120-416: The term cardial may refer to: cardial or cardiac , pertaining to the heart (Ancient Greek καρδιά, kardiá , "heart") Cardial Ware , a Neolithic decorative style Topics referred to by the same term [REDACTED] This disambiguation page lists articles associated with the title Cardial . If an internal link led you here, you may wish to change
240-402: 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
360-440: 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
480-456: 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
600-417: A lower lobe, by the oblique fissure, which extends from the costal to the mediastinal surface of the lung both above and below the hilum . The left lung, unlike the right, does not have a middle lobe, though it does have a homologous feature, a projection of the upper lobe termed the lingula . Its name means "little tongue". The lingula on the left lung serves as an anatomic parallel to the middle lobe on
720-438: 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
840-400: 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
960-467: 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
1080-425: 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
1200-402: 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
1320-460: 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
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#17328485243611440-447: A right lung and a left lung. They are situated within the thoracic cavity of the chest . The right lung is bigger than the left, the left lung shares space in the chest with the heart. The lungs together weigh approximately 1.3 kilograms (2.9 lb), and the right is heavier. The lungs are part of the lower respiratory tract that begins at the trachea and branches into the bronchi and bronchioles , and which receive air breathed in via
1560-485: A right lung with only two lobes, or a left lung with three lobes. A variation in the airway branching structure has been found specifically in the central airway branching. This variation is associated with the development of COPD in adulthood. The development of the human lungs arise from the laryngotracheal groove and develop to maturity over several weeks in the foetus and for several years following birth. The larynx , trachea , bronchi and lungs that make up
1680-480: 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
1800-414: Is also responsible for the elastic recoil needed. Elastin is more concentrated in areas of high stress such as the openings of the alveoli, and alveolar junctions. The connective tissue links all the alveoli to form the lung parenchyma which has a sponge-like appearance. The alveoli have interconnecting air passages in their walls known as the pores of Kohn . All of the lower respiratory tract including
1920-400: 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
2040-404: 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
2160-422: Is divided into three lobes by a horizontal fissure , and an oblique fissure . The left lung is divided into two lobes by an oblique fissure which is closely aligned with the oblique fissure in the right lung. In the right lung the upper horizontal fissure, separates the upper (superior) lobe from the middle lobe. The lower, oblique fissure separates the lower lobe from the middle and upper lobes. Variations in
2280-475: Is driven by different muscular systems in different species. Mammals, reptiles and birds use their musculoskeletal systems to support and foster breathing. In early tetrapods, air was driven into the lungs by the pharyngeal muscles via buccal pumping , a mechanism still seen in amphibians. In humans, the primary muscle that drives breathing is the diaphragm . The lungs also provide airflow that makes vocalisation including speech possible. Humans have two lungs,
2400-401: Is held in the fluid-filled amniotic sac and so they do not function to breathe. Blood is also diverted from the lungs through the ductus arteriosus . At birth however, air begins to pass through the lungs, and the diversionary duct closes, so that the lungs can begin to respire. The lungs only fully develop in early childhood. In humans the lungs are located in the chest on either side of
2520-427: Is likely to be made up of between 30 and 50 primary lobules. The lobule is supplied by a terminal bronchiole that branches into respiratory bronchioles. The respiratory bronchioles supply the alveoli in each acinus and is accompanied by a pulmonary artery branch. Each lobule is enclosed by an interlobular septum. Each acinus is incompletely separated by an intralobular septum. The respiratory bronchiole gives rise to
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#17328485243612640-428: 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 )
2760-480: 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
2880-451: 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
3000-612: 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
3120-435: Is the part of the lung distal to the respiratory bronchiole. Thus, it includes the alveolar ducts, sacs, and alveoli but not the respiratory bronchioles. The unit described as the secondary pulmonary lobule is the lobule most referred to as the pulmonary lobule or respiratory lobule . This lobule is a discrete unit that is the smallest component of the lung that can be seen without aid. The secondary pulmonary lobule
3240-404: 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
3360-498: 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
3480-402: 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
3600-436: 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,
3720-425: The carina where the trachea divides into the two main bronchi. The cardiac impression is an indentation formed on the surfaces of the lungs where they rest against the heart. Both lungs have a central recession called the hilum , where the blood vessels and airways pass into the lungs making up the root of the lung . There are also bronchopulmonary lymph nodes on the hilum. The lungs are surrounded by
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3840-470: The circulation , and carbon dioxide diffuses from the blood into the lungs to be breathed out . Estimates of the total surface area of lungs vary from 50 to 75 square metres (540 to 810 sq ft); although this is often quoted in textbooks and the media being "the size of a tennis court", it is actually less than half the size of a singles court . The bronchi in the conducting zone are reinforced with hyaline cartilage in order to hold open
3960-523: The conducting zone . These divide until air reaches microscopic alveoli , where gas exchange takes place. Together, the lungs contain approximately 2,400 kilometres (1,500 mi) of airways and 300 to 500 million alveoli. Each lung is enclosed within a pleural sac of two pleurae which allows the inner and outer walls to slide over each other whilst breathing takes place, without much friction. The inner visceral pleura divides each lung as fissures into sections called lobes. The right lung has three lobes and
4080-484: 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
4200-438: The esophagus behind the hilum and the pulmonary ligament , and near the lower part of the esophageal groove is a deeper groove for the inferior vena cava before it enters the heart. The weight of the right lung varies between individuals, with a standard reference range in men of 155–720 g (0.342–1.587 lb) and in women of 100–590 g (0.22–1.30 lb). The left lung is divided into two lobes, an upper and
4320-418: The heart in the rib cage . They are conical in shape with a narrow rounded apex at the top, and a broad concave base that rests on the convex surface of the diaphragm . The apex of the lung extends into the root of the neck, reaching shortly above the level of the sternal end of the first rib . The lungs stretch from close to the backbone in the rib cage to the front of the chest and downwards from
4440-672: The immune system . They remove substances which deposit in the alveoli including loose red blood cells that have been forced out from blood vessels. There is a large presence of microorganisms in the lungs known as the lung microbiota that interacts with the airway epithelial cells; an interaction of probable importance in maintaining homeostasis. The microbiota is complex and dynamic in healthy people, and altered in diseases such as asthma and COPD . For example significant changes can take place in COPD following infection with rhinovirus . Fungal genera that are commonly found as mycobiota in
4560-405: 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,
4680-402: 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
4800-418: 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
4920-430: 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
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5040-427: The pulmonary pleurae . The pleurae are two serous membranes ; the outer parietal pleura lines the inner wall of the rib cage and the inner visceral pleura directly lines the surface of the lungs. Between the pleurae is a potential space called the pleural cavity containing a thin layer of lubricating pleural fluid . Middle Lower Lingula Lower Each lung is divided into sections called lobes by
5160-404: 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
5280-411: 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
5400-463: 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
5520-405: 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
5640-565: 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
5760-458: 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,
5880-473: The airways initiate a reflex known as the Hering–Breuer reflex that prevents the lungs from over-inflation, during forceful inspiration. The lungs have a dual blood supply provided by a bronchial and a pulmonary circulation . The bronchial circulation supplies oxygenated blood to the airways of the lungs, through the bronchial arteries that leave the aorta . There are usually three arteries, two to
6000-399: The airways. The bronchioles have no cartilage and are surrounded instead by smooth muscle . Air is warmed to 37 °C (99 °F), humidified and cleansed by the conducting zone. Particles from the air being removed by the cilia on the respiratory epithelium lining the passageways, in a process called mucociliary clearance . Pulmonary stretch receptors in the smooth muscle of
6120-464: The alveolar ducts that lead to the alveolar sacs, which contain two or more alveoli. The walls of the alveoli are extremely thin allowing a fast rate of diffusion . The alveoli have interconnecting small air passages in their walls known as the pores of Kohn . Alveoli consist of two types of alveolar cell and an alveolar macrophage . The two types of cell are known as type I and type II cells (also known as pneumocytes). Types I and II make up
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#17328485243616240-474: The alveolar septa which separate each alveolus. The septa consist of an epithelial lining and associated basement membranes . Type I cells are not able to divide, and consequently rely on differentiation from Type II cells. Type II are larger and they line the alveoli and produce and secrete epithelial lining fluid, and lung surfactant . Type II cells are able to divide and differentiate to Type I cells. The alveolar macrophages have an important role in
6360-458: The alveoli. The four genes mostly associated with branching morphogenesis in the lung are the intercellular signalling protein – sonic hedgehog (SHH), fibroblast growth factors FGF10 and FGFR2b, and bone morphogenetic protein BMP4 . FGF10 is seen to have the most prominent role. FGF10 is a paracrine signalling molecule needed for epithelial branching, and SHH inhibits FGF10. The development of
6480-400: 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),
6600-400: 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
6720-402: 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
6840-409: 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,
6960-403: 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
7080-434: 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
7200-450: 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
7320-443: 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
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#17328485243617440-410: The base of the lung. By standard reference range , the weight of the left lung is 110–675 g (0.243–1.488 lb) in men and 105–515 g (0.231–1.135 lb) in women. The lungs are part of the lower respiratory tract , and accommodate the bronchial airways when they branch from the trachea. The bronchial airways terminate in alveoli which make up the functional tissue ( parenchyma ) of
7560-415: 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
7680-416: The branch. In the development of the lungs (as in some other organs) the epithelium forms branching tubes. The lung has a left-right symmetry and each bud known as a bronchial bud grows out as a tubular epithelium that becomes a bronchus. Each bronchus branches into bronchioles. The branching is a result of the tip of each tube bifurcating. The branching process forms the bronchi, bronchioles, and ultimately
7800-402: The bronchus and bronchioles, and increases the secretions from glands. The lungs also have a sympathetic tone from norepinephrine acting on the beta 2 adrenoceptors in the respiratory tract, which causes bronchodilation . The action of breathing takes place because of nerve signals sent by the respiratory center in the brainstem , along the phrenic nerve from the cervical plexus to
7920-444: The cell only once it has a sufficiently high charge, and so are called voltage-gated . Shortly after this, the calcium channels close and potassium channels open, allowing potassium to leave the cell. This causes the cell to have a negative resting charge and is called repolarisation . When the membrane potential reaches approximately −60 mV, the potassium channels close and the process may begin again. Lung The lungs are
8040-533: The composition of which is tightly regulated and determines how well mucociliary clearance works. Pulmonary neuroendocrine cells are found throughout the respiratory epithelium including the alveolar epithelium, though they only account for around 0.5 percent of the total epithelial population. PNECs are innervated airway epithelial cells that are particularly focused at airway junction points. These cells can produce serotonin, dopamine, and norepinephrine, as well as polypeptide products. Cytoplasmic processes from
8160-436: 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
8280-423: The diaphragm. The lobes of the lung are subject to anatomical variations . A horizontal interlobar fissure was found to be incomplete in 25% of right lungs, or even absent in 11% of all cases. An accessory fissure was also found in 14% and 22% of left and right lungs, respectively. An oblique fissure was found to be incomplete in 21% to 47% of left lungs. In some cases a fissure is absent, or extra, resulting in
8400-403: 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
8520-438: 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
8640-417: 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
8760-460: The fissures are fairly common being either incompletely formed or present as an extra fissure as in the azygos fissure , or absent. Incomplete fissures are responsible for interlobar collateral ventilation , airflow between lobes which is unwanted in some lung volume reduction procedures. The main or primary bronchi enter the lungs at the hilum and initially branch into secondary bronchi also known as lobar bronchi that supply air to each lobe of
8880-478: 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
9000-593: 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
9120-405: 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
9240-399: 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
9360-406: 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
9480-414: 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
9600-413: 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
9720-729: 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
9840-414: 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
9960-406: The hilum, is a well-marked curved groove for the aortic arch , and a groove below it for the descending aorta . The left subclavian artery , a branch off the aortic arch, sits in a groove from the arch to near the apex of the lung. A shallower groove in front of the artery and near the edge of the lung, lodges the left brachiocephalic vein . The esophagus may sit in a wider shallow impression at
10080-413: The infoldings of the visceral pleura as fissures. Lobes are divided into segments, and segments have further divisions as lobules. There are three lobes in the right lung and two lobes in the left lung. The fissures are formed in early prenatal development by invaginations of the visceral pleura that divide the lobar bronchi, and section the lungs into lobes that helps in their expansion. The right lung
10200-628: The left has two. The lobes are further divided into bronchopulmonary segments and lobules. The lungs have a unique blood supply, receiving deoxygenated blood sent from the heart for the purposes of receiving oxygen (the pulmonary circulation ) and a separate supply of oxygenated blood (the bronchial circulation ). The tissue of the lungs can be affected by a number of respiratory diseases , including pneumonia and lung cancer . Chronic diseases such as chronic obstructive pulmonary disease and emphysema can be related to smoking or exposure to harmful substances. Diseases such as bronchitis can also affect
10320-458: The left lung and one to the right, and they branch alongside the bronchi and bronchioles. The pulmonary circulation carries deoxygenated blood from the heart to the lungs and returns the oxygenated blood to the heart to supply the rest of the body. The blood volume of the lungs is about 450 millilitres on average, about 9% of the total blood volume of the entire circulatory system. This quantity can easily fluctuate from between one-half and twice
10440-445: The link to point directly to the intended article. Retrieved from " https://en.wikipedia.org/w/index.php?title=Cardial&oldid=932746955 " Category : Disambiguation pages Hidden categories: Short description is different from Wikidata All article disambiguation pages All disambiguation pages Heart The heart is a muscular organ found in most animals . This organ pumps blood through
10560-420: The lower part of the trachea to the diaphragm. The left lung shares space with the heart, and has an indentation in its border called the cardiac notch of the left lung to accommodate this. The front and outer sides of the lungs face the ribs, which make light indentations on their surfaces. The medial surfaces of the lungs face towards the centre of the chest, and lie against the heart, great vessels , and
10680-495: The lung, and veins, arteries, nerves, and lymphatic vessels . The trachea and bronchi have plexuses of lymph capillaries in their mucosa and submucosa. The smaller bronchi have a single layer of lymph capillaries, and they are absent in the alveoli. The lungs are supplied with the largest lymphatic drainage system of any other organ in the body. Each lung is surrounded by a serous membrane of visceral pleura , which has an underlying layer of loose connective tissue attached to
10800-415: The lung. The lobar bronchi branch into tertiary bronchi also known as segmental bronchi and these supply air to the further divisions of the lobes known as bronchopulmonary segments . Each bronchopulmonary segment has its own (segmental) bronchus and arterial supply . Segments for the left and right lung are shown in the table. The segmental anatomy is useful clinically for localising disease processes in
10920-419: The lungs. A segment is a discrete unit that can be surgically removed without seriously affecting surrounding tissue. The right lung has both more lobes and segments than the left. It is divided into three lobes, an upper, middle, and a lower lobe by two fissures, one oblique and one horizontal. The upper, horizontal fissure, separates the upper from the middle lobe. It begins in the lower oblique fissure near
11040-413: 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
11160-409: The microbiota include Candida , Malassezia , Saccharomyces , and Aspergillus . The lower respiratory tract is part of the respiratory system , and consists of the trachea and the structures below this including the lungs. The trachea receives air from the pharynx and travels down to a place where it splits (the carina ) into a right and left primary bronchus . These supply air to
11280-419: 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
11400-419: 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
11520-416: The normal volume. Also, in the event of blood loss through hemorrhage, blood from the lungs can partially compensate by automatically transferring to the systemic circulation. The lungs are supplied by nerves of the autonomic nervous system . Input from the parasympathetic nervous system occurs via the vagus nerve . When stimulated by acetylcholine , this causes constriction of the smooth muscle lining
11640-400: 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
11760-406: The posterior border of the lung, and, running horizontally forward, cuts the anterior border on a level with the sternal end of the fourth costal cartilage ; on the mediastinal surface it may be traced back to the hilum . The lower, oblique fissure, separates the lower from the middle and upper lobes and is closely aligned with the oblique fissure in the left lung. The mediastinal surface of
11880-414: 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
12000-433: The primary organs of the respiratory system in many animals, including humans. In mammals and most other tetrapods , two lungs are located near the backbone on either side of the heart . Their function in the respiratory system is to extract oxygen from the atmosphere and transfer it into the bloodstream, and to release carbon dioxide from the bloodstream into the atmosphere, in a process of gas exchange . Respiration
12120-467: The pulmonary neuroendocrine cells extend into the airway lumen where they may sense the composition of inspired gas. In the bronchi there are incomplete tracheal rings of cartilage and smaller plates of cartilage that keep them open. Bronchioles are too narrow to support cartilage and their walls are of smooth muscle , and this is largely absent in the narrower respiratory bronchioles which are mainly just of epithelium. The absence of cartilage in
12240-515: 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
12360-422: 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
12480-404: The respiratory tract, begin to form during the fourth week of embryogenesis from the lung bud which appears ventrally to the caudal portion of the foregut . The respiratory tract has a branching structure, and is also known as the respiratory tree. In the embryo this structure is developed in the process of branching morphogenesis , and is generated by the repeated splitting of the tip of
12600-452: The respiratory tract. Medical terms related to the lung often begin with pulmo-, from the Latin pulmonarius (of the lungs) as in pulmonology, or with pneumo- (from Greek πνεύμων "lung") as in pneumonia. In embryonic development , the lungs begin to develop as an outpouching of the foregut , a tube which goes on to form the upper part of the digestive system . When the lungs are formed the fetus
12720-427: 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
12840-429: The right and left lungs, splitting progressively into the secondary and tertiary bronchi for the lobes of the lungs, and into smaller and smaller bronchioles until they become the respiratory bronchioles . These in turn supply air through alveolar ducts into the alveoli , where the exchange of gases take place. Oxygen breathed in , diffuses through the walls of the alveoli into the enveloping capillaries and into
12960-424: 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
13080-414: 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
13200-403: The right lung is indented by a number of nearby structures. The heart sits in an impression called the cardiac impression. Above the hilum of the lung is an arched groove for the azygos vein , and above this is a wide groove for the superior vena cava and right brachiocephalic vein ; behind this, and close to the top of the lung is a groove for the brachiocephalic artery . There is a groove for
13320-425: The right lung, with both areas being predisposed to similar infections and anatomic complications. There are two bronchopulmonary segments of the lingula: superior and inferior. The mediastinal surface of the left lung has a large cardiac impression where the heart sits. This is deeper and larger than that on the right lung, at which level the heart projects to the left. On the same surface, immediately above
13440-441: The substance of the lung. The connective tissue of the lungs is made up of elastic and collagen fibres that are interspersed between the capillaries and the alveolar walls. Elastin is the key protein of the extracellular matrix and is the main component of the elastic fibres . Elastin gives the necessary elasticity and resilience required for the persistent stretching involved in breathing, known as lung compliance . It
13560-471: 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
13680-511: 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
13800-408: 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
13920-467: The terminal bronchioles gives them an alternative name of membranous bronchioles . The conducting zone of the respiratory tract ends at the terminal bronchioles when they branch into the respiratory bronchioles. This marks the beginning of the terminal respiratory unit called the acinus which includes the respiratory bronchioles, the alveolar ducts, alveolar sacs , and alveoli. An acinus measures up to 10 mm in diameter. A primary pulmonary lobule
14040-451: The trachea, bronchi, and bronchioles is lined with respiratory epithelium . This is a ciliated epithelium interspersed with goblet cells which produce mucin the main component of mucus , ciliated cells, basal cells , and in the terminal bronchioles – club cells with actions similar to basal cells, and macrophages . The epithelial cells, and the submucosal glands throughout the respiratory tract secrete airway surface liquid (ASL),
14160-414: 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
14280-401: 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,
14400-464: The walls and alveolar septa . Type I cells provide 95% of the surface area of each alveoli and are flat (" squamous "), and Type II cells generally cluster in the corners of the alveoli and have a cuboidal shape. Despite this, cells occur in a roughly equal ratio of 1:1 or 6:4. Type I are squamous epithelial cells that make up the alveolar wall structure. They have extremely thin walls that enable an easy gas exchange. These type I cells also make up
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