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INTRODUCTION
The cardiac-circulatory system may be thought of as a transportation system. It takes nourishment and oxygen to the cells and carries away waste products. The closed system is kept in motion by the force of the heartbeat. Diseases that attack any part of this system interfere with the overall function. Long-standing diseases of the cardiovascular system eventually affect the pulmonary system as well.
STRUCTURE AND FUNCTION
The organs of the cardiovascular system include:1. Heart: A central pumping station.
2. Blood Vessels
A. Arteries: Tubes that carry blood away from the heart.
- They have muscular, elastic walls with smooth linings.
- They branch to form arterioles with thinner walls. Arterioles then become capillaries.
- They carry blood with high concentration of nutrients and oxygen (O2) to the body cells.
Major Arteries of the Body
B. Veins: Tubes that carry blood toward the heart.
- They have thinner muscular walls.
- They carry blood back to the heart.
- They carry blood with a lower concentration of oxygen, more carbon dioxide (CO2), and more waste products.
- They have cup-like valves that help move the blood.
Major Veins of the Body
C. Capillaries: Tubes that connect arteries and veins.
- They have walls only one cell thick.
- They are the site of exchange of nutrients and oxygen from the blood to the cells, and carbon dioxide and waste products from the cells to the blood.
3. Lymphatic Vessels: Tubes that carry lymph or tissue fluid to the blood stream. Fluid from the blood stream passes into the tissue spaces, where it is called tissue fluid. Some of the tissue fluid returns to the bloodstream by way of the capillaries. Some of it is first drawn off into the lymphatic vessels, where it is called lymph. Eventually the lymph is returned to general circulation and once more becomes part of the blood.
4. Lymph Nodes: Masses of lymphatic tissue along the pathway of the lymph. They filter the lymph.
5. Spleen: A lymphatic organ. The spleen produces some of the blood cells and helps destroy worn-out blood cells. It acts as a blood reservoir or blood bank.
6. Blood: A connective tissue made up of a liquid (plasma) and cellular elements.
THE BLOOD
Blood is a red body fluid composed of plasma and cellular elements. The body contains 4 to 6 quarts (liters) of blood.
PLASMA
Plasma forms 55 percent of the blood and is the liquid watery solution containing:
- Antibodies (gamma globulins) - chemicals to fight infection.
- Nutrients - such as glucose, amino acids, fats, and salts.
- Gases - such as oxygen and carbon dioxide.
- Waste products - such as urea and creatine.
BLOOD CELLS
The blood cells are produced in the bone marrow and lymphatic tissues of the body. The bone marrow, liver, and spleen destroy worn-out blood cells. The red blood cells include red blood cells, white blood cells, and thrombocytes.
- Red Blood Cells (RBC): Called erythrocytes, carry most of the oxygen and small amounts of carbon dioxide. There are 4.5 to 5 million RBC per cubic millimeter (mm3).
- White Blood Cells (WBC): Called leukocytes, fight infection. There are 7,000 to 8,000 WBC/ mm3.
- Thrombocytes: Also called platelets, are not whole cells but only parts of cells. They seal small leaks in the walls of blood vessels and initiate blood clotting. There are 200,000 to 400,000 thrombocytes/ mm3.
THE HEART
External view of the heart & blood vessels.
The heart is a hollow muscular organ about the size of fist. It is divided into a right and left side by a muscular wall called the septum and into four chambers. There are 3 layers in the heart wall. The endocardium lines the heart chambers. The myocardium is the muscle layer. The pericardium is a membranous outer coating.
The four chambers are:1. The Right Atrium (RA): (right upper heart chamber) receives blood from all over the body. This blood has a low oxygen content and a relatively high carbon dioxide level. It is called deoxygenated blood.
2. The Right Ventricle (RV): (right lower heart chamber) receives blood from the right atrium and sends it out to the lungs through the pulmonary artery to pick up oxygen and get rid of the carbon dioxide.
3. The Left Atrium (LA): (left upper heart chamber) receives oxygenated blood from the lungs and sends it to the left ventricle.
4. The Left Ventricle (LV): (left lower heart chamber) receives oxygenated blood from left atrium and sends it out through the aorta to the entire body.
Valves separate the chambers. They also guard the exit of the pulmonary artery and aorta to prevent backflow and maintain a constant forward motion. The pulmonary artery carries blood to the lungs. The aorta is the largest blood vessel in the body. The valves are located as follows:
- Tricuspid valve - between right atrium and right ventricle.
- Bicuspid (mitral) valve - between left atrium and left ventricle.
- Pulmonary semilunar valves - between right ventricle and pulmonary artery.
- Aortic semilunar valve - between left ventricle and aorta.
Nerve impulses make the heart contract regularly according to body needs. For example, when you run, your body cells need more oxygen. The cells signal the brain that they need more oxygen. The brain sends a signal to the heart through the nerves, telling it to supply more blood. These nerve impulses cause the heart to beat faster. Thus, more oxygenated blood is pumped to the body cells to supply the oxygen required due to these impulses causing the heart to beat at a faster rate.
THE CARDIAC CYCLE
Heart Anatomy & the Cardiac Cycle
The heart pumps blood through the body by a series of movements known as the cardiac cycle.1. First the upper chambers of the heart, called the atria, relax and fill with blood as the lower chambers contract, forcing blood out of the heart through the aorta and pulmonary arteries.
2. Next, the lower chambers relax, allowing blood to flow into them from the contracting upper chambers.
3. Then the cycle is repeated.
Flow of blood from the heart to the lungs,
to the body, and back to the heart to
begin the cycle again.
Each cycle lasts about 0.8 second. This happens about 70 to 80 times per minute in the average adult.
The pulse you feel at the radial artery corresponds to the ventricular contraction. The sounds you hear when listening to the heart and when taking a blood pressure are the sounds made by the closing of the valves during the cardiac cycle.
The rate and rhythm of the cardiac cycle are regulated by the conduction system. The conduction system is made up of special neuromuscular tissue that sends out impulses. The impulses eventually reach the myocardial cells, which respond by contracting.
- The impulses begin at the S-A node in the right atrium and spread across the two atria.
- The atria contract.
- Impulses from the S-A node reach the A-V node in the right atrium.
- Messages from the A-V node then spread through the bundle of His in the septum. From there they go through the Purkinje fibers to the walls of the ventricles.
- The ventricles contract, forcing the blood forward.
An electrocardiogram, called an ECG or an EKG, is a test that traces the electrical impulses of the heart. Heart disease may be detected with this test.
BLOOD VESSELS
Many large arteries and veins take their names from the bones they are near of from the part of the body they serve. For example, the femoral artery and vein run close to the femur (thigh bone). The subclavian arteries and veins are found under the clavicle. The axillary arteries and veins are found in the axillary (armpit) area.
This figure shows the arterial system that distributes blood from the heart.
This figure shows the venous system that returns blood to the heart.
CARDIOVASCULAR & CIRCULATORY DISEASE INFORMATION, SUPPLEMENTS & PRODUCTS:
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