Cardiovascular System PDF

11/7/24 Learning Objectives 1. Describe and discuss the heart and related structures...

11/7/24 Learning Objectives 1. Describe and discuss the heart and related structures 2. Identify and discuss the parts of the heart and associated arteries and veins using a model Cardiovascular System 3. Discuss the circulatory pathways for the flow of blood By : Marc Anthony Cueto MD within the body 4. Trace the flow of blood from one structure to another structure 1 2 Cardiovascular System Middle Mediastinum The cardiovascular system is a closed system of the heart and u blood vessels. u The middle mediastinum is u The heart pumps blood through a closed system of blood centrally located in the thoracic vessels. cavity. u Blood vessels allow blood to circulate to all parts of the body. u It contains the pericardium, u Arteries usually colored red because oxygen rich, carry blood heart, origins of the great away from the heart to capillaries within the tissues. vessels, various nerves, and Veins usually colored blue because oxygen poor, carry blood to u the heart from the capillaries. smaller vessels. u Capillaries are the smallest vessels within the tissues where gas exchange take place. u The function of the cardiovascular system is to deliver oxygen and nutrients to the body tissues and remove carbon dioxide and wastes products. 3 4 Pericardium Pericardium u The pericardium is a fibroserous sac u The parietal and visceral layers of serous surrounding the heart and the roots of the pericardium are continuous at the roots of great vessels. the great vessels. u It consists of two components, the fibrous u The narrow space known as the pericardium and the serous pericardium. pericardial cavity is formed between the u The fibrous pericardium is a tough connective two layers of the serous pericardium and tissue outer layer that defines the boundaries of the middle mediastinum. contains a small amount of fluid called pericardial fluid. u The serous pericardium is thin and consists of two parts: u This potential space allows for the u The parietal (wall) layer of serous relatively uninhibited movement of the pericardium lines the inner surface of the heart. fibrous pericardium. u The visceral layer (epicardium) of serous pericardium adheres to the heart and forms its outer covering. 5 6 1  11/7/24 Fibrous Pericardium Fibrous Pericardium u The fibrous pericardium is a cone-shaped bag with its base on the diaphragm and its u The phrenic nerves, which innervate the apex continuous with the adventitia of the diaphragm and originate from spinal cord great vessels. levels C3 to C5, pass through the fibrous pericardium and innervate the fibrous u The base is attached to the central tendon pericardium as they travel from their point of of the diaphragm and to a small muscular origin to their final destination. area of the diaphragm on the left side. u The pericardiacophrenic vessels are also u Anteriorly, it is attached to the posterior located within and supply the fibrous surface of the sternum by sternopericardial pericardium as they pass through the thoracic ligam ents. cavity. u These attachments help to retain the heart in its position in the thoracic cavity. The sac also limits cardiac distention. 7 8 Serous Pericardium u The parietal layer of serous pericardium is continuous with the visceral layer of serous pericardium around the roots of the great vessels. u The pericardium is supplied by branches from the internal thoracic, pericardiacophrenic, musculophrenic, and inferior phrenic arteries, and the thoracic aorta. u Veins from the pericardium enter the azygos system of veins and the internal thoracic and superior phrenic veins. u Nerves supplying the pericardium arise from the vagus nerve [X], the sympathetic trunks, and the phrenic nerves. 9 10 Cardiac Orientation u The general shape and orientation of the heart are that of a pyramid that has fallen over and is resting on one of its sides. u Placed in the thoracic cavity, the apex of this pyramid projects forward, downward, and to the left, whereas the base is opposite the apex and faces in a posterior direction. u The sides of the pyramid consist of: Heart u u a diaphragmatic (inferior) surface on which the pyramid rests, an anterior (sternocostal) surface oriented anteriorly, u a right pulmonary surface, and u a left pulmonary surface. 11 12 2  11/7/24 Heart Position Base and Apex u The heart is located in the thoracic cavity, within the mediastinum. u The base of the heart is quadrilateral and Specifically, it is positioned slightly left of the midline, behind the directed posteriorly. It consists of: sternum, and between the lungs. It extends from the level of the second u the left atrium, rib down to approximately the fifth intercostal space. Here’s a u a small portion of the right atrium, and breakdown of its orientation: u the proximal parts of the great veins Base: Located at the top, near the second rib, and angled towards the right (superior and inferior venae cavae and the pulmonary veins) shoulder. This part of the heart is where major vessels (like the aorta and pulmonary arteries) emerge. u Because the great veins enter the base of the heart, the base of the heart is fixed Apex: Pointed end that faces downward, forward, and to the left, typically posteriorly to the pericardial wall, opposite the bodies of vertebrae TV to TVIII (TVI to at the level of the fifth intercostal space, close to the midclavicular line. TIX when standing). u The heart lies more posteriorly at the base and is tilted in such a way u The esophagus lies immediately posterior to that the left side is more anterior, while the right side sits more the base. posteriorly in the chest. 13 14 Base and Apex u From the base the heart projects forward, downward, and to the left, ending in the apex. u The apex of the heart is formed by the inferolateral part of the left ventricle and is positioned deep to the left fifth intercostal space, 8 to 9 cm from the midsternal line. 15 16 R Surfaces of the heart u The anterior surface faces anteriorly and consists m ostly of the right ventricle, with some of the right atrium on the right and some of the left ventricle on the left. 8-9cm Mid Sternal Line 17 18 3  11/7/24 Surfaces of the heart Surfaces of the heart R u The heart in the anatomical position rests u The left pulm onary surface faces the on the diaphragm atic surface, which consists of the left ventricle and a sm all left lung, is broad and convex, and consists of the left ventricle and a portion of the right ventricle separated by the posterior interventricular groove. portion of the left atrium. u The right pulm onary surface faces the u This surface faces inferiorly, rests on the diaphragm, is separated from the base of right lung, is broad and convex, and consists of the right atrium. the heart by the coronary sinus, and extends from the base to the apex of the heart. 19 20 External sulci Cardiac chambers u Internal partitions divide the heart into four chambers u The heart functionally consists of two pumps (i.e., two atria and two ventricles) and produce surface separated by a partition. or external grooves referred to as sulci. u The right pump receives deoxygenated blood from u The coronary sulcus circles the heart, separating the the body and sends it to the lungs. atria from the ventricles. As it circles the heart, it contains the right coronary artery, the small cardiac u The left pump receives oxygenated blood from vein, the coronary sinus, and the circumflex branch of the lungs and sends it to the body. the left coronary artery. u Each pump consists of an atrium and a ventricle separated by a valve. u The anterior and posterior interventricular sulci separate the two ventricles—the anterior u The thin-walled atria receive blood coming into interventricular sulcus is on the anterior surface of the the heart, whereas the relatively thick-walled heart and contains ventricles pump blood out of the heart. u the anterior interventricular artery and the u More force is required to pump blood through u great cardiac vein, and the body than through the lungs, so the muscular wall of the left ventricle is thicker u the posterior interventricular sulcus is on the than the right. diaphragmatic surface of the heart and contains the u Interatrial, interventricular, and atrioventricular u posterior interventricular artery and the septa separate the four chambers of the heart. u m iddle cardiac vein. u The internal anatomy of each chamber is critical to its function. 21 22 Right atrium Right atrium u The superior vena cava enters the upper u In the anatomical position, the right posterior portion of the right atrium, and the border of the heart is formed by the inferior vena cava and coronary sinus enter right atrium. This chamber also the lower posterior portion of the right contributes to the right portion of the atrium. heart’s anterior surface. u From the right atrium, blood passes into the u Blood returning to the right atrium right ventricle through the right enters through one of three vessels. atrioventricular orifice. These are: u This opening faces forward and medially and u the superior and inferior venae is closed during ventricular contraction by the tricuspid valve. cavae, which together deliver blood to the heart from the body; and u the coronary sinus, which returns blood from the walls of the heart itself. 23 24 4  11/7/24 Right atrium u Separating the right atrium from the left atrium is the interatrial septum, which faces forward and to the right because the left atrium lies posteriorly and to the left of the right atrium. u A depression is clearly visible in the septum just above the orifice of the inferior vena cava. This is the fossa ovalis (oval fossa), with its prominent margin, the limbus fossa ovalis (border of the oval fossa). u The fossa ovalis marks the location of the embryonic foramen ovale, which is an important part of fetal circulation. u The foramen ovale allows oxygenated blood entering the right atrium through the inferior vena cava to pass directly to the left atrium and so bypass the lungs, which are nonfunctional before birth. 25 26 Right ventricle Right ventricle u The outflow tract of the right ventricle, which u In the anatomical position, the right ventricle leads to the pulmonary trunk, is the conus forms most of the anterior surface of the arteriosus (infundibulum). This area has heart and a portion of the diaphragmatic smooth walls and derives from the embryonic bulbus cordis. surface. u The walls of the inflow portion of the right u The right atrium is to the right of the right ventricle have numerous muscular, irregular ventricle and the right ventricle is located in structures called trabeculae carneae. front of and to the left of the right u Most of these are either attached to the atrioventricular orifice. ventricular walls throughout their length, forming ridges, or attached at both ends, u Blood entering the right ventricle from the forming bridges. right atrium therefore moves in a horizontal u A few trabeculae carneae (papillary muscles) and forward direction. have only one end attached to the ventricular surface, while the other end serves as the point of attachment for tendon-like fibrous cords (the chordae tendineae), which connect to the free edges of the cusps of the tricuspid valve. 27 28 Right ventricle Tricuspid valve u There are three papillary muscles in the right u The right atrioventricular orifice is closed ventricle. Named relative to their point of during ventricular contraction by the tricuspid valve (right atrioventricular valve), so named origin on the ventricular surface, they are the because it usually consists of three cusps or anterior, posterior, and septal papillary leaflets. muscles: u The base of each cusp is secured to the fibrous u The anterior papillary muscle is the largest ring that surrounds the atrioventricular orifice. and most constant papillary muscle, and arises from the anterior wall of the ventricle. u This fibrous ring helps to maintain the shape of the opening. The cusps are continuous with u The posterior papillary muscle may consist each other near their bases at sites termed of one, two, or three structures, with some commissures. chordae tendineae arising directly from the u The naming of the three cusps, the anterior, ventricular wall. septal, and posterior cusps, is based on their relative position in the right ventricle. The free u The septal papillary muscle is the most margins of the cusps are attached to the inconsistent papillary muscle, being either chordae tendineae, which arise from the tips of small or absent, with chordae tendineae the papillary muscles. emerging directly from the septal wall. u During filling of the right ventricle, the tricuspid valve is open, and the three cusps project into the right ventricle. 29 30 5  11/7/24 Pulmonary valve Left atrium u At the apex of the infundibulum, the outflow u The left atrium forms most of the base tract of the right ventricle, the opening into or posterior surface of the heart. the pulmonary trunk is closed by the u The interatrial septum is part of the pulm onary valve, which consists of three sem ilunar cusps with free edges projecting anterior wall of the left atrium. upward into the lumen of the pulmonary u The thin area or depression in the trunk. septum is the valve of the foramen ovale u The cusps are named the left, right, and and is opposite the floor of the fossa anterior sem ilunar cusps, relative to their ovalis in the right atrium. fetal position before rotation of the outflow tracts from the ventricles is complete. 31 32 Left ventricle Left ventricle u The left ventricle lies anterior to the left u The trabeculae carneae in the left atrium. ventricle are fine and delicate in contrast to those in the right ventricle. u It contributes to the anterior, diaphragmatic, and left pulmonary u The general appearance of the surfaces of the heart, and forms the apex. trabeculae with muscular ridges and bridges is similar to that of the right u Blood enters the ventricle through the ventricle. left atrioventricular orifice and flows in a forward direction to the apex. u Papillary muscles, together with chordae tendineae, are also observed u The chamber itself is conical, is longer and their structure is as described than the right ventricle, and has the above for the right ventricle. thickest layer of myocardium. u Two papillary muscles, the anterior and u The outflow tract (the aortic vestibule) is posterior papillary m uscles, are posterior to the infundibulum of the right usually found in the left ventricle and ventricle, has smooth walls, and is are larger than those of the right derived from the embryonic bulbus cordis. ventricle. 33 34 Left ventricle Mitral valve u In the anatomical position, the left u The left atrioventricular orifice opens into ventricle is somewhat posterior to the right ventricle. the posterior right side of the superior part of the left ventricle. u The interventricular septum therefore forms the anterior wall and some of the u It is closed during ventricular contraction wall on the right side of the left ventricle. by the m itral valve (left atrioventricular The septum is described as having two valve), which is also referred to as the parts: bicuspid valve because it has two cusps, u a muscular part, and the anterior and posterior cusps. u a membranous part. u The bases of the cusps are secured to a u The muscular part is thick and forms the fibrous ring surrounding the opening, and major part of the septum, whereas the the cusps are continuous with each other membranous part is the thin, upper part at the commissures. of the septum. u A third part of the septum may be u The coordinated action of the papillary considered an atrioventricular part muscles and chordae tendineae is as because of its position above the septal described for the right ventricle. cusp of the tricuspid valve. This superior location places this part of the septum between the left ventricle and right atrium. 35 36 6  11/7/24 Aortic valve u The aortic vestibule, or outflow tract of the left ventricle, is continuous superiorly with the ascending aorta. u The opening from the left ventricle into the aorta is closed by the aortic valve. u This valve is similar in structure to the pulmonary valve. It consists of three semilunar cusps with the free edge of each projecting upward into the lumen of the ascending aorta. u Between the semilunar cusps and the wall of the Valvular heart disease ascending aorta are pocket-like sinuses—the right, left, and posterior aortic sinuses. u The right and left coronary arteries originate from the right and left aortic sinuses. u The functioning of the aortic valve is similar to that of the pulmonary valve with one important additional process: as blood recoils after ventricular contraction and fills the aortic sinuses, it is automatically forced into the coronary arteries because these vessels originate from the right and left aortic sinuses. 37 38 Valvular heart disease Valvular Heart disease u Any disease process involving one or more of the four valves of the u Diagnosis involves clinical evaluation and heart. echocardiography. u Any heart valve can become u Standard 2-dimensional studies show the anatomy. stenotic or insufficient, causing hemodynamic changes long before u Doppler echocardiography evaluates pressure symptoms. gradients and blood flow. u Most often, valvular stenosis or insufficiency occurs in isolation in u Evaluation also includes ECG (to detect heart rhythm individual valves, but multiple and chamber alterations) and chest x-ray (to detect valvular disorders may coexist, and a single valve may be both chamber alterations, pulmonary congestion, and stenosed and insufficient. other lung pathology). 39 40 Heart Sounds Valvular heart disease u Management of a valvular lesion commonly requires only periodic observation, with no active treatment for many years. u Intervention is usually indicated only when a moderate or severe valvular lesion causes symptoms or cardiac dysfunction. u The intervention may involve valvuloplasty or valve repair or replacement and may be carried out either percutaneously or surgically. 41 42 7  11/7/24 Rheumatic Heart Disease u Rheumatic heart disease is a condition in which the heart valves have been permanently damaged by rheumatic fever. u The heart valve damage may start shortly after untreated or under-treated streptococcal infection such as strep throat or scarlet fever. u An immune response causes an Rheumatic Heart disease inflammatory condition in the body which can result in on-going valve damage. u Rheumatic heart disease is caused by rheumatic fever, an inflammatory disease that can affect many connective tissues, especially in the heart, joints, skin, or brain. 43 44 Rheumatic Heart Disease Rheumatic Heart Disease u These are the most common symptoms of rheumatic fever: u The heart valves can be inflamed and become scarred over time. u Fever u This can result in narrowing or leaking of the heart valve making it harder for u Swollen, tender, red and extremely painful joints — particularly the knees and the heart to function normally. ankles u This may take years to develop and can result in heart failure. u Nodules (lumps under the skin) u Rheumatic fever can occur at any age, but usually occurs in children ages 5 to u Red, raised, lattice-like rash, usually on the chest, back, and abdomen 15 years old. u Shortness of breath and chest discomfort u A recent history of strep infection or rheumatic fever is key to the diagnosis u Uncontrolled movements of arms, legs, or facial muscles – Sydenham’s Chorea of rheumatic heart disease. u Weakness u Symptoms of rheumatic fever vary and typically begin 1 to 6 weeks after a u Symptoms of rheumatic heart disease depend on the degree of valve damage and may include: bout of strep throat. u Shortness of breath (especially with activity or when lying down) u In some cases, the infection may have been too mild to have been u Chest pain recognized, or it may be gone by the time the person sees a doctor. u Swelling 45 46 Rheumatic Heart Disease Rheumatic Heart Disease u People with rheumatic heart disease will have or recently had a strep u Treatm ent depends in large part on how m uch dam age has been done to the infection. A throat culture or blood test may be used to check for strep. heart valves. In severe cases, treatment may include surgery to replace or u They may have a murmur or rub that may be heard during a routine repair a badly damaged valve. physical exam. The murmur is caused by the blood leaking around the u The best treatment is to prevent rheumatic fever. Antibiotics can usually damages valve. The rub is caused when the inflamed heart tissues move treat strep infections and keep rheumatic fever from developing. Anti- or rub against each other. inflammatory drugs may be used to reduce inflammation and lower the risk of u Along with a complete medical history and physical exam, tests used to heart damage. Other medicines may be needed to manage heart failure. diagnose rheumatic heart disease may include: u People who have had rheumatic fever are often given daily or monthly u Echocardiogram (echo). antibiotic treatments, possibly for life, to prevent recurrent infections and u Electrocardiogram (ECG). lower the risk of further heart damage. To reduce inflammation, aspirin, steroids, or non-steroidal medicines may be given. u Chest X-ray. u Cardiac MRI. u Blood tests. 47 48 8  11/7/24 Coronary Vasculature 49 50 Right coronary artery Coronary vasculature u The right coronary artery originates from the right aortic sinus of the ascending aorta. u Two coronary arteries arise from the aortic sinuses u It passes anteriorly and then descends vertically in in the initial portion of the ascending aorta and the coronary sulcus, between the right atrium and supply the muscle and other tissues of the heart. right ventricle. u They circle the heart in the coronary sulcus, with u On reaching the inferior margin of the heart, it marginal and interventricular branches, in the turns posteriorly and continues in the sulcus onto interventricular sulci, converging toward the apex the diaphragmatic surface and base of the heart. of the heart. u During this course, several branches arise from the u The returning venous blood passes through cardiac main stem of the vessel: veins, most of which empty into the coronary u Atrial branch w hich gives off sino atrial branch sinus. u Right m arginal branch u This large venous structure is located in the coronary sulcus on the posterior surface of the u Posterior interventricular branch heart between the left atrium and left ventricle. u The right coronary artery supplies the right atrium u The coronary sinus empties into the right atrium and right ventricle, the sinu-atrial and between the opening of the inferior vena cava and atrioventricular nodes, the interatrial septum, a the right atrioventricular orifice. portion of the left atrium, the posteroinferior one third of the interventricular septum, and a portion of the posterior part of the left ventricle. 51 52 Left coronary artery Cardiac veins u The left coronary artery originates from u The great cardiac vein begins at the apex of the heart. It ascends in the anterior the left aortic sinus of the ascending interventricular sulcus, where it is related to aorta. the anterior interventricular artery and is u It passes between the pulmonary trunk often termed the anterior interventricular and the left auricle before entering the vein. coronary sulcus. u The great cardiac vein begins at the apex of u Emerging from behind the pulmonary the heart. It ascends in the anterior trunk, the artery divides into its two interventricular sulcus, where it is related to the anterior interventricular artery and is terminal branches, the anterior often termed the anterior interventricular interventricular and the circumflex. vein. u The distribution pattern of the left u The small cardiac vein begins in the lower coronary artery enables it to supply m ost anterior section of the coronary sulcus of the left atrium and left ventricle, and between the right atrium and right ventricle. most of the interventricular septum, including the atrioventricular bundle and u The posterior cardiac vein lies on the its branches. posterior surface of the left ventricle just to the left of the middle cardiac vein (Fig 53 54 9  11/7/24 MYOCARDIAL INFARCTION u Also called coronary thrombosis or heart attack u Results from the COMPLETE occlusion of one or more coronary arteries. u It arises when MYOCARDIAL INFARCTION atherosclerotic plaques rupture causing platelet activation, adhesion and aggregation with subsequent thrombus formation within the coronary circulation. 55 56 FEATURES OF AMI DIAGNOSIS u Chest pain described as a pressure sensation, fullness or squeezing in the mid u Clinical features portion of the thorax u ECG u Radiation of chest pain into the jaw/teeth, shoulder, arm and or back u Changes in serum level of cardiac u Dyspnea or shortness of breath enzymes u Epigastric discomfort with or without nausea and vomiting u Troponin T u Diaphoresis or sweating (cold clammy) u Creatine kinase MB u Syncope or near syncope u Aspartate transaminase u Impairment of cognitive function u Lactic dehydrogenase 57 58 TREATMENT u An MI requires immediate medical attention. u Treatment attempts to save as much viable heart muscle as possible and to prevent further complications, hence the phrase "time is [heart] muscle". u Aspirin and nitroglycerin may be administered. u Nitroglycerin (administered under the tongue or Cardiac Conduction System intravenously) may be administered to improve the blood supply to the heart. u Morphine may be used if nitroglycerin is not effective. 59 60 10  11/7/24 Cardiac innervation Cardiac conduction system u The autonomic division of the peripheral nervous system is directly u The musculature of the atria and ventricles is capable of contracting spontaneously. responsible for regulating: u The cardiac conduction system initiates and u heart rate, coordinates contraction. u force of each contraction, and u The conduction system consists of nodes u cardiac output. and networks of specialized cardiac muscle cells organized into four basic components: u Stimulation of the parasympathetic system: u the sinu-atrial node, u decreases heart rate, u the atrioventricular node, u reduces force of contraction, and u the atrioventricular bundle with its right and left bundle branches, and u constricts the coronary arteries. u the subendocardial plexus of conduction u Stimulation of the sympathetic system: cells (the Purkinje fibers). u increases heart rate, and u The unique distribution pattern of the cardiac conduction system establishes an u increases the force of contraction. important unidirectional pathway of excitation/contraction. 61 62 Introduction/ Basics Introduction/Basics u The normal electrical conduction in u Under normal conditions, electrical the heart allows the impulse that is activity is spontaneously generated generated by the sinoatrial node (SA by the SA node, the physiological node) of the heart to be propagated pacemaker. to, and stimulate, the cardiac u This electrical impulse is muscle (myocardium). propagated throughout the u The myocardium contracts after right atrium, and stimulation. through Bachmann's bundle to the u It is the ordered, rhythmic left atrium, stimulating stimulation of the myocardium the myocardium of the atria to during the cardiac cycle that allows contract. efficient contraction of the heart, u The conduction of the electrical thereby allowing blood to be impulse throughout the atria is seen pumped throughout the body. on the ECG as the P wave. 63 64 Introduction/ Basics Introduction/ Basics u The AV node functions as a u The two bundle branches taper out critical delay in the conduction to produce numerous Purkinje system. Without this delay, fibers, which stimulate individual the atria and ventricles would groups of myocardial cells to contract at the same time, and contract. blood wouldn't flow effectively u The spread of electrical activity from the atria to the ventricles. through the ventricular The delay in the AV node forms myocardium produces the QRS much of the PR segment on complex on the ECG. the ECG. And part of atrial repolarization can be represented by PR segment. 65 66 11  11/7/24 Introduction/ Basics Arrythmias u The normal heart beats in a regular, coordinated way because electrical impulses generated and spread by myocytes with unique u The last event of the cycle is the electrical properties trigger a sequence of organized myocardial repolarization of the ventricles. It contractions. is the restoring of the resting u Arrhythmias and conduction disorders are caused by abnormalities in state. In the ECG, repolarization includes the J point, ST-segment, the generation or conduction of these electrical impulses or both. and T- and U-waves. u Any heart disorder, including congenital abnormalities of structure (eg, accessory atrioventricular connection) or function (eg, hereditary ion channelopathies), can disturb rhythm. u Systemic factors that can cause or contribute to a rhythm disturbance include electrolyte abnormalities (particularly low K or Mg), hypoxia, hormonal imbalances (eg, hypothyroidism, hyperthyroidism), and drugs and toxins (eg, alcohol, caffeine). 67 68 Arrythmias u Arrhythmia and conduction disturbances may be asymptomatic or cause palpitations (sensation of skipped beats or rapid or forceful beats), symptoms of hemodynamic compromise (eg, dyspnea, chest discomfort, presyncope, syncope), or cardiac arrest. u A number of tests can help with diagnosis including an electrocardiogram (ECG) and holter monitor. u The need for treatment varies; it is guided by symptoms and risks of the arrhythmia. u Asymptomatic arrhythmias without serious risks do not require treatment even if they worsen. u Symptomatic arrhythmias may require treatment to improve quality of life. u Potentially life-threatening arrhythmias require treatment. 69 70 Arteries & Veins u Arteries and veins transport blood in two distinct circuits: the systemic circuit and the pulmonary circuit. u Systemic arteries provide blood rich in oxygen to the body’s tissues. u The blood returned to the heart through systemic veins has less oxygen, since much of the oxygen carried by the arteries has been delivered to the cells. Arteries and Veins u u In contrast, in the pulmonary circuit, arteries carry blood low in oxygen exclusively to the lungs for gas exchange. Pulmonary veins then return freshly oxygenated blood from the lungs to the heart to be pumped back out into systemic circulation. u Although arteries and veins differ structurally and functionally, they share certain features. 71 72 12  11/7/24 Arteries & Veins 73 74 Artery Artery u An artery is a blood vessel that conducts blood away from the heart. u Farther from the heart, where the surge of blood has dampened, the percentage of elastic fibers in an artery’s tunica intima decreases and the amount of smooth muscle in its tunica u All arteries have relatively thick walls that can withstand the high pressure of blood media increases. ejected from the heart. u The artery at this point is described as a muscular artery. u However, those close to the heart have the thickest walls, containing a high percentage u The diameter of muscular arteries typically ranges from 0.1 mm to 10 mm. of elastic fibers in all three of their tunics. u Their thick tunica media allows muscular arteries to play a leading role in vasoconstriction. In u This type of artery is known as an elastic artery. contrast, their decreased quantity of elastic fibers limits their ability to expand. Fortunately, u Vessels larger than 10 mm in diameter are typically elastic. because the blood pressure has eased by the time it reaches these more distant vessels, elasticity has become less important. u Their abundant elastic fibers allow them to expand, as blood pumped from the u Notice that although the distinctions between elastic and muscular arteries are important, ventricles passes through them, and then to recoil after the surge has passed. there is no “line of demarcation” where an elastic artery suddenly becomes muscular. u An elastic artery is also known as a conducting artery, because the large diameter of u Rather, there is a gradual transition as the vascular tree repeatedly branches. In turn, muscular the lumen enables it to accept a large volume of blood from the heart and conduct it arteries branch to distribute blood to the vast network of arterioles. For this reason, a muscular to smaller branches. artery is also known as a distributing artery. 75 76 Arterioles u An arteriole is a very small artery that leads to a capillary. u Arterioles have the same three tunics as the larger vessels, but the thickness of each is greatly diminished. u The critical endothelial lining of the tunica intima is intact. The tunica media is restricted to one or two smooth muscle cell layers in thickness. The tunica externa remains but is very thin. u With a lumen averaging 30 micrometers or less in diameter, arterioles are critical in slowing down—or resisting—blood flow and, thus, causing a substantial drop in blood pressure. Because of this, you may see them referred to as resistance vessels. u The muscle fibers in arterioles are normally slightly contracted, causing arterioles to maintain a consistent muscle tone—in this case referred to as vascular tone—in a similar manner to the muscular tone of skeletal muscle. u In reality, all blood vessels exhibit vascular tone due to the partial contraction of smooth muscle. u The importance of the arterioles is that they will be the primary site of both resistance and regulation of blood pressure. u The precise diameter of the lumen of an arteriole at any given moment is determined by neural and chemical controls, and vasoconstriction and vasodilation in the arterioles are the primary mechanisms for distribution of blood flow. 77 78 13  11/7/24 Capillaries Continuous Capillaries u A capillary is a microscopic channel that supplies blood to the tissues themselves, a process called perfusion. u The most common type of capillary, u Exchange of gases and other substances occurs in the capillaries the continuous capillary, is found in almost between the blood and the surrounding cells and their tissue fluid all vascularized tissues. (interstitial fluid). u The diameter of a capillary lumen ranges from 5–10 micrometers; u Continuous capillaries are characterized by a complete endothelial lining with tight the smallest are just barely wide enough for an erythrocyte to squeeze through. Flow through capillaries is often described junctions between endothelial cells. as microcirculation. u Although a tight junction is usually u The wall of a capillary consists of the endothelial layer surrounded impermeable and only allows for the by a basement membrane with occasional smooth muscle fibers. passage of water and ions, they are often u There is some variation in wall structure: In a large capillary, incomplete in capillaries, leaving several endothelial cells bordering each other may line the lumen; intercellular clefts that allow for exchange in a small capillary, there may be only a single cell layer that wraps of water and other very small molecules around to contact itself. between the blood plasma and the u For capillaries to function, their walls must be leaky, allowing interstitial fluid. substances to pass through. u Substances that can pass between cells u There are three major types of capillaries, which differ according include metabolic products, such as glucose, to their degree of “leakiness:” continuous, fenestrated, and water, and small hydrophobic molecules like sinusoid capillaries. gases and hormones, as well as various leukocytes. 79 80 Sinusoid capillaries Fenestrated Capillaries u A sinusoid capillary (or sinusoid) is the least com m on type of capillary. u A fenestrated capillary is one that has u Sinusoid capillaries are flattened, and they have extensive pores (or fenestrations) in addition to tight intercellular gaps and incom plete basem ent m em branes, in addition junctions in the endothelial lining. to intercellular clefts and fenestrations. This gives them an appearance not unlike Sw iss cheese. u These make the capillary permeable to u These very large openings allow for the passage of the largest larger molecules. The number of m olecules, including plasm a proteins and even cells. fenestrations and their degree of u Blood flow through sinusoids is very slow, allow ing m ore tim e for permeability vary, however, according to exchange of gases, nutrients, and wastes. their location. u Sinusoids are found in the liver and spleen, bone m arrow, lym ph u Fenestrated capillaries are common in the nodes (w here they carry lym ph, not blood), and m any endocrine small intestine, which is the primary site of glands including the pituitary and adrenal glands. W ithout these nutrient absorption, as well as in the specialized capillaries, these organs w ould not be able to provide kidneys, which filter the blood. their myriad of functions. u They are also found in the choroid plexus of u For exam ple, w hen bone m arrow form s new blood cells, the cells m ust enter the blood supply and can only do so through the large the brain and many endocrine structures, openings of a sinusoid capillary; they cannot pass through the sm all including the hypothalamus, pituitary, openings of continuous or fenestrated capillaries. pineal, and thyroid glands. u The liver also requires extensive specialized sinusoid capillaries in order to process the m aterials brought to it by the hepatic portal vein from both the digestive tract and spleen, and to release plasm a proteins into circulation. 81 82 Metarterioles and Capillary beds Venules u A venule is an extremely small vein, u A metarteriole is a type of vessel that generally 8–100 micrometers in diameter. has structural characteristics of both an u Postcapillary venules join multiple arteriole and a capillary. capillaries exiting from a capillary bed. Multiple venules join to form veins. u Slightly larger than the typical capillary, the smooth muscle of the tunica media u The walls of venules consist of endothelium, of the metarteriole is not continuous a thin middle layer with a few muscle cells and elastic fibers, plus an outer layer of but forms rings of smooth muscle connective tissue fibers that constitute a (sphincters) prior to the entrance to very thin tunica externa. the capillaries. u Venules as well as capillaries are the u Each metarteriole arises from a primary sites of emigration or diapedesis, in terminal arteriole and branches to which the white blood cells adhere to the endothelial lining of the vessels and then supply blood to a capillary bed that squeeze through adjacent cells to enter the may consist of 10–100 capillaries. tissue fluid. 83 84 14  11/7/24 Vein u A vein is a blood vessel that conducts blood toward the heart. Compared to arteries, veins are thin-walled vessels with large and irregular lumens. u Because they are low-pressure vessels, larger veins are commonly equipped with valves that promote the unidirectional flow of blood toward the heart and prevent backflow toward the capillaries caused by the inherent low blood pressure in veins as well as the pull of gravity. 85 86 Pulmonary Circulation Systemic Circulation u In the pulmonary loop, deoxygenated blood u In the systemic loop, oxygenated blood is exits the right ventricle of the heart and passes pumped from the left ventricle of the heart through the pulmonary trunk. through the aorta, the largest artery in the body. u The pulmonary trunk splits into the right and left pulmonary arteries. These arteries u The blood moves from the aorta through transport the deoxygenated blood to arterioles the systemic arteries, then to arterioles and and capillary beds in the lungs. There, carbon capillary beds that supply body tissues. dioxide is released and oxygen is absorbed. u Here, oxygen and nutrients are released and carbon dioxide and other waste u Oxygenated blood then passes from the substances are absorbed. capillary beds through venules into the pulmonary veins. u Deoxygenated blood then moves from the capillary beds through venules into the u The pulmonary veins transport it to the left systemic veins. atrium of the heart. u The systemic veins feed into the inferior u The pulmonary arteries are the only arteries and superior venae cavae, the largest veins that carry deoxygenated blood, and the in the body. pulmonary veins are the only veins that carry u The venae cavae flow deoxygenated blood oxygenated blood. to the right atrium of the heart. 87 88 Coronary Circulation Coronary Circulation u The coronary circulation refers to the blood supply to the u The venous drainage of the heart is heart itself. It is a component of the systemic circulation. achieved by the coronary sinus, u The right and left coronary arteries branch directly from the ascending aorta, immediately above the aortic valve. which drains the main veins of the u The right coronary artery passes to the right and gives off heart: two main branches: the right marginal branch along the right border of the heart and the posterior the great cardiac vein, interventricular (posterior descending) artery, which descends along the interventricular septum on the base the middle cardiac vein, and of the heart. the small cardiac vein, which drains u The left coronary artery passes to the left, and gives off the anterior interventricular (Ieft anterior descending) directly into the right atrium. artery which descends on the anterior aspect of the interventricular septum to anastamose with the posterior interventricular artery at the apex of the heart. It also gives off the circumflex artery. 89 90 15  11/7/24 Pulmonary Trunk Pulmonary Trunk u The pulm onary trunk is contained u The pulmonary trunk divides within the pericardial sac. into: u It arises from the conus arteriosus u the right pulmonary of the right ventricle at the artery, which passes to the opening of the pulmonary trunk right, posterior to the slightly anterior to the aortic orifice and ascends, moving ascending aorta and the posteriorly and to the left, lying superior vena cava, to enter initially anterior and then to the the right lung; and left of the ascending aorta. u the left pulmonary artery, which passes inferiorly to the arch of the aorta and anteriorly to the descending aorta to enter the left lung. 91 92 Aorta Ascending Aorta u The aorta is the largest artery in the body, initially u The ascending aorta arises from the aortic being an inch wide in diameter. It receives the cardiac output from the left ventricle and orifice from the left ventricle and ascends to supplies the body with oxygenated blood via the become the aortic arch. It is 2 inches long in systemic circulation. length and travels with the pulmonary trunk u The aorta can be divided into four sections: in the pericardial sheath. the ascending aorta, the aortic arch, the thoracic (descending) aorta and the abdominal aorta. u Branches u It terminates at the level of L4 by bifurcating into u The left and right aortic sinuses are dilations the left and right common iliac arteries. in the ascending aorta, located at the level of u The aorta is classified as a large elastic artery. the aortic valve. They give rise to the left and right coronary arteries that supply the myocardium. 93 94 Thoracic Aorta Aortic Arch u The thoracic (descending) aorta spans from the level of T4 to T12. Continuing from the aortic u The aortic arch is a continuation of the ascending aorta and begins at arch, it initially begins to the left of the vertebral the level of the second sternocostal joint. It arches superiorly, column but approaches the midline as it posteriorly and to the left before moving inferiorly. descends. It leaves the thorax via the aortic hiatus in the diaphragm, and becomes the u The aortic arch ends at the level of the T4 vertebra. The arch is still abdominal aorta. connected to the pulmonary trunk by the ligamentum u Branches arteriosum (remnant of the foetal ductus arteriosus). u In descending order: u Branches Bronchial arteries: Paired visceral branches u There are three major branches arising from the aortic arch. Proximal arising laterally to supply bronchial and peribronchial tissue and visceral pleura. to distal: However, most commonly, only the paired left Brachiocephalic trunk: The first and largest branch that ascends bronchial artery arises directly from the aorta laterally to split into the right common carotid and right subclavian whilst the right branches off usually from the third posterior intercostal artery. arteries. These arteries supply the right side of the head and neck, and the right upper limb. Mediastinal arteries: Small arteries that supply the lymph glands and loose areolar tissue in Left common carotid artery: Supplies the left side of the head and the posterior mediastinum. neck. Oesophageal arteries: Unpaired visceral branches arising anteriorly to supply Left subclavian artery: Supplies the left upper limb. the oesophagus. 95 96 16  11/7/24 Thoracic Aorta Abdominal Aorta u The abdominal aorta is a continuation of the thoracic aorta beginning Pericardial arteries: Small unpaired arteries that at the level of the T12 vertebrae. It is approximately 13cm long and arise anteriorly to supply the dorsal portion of ends at the level of the L4 vertebra. At this level, the aorta terminates the pericardium. by bifurcating into the right and left common iliac arteries that supply Superior phrenic arteries: Paired parietal the lower body. branches that supply the superior portion of u Branches the diaphragm. u In descending order: Intercostal and subcostal arteries: Small paired arteries that branch off throughout the length of Inferior phrenic arteries: Paired parietal arteries arising posteriorly at the posterior thoracic aorta. The 9 pairs of the level of T12. They supply the diaphragm. intercostal arteries supply the intercostal spaces, Coeliac artery: A large, unpaired visceral artery arising anteriorly at with the exception of the first and second (they the level of T12. It is also known as the celiac trunk and supplies the are supplied by a branch from the subclavian liver, stomach, abdominal oesophagus, spleen, the superior artery). The subcostal arteries supply the flat duodenum and the superior pancreas. abdominal wall muscles. Superior mesenteric artery: A large, unpaired visceral artery arising anteriorly, just below the celiac artery. It supplies the distal duodenum, jejuno-ileum, ascending colon and part of the transverse colon. It arises at the lower level of L1. 97 98 Abdominal Aorta Superior Vena Cava Middle suprarenal arteries: Small paired visceral arteries that arise either side posteriorly at the level of L1 to supply the adrenal glands. u The superior vena cava (SVC) is a large, valveless vein that conveys venous blood from the upper half of the body Renal arteries: Paired visceral arteries that arise laterally at the level between L1 and L2. They supply and returns it to the right atrium. the kidneys. u The superior vena cava is classified as a large vein, with a Gonadal arteries: Paired visceral arteries that arise wide diameter of up to 2cm and a length of approximately laterally at the level of L2. Note that the male gonadal artery is referred to as the testicular artery and in 7cm. females, the ovarian artery. u It arises from the union of the left and right Inferior mesenteric artery: A large, unpaired visceral brachiocephalic veins, posterior to the first right costal artery that arises anteriorly at the level of L3. It cartilage. It descends vertically through the superior supplies the large intestine from the splenic flexure to the upper part of the rectum. mediastinum, behind the intercostal spaces and to the Median sacral artery: An unpaired parietal artery that right of the aorta and trachea. arises posteriorly at the level of L4 to supply the coccyx, lumbar vertebrae and the sacrum. u At the level of the second costal cartilage, the SVC enters the middle mediastinum and becomes surrounded by the Lumbar arteries: There are four pairs of parietal lumbar arteries that arise posterolaterally between fibrous pericardium. It terminates by emptying into the the levels of L1 and L4 to supply the abdominal wall superior aspect of the right atrium at the level of the third and spinal cord. costal cartilage. 99 100 Superior Vena Cava Inferior Vena Cava u The superior vena cava contains u After passing through the diaphragm, venous blood from the head, neck, at approximately the level of vertebra both upper limbs and from structures TVIII, the inferior vena cava enters within the thorax u It is formed by the union of the right the fibrous pericardium. and left brachiocephalic veins – which u A short portion of this vessel is within provide venous drainage of the head, the pericardial sac before entering the neck, and upper limbs. At the level of right atrium. T4, the superior vena cava receives the azygous vein, which drains the upper u W hile within the pericardial sac, it is lumbar region and thoracic wall. covered by serous pericardium except u The SVC receives tributaries from for a small portion of its posterior several minor vein groups: surface Mediastinal veins Oesophageal veins Pericardial veins 101 102 17  11/7/24 Inferior Vena Cava Inferior Vena Cava u The inferior vena cava arises from the confluence of the com m on iliac veins at the level of L5 vertebra, u Tributaries : just inferior to the bifurcation of the abdominal aorta. u T8: paired inferior phrenic veins u It then ascends the posterior abdominal wall, to the right side of u T8: hepatic veins 3 the aorta and the bodies of the L3- u L1: right suprarenal vein L5 vertebrae. u L1: renal veins u After passing through its fossa on the posterior liver surface, the IVC u L2: right gonadal vein enters the thorax by traversing u L1-L5: lumbar veins the inferior vena caval foramen of the diaphragm. u L5: common iliac veins (origin) 103 104 Thank you ! 105 18