1、 Circulation:Cardiovascular SystemWang BinDepartment of AnesthesiologyHeart The heart is located between the lungs,with its point or apex directed toward the left.The thick muscle layer of the heart wall is the myocardium.This is lined on the inside with a thin endocardium and is covered on the outs
2、ide with a thin epicardium.The heart is contained within a fibrous sac,the pericardium.Heart Each of the upper receiving chambers of the heart is an atrium(plural,atria).Each of the lower pumping chambers is a ventricle(plural,ventricles).The chambers of the heart are divided by walls,each of which
3、is called a septum.The interventricular septum separates the two ventricles;the interatrial septum divides the two atria.There is also a septum between the atrium and ventricle on each side.Heart The heart pumps blood through two circuits.The right side pumps blood to the lungs to be oxygenated thro
4、ugh the pulmonary circuit.The left side pumps to the remainder of the body through the systemic circuit.The pathway of blood through the heart is shown by the arrows.The right atrium receives blood low in oxygen from all body tissues through the superior vena cava and the inferior vena cava.The bloo
5、d then enters the right ventricle and is pumped to the lungs through the pulmonary artery.Blood returns from the lungs high in oxygen and enters the left atrium through the pulmonary veins.From here it enters the left ventricle and is forcefully pumped into the aorta to be distributed to all tissues
6、.Blood is kept moving in a forward direction by one-way valves.The valve in the septum between the right atrium and ventricle is the tricuspid valve;the valve in the septum between the left atrium and ventricle is the bicuspid valve,usually called the mitral valve.The valves leading into the pulmona
7、ry artery and the aorta have three cusps.Each cusp is shaped like a half-moon,so these valves are described as semilunar valves.The valve at the entrance to the pulmonary artery is specifically named the pulmonic valve;the valve at the entrance to the aorta is the aortic valve.Heart sounds are produ
8、ced as the heart functions.The loudest of these,the familiar lubb and dupp that can be heard through the chest wall,are produced by alternate closing of the valves.The first heart sound(S1)is heard when the valves between the chambers close.The second heart sound(S2)is produced when the valves leadi
9、ng into the aorta and pulmonary artery close.Any sound made as the heart functions normally is termed a functional murmur.(The word murmur used alone with regard to the heart describes an abnormal sound.)Each contraction of the heart,termed systole,is followed by a relaxation phase,diastole,during w
10、hich the chambers fill.Each time the heart beats,both atria contract and immediately thereafter both ventricles contract.The wave of increased pressure produced in the vessels each time the ventricles contract is the pulse.Contractions are stimulated by a built-in system that regularly transmits ele
11、ctrical impulses through the heart.The components of this conduction system are shown in Figure 9-3.They include the sinoatrial(SA)node,called the pacemaker because it sets the rate of the heartbeat,the atrioventricular(AV)node,the AV bundle(bundle of His),the left and right bundle branches,and Purk
12、inje fibers.Although the heart itself generates the heartbeat,factors such as nervous system stimulation,hormones,and drugs can influence the rate and the force of heart contractions.Blood pressure is the force exerted by blood against the wall of a blood vessel.It is commonly measured in a large ar
13、tery with an inflatable cuff(Fig.9-4)known as a blood pressure cuff or blood pressure apparatus,but technically called a sphygmomanometer.Both systolic and diastolic pressures are measured and reported as systolic then diastolic separated by a slash,such as 120/80.Pressure is expressed as millimeter
14、s of mercury(mm Hg),that is,the height to which the pressure can push a column of mercury in a tube.Blood pressure is a valuable diagnostic measurement that is easily obtained.The vascular system consists of:1.Arteries that carry blood away from the heart(Fig.9-5).Arterioles are small arteries that
15、lead into the capillaries.2.Capillaries,the smallest vessels,through which exchanges take place between the blood and the tissues.3.Veins that carry blood back to the heart(Fig.9-6).The small veins that receive blood from the capillaries and drain into the veins are venules.All arteries,except the p
16、ulmonary artery(and the umbilical artery in the fetus),carry blood high in oxygen.They are thick-walled,elastic vessels that carry blood under high pressure.All veins,except the pulmonary vein(and the umbilical vein in the fetus),carry blood low in oxygen.Veins have thinner,less elastic walls and te
17、nd to give way under pressure.Like the heart,veins have one-way valves that keep blood flowing forward.Nervous system stimulation can cause the diameter of a vessel to increase(vasodilation)or decrease(vasoconstriction).These changes alter blood flow to the tissues and affect blood pressure.The lymp
18、hatic system is a widely distributed system with multiple functions.Its role in circulation is to return excess fluid and proteins from the tissues to the bloodstream.The fluid carried in the lymphatic system is called lymph.Lymph drains from the lower part of the body and the upper left side into t
19、he thoracic duct,which travels upward through the chest and empties into the left subclavian vein near the heart.The right lymphatic duct drains the upper right side of the body and empties into the right subclavian vein.Another function of the lymphatic system is to absorb digested fats from the sm
20、all intestine(see Chapter 12).These fats are then added to the blood near the heart.One other major function of the lymphatic system is to protect the body from impurities and invading microorganisms.Along the path of the lymphatic vessels are small masses of lymphoid tissue,the lymph nodes.Their fu
21、nction is to filter the lymph as it passes through.They are concentrated in the cervical(neck),axillary(armpit),mediastinal(chest),and inguinal(groin)regions.The lymph nodes and the remainder of the lymphatic system also play a role in immunity(see Chapter 10).Other organs and tissues of the lymphat
22、ic system include the tonsils,located in the throat,the thymus gland in the chest,and the spleen in the upper left region of the abdomen The accumulation of fatty deposits within the lining of an artery is termed atherosclerosis(Fig.9-8).This type of deposit,called a plaque,begins to form when a ves
23、sel receives tiny injuries,usually at a point of branching.Plaques gradually thicken and harden with fibrous material,cells,and other deposits,restricting the lumen(opening)of the vessel and reducing blood flow to the tissues,a condition known as ischemia.A major risk factor for the development of a
24、therosclerosis is dyslipidemia,abnormally high levels or imbalance in lipoproteins that are carried in the blood,especially high levels of cholesterol-containing low-density lipoproteins(LDL).Other risk factors for atherosclerosis include smoking,high blood pressure,poor diet,inactivity,stress,and f
25、amily history of the disorder.Atherosclerosis may involve any arteries,but most of its effects are seen in the coronary vessels of the heart,the aorta,the carotid arteries in the neck,and vessels in the brain.Atherosclerosis predisposes a person to thrombosis,the formation of a blood clot within a v
26、essel.The clot,called a thrombus,interrupts blood flow to the tissues supplied by that vessel,resulting in necrosis(tissue death).Blockage of a vessel by a thrombus or other mass carried in the bloodstream is an embolism,and the mass itself is called an embolus.Usually the mass is a blood clot that
27、breaks loose from the wall of a vessel,but it may also be air(as from injection or trauma),fat(as from marrow released after a bone break),bacteria,orother solid materials.Often a venous thrombus will travel through the heart and then lodge in an artery of the lungs,resulting in a life-threatening p
28、ulmonary embolism.An embolus from a carotid artery often blocks a cerebral vessel,causing a cerebrovascular accident(CVA),commonly called stroke.An arterial wall weakened by atherosclerosis,malformation,injury,or other causes may balloon out,forming an aneurysm.If an aneurysm ruptures,hemorrhage res
29、ults.Rupture of a cerebral artery is another cause of stroke.The abdominal aorta and carotid arteries are also common sites of aneurysm.In a dissecting aneurysm(Fig.9-9),blood hemorrhages into the thick middle layer of the artery wall,separating the muscle as it spreads and sometimes rupturing the v
30、essel.The aorta is most commonly involved.It may be possible to repair a dissecting aneurysm surgically with a graft.High blood pressure,or hypertension(HTN),is a contributing factor in all of the conditions described above.In simple terms,hypertension is defined as a systolic pressure greater than
31、140 mm Hg or a diastolic pressure greater than 90 mm Hg.Hypertension causes the left ventricle to enlarge (hypertrophy)as a result of increased work.Some cases of HTN are secondary to other disorders,such as kidney malfunction or endocrine disturbance,but most of the time the causes are unknown,a co
32、ndition described as primary or essential hypertension.Changes in diet and life habits are the first line of defense in controlling HTN.Drugs that are used include diuretics to eliminate fluids,vasodilators to relax the blood vessels,and drugs that prevent the formation or action of angiotensin,a su
33、bstance in the blood that normally acts to increase blood pressure.Coronary artery disease(CAD),which results from atherosclerosis of the vessels that supply blood to the heart muscle,is a leading cause of death in industrialized countries(see Fig.9-8).An early sign of CAD is the type of chest pain
34、known as angina pectoris.This is a feeling of constriction around the heart or pain that may radiate to the left arm or shoulder,usually brought on by exertion.Often there is anxiety,diaphoresis (profuse sweating),and dyspnea(difficulty in breathing).CAD is treated by control of exercise and adminis
35、tration of nitroglycerin to dilate coronary vessels.Other drugs may be used to regulate the heartbeat,strengthen the force of heart contraction,or prevent formation of blood clots.Patients with severe cases of CAD may be candidates for angioplasty,surgical dilatation of the blocked vessel by means o
36、f a catheter,technically called percutaneous transluminal coronary angioplasty(PTCA)(Fig.9-10).If further intervention is required,the blocked vessel may be surgically bypassed with a vascular graft.In this procedure,known as a coronary artery bypass graft(CABG),another vessel or a piece of another
37、vessel,usually the aphenous vein of the leg or the left internal mammary artery,is used to carry blood from the aorta to a point past the obstruction in a coronary vessel.CAD is diagnosed by electrocardiography(ECG),study of the electrical impulses given off by the heart as it functions,stress tests
38、,coronary angiography(imaging),echocardiography,and other tests.Degenerative changes in the arteries predispose a person to thrombosis and sudden occlusion(obstruction)of a coronary artery.The resultant area of myocardial necrosis is termed an infarct,and the process is known as myocardial infarctio
39、n(MI),the“heart attack”that may cause sudden death.Symptoms of MI include pain over the heart(precordial pain)or upper part of the abdomen(epigastric pain)that may extend to the jaw or arms,pallor(paleness),diaphoresis,nausea,and dyspnea.There may be a burning sensation similar to indigestion or hea
40、rtburn MI is diagnosed by electrocardiography,by measurement of certain enzymes(CK,LDH,AST)released into the blood from the damaged heart muscle and by a variety of other methods described later in this chapter.Patient outcome is based on the degree of damage and early treatment to dissolve the clot
41、 and re-establish normal heart rhythm.Arrhythmia is any irregularity of heart rhythm,such as a higher-or lower-than-average heart rate,extra beats,or an alteration in the pattern of the beat.Bradycardia is a slower-than-average rate,and tachycardia is a higher-than-average rate.In cases of MI,there
42、is often fibrillation,an extremely rapid,ineffective beating of the heart.MI may also result in heart block,an interruption in the electrical conduction system of the heart.Cardioversion is the general term for restoration of a normal heart rhythm,either by drugs or application of electric current.S
43、everal devices are in use for electrical defibrillation.If,for any reason,the SA node is not generating a normal heartbeat,an artificial pacemaker may be implanted in the chest to regulate the beat.The general term heart failure refers to any condition in which the heart fails to empty effectively.T
44、he resulting increased pressure in the venous system leads to edema,often in the lungs(pulmonary edema),and justifies the description congestive heart failure(CHF).Other symptoms of congestive heart failure arecyanosis,dyspnea,and syncope.Heart failure is one cause of shock,a severe disturbance in t
45、he circulatory system resulting in inadequate delivery of blood to the tissues.Heart failure is treated with rest,drugs to strengthen heart contractions,diuretics to eliminate fluid,and restriction of salt in the diet.A congenital defect is any defect that is present at birth.The most common type of
46、 congenital heart defect is a hole in the septum(wall)that separates the atria or the ventricles.The result of a septal defect is that blood is shunted from the left to the right side of the heart and goes back to the lungs instead of out to the body.The heart has to work harder to meet the bodys ne
47、ed for oxygen.Symptoms of septal defect include cyanosis(leading to the description“blue baby”),syncope,and clubbing of the fingers.Most such congenital defects can be corrected surgically.Another type of congenital defect is malformation of a heart valve.Failure of a valve to open or close properly
48、 is evidenced by a murmur,an abnormal sound heard as the heart cycles.Still other congenital defects result from failure of fetal modifications to convert to their adult form at birth.In patent ductus arteriosus,a vessel present in the fetus to bypass the lungs fails to close at birth.Blood can then
49、 flow from the aorta to the pulmonary artery and return to the lungs.In rheumatic heart disease,infection with a specific type of streptococcus sets up an immune reaction that ultimately damages the heart valves.The infection usually begins as a“strep throat,”and most often it is the mitral valve th
50、at is involved.Scar tissue fuses the leaflets of the valve,causing a narrowing or stenosis that interferes with proper function.People with rheumatic heart disease are subject to repeated infections of the valves and must take antibiotics prophylactically(preventively)before any type of surgery and
