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Cardiovascular System The Heart and Vessels Function of the Cardiovascular System the delivery of oxygen, nutrient molecules, and hormones to the tissues removal of carbon dioxide, ammonia and other metabolic wastes. Components of the circulatory system include heart: a muscular pump to move the blood blood vessels: arteries, capillaries and veins that deliver blood to all tissues blood: a connective tissue of liquid plasma and cells http://www.getbodysmart.com/ap/cir culatory/menu/circulatory.html A pump for all seasons THE HEART The Heart composed of cardiac muscle. adjusts the rate of muscular contraction, allowing the heart to maintain a regular pumping rhythm. The main parts of the heart are the chambers, the valves, and the electrical nodes. Heart Chambers two types atrium (plural is atria), receives blood returning to the heart through the veins. The right atrium pumps blood to the right ventricle, and the left atrium pumps blood into the left ventricle. ventricles - much larger than the atria and their thick, muscular walls are used to forcefully pump the blood from the heart to the body and lungs (or gills). Valves found within the heart between the atria and ventricles, and between the ventricles and major arteries. opened and closed by pressure changes within the chambers, and act as a barrier to prevent the backflow of blood. The characteristic "lub-dub, lub-dub" heart sounds heard through a stethoscope are the result of vibrations caused by the closing of the respective valves. Two different electrical nodes, or groups of specialized cells, located in the cardiac tissue. ELECTRICAL NODES Sinoatrial (SA) node Commonly called the pacemaker which controls the heart beat. embedded in the wall of the right atrium, composed of muscle tissue that sends electrical impulses to the rest of both atria to contract. The impulse then spreads to the ventricles, causing them to contract. atrioventricular (AV) node relays the impulse of the SA node to the ventricles. It delays the impulse to prevent the ventricles from contracting at the same time as the atria, thus giving them time to fill with blood. The cycle of contraction of the heart muscle is called a heartbeat the rate varies greatly between organisms. The heart cycle involves three phases: HEARTBEATS Phase one The atria contract and force blood into the ventricles. If the atria don’t contract, this is called atrial fibrillation and pooled blood in the atria can begin to clot. When the atria start beating normally again, these clots may be sent throughout the person’s system. If one of these clots lodges in an arteriole somewhere, it could cause a stroke, heart attack, or similar problem. As blood is pushed into the ventricles, when the A-V valves close, the ventricular walls vibrate a little causing the first sound of the heart beat, the “lubb” sound. Phase two The ventricles contract and force blood into the arteries. This is called systole and the systolic blood pressure (BP) is the higher of the two numbers, when the heart is actively contracting and putting pressure on the blood. When the semilunar valves snap shut, this causes the second sound of the heart beat, the “dup.” Phase three The heart relaxes and blood flows into the atria and ventricles. This is called diastole. The diastolic BP is the lower of the two numbers, when the heart is relaxed, and so, is a measure of how much pressure the arteries, themselves, are putting on the blood. Clogged arteries are less elastic, so the blood is under more pressure, thus more likely to cause the arteries to burst. Heartbeats 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. When two or more of such cells are in proximity to each other their contractions synch up and they beat as one. Measuring the change ELECTROCARDIOGRAM Electrocardiogram (ECG) measures changes in electrical potential across the heart, and can detect the contraction pulses that pass over the surface of the heart. ECGs are useful in diagnosing heart abnormalities. There are three slow, negative changes, known as P, R, and T. Positive deflections are the Q and S waves. The P wave represents the contraction impulse of the atria, the T wave the ventricular contraction. Normal cardiac pattern (top) and some abnormal patterns (bottom). average heart rates of some common mammals. Heart Rates Comparison (beats/minute) Organism Human Cat Cow Dog Guinea Pig Hamster Horse Rabbit Rat Average RateNormal Range 70 65 115 280 450 44 205 120 328 58 – 104 110 – 140 60 – 70 100 – 130 260 – 400 300 – 600 23 – 70 123 – 304 261 - 600 The Vascular System Two main routes for circulation: the pulmonary (to and from the lungs) 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. to the heart. 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. A vessel is a hollow tube for transporting something, like a garden hose transporting water. VESSELS Vessels A blood vessel is a hollow tube for transporting blood. There are three main types of blood vessels: Arteries Capillaries Veins These main blood vessels function to transport blood through the entire body and exchange oxygen and nutrients for carbon dioxide and wastes. Arteries The arteries carry blood away from the heart, and are under high pressure from the pumping of the heart. To maintain their structure under this pressure, they have thick, elastic walls to allow stretch and recoil. The large pulmonary artery carries unoxygenated blood from the right ventricles to the lung, where it gives off carbon dioxide and receives oxygen. The aorta is the largest artery. It carries oxygenated blood from the left ventricle to the body. The arteries branch and eventually lead to capillary beds. Structure of an artery The aorta is the main artery leaving the heart. The pulmonary artery is the only artery that carries oxygen-poor blood. carries deoxygenated blood to the lungs. In the lungs, gas exchange occurs, carbon dioxide diffuses out, oxygen diffuses in. Arterioles are small arteries that connect larger arteries with capillaries. Small arterioles branch into collections of capillaries known as capillary beds, 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, is usually the result of gradual buildup of lipids and cholesterol in the inner wall of the coronary artery. 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. Development of arterial plaque. Capillaries capillaries make up a network of tiny vessels with extremely thin, highly permeable walls. They are present in all of the major tissues of the body. Capillaries are the points of exchange between the blood and surrounding tissues. Materials cross in and out of the capillaries by passing through or between the cells that line the capillary In the capillary, the wall is only one cell layer thick. Capillaries are concentrated into capillary beds. Some capillaries have small pores between the cells of the capillary wall, allowing materials to flow in and out of capillaries as well as the passage of white blood cells. Nutrients, wastes, gases, and hormones are exchanged across the thin walls of capillaries. Capillaries are microscopic in size, although blushing is one manifestation of blood flow into capillaries. Control of blood flow into capillary beds is done by nerve-controlled sphincters. Changes in blood pressure also occur in the various vessels of the circulatory system. Capillary structure, and relationships of capillaries to arteries and veins. Capillary beds and their feeder vessels Blood leaving the capillary beds flows into a progressively larger series of venules that in turn join to form veins. Venules are smaller veins that gather blood from capillary beds into veins. Veins At the opposite side of the capillary beds, the capillaries merge to form veins, which return the blood back to the heart. The veins are under much less pressure than the arteries and therefore have much thinner walls. The veins also contain one-way valves in order to prevent the blood from flowing the wrong direction in the absence of pressure. The pulmonary vein returns oxygenated blood from the lungs to the left atria. The vena cava returns blood from the body to the right atria. The blood that is returned to the heart is then recycled through the cardiovascular system. Structure of a vein the actions of muscles to propel blood through the veins. Types of systems There are several types of circulatory systems Circulatory systems of an insect and mollusk. The open circulatory system, examples of which are diagrammed, is common to mollusks and arthropods. Open circulatory systems (evolved in insects, mollusks and other invertebrates) pump blood into a hemocoel with the blood diffusing back to the circulatory system between cells. Blood is pumped by a heart into the body cavities, where tissues are surrounded by the blood. The resulting blood flow is sluggish. insect (top) and mollusk (bottom). closed circulatory system Vertebrates, and a few invertebrates, have a closed circulatory system. Closed circulatory systems (evolved in echinoderms and vertebrates) have the blood closed at all times within vessels of different size and wall thickness. In this type of system, blood is pumped by a heart through vessels, and does not normally fill body cavities. Blood flow is not sluggish. Hemoglobin causes vertebrate blood to turn red in the presence of oxygen; but more importantly hemoglobin molecules in blood cells transport oxygen. The human closed circulatory system is sometimes called the cardiovascular system. A secondary circulatory system, the lymphatic circulation, collects fluid and cells and returns them to the cardiovascular system. Mammals Mammals and Birds Mammalian and avian hearts have four chambers – two atria and two ventricles. This is the most efficient system, as deoxygenated and oxygenated bloods are not mixed. The right atrium receives deoxygenated blood from the body through both the inferior and superior vena cava. The blood then passes to the right ventricle to be pumped through the pulmonary arteries to the lungs, where it becomes oxygenated. It returns to the left atrium via the pulmonary veins, this oxygen-rich blood is then passed to the left ventricle and pumped through the aorta to the rest of the body. The aorta is the largest artery and has an enormous amount of stretch and elasticity to withstand the pressure created by the pumping ventricle. The four-chambered heart ensures that the tissues of the body are supplied with oxygen-saturated blood to facilitate sustained muscle movement. Also, the larger oxygen supply allows these warmblooded organisms to achieve thermoregulation (body temperature maintenance). Mammal and Bird Blood flow through the closed system Amphibians and Reptiles Amphibians and reptiles have a three-chambered heart. Consists of two atria and one ventricle. Blood leaving the ventricle passes into one of two vessels. It travels through the pulmonary arteries leading to the lungs or through a forked aorta leading to the rest of the body. Oxygenated blood returning to the heart from the lungs through the pulmonary vein passes into the left atrium, while deoxygenated blood returning from the body through the sinus venosus passes into the right atrium. Both atria empty into the single ventricle, mixing the oxygen-rich blood returning from the lungs with the oxygen-depleted blood from the body tissues. Amphibians and Reptiles While this system assures that some blood always passes to the lungs and then back to the heart, the mixing of blood in the single ventricle means the organs are not getting blood saturated with oxygen. This is not as efficient as a four-chambered system, which keeps the two circuits separate, but it is sufficient for these cold-blooded organisms. The heart rate of amphibians and reptiles is very dependent upon temperature. Amphibian Blood flow through the system Reptile Blood flow through the system Vitals Temperature Average Rate (Celsius) (beats/minute) 10 C 1–8 18 C 15 – 20 28 C 24 – 40 >40 C Irreversible cardiac damage Fish Heart Fish possess the simplest type of true heart – a two-chambered organ composed of one atrium and one ventricle. A rudimentary valve is located between the two chambers. Blood is pumped from the ventricle through the conus arteriosus to the gills. The conus arteriosus is like the aorta in other species. Fish At the gills, the blood receives oxygen and gets rid of carbon dioxide. Blood then moves on to the organs of the body, where nutrients, gases, and wastes are exchanged. There is no division of the circulation between the gills and the body. That is, the blood travels from the heart to the gills, and then directly to the body before returning to the atrium through the sinus venosus to be circulated again. The heart rates of fish fall within the wide range of 60-240 beats per minute, depending upon species and water temperature. The fish's heart rate will be slower at lower temperatures. What makes up blood? BLOOD PLASMA the liquid component of the blood. Mammalian blood consists of a liquid (plasma) and a number of cellular and cell fragment components. Plasma is about 60 % of a volume of blood; cells and fragments are 40%. Plasma has 90% water and 10% dissolved materials including proteins, glucose, ions, hormones, and gases. It acts as a buffer, maintaining pH near 7.4. Plasma contains nutrients, wastes, salts, proteins, etc. Proteins in the blood aid in transport of large molecules such as cholesterol. RED BLOOD CELLS also known as erythrocytes, are flattened, doubly concave cells about 7 µm in diameter that carry oxygen associated in the cell's hemoglobin. Mature erythrocytes lack a nucleus. They are small, 4 to 6 million cells per cubic millimeter of blood, and have 200 million hemoglobin molecules per cell. Humans have a total of 25 trillion red blood cells (about 1/3 of all the cells in the body). Red blood cells are continuously manufactured in red marrow of long bones, ribs, skull, and vertebrae. Life-span of an erythrocyte is only 120 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. Human Red Blood Cells, Platelets and Tlymphocyte (erythocytes = red; platelets = yellow; T-lymphocyte = light green) WHITE BLOOD CELLS also known as leukocytes, are larger than erythrocytes, have a nucleus, and lack hemoglobin. They function in the cellular immune response. White blood cells (leukocytes) are less than 1% of the blood's volume. 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 The formation and actions of blood clots. Blood Clot Formation (blood cells, platelets, fibrin clot) The Lymphatic System Water and plasma are forced from the capillaries into intracellular spaces. This interstitial fluid transports materials between cells. Most of this fluid is collected in the capillaries of a secondary circulatory system, the lymphatic system. Fluid in this system is known as lymph. Lymph flows from small lymph capillaries into lymph vessels that are similar to veins in having valves that prevent backflow. Lymph vessels connect to lymph nodes, lymph organs, or to the cardiovascular system at the thoracic duct and right lymphatic duct. Lymph nodes are small irregularly shaped masses through which lymph vessels flow. Clusters of nodes occur in the armpits, groin, and neck. Cells of the immune system line channels through the nodes and attack bacteria and viruses traveling in the lymph. MONITORING THE SYSTEM The rate of contraction is the heart rate. The pulse is a wave of contraction of the artery walls (which roughly corresponds to the heart rate) as blood is forced into the arteries. Pulse is usually measured using the radial artery (the one along the radius). Blood pressure is maximum during systole, when the heart is pushing, and minimum during diastole, when the heart is relaxed. A sphygmomanometer is the instrument used to determine BP. The artery used to determine BP is the brachial artery, which runs down the upper arm, splitting into the radial and ulnar arteries near the elbow. The cuff of the sphygmomanomet er is wrapped around the arm just above the elbow and pumped up to block off blood flow (the pressure exerted by the cuff is higher than the systolic pressure). The pressure in the cuff is gradually decreased, and when it equals the person’s systolic pressure, the heart can force blood under the cuff, and a sound is heard as the pulses of blood surge under the cuff. As the pressure in the cuff is lowered, when it equals the diastolic pressure, blood can flow freely, so the sound disappears (not enough pressure is exerted by cuff to restrict blood flow). Thus, by listening for the first sound, and when the sound becomes faint, while watching the pressure indicator on the sphygomomanometer, it is possible to determine someone’s blood pressure. PROBLEMS A hemorrhage is bleeding, especially profuse, and can be severe if internal. A hematoma is a local swelling or tumor filled with blood; a bruise, especially a large one. Sometimes, if the injury is extensive, it can calcify as it heals, leading to a hard lump (which may need to be surgically removed). A thrombus is a blood clot (platelets and fibrin) which forms within a vessel and blocks the blood flow. An embolus is a moving thrombus which may “get stuck” somewhere. If thrombi or emboli lodge in an artery supplying blood to the heart, this can cause a coronary embolism or heart attack or myocardial infarction. If one of these becomes lodged in an artery in the lungs, it is also a life-threatening pulmonary embolism, and if in the brain, a cerebral (or cerebellar) embolism or stroke or cerebrovascular accident Edema is an accumulation of fluid (plasma) within tissues and/or the lymph system. There are many possible causes of edema from injury, to too much salt, to improperly functioning kidneys, to lack of exercise, to female hormonal changes, to a number of other possible causes. Much like a heat pump for your house or your refrigerator coils, your cardiovascular system is also involved in countercurrent heating/cooling of your body. Arteries and veins lying near each other in your extremities, but flowing in opposite directions can absorb heat from each other as needed. When your core temperature is too high, the arteries carry heat to the extremities to be dissipated. As the blood returns via the veins, any excess heat still in the blood is transferred to the arterial blood and sent to the extremities, again. When your core temperature is too low, as the blood flows out in the arteries to nourish the extremities, its heat is transferred to the venous blood and sent back into the body to keep it warm.