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The cardiac cycle. Blood flows through the heart from veins to atria to ventricles out by arteries. Heart valves limit flow to a single direction. One heartbeat, or cardiac cycle, includes atrial contraction and relaxation, ventricular contraction and relaxation, and a short pause. Normal cardiac cycles at rest take 0.

Blood from the body flows into the vena cava, which empties into the right atrium. At the same time, oxygenated blood from the lungs flows from the pulmonary vein into the left atrium.

Anatomy of the Heart and Cardiovascular System

The muscles of both atria contract, forcing blood downward through each AV valve into each ventricle. Diastole is the filling of the ventricles with blood. Ventricular systole opens the SL valves, forcing blood out of the ventricles through the pulmonary artery or aorta. The sound of the heart contracting and the valves opening and closing produces a characteristic "lub-dub" sound.

Lub is associated with closure of the AV valves, dub is the closing of the SL valves. Human heartbeats originate from the sinoatrial node SA node near the right atrium.

Modified muscle cells contract, sending a signal to other muscle cells in the heart to contract. The signal spreads to the atrioventricular node AV node. Signals carried from the AV node, slightly delayed, through bundle of His fibers and Purkinjie fibers cause the ventricles to contract simultaneously.

The circulatory system

Figure 13 illustrates several aspects of this. The contraction of the heart and the action of the nerve nodes located on the heart. Heartbeats are coordinated contractions of heart cardiac cells, shown in an animate GIF image in Figure When two or more of such cells are in proximity to each other their contractions synch up and they beat as one.

Animated GIF image of a single human heart muscle cell beating. An electrocardiogram ECG measures changes in electrical potential across the heart, and can detect the contraction pulses that pass over the surface of the heart.


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There are three slow, negative changes, known as P, R, and T as shown in Figure Positive deflections are the Q and S waves. The P wave represents the contraction impulse of the atria, the T wave the ventricular contraction. ECGs are useful in diagnosing heart abnormalities.

Normal cardiac pattern top and some abnormal patterns bottom. Cardiac muscle cells are serviced by a system of coronary arteries. During exercise the flow through these arteries is up to five times normal flow. Blocked flow in coronary arteries can result in death of heart muscle, leading to a heart attack. Blockage of coronary arteries, shown in Figure 16, is usually the result of gradual buildup of lipids and cholesterol in the inner wall of the coronary artery.

Top 10 facts

Occasional chest pain, angina pectoralis, can result during periods of stress or physical exertion. Angina indicates oxygen demands are greater than capacity to deliver it and that a heart attack may occur in the future. Heart muscle cells that die are not replaced since heart muscle cells do not divide. Heart disease and coronary artery disease are the leading causes of death in the United States. Development of arterial plaque. Causes in most cases are unknown, although stress, obesity, high salt intake, and smoking can add to a genetic predisposition.

Two main routes for circulation are the pulmonary to and from the lungs and the systemic to and from the body. Pulmonary arteries carry blood from the heart to the lungs. In the lungs gas exchange occurs. Pulmonary veins carry blood from lungs to heart. The aorta is the main artery of systemic circuit. The vena cavae are the main veins of the systemic circuit. Coronary arteries deliver oxygenated blood, food, etc. Animals often have a portal system , which begins and ends in capillaries, such as between the digestive tract and the liver. Fish pump blood from the heart to their gills, where gas exchange occurs, and then on to the rest of the body.

Mammals pump blood to the lungs for gas exchange, then back to the heart for pumping out to the systemic circulation. Blood flows in only one direction. Plasma is the liquid component of the blood. Mammalian blood consists of a liquid plasma and a number of cellular and cell fragment components as shown in Figure It acts as a buffer, maintaining pH near 7.

Plasma contains nutrients, wastes, salts, proteins, etc. Proteins in the blood aid in transport of large molecules such as cholesterol. Mature erythrocytes lack a nucleus.

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How Your Body is Like a Factory | The Franklin Institute

They are small, 4 to 6 million cells per cubic millimeter of blood, and have million hemoglobin molecules per cell. Red blood cells are continuously manufactured in red marrow of long bones, ribs, skull, and vertebrae. Life-span of an erythrocyte is only days, after which they are destroyed in liver and spleen. Iron from hemoglobin is recovered and reused by red marrow. The liver degrades the heme units and secretes them as pigment in the bile, responsible for the color of feces.

Each second two million red blood cells are produced to replace those thus taken out of circulation. White blood cells , also known as leukocytes , are larger than erythrocytes, have a nucleus, and lack hemoglobin. They function in the cellular immune response. They are made from stem cells in bone marrow. There are five types of leukocytes, important components of the immune system.

Neutrophils enter the tissue fluid by squeezing through capillary walls and phagocytozing foreign substances. Macrophages release white blood cell growth factors, causing a population increase for white blood cells. Lymphocytes fight infection. T-cells attack cells containing viruses. B-cells produce antibodies. Antigen-antibody complexes are phagocytized by a macrophage. White blood cells can squeeze through pores in the capillaries and fight infectious diseases in interstitial areas.

Platelets result from cell fragmentation and are involved with clotting, as is shown by Figures 17 and Platelets are cell fragments that bud off megakaryocytes in bone marrow. Bones are also responsible for the production of red blood cells, platelets and most white blood cells. Human Skeletal System: Learn about the skeletal system components, types of bones, and types of joints. Systems: Skeletal System: Learn about the skeletal system inside and out by clicking on this link. While reading this page, people can also learn what the skeletal system does and how it works with other systems in the body.

Learn the Skeletal System:Label the Bones: An interactive game for grades 4 and 5 that allows kids to label the various bones of the skeletal system. Human Body: Human Skeleton Printout: Kids can ask their parents to print out this skeleton for coloring, or it can be colored online. Spaces are available for labeling the various parts. Skeleton Match Activity: Learning about the common and proper names of bones can be fun. Print this PDF and connect the common names of the bones with the proper names.


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