allow blood to flow from the left atrium into the left ventricle.
As the left atrium contracts, more blood flows into the left ventricle.
When the left ventricle contracts, the mitral valve closes and the aortic valve opens, so blood flows into the aorta.
What is heart valve disease?
Heart valves can have one of two malfunctions:
- regurgitation (or leakage of the valve): The valve(s) does not close completely, causing the blood to flow backward through the valve. This results in leakage of blood back back into the atria from the ventricles (in the case of the mitral and tricuspid valves) or leakage of blood back into the ventricles (in the case of the aortic and pulmonary valves).
- stenosis (or narrowing of the valve): The valve(s) opening becomes narrowed or valves become damaged or scarred (stiff), inhibiting the flow of blood out of the ventricles or atria. The heart is forced to pump blood with increased force in order to move blood through the narrowed or stiff (stenotic) valve(s).
Heart valves can have both malfunctions at the same time (regurgitation and stenosis). Also, more than one heart valve can be affected at the same time. When heart valves fail to open and close properly, the implications for the heart can be serious, possibly hampering the heart's ability to pump blood adequately through the body. Heart valve problems are one cause of heart failure.
The heart is an organ, about the size of a fist. It is made of muscle and pumps blood through the body. Blood is carried through the body in blood vessels, or tubes, called arteries and veins. The process of moving blood through the body is called circulation. Together, the heart and vessels make up the cardiovascular system.
Structure of the Heart
The heart has four chambers (two atria and two ventricles). There is a wall (septum) between the two atria and another wall between the two ventricles. Arteries and veins go into and out of the heart. Arteries carry blood away from the heart and veins carry blood to the heart. The flow of blood through the vessels and chambers of the heart is controlled by valves.
Blood Flow Through the Heart
(Abbreviations refer to labels in the illustration)
The heart pumps blood to all parts of the body. Blood provides oxygen and nutrients to the body and removes carbon dioxide and wastes. As blood travels through the body, oxygen is used up, and the blood becomes oxygen poor.
- Oxygen-poor blood returns from the body to the heart through the superior vena cava (SVC) and inferior vena cava (IVC), the two main veins that bring blood back to the heart.
- The oxygen-poor blood enters the right atrium (RA), or the right upper chamber of the heart.
- From there, the blood flows through the tricuspid valve (TV) into the right ventricle (RV), or the right lower chamber of the heart.
- The right ventricle (RV) pumps oxygen-poor blood through the pulmonary valve (PV) into the main pulmonary artery (MPA).
- From there, the blood flows through the right and left pulmonary arteries into the lungs.
- In the lungs, oxygen is put into the blood and carbon dioxide is taken out of the blood during the process of breathing. After the blood gets oxygen in the lungs, it is called oxygen-rich blood.
- Oxygen-rich blood flows from the lungs back into the left atrium (LA), or the left upper chamber of the heart, through four pulmonary veins.
- Oxygen-rich blood then flows through the mitral valve (MV) into the left ventricle (LV), or the left lower chamber.
- The left ventricle (LV) pumps the oxygen-rich blood through the aortic valve (AoV) into the aorta (Ao), the main artery that takes oxygen-rich blood out to the rest of the body.