Because of the size narrow of the coronary arteries and their function in serving the heart itself, atherosclerosis can be deadly in these arteries.
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The slowdown of blood flow and subsequent oxygen deprivation that results from atherosclerosis causes severe pain, known as angina , and complete blockage of the arteries will cause myocardial infarction : the death of cardiac muscle tissue, commonly known as a heart attack. The main purpose of the heart is to pump blood through the body; it does so in a repeating sequence called the cardiac cycle. The cardiac cycle is the coordination of the filling and emptying of the heart of blood by electrical signals that cause the heart muscles to contract and relax.
The human heart beats over , times per day.
In each cardiac cycle, the heart contracts systole , pushing out the blood and pumping it through the body; this is followed by a relaxation phase diastole , where the heart fills with blood, as illustrated in Figure The atria contract at the same time, forcing blood through the atrioventricular valves into the ventricles. Following a brief delay, the ventricles contract at the same time forcing blood through the semilunar valves into the aorta and the artery transporting blood to the lungs via the pulmonary artery. The pumping of the heart is a function of the cardiac muscle cells, or cardiomyocytes, that make up the heart muscle.
tairegesa.cf Cardiomyocytes , shown in Figure They are self-stimulated for a period of time and isolated cardiomyocytes will beat if given the correct balance of nutrients and electrolytes. The electrical signals and mechanical actions, illustrated in Figure The internal pacemaker starts at the sinoatrial SA node , which is located near the wall of the right atrium.
Electrical charges spontaneously pulse from the SA node causing the two atria to contract in unison. The pulse reaches a second node, called the atrioventricular AV node, between the right atrium and right ventricle where it pauses for approximately 0. From the AV node, the electrical impulse enters the bundle of His, then to the left and right bundle branches extending through the interventricular septum.
Finally, the Purkinje fibers conduct the impulse from the apex of the heart up the ventricular myocardium, and then the ventricles contract. This pause allows the atria to empty completely into the ventricles before the ventricles pump out the blood. The electrical impulses in the heart produce electrical currents that flow through the body and can be measured on the skin using electrodes. This information can be observed as an electrocardiogram ECG —a recording of the electrical impulses of the cardiac muscle.
The blood from the heart is carried through the body by a complex network of blood vessels Figure Arteries take blood away from the heart. The main artery is the aorta that branches into major arteries that take blood to different limbs and organs. These major arteries include the carotid artery that takes blood to the brain, the brachial arteries that take blood to the arms, and the thoracic artery that takes blood to the thorax and then into the hepatic, renal, and gastric arteries for the liver, kidney, and stomach, respectively.
The iliac artery takes blood to the lower limbs.
The major arteries diverge into minor arteries, and then smaller vessels called arterioles , to reach more deeply into the muscles and organs of the body. Arterioles diverge into capillary beds. Capillary beds contain a large number 10 to of capillaries that branch among the cells and tissues of the body.
Capillaries are narrow-diameter tubes that can fit red blood cells through in single file and are the sites for the exchange of nutrients, waste, and oxygen with tissues at the cellular level. Fluid also crosses into the interstitial space from the capillaries. The capillaries converge again into venules that connect to minor veins that finally connect to major veins that take blood high in carbon dioxide back to the heart. Veins are blood vessels that bring blood back to the heart. The major veins drain blood from the same organs and limbs that the major arteries supply.
Fluid is also brought back to the heart via the lymphatic system. The structure of the different types of blood vessels reflects their function or layers. There are three distinct layers, or tunics, that form the walls of blood vessels Figure The first tunic is a smooth, inner lining of endothelial cells that are in contact with the red blood cells. The endothelial tunic is continuous with the endocardium of the heart. In capillaries, this single layer of cells is the location of diffusion of oxygen and carbon dioxide between the endothelial cells and red blood cells, as well as the exchange site via endocytosis and exocytosis.
The movement of materials at the site of capillaries is regulated by vasoconstriction , narrowing of the blood vessels, and vasodilation, widening of the blood vessels; this is important in the overall regulation of blood pressure. Veins and arteries both have two further tunics that surround the endothelium: the middle tunic is composed of smooth muscle and the outermost layer is connective tissue collagen and elastic fibers.
The elastic connective tissue stretches and supports the blood vessels, and the smooth muscle layer helps regulate blood flow by altering vascular resistance through vasoconstriction and vasodilation.
The arteries have thicker smooth muscle and connective tissue than the veins to accommodate the higher pressure and speed of freshly pumped blood. The veins are thinner walled as the pressure and rate of flow are much lower. In addition, veins are structurally different than arteries in that veins have valves to prevent the backflow of blood.
Because veins have to work against gravity to get blood back to the heart, contraction of skeletal muscle assists with the flow of blood back to the heart. The heart muscle pumps blood through three divisions of the circulatory system: coronary, pulmonary, and systemic. The pumping of the heart is a function of cardiomyocytes, distinctive muscle cells that are striated like skeletal muscle but pump rhythmically and involuntarily like smooth muscle.
The internal pacemaker starts at the sinoatrial node, which is located near the wall of the right atrium. Electrical charges pulse from the SA node causing the two atria to contract in unison; then the pulse reaches the atrioventricular node between the right atrium and right ventricle.
A pause in the electric signal allows the atria to empty completely into the ventricles before the ventricles pump out the blood. The blood from the heart is carried through the body by a complex network of blood vessels; arteries take blood away from the heart, and veins bring blood back to the heart. Skip to content Increase Font Size. Unit 4: Animal Structure and Function. Learning Objectives By the end of this section, you will be able to: Describe the structure of the heart and explain how cardiac muscle is different from other muscles Describe the cardiac cycle Explain the structure of arteries, veins, and capillaries, and how blood flows through the body.
Figure The mammalian circulatory system is divided into three circuits: the systemic circuit, the pulmonary circuit, and the coronary circuit. Blood is pumped from veins of the systemic circuit into the right atrium of the heart, then into the right ventricle. Blood then enters the pulmonary circuit, and is oxygenated by the lungs. From the pulmonary circuit, blood re-enters the heart through the left atrium. From the left ventricle, blood re-enters the systemic circuit through the aorta and is distributed to the rest of the body.
The coronary circuit, which provides blood to the heart, is not shown. Blood in the pulmonary vein is deoxygenated. Global Space brings together, and was developed in collaboration with, the entire space industry. It provides a platform for the latest innovations and technologies, as well as being a catalyst for meetings and collaborations Space has never been so close.
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