An organ system is a biological system consisting of a group of organs that work together to perform one or more functions. Each organ has a specialized role in an organism body, and is made up of distinct tissues .
120-416: The circulatory system is a system of organs that includes the heart , blood vessels , and blood which is circulated throughout the entire body of a human or other vertebrate. It includes the cardiovascular system , or vascular system , that consists of the heart and blood vessels (from Greek kardia meaning heart , and from Latin vascula meaning vessels ). The circulatory system has two divisions,
240-520: A CT pulmonary angiogram may be used. Vascular ultrasonography may be used to investigate vascular diseases affecting the venous system and the arterial system including the diagnosis of stenosis , thrombosis or venous insufficiency . An intravascular ultrasound using a catheter is also an option. There are a number of surgical procedures performed on the circulatory system: Cardiovascular procedures are more likely to be performed in an inpatient setting than in an ambulatory care setting; in
360-402: A developmental axial twist in the early embryo. The heart pumps blood with a rhythm determined by a group of pacemaker cells in the sinoatrial node . These generate an electric current that causes the heart to contract, traveling through the atrioventricular node and along the conduction system of the heart . In humans, deoxygenated blood enters the heart through the right atrium from
480-422: A pulmonary circulation , and a systemic circulation . The pulmonary circulation is a circuit loop from the right heart taking deoxygenated blood to the lungs where it is oxygenated and returned to the left heart . The systemic circulation is a circuit loop that delivers oxygenated blood from the left heart to the rest of the body, and returns deoxygenated blood back to the right heart via large veins known as
600-462: A shoot system , and a root system . The shoot system consists stems, leaves, and the reproductive parts of the plant (flowers and fruits). The shoot system generally grows above ground, where it absorbs the light needed for photosynthesis . The root system, which supports the plants and absorbs water and minerals, is usually underground. Left heart The heart is a muscular organ found in most animals . This organ pumps blood through
720-450: A systemic circulation or circuit , and a pulmonary circulation or circuit . Some sources use the terms cardiovascular system and vascular system interchangeably with circulatory system . The network of blood vessels are the great vessels of the heart including large elastic arteries , and large veins ; other arteries, smaller arterioles , capillaries that join with venules (small veins), and other veins. The circulatory system
840-440: A crucial role in cardiac conduction. It arises from the lower part of the interventricular septum and crosses the interior space of the right ventricle to connect with the inferior papillary muscle. The right ventricle tapers into the pulmonary trunk , into which it ejects blood when contracting. The pulmonary trunk branches into the left and right pulmonary arteries that carry the blood to each lung. The pulmonary valve lies between
960-492: A dual blood supply, an anterior and a posterior circulation from arteries at its front and back. The anterior circulation arises from the internal carotid arteries to supply the front of the brain. The posterior circulation arises from the vertebral arteries , to supply the back of the brain and brainstem . The circulation from the front and the back join ( anastomise ) at the circle of Willis . The neurovascular unit , composed of various cells and vasculature channels within
1080-405: A dye into an artery to visualise an arterial tree, can be used in the heart ( coronary angiography ) or brain. At the same time as the arteries are visualised, blockages or narrowings may be fixed through the insertion of stents , and active bleeds may be managed by the insertion of coils. An MRI may be used to image arteries, called an MRI angiogram . For evaluation of the blood supply to the lungs
1200-456: A figure 8 around the two ventricles and proceeding toward the apex. This complex swirling pattern allows the heart to pump blood more effectively. There are two types of cells in cardiac muscle: muscle cells which have the ability to contract easily, and pacemaker cells of the conducting system. The muscle cells make up the bulk (99%) of cells in the atria and ventricles. These contractile cells are connected by intercalated discs which allow
1320-408: A macrocirculation and a microcirculation . The blood vessels of the circulatory system are the arteries , veins , and capillaries . The large arteries and veins that take blood to, and away from the heart are known as the great vessels . Oxygenated blood enters the systemic circulation when leaving the left ventricle, via the aortic semilunar valve . The first part of the systemic circulation
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#17328559223351440-438: A main left and a main right trunk, which travel up the groove between the ventricles that exists on the heart's surface, receiving smaller vessels as they travel up. These vessels then travel into the atrioventricular groove, and receive a third vessel which drains the section of the left ventricle sitting on the diaphragm. The left vessel joins with this third vessel, and travels along the pulmonary artery and left atrium, ending in
1560-400: A mass of 250–350 grams (9–12 oz). The heart is often described as the size of a fist: 12 cm (5 in) in length, 8 cm (3.5 in) wide, and 6 cm (2.5 in) in thickness, although this description is disputed, as the heart is likely to be slightly larger. Well-trained athletes can have much larger hearts due to the effects of exercise on the heart muscle, similar to
1680-411: A muscular pharynx leads to an extensively branched digestive system that facilitates direct diffusion of nutrients to all cells. The flatworm's dorso-ventrally flattened body shape also restricts the distance of any cell from the digestive system or the exterior of the organism. Oxygen can diffuse from the surrounding water into the cells, and carbon dioxide can diffuse out. Consequently, every cell
1800-434: A number of cardiovascular diseases , affecting the heart and blood vessels; hematologic diseases that affect the blood, such as anemia , and lymphatic diseases affecting the lymphatic system. Cardiologists are medical professionals which specialise in the heart, and cardiothoracic surgeons specialise in operating on the heart and its surrounding areas. Vascular surgeons focus on the blood vessels. Diseases affecting
1920-467: A peak rate of 165–185 bpm early in the early 7th week (early 9th week after the LMP). After 9 weeks (start of the fetal stage) it starts to decelerate, slowing to around 145 (±25) bpm at birth. There is no difference in female and male heart rates before birth. The heart functions as a pump in the circulatory system to provide a continuous flow of blood throughout the body. This circulation consists of
2040-425: A posterior cusp. These cusps are also attached via chordae tendinae to two papillary muscles projecting from the ventricular wall. The papillary muscles extend from the walls of the heart to valves by cartilaginous connections called chordae tendinae. These muscles prevent the valves from falling too far back when they close. During the relaxation phase of the cardiac cycle, the papillary muscles are also relaxed and
2160-402: A primitive heart tube known as the tubular heart . Between the third and fourth week, the heart tube lengthens, and begins to fold to form an S-shape within the pericardium. This places the chambers and major vessels into the correct alignment for the developed heart. Further development will include the formation of the septa and the valves and the remodeling of the heart chambers. By the end of
2280-460: A rapid response to impulses of action potential from the pacemaker cells. The intercalated discs allow the cells to act as a syncytium and enable the contractions that pump blood through the heart and into the major arteries . The pacemaker cells make up 1% of cells and form the conduction system of the heart. They are generally much smaller than the contractile cells and have few myofibrils which gives them limited contractibility. Their function
2400-438: A single pump (consisting of two chambers). In amphibians and most reptiles, a double circulatory system is used, but the heart is not always completely separated into two pumps. Amphibians have a three-chambered heart. In reptiles, the ventricular septum of the heart is incomplete and the pulmonary artery is equipped with a sphincter muscle . This allows a second possible route of blood flow. Instead of blood flowing through
2520-480: A valve closes the foramen ovale and establishes the typical cardiac circulation pattern. A depression in the surface of the right atrium remains where the foramen ovale was, called the fossa ovalis. The embryonic heart begins beating at around 22 days after conception (5 weeks after the last normal menstrual period, LMP). It starts to beat at a rate near to the mother's which is about 75–80 beats per minute (bpm). The embryonic heart rate then accelerates and reaches
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#17328559223352640-436: Is hemocyanin . There are free-floating cells, the hemocytes , within the hemolymph. They play a role in the arthropod immune system . The circulatory systems of all vertebrates, as well as of annelids (for example, earthworms ) and cephalopods ( squids , octopuses and relatives) always keep their circulating blood enclosed within heart chambers or blood vessels and are classified as closed , just as in humans. Still,
2760-548: Is able to obtain nutrients, water and oxygen without the need of a transport system. Organ system Main article: List of systems of the human body There are 11 distinct organ systems in human beings, which form the basis of human anatomy and physiology . The 11 organ systems: the respiratory system, digestive and excretory system, circulatory system, urinary system, integumentary system, skeletal system, muscular system, endocrine system, lymphatic system, nervous system, and reproductive system. There are other systems in
2880-424: Is closed in vertebrates, which means that the blood never leaves the network of blood vessels. Some invertebrates such as arthropods have an open circulatory system . Diploblasts such as sponges , and comb jellies lack a circulatory system. Blood is a fluid consisting of plasma , red blood cells , white blood cells , and platelets ; it is circulated around the body carrying oxygen and nutrients to
3000-400: Is connected to the left ventricle by the mitral valve. The left ventricle is much thicker as compared with the right, due to the greater force needed to pump blood to the entire body. Like the right ventricle, the left also has trabeculae carneae , but there is no moderator band . The left ventricle pumps blood to the body through the aortic valve and into the aorta. Two small openings above
3120-404: Is created that travels through the heart, causing the heart muscle to contract. The sinoatrial node is found in the upper part of the right atrium near to the junction with the superior vena cava. The electrical signal generated by the sinoatrial node travels through the right atrium in a radial way that is not completely understood. It travels to the left atrium via Bachmann's bundle , such that
3240-409: Is deoxygenated (poor in oxygen) and passed into the right ventricle to be pumped through the pulmonary artery to the lungs for re-oxygenation and removal of carbon dioxide. The left atrium receives newly oxygenated blood from the lungs as well as the pulmonary vein which is passed into the strong left ventricle to be pumped through the aorta to the different organs of the body. The pulmonary circulation
3360-432: Is limited. When the heart relaxes, blood is drawn back toward the heart through open-ended pores (ostia). Hemolymph fills all of the interior hemocoel of the body and surrounds all cells . Hemolymph is composed of water , inorganic salts (mostly sodium , chloride , potassium , magnesium , and calcium ), and organic compounds (mostly carbohydrates, proteins , and lipids ). The primary oxygen transporter molecule
3480-428: Is located at the level of the third costal cartilage. The lower tip of the heart, the apex , lies to the left of the sternum (8 to 9 cm from the midsternal line ) between the junction of the fourth and fifth ribs near their articulation with the costal cartilages. The largest part of the heart is usually slightly offset to the left side of the chest ( levocardia ). In a rare congenital disorder ( dextrocardia )
3600-480: Is normalized to body size through body surface area and is called the cardiac index . The average cardiac output, using an average stroke volume of about 70mL, is 5.25 L/min, with a normal range of 4.0–8.0 L/min. The stroke volume is normally measured using an echocardiogram and can be influenced by the size of the heart, physical and mental condition of the individual, sex , contractility , duration of contraction, preload and afterload . Preload refers to
3720-451: Is often done by the taking of a medical history , listening to the heart-sounds with a stethoscope , as well as with ECG , and echocardiogram which uses ultrasound . Specialists who focus on diseases of the heart are called cardiologists , although many specialties of medicine may be involved in treatment. The human heart is situated in the mediastinum , at the level of thoracic vertebrae T5 - T8 . A double-membraned sac called
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3840-612: Is similar in many respects to neurons . Cardiac muscle tissue has autorhythmicity , the unique ability to initiate a cardiac action potential at a fixed rate—spreading the impulse rapidly from cell to cell to trigger the contraction of the entire heart. There are specific proteins expressed in cardiac muscle cells. These are mostly associated with muscle contraction, and bind with actin , myosin , tropomyosin , and troponin . They include MYH6 , ACTC1 , TNNI3 , CDH2 and PKP2 . Other proteins expressed are MYH7 and LDB3 that are also expressed in skeletal muscle. The pericardium
3960-409: Is the aorta, a massive and thick-walled artery. The aorta arches and gives branches supplying the upper part of the body after passing through the aortic opening of the diaphragm at the level of thoracic ten vertebra, it enters the abdomen. Later, it descends down and supplies branches to abdomen, pelvis, perineum and the lower limbs. The walls of the aorta are elastic. This elasticity helps to maintain
4080-424: Is the part of the circulatory system in which oxygen-depleted blood is pumped away from the heart, via the pulmonary artery , to the lungs and returned, oxygenated, to the heart via the pulmonary vein . Oxygen-deprived blood from the superior and inferior vena cava enters the right atrium of the heart and flows through the tricuspid valve (right atrioventricular valve) into the right ventricle, from which it
4200-404: Is the sac that surrounds the heart. The tough outer surface of the pericardium is called the fibrous membrane. This is lined by a double inner membrane called the serous membrane that produces pericardial fluid to lubricate the surface of the heart. The part of the serous membrane attached to the fibrous membrane is called the parietal pericardium, while the part of the serous membrane attached to
4320-409: Is then pumped through the pulmonary semilunar valve into the pulmonary artery to the lungs. Gas exchange occurs in the lungs, whereby CO 2 is released from the blood, and oxygen is absorbed. The pulmonary vein returns the now oxygen-rich blood to the left atrium . A separate circuit from the systemic circulation, the bronchial circulation supplies blood to the tissue of the larger airways of
4440-498: The Frank-Starling mechanism . This states that the force of contraction is directly proportional to the initial length of muscle fiber, meaning a ventricle will contract more forcefully, the more it is stretched. Afterload , or how much pressure the heart must generate to eject blood at systole, is influenced by vascular resistance . It can be influenced by narrowing of the heart valves ( stenosis ) or contraction or relaxation of
4560-402: The beta–1 receptor . The heart is the first functional organ to develop and starts to beat and pump blood at about three weeks into embryogenesis . This early start is crucial for subsequent embryonic and prenatal development . The heart derives from splanchnopleuric mesenchyme in the neural plate which forms the cardiogenic region . Two endocardial tubes form here that fuse to form
4680-424: The blood pressure throughout the body. When the aorta receives almost five litres of blood from the heart, it recoils and is responsible for pulsating blood pressure. As the aorta branches into smaller arteries, their elasticity goes on decreasing and their compliance goes on increasing. Arteries branch into small passages called arterioles and then into the capillaries . The capillaries merge to bring blood into
4800-436: The blood vessels . Heart and blood vessels together make the circulatory system . The pumped blood carries oxygen and nutrients to the tissue, while carrying metabolic waste such as carbon dioxide to the lungs . In humans , the heart is approximately the size of a closed fist and is located between the lungs, in the middle compartment of the chest , called the mediastinum . In humans, other mammals, and birds,
4920-484: The coronary sinus , which is immediately above and to the middle of the opening of the inferior vena cava. In the wall of the right atrium is an oval-shaped depression known as the fossa ovalis , which is a remnant of an opening in the fetal heart known as the foramen ovale . Most of the internal surface of the right atrium is smooth, the depression of the fossa ovalis is medial, and the anterior surface has prominent ridges of pectinate muscles , which are also present in
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5040-472: The dorsal side of the embryo, are initially present on both sides of the embryo. They later fuse to form the basis for the aorta itself. Approximately thirty smaller arteries branch from this at the back and sides. These branches form the intercostal arteries , arteries of the arms and legs, lumbar arteries and the lateral sacral arteries. Branches to the sides of the aorta will form the definitive renal , suprarenal and gonadal arteries . Finally, branches at
5160-417: The embryo . The human arterial and venous systems develop from different areas in the embryo. The arterial system develops mainly from the aortic arches , six pairs of arches that develop on the upper part of the embryo. The venous system arises from three bilateral veins during weeks 4 – 8 of embryogenesis . Fetal circulation begins within the 8th week of development. Fetal circulation does not include
5280-405: The inferior tracheobronchial node . The right vessel travels along the right atrium and the part of the right ventricle sitting on the diaphragm. It usually then travels in front of the ascending aorta and then ends in a brachiocephalic node. The heart receives nerve signals from the vagus nerve and from nerves arising from the sympathetic trunk . These nerves act to influence, but not control,
5400-431: The lymphatic system is complementary to the circulatory system. The lymphatic system carries excess plasma ( filtered from the circulatory system capillaries as interstitial fluid between cells) away from the body tissues via accessory routes that return excess fluid back to blood circulation as lymph . The lymphatic system is a subsystem that is essential for the functioning of the blood circulatory system; without it
5520-402: The pericardium surrounds the heart and attaches to the mediastinum. The back surface of the heart lies near the vertebral column , and the front surface known as the sternocostal surface sits behind the sternum and rib cartilages . The upper part of the heart is the attachment point for several large blood vessels—the venae cavae , aorta and pulmonary trunk . The upper part of the heart
5640-418: The posterior cardiac vein (draining the back of the left ventricle), the middle cardiac vein (draining the bottom of the left and right ventricles), and small cardiac veins . The anterior cardiac veins drain the front of the right ventricle and drain directly into the right atrium. Small lymphatic networks called plexuses exist beneath each of the three layers of the heart. These networks collect into
5760-430: The pulmonary artery . This has three cusps which are not attached to any papillary muscles. When the ventricle relaxes blood flows back into the ventricle from the artery and this flow of blood fills the pocket-like valve, pressing against the cusps which close to seal the valve. The semilunar aortic valve is at the base of the aorta and also is not attached to papillary muscles. This too has three cusps which close with
5880-404: The right atrial appendage , or auricle, and another in the upper left atrium, the left atrial appendage . The right atrium and the right ventricle together are sometimes referred to as the right heart . Similarly, the left atrium and the left ventricle together are sometimes referred to as the left heart . The ventricles are separated from each other by the interventricular septum , visible on
6000-411: The right atrial appendage . The right atrium is connected to the right ventricle by the tricuspid valve. The walls of the right ventricle are lined with trabeculae carneae , ridges of cardiac muscle covered by endocardium. In addition to these muscular ridges, a band of cardiac muscle, also covered by endocardium, known as the moderator band reinforces the thin walls of the right ventricle and plays
6120-463: The sinoatrial node , a group of pacemaking cells found in the wall of the right atrium. Cells in the sinoatrial node do this by creating an action potential . The cardiac action potential is created by the movement of specific electrolytes into and out of the pacemaker cells. The action potential then spreads to nearby cells. When the sinoatrial cells are resting, they have a negative charge on their membranes. A rapid influx of sodium ions causes
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#17328559223356240-423: The sinus venosus . About 98.5% of the oxygen in a sample of arterial blood in a healthy human, breathing air at sea-level pressure, is chemically combined with hemoglobin molecules. About 1.5% is physically dissolved in the other blood liquids and not connected to hemoglobin. The hemoglobin molecule is the primary transporter of oxygen in vertebrates. Many diseases affect the circulatory system. These include
6360-405: The superior and inferior venae cavae . Blood collects in the right and left atrium continuously. The superior vena cava drains blood from above the diaphragm and empties into the upper back part of the right atrium. The inferior vena cava drains the blood from below the diaphragm and empties into the back part of the atrium below the opening for the superior vena cava. Immediately above and to
6480-565: The superior and inferior venae cavae and passes to the right ventricle. From here, it is pumped into pulmonary circulation to the lungs , where it receives oxygen and gives off carbon dioxide. Oxygenated blood then returns to the left atrium, passes through the left ventricle and is pumped out through the aorta into systemic circulation , traveling through arteries , arterioles , and capillaries —where nutrients and other substances are exchanged between blood vessels and cells, losing oxygen and gaining carbon dioxide—before being returned to
6600-458: The systemic circulation to and from the body and the pulmonary circulation to and from the lungs. Blood in the pulmonary circulation exchanges carbon dioxide for oxygen in the lungs through the process of respiration . The systemic circulation then transports oxygen to the body and returns carbon dioxide and relatively deoxygenated blood to the heart for transfer to the lungs. The right heart collects deoxygenated blood from two large veins,
6720-428: The venae cavae . The systemic circulation can also be defined as two parts – a macrocirculation and a microcirculation . An average adult contains five to six quarts (roughly 4.7 to 5.7 liters) of blood, accounting for approximately 7% of their total body weight. Blood consists of plasma , red blood cells , white blood cells , and platelets . The digestive system also works with the circulatory system to provide
6840-546: The United States, only 28% of cardiovascular surgeries were performed in the ambulatory care setting. While humans, as well as other vertebrates , have a closed blood circulatory system (meaning that the blood never leaves the network of arteries, veins and capillaries), some invertebrate groups have an open circulatory system containing a heart but limited blood vessels. The most primitive, diploblastic animal phyla lack circulatory systems. An additional transport system,
6960-400: The anatomy of the arteries that supply the heart The arteries divide at their furthest reaches into smaller branches that join at the edges of each arterial distribution. The coronary sinus is a large vein that drains into the right atrium, and receives most of the venous drainage of the heart. It receives blood from the great cardiac vein (receiving the left atrium and both ventricles),
7080-477: The aorta by two coronary arteries : the right coronary artery and the left coronary artery . After nourishing the heart muscle, blood returns through the coronary veins into the coronary sinus and from this one into the right atrium. Backflow of blood through its opening during atrial systole is prevented by the Thebesian valve . The smallest cardiac veins drain directly into the heart chambers. The brain has
7200-400: The aorta into two vessels, the left anterior descending and the left circumflex artery . The left anterior descending artery supplies heart tissue and the front, outer side, and septum of the left ventricle. It does this by branching into smaller arteries—diagonal and septal branches. The left circumflex supplies the back and underneath of the left ventricle. The right coronary artery supplies
7320-402: The aortic and pulmonary valves close. The ventricles start to relax, the mitral and tricuspid valves open, and the cycle begins again. Cardiac output (CO) is a measurement of the amount of blood pumped by each ventricle (stroke volume) in one minute. This is calculated by multiplying the stroke volume (SV) by the beats per minute of the heart rate (HR). So that: CO = SV x HR. The cardiac output
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#17328559223357440-409: The aortic and pulmonary valves open. Blood is ejected from the heart, causing the pressure within the ventricles to fall. Simultaneously, the atria refill as blood flows into the right atrium through the superior and inferior vena cavae , and into the left atrium through the pulmonary veins. Finally, when the pressure within the ventricles falls below the pressure within the aorta and pulmonary arteries,
7560-403: The aortic valve carry blood to the heart muscle ; the left coronary artery is above the left cusp of the valve, and the right coronary artery is above the right cusp. The heart wall is made up of three layers: the inner endocardium , middle myocardium and outer epicardium . These are surrounded by a double-membraned sac called the pericardium. The innermost layer of the heart is called
7680-478: The arteries. It is also a risk factor for acute coronary syndromes , which are diseases that are characterised by a sudden deficit of oxygenated blood to the heart tissue. Atherosclerosis is also associated with problems such as aneurysm formation or splitting ("dissection") of arteries. Another major cardiovascular disease involves the creation of a clot, called a "thrombus" . These can originate in veins or arteries. Deep venous thrombosis , which mostly occurs in
7800-434: The atria, and the interventricular septum separates the ventricles. The interventricular septum is much thicker than the interatrial septum since the ventricles need to generate greater pressure when they contract. The heart has four valves, which separate its chambers. One valve lies between each atrium and ventricle, and one valve rests at the exit of each ventricle. The valves between the atria and ventricles are called
7920-450: The atrioventricular node only. The signal then travels along the bundle of His to left and right bundle branches through to the ventricles of the heart. In the ventricles the signal is carried by specialized tissue called the Purkinje fibers which then transmit the electric charge to the heart muscle. The normal resting heart rate is called the sinus rhythm , created and sustained by
8040-443: The atrioventricular valves. Between the right atrium and the right ventricle is the tricuspid valve . The tricuspid valve has three cusps, which connect to chordae tendinae and three papillary muscles named the anterior, posterior, and septal muscles, after their relative positions. The mitral valve lies between the left atrium and left ventricle. It is also known as the bicuspid valve due to its having two cusps, an anterior and
8160-415: The blood is pumped into the pulmonary trunk through the pulmonary valve. The pulmonary trunk divides into pulmonary arteries and progressively smaller arteries throughout the lungs, until it reaches capillaries . As these pass by alveoli carbon dioxide is exchanged for oxygen. This happens through the passive process of diffusion . In the left heart , oxygenated blood is returned to the left atrium via
8280-452: The blood would become depleted of fluid. The lymphatic system also works with the immune system. The circulation of lymph takes much longer than that of blood and, unlike the closed (blood) circulatory system, the lymphatic system is an open system. Some sources describe it as a secondary circulatory system . The circulatory system can be affected by many cardiovascular diseases . Cardiologists are medical professionals which specialise in
8400-638: The body that are not organ systems—for example, the immune system protects the organism from infection, but it is not an organ system since it is not composed of organs. Some organs are in more than one system—for example, the nose is in the respiratory system and also serves as a sensory organ in the nervous system; the testes and ovaries are both part of the reproductive and endocrine systems. Other animals have similar organ systems to humans although simpler animals may have fewer organs in an organ system or even fewer organ systems. Plants have two major organs systems. Vascular plants have two distinct organ systems:
8520-429: The brain, regulates the flow of blood to activated neurons in order to satisfy their high energy demands. The renal circulation is the blood supply to the kidneys , contains many specialized blood vessels and receives around 20% of the cardiac output. It branches from the abdominal aorta and returns blood to the ascending inferior vena cava . The development of the circulatory system starts with vasculogenesis in
8640-471: The cardiovascular system are called cardiovascular disease . Many of these diseases are called " lifestyle diseases " because they develop over time and are related to a person's exercise habits, diet, whether they smoke, and other lifestyle choices a person makes. Atherosclerosis is the precursor to many of these diseases. It is where small atheromatous plaques build up in the walls of medium and large arteries. This may eventually grow or rupture to occlude
8760-424: The circulatory changes that are supposed to happen after birth do not. Not all congenital changes to the circulatory system are associated with diseases, a large number are anatomical variations . The function and health of the circulatory system and its parts are measured in a variety of manual and automated ways. These include simple methods such as those that are part of the cardiovascular examination , including
8880-424: The circulatory system. Another major function is working together with the immune system to provide defense against pathogens . The heart pumps blood to all parts of the body providing nutrients and oxygen to every cell , and removing waste products. The left heart pumps oxygenated blood returned from the lungs to the rest of the body in the systemic circulation . The right heart pumps deoxygenated blood to
9000-436: The coronary circulation, which includes arteries , veins , and lymphatic vessels . Blood flow through the coronary vessels occurs in peaks and troughs relating to the heart muscle's relaxation or contraction. Heart tissue receives blood from two arteries which arise just above the aortic valve. These are the left main coronary artery and the right coronary artery . The left main coronary artery splits shortly after leaving
9120-403: The endocardium. It is made up of a lining of simple squamous epithelium and covers heart chambers and valves. It is continuous with the endothelium of the veins and arteries of the heart, and is joined to the myocardium with a thin layer of connective tissue. The endocardium, by secreting endothelins , may also play a role in regulating the contraction of the myocardium. The middle layer of
9240-438: The fifth week, the septa are complete, and by the ninth week, the heart valves are complete. Before the fifth week, there is an opening in the fetal heart known as the foramen ovale . The foramen ovale allowed blood in the fetal heart to pass directly from the right atrium to the left atrium, allowing some blood to bypass the lungs. Within seconds after birth, a flap of tissue known as the septum primum that previously acted as
9360-417: The filling pressure of the atria at the end of diastole, when the ventricles are at their fullest. A main factor is how long it takes the ventricles to fill: if the ventricles contract more frequently, then there is less time to fill and the preload will be less. Preload can also be affected by a person's blood volume. The force of each contraction of the heart muscle is proportional to the preload, described as
9480-478: The force of contraction are "positive" inotropes, and include sympathetic agents such as adrenaline , noradrenaline and dopamine . "Negative" inotropes decrease the force of contraction and include calcium channel blockers . The normal rhythmical heart beat, called sinus rhythm , is established by the heart's own pacemaker, the sinoatrial node (also known as the sinus node or the SA node). Here an electrical signal
9600-422: The front of the aorta consist of the vitelline arteries and umbilical arteries . The vitelline arteries form the celiac , superior and inferior mesenteric arteries of the gastrointestinal tract. After birth, the umbilical arteries will form the internal iliac arteries . The human venous system develops mainly from the vitelline veins , the umbilical veins and the cardinal veins , all of which empty into
9720-593: The heart called the cardiac plexus . The vagus nerve is a long, wandering nerve that emerges from the brainstem and provides parasympathetic stimulation to a large number of organs in the thorax and abdomen, including the heart. The nerves from the sympathetic trunk emerge through the T1–T4 thoracic ganglia and travel to both the sinoatrial and atrioventricular nodes, as well as to the atria and ventricles. The ventricles are more richly innervated by sympathetic fibers than parasympathetic fibers. Sympathetic stimulation causes
9840-405: The heart due to heart valves , which prevent backflow . The heart is enclosed in a protective sac, the pericardium , which also contains a small amount of fluid . The wall of the heart is made up of three layers: epicardium , myocardium , and endocardium . In all vertebrates , the heart has an asymmetric orientation, almost always on the left side. According to one theory, this is caused by
9960-445: The heart into two pumps, for a total of four heart chambers; it is thought that the four-chambered heart of birds and crocodilians evolved independently from that of mammals. Double circulatory systems permit blood to be repressurized after returning from the lungs, speeding up delivery of oxygen to tissues. Circulatory systems are absent in some animals, including flatworms . Their body cavity has no lining or enclosed fluid. Instead,
10080-399: The heart is divided into four chambers: upper left and right atria and lower left and right ventricles . Commonly, the right atrium and ventricle are referred together as the right heart and their left counterparts as the left heart . Fish, in contrast, have two chambers, an atrium and a ventricle, while most reptiles have three chambers. In a healthy heart, blood flows one way through
10200-406: The heart is known as the visceral pericardium. The pericardium is present in order to lubricate its movement against other structures within the chest, to keep the heart's position stabilised within the chest, and to protect the heart from infection. Heart tissue, like all cells in the body, needs to be supplied with oxygen , nutrients and a way of removing metabolic wastes . This is achieved by
10320-414: The heart is offset to the right side and is felt to be on the left because the left heart is stronger and larger, since it pumps to all body parts. Because the heart is between the lungs , the left lung is smaller than the right lung and has a cardiac notch in its border to accommodate the heart. The heart is cone-shaped, with its base positioned upwards and tapering down to the apex. An adult heart has
10440-413: The heart rate. Sympathetic nerves also influence the force of heart contraction. Signals that travel along these nerves arise from two paired cardiovascular centres in the medulla oblongata . The vagus nerve of the parasympathetic nervous system acts to decrease the heart rate, and nerves from the sympathetic trunk act to increase the heart rate. These nerves form a network of nerves that lies over
10560-729: The heart through venules and veins . The heart beats at a resting rate close to 72 beats per minute. Exercise temporarily increases the rate, but lowers it in the long term, and is good for heart health. Cardiovascular diseases are the most common cause of death globally as of 2008, accounting for 30% of all human deaths. Of these more than three-quarters are a result of coronary artery disease and stroke . Risk factors include: smoking , being overweight , little exercise, high cholesterol , high blood pressure , and poorly controlled diabetes , among others. Cardiovascular diseases do not frequently have symptoms but may cause chest pain or shortness of breath . Diagnosis of heart disease
10680-414: The heart wall is the myocardium, which is the cardiac muscle —a layer of involuntary striated muscle tissue surrounded by a framework of collagen . The cardiac muscle pattern is elegant and complex, as the muscle cells swirl and spiral around the chambers of the heart, with the outer muscles forming a figure 8 pattern around the atria and around the bases of the great vessels and the inner muscles, forming
10800-425: The heart, and cardiothoracic surgeons specialise in operating on the heart and its surrounding areas. Vascular surgeons focus on disorders of the blood vessels, and lymphatic vessels. The circulatory system includes the heart , blood vessels , and blood . The cardiovascular system in all vertebrates, consists of the heart and blood vessels. The circulatory system is further divided into two major circuits –
10920-410: The heart, the hepatic portal vein branches into a second capillary system in the liver . The heart itself is supplied with oxygen and nutrients through a small "loop" of the systemic circulation and derives very little from the blood contained within the four chambers. The coronary circulation system provides a blood supply to the heart muscle itself. The coronary circulation begins near the origin of
11040-419: The legs, is one cause of clots in the veins of the legs, particularly when a person has been stationary for a long time. These clots may embolise , meaning travel to another location in the body. The results of this may include pulmonary embolus , transient ischaemic attacks , or stroke . Cardiovascular diseases may also be congenital in nature, such as heart defects or persistent fetal circulation , where
11160-456: The lung. The systemic circulation is a circuit loop that delivers oxygenated blood from the left heart to the rest of the body through the aorta . Deoxygenated blood is returned in the systemic circulation to the right heart via two large veins, the inferior vena cava and superior vena cava , where it is pumped from the right atrium into the pulmonary circulation for oxygenation. The systemic circulation can also be defined as having two parts –
11280-399: The lungs in the pulmonary circulation . In the human heart there is one atrium and one ventricle for each circulation, and with both a systemic and a pulmonary circulation there are four chambers in total: left atrium , left ventricle , right atrium and right ventricle . The right atrium is the upper chamber of the right side of the heart. The blood that is returned to the right atrium
11400-572: The lungs, which are bypassed via the truncus arteriosus . Before birth the fetus obtains oxygen (and nutrients ) from the mother through the placenta and the umbilical cord . The human arterial system originates from the aortic arches and from the dorsal aortae starting from week 4 of embryonic life. The first and second aortic arches regress and form only the maxillary arteries and stapedial arteries respectively. The arterial system itself arises from aortic arches 3, 4 and 6 (aortic arch 5 completely regresses). The dorsal aortae, present on
11520-470: The lymphatic system, which is only found in animals with a closed blood circulation, is an open system providing an accessory route for excess interstitial fluid to be returned to the blood. The blood vascular system first appeared probably in an ancestor of the triploblasts over 600 million years ago, overcoming the time-distance constraints of diffusion, while endothelium evolved in an ancestral vertebrate some 540–510 million years ago. In arthropods ,
11640-413: The membrane's charge to become positive; this is called depolarisation and occurs spontaneously. Once the cell has a sufficiently high charge, the sodium channels close and calcium ions then begin to enter the cell, shortly after which potassium begins to leave it. All the ions travel through ion channels in the membrane of the sinoatrial cells. The potassium and calcium start to move out of and into
11760-399: The microcirculation to reach organs. The lymphatic system is an essential subsystem of the circulatory system consisting of a network of lymphatic vessels , lymph nodes , organs , tissues and circulating lymph . This subsystem is an open system . A major function is to carry the lymph, draining and returning interstitial fluid into the lymphatic ducts back to the heart for return to
11880-419: The middle of the opening of the inferior vena cava is the opening of the thin-walled coronary sinus. Additionally, the coronary sinus returns deoxygenated blood from the myocardium to the right atrium. The blood collects in the right atrium. When the right atrium contracts, the blood is pumped through the tricuspid valve into the right ventricle. As the right ventricle contracts, the tricuspid valve closes and
12000-419: The muscles of the left and right atria contract together. The signal then travels to the atrioventricular node . This is found at the bottom of the right atrium in the atrioventricular septum , the boundary between the right atrium and the left ventricle. The septum is part of the cardiac skeleton , tissue within the heart that the electrical signal cannot pass through, which forces the signal to pass through
12120-456: The nutrients the system needs to keep the heart pumping. Further circulatory routes are associated, such as the coronary circulation to the heart itself, the cerebral circulation to the brain , renal circulation to the kidneys , and bronchial circulation to the bronchi in the lungs. The human circulatory system is closed , meaning that the blood is contained within the vascular network . Nutrients travel through tiny blood vessels of
12240-405: The open circulatory system is a system in which a fluid in a cavity called the hemocoel bathes the organs directly with oxygen and nutrients, with there being no distinction between blood and interstitial fluid; this combined fluid is called hemolymph or haemolymph. Muscular movements by the animal during locomotion can facilitate hemolymph movement, but diverting flow from one area to another
12360-400: The peripheral blood vessels. The strength of heart muscle contractions controls the stroke volume. This can be influenced positively or negatively by agents termed inotropes . These agents can be a result of changes within the body, or be given as drugs as part of treatment for a medical disorder, or as a form of life support , particularly in intensive care units . Inotropes that increase
12480-414: The pressure of the blood flowing back from the aorta. The right heart consists of two chambers, the right atrium and the right ventricle, separated by a valve, the tricuspid valve . The right atrium receives blood almost continuously from the body's two major veins , the superior and inferior venae cavae . A small amount of blood from the coronary circulation also drains into the right atrium via
12600-473: The pulmonary artery to the lungs, the sphincter may be contracted to divert this blood flow through the incomplete ventricular septum into the left ventricle and out through the aorta . This means the blood flows from the capillaries to the heart and back to the capillaries instead of to the lungs. This process is useful to ectothermic (cold-blooded) animals in the regulation of their body temperature. Mammals, birds and crocodilians show complete separation of
12720-515: The pulmonary veins. It is then pumped into the left ventricle through the mitral valve and into the aorta through the aortic valve for systemic circulation. The aorta is a large artery that branches into many smaller arteries, arterioles , and ultimately capillaries. In the capillaries, oxygen and nutrients from blood are supplied to body cells for metabolism, and exchanged for carbon dioxide and waste products. Capillary blood, now deoxygenated, travels into venules and veins that ultimately collect in
12840-422: The release of the neurotransmitter norepinephrine (also known as noradrenaline ) at the neuromuscular junction of the cardiac nerves . This shortens the repolarisation period, thus speeding the rate of depolarisation and contraction, which results in an increased heart rate. It opens chemical or ligand-gated sodium and calcium ion channels, allowing an influx of positively charged ions . Norepinephrine binds to
12960-427: The response of skeletal muscle. The heart has four chambers, two upper atria , the receiving chambers, and two lower ventricles , the discharging chambers. The atria open into the ventricles via the atrioventricular valves , present in the atrioventricular septum . This distinction is visible also on the surface of the heart as the coronary sulcus . There is an ear-shaped structure in the upper right atrium called
13080-442: The right atrium of the heart. The general rule is that arteries from the heart branch out into capillaries, which collect into veins leading back to the heart. Portal veins are a slight exception to this. In humans, the only significant example is the hepatic portal vein which combines from capillaries around the gastrointestinal tract where the blood absorbs the various products of digestion; rather than leading directly back to
13200-424: The right atrium, right ventricle, and lower posterior sections of the left ventricle. The right coronary artery also supplies blood to the atrioventricular node (in about 90% of people) and the sinoatrial node (in about 60% of people). The right coronary artery runs in a groove at the back of the heart and the left anterior descending artery runs in a groove at the front. There is significant variation between people in
13320-414: The right heart and the pulmonary trunk. The left heart has two chambers: the left atrium and the left ventricle, separated by the mitral valve . The left atrium receives oxygenated blood back from the lungs via one of the four pulmonary veins . The left atrium has an outpouching called the left atrial appendage . Like the right atrium, the left atrium is lined by pectinate muscles . The left atrium
13440-471: The superior and inferior vena cavae, and into the right heart. The cardiac cycle is the sequence of events in which the heart contracts and relaxes with every heartbeat. The period of time during which the ventricles contract, forcing blood out into the aorta and main pulmonary artery, is known as systole , while the period during which the ventricles relax and refill with blood is known as diastole . The atria and ventricles work in concert, so in systole when
13560-511: The surface of the heart as the anterior longitudinal sulcus and the posterior interventricular sulcus . The fibrous cardiac skeleton gives structure to the heart. It forms the atrioventricular septum, which separates the atria from the ventricles, and the fibrous rings, which serve as bases for the four heart valves . The cardiac skeleton also provides an important boundary in the heart's electrical conduction system since collagen cannot conduct electricity . The interatrial septum separates
13680-441: The systems of fish , amphibians , reptiles , and birds show various stages of the evolution of the circulatory system. Closed systems permit blood to be directed to the organs that require it. In fish, the system has only one circuit, with the blood being pumped through the capillaries of the gills and on to the capillaries of the body tissues. This is known as single cycle circulation. The heart of fish is, therefore, only
13800-577: The taking of a person's pulse as an indicator of a person's heart rate , the taking of blood pressure through a sphygmomanometer or the use of a stethoscope to listen to the heart for murmurs which may indicate problems with the heart's valves . An electrocardiogram can also be used to evaluate the way in which electricity is conducted through the heart. Other more invasive means can also be used. A cannula or catheter inserted into an artery may be used to measure pulse pressure or pulmonary wedge pressures . Angiography, which involves injecting
13920-408: The tension on the chordae tendineae is slight. As the heart chambers contract, so do the papillary muscles. This creates tension on the chordae tendineae, helping to hold the cusps of the atrioventricular valves in place and preventing them from being blown back into the atria. Two additional semilunar valves sit at the exit of each of the ventricles. The pulmonary valve is located at the base of
14040-404: The tissues and collecting and disposing of waste materials . Circulated nutrients include proteins and minerals and other components include hemoglobin , hormones , and gases such as oxygen and carbon dioxide . These substances provide nourishment, help the immune system to fight diseases , and help maintain homeostasis by stabilizing temperature and natural pH . In vertebrates,
14160-412: The venous system. The total length of muscle capillaries in a 70 kg human is estimated to be between 9,000 and 19,000 km. Capillaries merge into venules , which merge into veins. The venous system feeds into the two major veins: the superior vena cava – which mainly drains tissues above the heart – and the inferior vena cava – which mainly drains tissues below the heart. These two large veins empty into
14280-414: The ventricles are contracting, the atria are relaxed and collecting blood. When the ventricles are relaxed in diastole, the atria contract to pump blood to the ventricles. This coordination ensures blood is pumped efficiently to the body. At the beginning of the cardiac cycle, the ventricles are relaxing. As they do so, they are filled by blood passing through the open mitral and tricuspid valves. After
14400-401: The ventricles have completed most of their filling, the atria contract, forcing further blood into the ventricles and priming the pump. Next, the ventricles start to contract. As the pressure rises within the cavities of the ventricles, the mitral and tricuspid valves are forced shut. As the pressure within the ventricles rises further, exceeding the pressure with the aorta and pulmonary arteries,
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