The circulatory system is made up of the vessels and the muscles that help and control the flow of the blood around the body. This process is called circulation. The main parts of the system are the heart, arteries, capillaries and veins. As blood begins to circulate, it leaves the heart from the left ventricle and goes into the aorta. The aorta is the largest artery in the body. The blood leaving the aorta is full of oxygen. This is important for the cells in the brain and the body to do their work.
The oxygen rich blood travels throughout the body in its system of arteries into the smallest arterioles. On its way back to the heart, the blood travels through a system of veins. As it reaches the lungs, the carbon dioxide (a waste product) is removed from the blood and replace with fresh oxygen that we have inhaled through the lungs. The Heart The heart is a muscle about the size of an adult fist. It is composed of two sides and four chambers: the left and right atria and the left and right ventricles. The two atria are located on the top of the heart and receive blood from various parts of the body.
The two ventricles are located on the bottom of the heart and pump blood away from the heart, to the body. The right ventricle is responsible for pumping deoxygentated blood to the lungs. The left ventricle pumps oxygenated blood to the rest of the body. Between the chambers are valves. Valves control the flow of blood, insuring that it flows in one direction. The Blood Vessels Blood vessels are a series of elastic tubing that carry blood to and from the heart. Oxygenated blood leaves the heart and supplies oxygen and nutrients to the body via the arteries.
After crossing capillaries, veins return deoxygenated blood and waste products to the heart through the vena cava. After leaving the right ventricle through the pulmonary arteries, the blood gets oxygenated in the lungs, disposes of carbon dioxide from the body, returns to the left atrium from the pulmonary vein and then to the left ventricle to repeat the process again. The Blood Blood is a semi-viscous fluid that contains red blood cells, white blood cells, platelets and a watery substance called plasma that contains proteins, sugars, fats and minerals.
The average adult body circulates 10 pints of blood through a cardiac cycle. The red blood cells contain hemoglobin, which is responsible for transporting oxygen to the cells and carries carbon dioxide back to the heart. Cardiovascular function and control The electrocardiogram (ecg) The electrocardiogram (ECG or EKG) is a diagnostic tool that is routinely used to assess the electrical and muscular functions of the heart. While it is a relatively simple test to perform, the interpretation of the ECG tracing requires significant amounts of training.
Numerous textbooks are devoted to the subject. The heart is a two stage electrical pump and the heart’s electrical activity can be measured by electrodes placed on the skin. The electrocardiogram can measure the rate and rhythm of the heartbeat, as well as provide indirect evidence of blood flow to the heart muscle. A standardized system has been developed for the electrode placement for a routine ECG. Ten electrodes are needed to produce 12 electrical views of the heart. An electrode lead, or patch, is placed on each arm and leg and six are placed across the chest wall.
The signals received from each electrode are recorded. The printed view of these recordings is the electrocardiogram. By comparison, a heart monitor requires only three electrode leads – one each on the right arm, left arm, and left chest. It only measures the rate and rhythm of the heartbeat. This kind of monitoring does not constitute a complete ECG. The cardiac cycle The cardiac cycle is a term referring to all or any of the events related to the flow or blood pressure that occurs from the beginning of one heartbeat to the beginning of the next.
The frequency of the cardiac cycle is described by the heart rate. Each beat of the heart involves five major stages. The first two stages, often considered together as the “ventricular filling” stage, involve the movement of blood from atria into ventricles. The next three stages involve the movement of blood from the ventricles to the pulmonary artery (in the case of the right ventricle) and the aorta (in the case of the left ventricle).  The first, “early diastole,” is when the semilunar valves close, the atrioventricular (AV) valves are open, and the whole heart is relaxed.
The second, “atrial systole,” is when the atrium contracts, and blood flows from atrium to the ventricle. The third, “isovolumic ventricular contraction,” is when the ventricles begin to contract, the AV and semilunar valves close, and there is no change in volume. The fourth, “ventricular ejection,” is when the ventricles are empty and contracting, and the semilunar valves are open. During the fifth stage, “Isovolumic ventricular relaxation,” pressure decreases, no blood enters the ventricles, the ventricles stop contracting and begin to relax, and the semilunar valves close due to the pressure of blood in the aorta.
Throughout the cardiac cycle, blood pressure increases and decreases. The cardiac cycle is coordinated by a series of electrical impulses that are produced by specialized heart cells found within the sinoatrial node and the atrioventricular node. The cardiac muscle is composed of myocytes which initiate their own contraction without help of external nerves (with the exception of modifying the heart rate due to metabolic demand). Under normal circumstances, each cycle takes approximately one second.
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