No. 14No. 14

1. Introduction of the Cardiovascular 1. Introduction of the Cardiovascular SystemSystem

2. Heart (1)2. Heart (1) The location of heartThe location of heart The external features of heartThe external features of heart The chambers of heartThe chambers of heart The Structure of heartThe Structure of heart

PART ANGIOLOGYⅣPART ANGIOLOGYⅣ

Introduction:Introduction: Physico-chemical properties and composition Physico-chemical properties and composition of the micro-environment of the cells comprisiof the micro-environment of the cells comprising the various tissues of the body remain relatng the various tissues of the body remain relatively constant, by the operation of a complex sively constant, by the operation of a complex series of homeostatic control mechanisms, whieries of homeostatic control mechanisms, which depend for effectiveness upon adequate circh depend for effectiveness upon adequate circulatory systemculatory system

The circulatory system can be separated The circulatory system can be separated into two divisions: the into two divisions: the cardiovascular scardiovascular systemystem consisting the heart and blood ve consisting the heart and blood vessels through which the blood circulates,ssels through which the blood circulates, and the and the lymphatic systemlymphatic system consisting of consisting of lymph nodes and vessels which conduct lymph nodes and vessels which conduct the lymph fluid. the lymph fluid.

The cardiovascular system includes the The cardiovascular system includes the heartheart, which serves as a pump for the , which serves as a pump for the blood, and the blood, and the blood vesselsblood vessels, which , which transport the blood throughout the body.transport the blood throughout the body.

The lymphatic system consists of organs The lymphatic system consists of organs that play a role in specific immune that play a role in specific immune responses (tonsils, thymus, spleen, lymph responses (tonsils, thymus, spleen, lymph nodes, and lymphatic nodules) and vessels nodes, and lymphatic nodules) and vessels that collect tissue fluid from between the that collect tissue fluid from between the cells of the body and transport it to the cells of the body and transport it to the cardiovascular system.cardiovascular system.

Chapter 1 The Chapter 1 The Cardiovascular SystemCardiovascular System

Section 1 IntroductionSection 1 Introduction The cardiovascular system is a closed circular The cardiovascular system is a closed circular

system. Confined to the heart and the numerous system. Confined to the heart and the numerous vessels, blood continuously travels a circular vessels, blood continuously travels a circular route through the heart, into arteries, then to route through the heart, into arteries, then to capillaries, into veins, and back to the heart.capillaries, into veins, and back to the heart.

Normally, blood does not leave this system, Normally, blood does not leave this system, although some of the fluid part of the blood does although some of the fluid part of the blood does pass through the walls of the capillaries to join pass through the walls of the capillaries to join the tissue fluid between the cells. However, even the tissue fluid between the cells. However, even this fluid is returned to the cardiovascular system this fluid is returned to the cardiovascular system directly or by way of the lymphatic systemdirectly or by way of the lymphatic system

ⅠⅠ. Organization of the . Organization of the Cardiovascular SystemCardiovascular System

The The Cardiovascular systemCardiovascular system comprises the comprises the heartheart and and blood blood vesselsvessels. The blood vessels consist of . The blood vessels consist of arteriesarteries, , veinsveins and and capillariescapillaries. .

ⅠⅠ) Heart) Heart The The heartheart is a hollow, muscular organ is a hollow, muscular organ

situated within the thorax. Its situated within the thorax. Its contraction expels blood to all parts contraction expels blood to all parts of the body through a complicated of the body through a complicated series of tubes, termed series of tubes, termed arteriesarteries..

In order to function as a pump, the heart must In order to function as a pump, the heart must have both receiving and delivery chambers, have both receiving and delivery chambers, valves to direct the flow of blood through the valves to direct the flow of blood through the heart, a wall that is strongly compressible and heart, a wall that is strongly compressible and thus provides the force to propel blood, and thus provides the force to propel blood, and vessels to deliver blood to and from the heart. vessels to deliver blood to and from the heart. The heart consists of four chambers: right and left The heart consists of four chambers: right and left atria and right and left ventricles, of which two atria and right and left ventricles, of which two are receiving and two are distributing chambers. are receiving and two are distributing chambers. The right and left atria receive the blood from the The right and left atria receive the blood from the great veins and expel it into the right and left great veins and expel it into the right and left ventricles. From the ventricles the blood is ventricles. From the ventricles the blood is pumped into the arterial system and carried to pumped into the arterial system and carried to the various organs of the body.the various organs of the body.

Each atrium communicates with the corEach atrium communicates with the corresponding ventricle through atrioventriresponding ventricle through atrioventricular orifices, but the right and left chamcular orifices, but the right and left chambers of the heart are separated from one bers of the heart are separated from one another by partitions, called septa.another by partitions, called septa.

ⅡⅡ) Arteries) Arteries The arteries carry blood away from the heart. The arteries carry blood away from the heart. They transport blood to the various body tissuThey transport blood to the various body tissues under high pressure exerted by the pumpines under high pressure exerted by the pumping action of the heart. It is, therefore, imperativg action of the heart. It is, therefore, imperative that they possess strong, elastic walls to insue that they possess strong, elastic walls to insure fast, efficient blood flow to the tissues. Comre fast, efficient blood flow to the tissues. Compared to the other types of blood vessels, arterpared to the other types of blood vessels, arteries must be able to withstand the greatest inteies must be able to withstand the greatest internal pressrue.rnal pressrue.

Arteries are classified according to size as largArteries are classified according to size as large, medium, and small ones.e, medium, and small ones. The wall of an artery consists of three layers, wThe wall of an artery consists of three layers, which are named from within outwards: the hich are named from within outwards: the tuntunica intimaica intima, the , the tunica mediatunica media, and the , and the tunica tunica adventitiaadventitia.. The The arteriesarteries ramify extensively in their course t ramify extensively in their course throughout the body, and end in minute vesselhroughout the body, and end in minute vessels, called s, called arteriolesarterioles, which open into a close-m, which open into a close-meshed network, eshed network, capillariescapillaries. .

ⅢⅢ) Capillary) Capillary They are simply thin endothelial tubes with a layer of They are simply thin endothelial tubes with a layer of basement membrane.basement membrane. They have an average diameter of 7They have an average diameter of 7 ～～ 8μ.8μ. They have extremely thin walls. As a consequence, theThey have extremely thin walls. As a consequence, they are sites at which the exchange of materials betweey are sites at which the exchange of materials between the blood and the interstitial fluid takes place. Acrosn the blood and the interstitial fluid takes place. Across their walls the fluids, oxygen, carbon dioxide, nutries their walls the fluids, oxygen, carbon dioxide, nutrients, vitamins, hormones, metabolic products and immnts, vitamins, hormones, metabolic products and immune substances are exchanged between the blood anune substances are exchanged between the blood and tissue fluid. In the body they anastomose with each d tissue fluid. In the body they anastomose with each other to form capillary networks except for in the cartiother to form capillary networks except for in the cartilage, hair, cornea and lens. lage, hair, cornea and lens.

ⅣⅣ) Veins) Veins After the blood has passed through the capillaries, it is collected iAfter the blood has passed through the capillaries, it is collected into a series of minute vessels, called nto a series of minute vessels, called venulesvenules, which join with on, which join with one another to form veins. The major veins return blood to the atria e another to form veins. The major veins return blood to the atria of the heart. The of the heart. The veinsveins unite with one another, and ultimately tw unite with one another, and ultimately two large venous trunks, named the superior and inferior venae cavo large venous trunks, named the superior and inferior venae cavae, are formed, which convey the blood to the heart. After the bloae, are formed, which convey the blood to the heart. After the blood leaves the capillaries, its pressure continues to drop; it is loweod leaves the capillaries, its pressure continues to drop; it is lowest near the right atrium of the heart in the superior and inferior vst near the right atrium of the heart in the superior and inferior venae cavae. With the progressive change from capillaries to venuenae cavae. With the progressive change from capillaries to venules to veins, the diameters of individual vessels and the thickness les to veins, the diameters of individual vessels and the thickness of their walls steadily increase, whereas the total cross-sectional of their walls steadily increase, whereas the total cross-sectional area of parallel vessels decreases. Venous pressure is always lowarea of parallel vessels decreases. Venous pressure is always lower than arterial pressure, and the walls of the veins are never as ter than arterial pressure, and the walls of the veins are never as thick as the walls of the corresponding arteries.hick as the walls of the corresponding arteries.

The walls of veins, like those of the arteriThe walls of veins, like those of the arteries, are composed of three coats: the intees, are composed of three coats: the internal being endothelial, the middle muscrnal being endothelial, the middle muscular and the external connective tissue. ular and the external connective tissue.

ⅡⅡ. The Cardiovascular Circuits. The Cardiovascular Circuits The superior and inferior venae cavae bring to the right The superior and inferior venae cavae bring to the right atrium the blood which has become deoxygenated and atrium the blood which has become deoxygenated and taken up carbon dioxide during its circulation through ttaken up carbon dioxide during its circulation through the tissues of the body. From the right atrium this venouhe tissues of the body. From the right atrium this venous blood passes into the right ventricle, by which it is exs blood passes into the right ventricle, by which it is expelled into the pulmonary trunk to be conveyed to the lpelled into the pulmonary trunk to be conveyed to the lungs. As it circulates through the pulmonary capillaries ungs. As it circulates through the pulmonary capillaries the blood is brought into close relationship with the insthe blood is brought into close relationship with the inspired air and it gives off some of its carbon dioxide and pired air and it gives off some of its carbon dioxide and acquires a fresh supply of oxygen. This oxygenated bloacquires a fresh supply of oxygen. This oxygenated blood is returned by the pulmonary veins to the left atrium od is returned by the pulmonary veins to the left atrium and thence passes into left ventricle. With each beat of and thence passes into left ventricle. With each beat of the heart the left ventricle pumps its contents into the the heart the left ventricle pumps its contents into the aorta, which distributes blood through its numerous braorta, which distributes blood through its numerous branches to all the tissues and organs of the body.anches to all the tissues and organs of the body.

Greater or systemic circulationGreater or systemic circulation and and lesser lesser or pulmonary circulationor pulmonary circulation::

The course of the blood from the left The course of the blood from the left ventricle through the whole body finally to ventricle through the whole body finally to the right atrium of the heart constitutes the right atrium of the heart constitutes the the greatergreater or or systemic circulationsystemic circulation. . While the passage from the right ventricle While the passage from the right ventricle through the lung to the left atrium of the through the lung to the left atrium of the heart is termed the heart is termed the lesserlesser or or pulmonary pulmonary circulationcirculation..

Ⅲ Ⅲ Anastomoses Anastomoses

1. Anastomoses between arteries:1. Anastomoses between arteries: Arteries do not always end in capillaries; Arteries do not always end in capillaries; in many cases they unite with one anothin many cases they unite with one another, forming what are called anastomoses.er, forming what are called anastomoses. Anastomosis between arterial trunks of Anastomosis between arterial trunks of nearly equal size is found in the brain annearly equal size is found in the brain and in the abdomen.d in the abdomen.

In the limbs, the anastomoses are largesIn the limbs, the anastomoses are largest and most numerous around the joints; t and most numerous around the joints; these anastomoses may be so numerous these anastomoses may be so numerous that they constitute a close that they constitute a close networknetwork. Art. Arteries often join end to end, forming the eries often join end to end, forming the arterial archarterial arch (e.g. the palmar and plant (e.g. the palmar and plantar arches).ar arches).

2. Anastomoses between veins:2. Anastomoses between veins: Veins join with one another to from the Veins join with one another to from the venous plexusvenous plexus or or networknetwork..

3. Anastomoses between arteries and veins:3. Anastomoses between arteries and veins: In a number of situations in the body direct coIn a number of situations in the body direct connections exist between the small arteries and nnections exist between the small arteries and corresponding veins, they are called the corresponding veins, they are called the arteriarteriovenous anastomosesovenous anastomoses.. The connecting vessel can conduct blood direThe connecting vessel can conduct blood directly from the artery to the vein and so partially ctly from the artery to the vein and so partially or completely exclude the capillary bed from tor completely exclude the capillary bed from the circulation for the time being.he circulation for the time being.

Arteriovenous anastomoses are found in Arteriovenous anastomoses are found in the skin of the nose, lips, hands and feet.the skin of the nose, lips, hands and feet. They function to regulate the local blooThey function to regulate the local blood flow and temperature.d flow and temperature.

4. 4. Collateral anastomosesCollateral anastomoses:: Each region or organ of the body is usualEach region or organ of the body is usually supplied by several vessels.ly supplied by several vessels. One of them, the largest in diameter, is cOne of them, the largest in diameter, is called the main vessel, while the smaller alled the main vessel, while the smaller ones are called the accessory or collaterones are called the accessory or collateral vessels; they communicate with one aal vessels; they communicate with one another through anastomotic channels.nother through anastomotic channels.

If a vessel is occluded by thrombosis, emIf a vessel is occluded by thrombosis, embolism or by ligation, the flow of blood tbolism or by ligation, the flow of blood through the collateral and anastomotic chrough the collateral and anastomotic channels will increase.hannels will increase. The anastomotic channels may become The anastomotic channels may become so enlarged as to replace the normal anso enlarged as to replace the normal and constitute an aberrant supply to a part.d constitute an aberrant supply to a part.

The blood circulation is thus partially restored The blood circulation is thus partially restored and the and the collateral circulationcollateral circulation is established. is established. Sudden occlusion of a vessel may be followed Sudden occlusion of a vessel may be followed in some situations by necrosis of the part suppin some situations by necrosis of the part supplied, while gradual occlusion may allow time flied, while gradual occlusion may allow time for the dilatation of the anastomosing channelor the dilatation of the anastomosing channels and the establishment of the collateral circuls and the establishment of the collateral circulation.ation.

Section 2 The HeartSection 2 The Heart TheThe heartheart is the pump that provides is the pump that provides

the force necessary to keep the the force necessary to keep the blood flowing through the system of blood flowing through the system of vessels.vessels.

It is a hollow, muscular organ of a It is a hollow, muscular organ of a somewhat conical form, about the somewhat conical form, about the size of a person’s fist and weighs size of a person’s fist and weighs about 260g in Chinese adult.about 260g in Chinese adult.

ⅠⅠ. The Location of Heart. The Location of Heart The heart is located in the middle mediaThe heart is located in the middle mediastinum between the lungs, and is enclosstinum between the lungs, and is enclosed in the pericardium.ed in the pericardium. It is obliquely in the chest behind the boIt is obliquely in the chest behind the body of the sternum and adjoining parts of dy of the sternum and adjoining parts of the costal cartilages, one-third of it on ththe costal cartilages, one-third of it on the right of the median plane and two-thire right of the median plane and two-thirds on the left.ds on the left.

ⅡⅡ. The External Features of Heart. The External Features of Heart

The heart is described as having a base, The heart is described as having a base, an apex, two surfaces (diaphragmatic anan apex, two surfaces (diaphragmatic and sternocostal surfaces), three borders ad sternocostal surfaces), three borders and four grooves.nd four grooves.

ⅠⅠ) Cardiac base) Cardiac base The The cardiac basecardiac base faces backwards and to faces backwards and to

the right.the right. It consists mainly of the left atrium, part of It consists mainly of the left atrium, part of

the right atrium. The four pulmonary the right atrium. The four pulmonary veins, two on each side, open into the left veins, two on each side, open into the left atrium, while the superior vena cava atrium, while the superior vena cava opens into the upper part, and the inferior opens into the upper part, and the inferior vena cava into the lower part, of the right vena cava into the lower part, of the right atrium.atrium.

ⅡⅡ) The ) The cardiac apexcardiac apex The cardiac apex, formed by the left venThe cardiac apex, formed by the left ventricle, is directed downwards, forwards atricle, is directed downwards, forwards and to the left, and is overlapped by left lnd to the left, and is overlapped by left lung and pleura.ung and pleura. It is situated in the 5th left intercostal spIt is situated in the 5th left intercostal space 1ace 1 ～～ 2 cm to the right of the left mid-2 cm to the right of the left mid-clavicular plane. Here the apex beat is pclavicular plane. Here the apex beat is palpable.alpable.

ⅢⅢ) The two surfaces) The two surfaces 1. The 1. The sternocostal surfacesternocostal surface, or called the ante, or called the anterior surface, is directed forwards, upwards and rior surface, is directed forwards, upwards and to the left.to the left. It consists of an atrial and a ventricular portion.It consists of an atrial and a ventricular portion. 2. The 2. The diaphragmatic surfacediaphragmatic surface The diaphragmatic surface, or called the inferiThe diaphragmatic surface, or called the inferior surface, is directed downwards and slightly or surface, is directed downwards and slightly backwards.backwards. It is formed by the ventricles (chiefly by the left It is formed by the ventricles (chiefly by the left ventricle), and rests upon the diaphragm.ventricle), and rests upon the diaphragm.

ⅣⅣ) Three borders) Three borders

1. The right border1. The right border The The right borderright border of the heart, formed by of the heart, formed by

the right atrium, is almost vertical.the right atrium, is almost vertical. 2. The left border2. The left border The The left borderleft border, formed mainly by the left , formed mainly by the left

ventricle, is rounded.ventricle, is rounded. 3. The inferior border3. The inferior border The The inferior borderinferior border, formed almost , formed almost

entirely by the right ventricle and the entirely by the right ventricle and the cardiac apex, is nearly horizontal.cardiac apex, is nearly horizontal.

ⅤⅤ) Four grooves) Four grooves 1. The coronary groove1. The coronary groove The The coronary groovecoronary groove separates the atria from separates the atria from the ventricles and contains the trunks of the cthe ventricles and contains the trunks of the coronary vessels of the heart. It is deficient in froronary vessels of the heart. It is deficient in front, where it is crossed by the root of the pulmont, where it is crossed by the root of the pulmonary trunk.onary trunk. 2. The anterior interventricular groove2. The anterior interventricular groove On the sternocostal surface, the line of separatOn the sternocostal surface, the line of separation between the ventricles being marked by thion between the ventricles being marked by the e anterior interventricular grooveanterior interventricular groove..

3. The posterior interventricular groove3. The posterior interventricular groove The diaphragmatic surface is traversed obliquThe diaphragmatic surface is traversed obliquely by the ely by the posterior interventricular grooveposterior interventricular groove.. 4. The posterior interatrial groove4. The posterior interatrial groove On the diaphragmatic surface, the sulcus betwOn the diaphragmatic surface, the sulcus between the right atrium and the right superior and een the right atrium and the right superior and inferior pulmonary veins.inferior pulmonary veins.

Cardiac apical incisureCardiac apical incisure:: The anterior and posterior interventricular groThe anterior and posterior interventricular grooves extend from the base of the ventricular poves extend from the base of the ventricular portion to a notch, termed the ortion to a notch, termed the cardiac apical incardiac apical incisurecisure, situated a little to right of the apex of t, situated a little to right of the apex of the heart.he heart. Crux:Crux: The crossing point of the posterior interatrial gThe crossing point of the posterior interatrial groove, the posterior interventricular groove anroove, the posterior interventricular groove and the coronary groove is thed the coronary groove is the cruxcrux..

ⅢⅢ. The Chambers of Heart. The Chambers of Heart The heart is divided into right and left halves, eThe heart is divided into right and left halves, each half is subdivided into two chambers. The ach half is subdivided into two chambers. The upper chambers, the atria, are separated by thupper chambers, the atria, are separated by the e interatrial septuminteratrial septum; the lower chambers, the ; the lower chambers, the ventricles, are separated by the ventricles, are separated by the interventriculinterventricular septumar septum.. The atria serve as receiving chambers for blooThe atria serve as receiving chambers for blood from the various parts of the body, the ventrid from the various parts of the body, the ventricles as pumping chambers.cles as pumping chambers.

ⅠⅠ) The Right Atrium) The Right Atrium It constitutes the right superior portion of the heart.It constitutes the right superior portion of the heart. Right auricleRight auricle: a small, conical, muscular pouch, terme: a small, conical, muscular pouch, termed the right auricle, projects towards the left from its ud the right auricle, projects towards the left from its upper and anterior part and overlaps the right side of tpper and anterior part and overlaps the right side of the ascending aorta.he ascending aorta. The cavity of right atrium is divided into two portions, The cavity of right atrium is divided into two portions, an anterior (atrium proper) and a posterior (sinus venan anterior (atrium proper) and a posterior (sinus venarum cavarum), by the arum cavarum), by the crista terminaliscrista terminalis, a smooth, m, a smooth, muscular ridge, which extends from the orifice of the suuscular ridge, which extends from the orifice of the superior vena cava to the orifice of the inferior vena cava.perior vena cava to the orifice of the inferior vena cava.

1. The 1. The atrium properatrium proper The anterior portion, called the atrium pThe anterior portion, called the atrium proper, has rough walls. Many nearly pararoper, has rough walls. Many nearly parallel muscular ridges, termed the llel muscular ridges, termed the pectinapectinate muscleste muscles, run forwards from the crista , run forwards from the crista terminalis towards the auricle. In the aurterminalis towards the auricle. In the auricle they are connected to one another sicle they are connected to one another so as to form a muscular network.o as to form a muscular network.

2. The 2. The sinus venarum cavarumsinus venarum cavarum The posterior portion, termed the sinus venarum cavaThe posterior portion, termed the sinus venarum cavarum, has smooth walls. There are three orifices opens rum, has smooth walls. There are three orifices opens into it:into it: ① ① Orifice of superior vena cavaOrifice of superior vena cava The superior vena cava returns the blood from the upThe superior vena cava returns the blood from the upper half of the body, and opens into the upper part of tper half of the body, and opens into the upper part of the sinus venarum cavarum.he sinus venarum cavarum. ② ② Orifice of inferior vena cavaOrifice of inferior vena cava The inferior vena cava returns the blood from the lowThe inferior vena cava returns the blood from the lower half of the body, and opens into the lowest part of ter half of the body, and opens into the lowest part of the sinus venarum cavarum.he sinus venarum cavarum. The The valve of inferior vena cavavalve of inferior vena cava (Eustachian valve) lie (Eustachian valve) lies anterior lip of the orifice of inferior vena cava.s anterior lip of the orifice of inferior vena cava.

③ ③ Orifices of coronary sinusOrifices of coronary sinus The coronary sinus returns the greater pThe coronary sinus returns the greater part of the blood from the substance of thart of the blood from the substance of the heart. Its opening, the orifice of coronae heart. Its opening, the orifice of coronary sinus, is placed between the orifice of ry sinus, is placed between the orifice of inferior vena cava and the right atrioveninferior vena cava and the right atrioventricular orifice.tricular orifice.

Fossa ovalis:Fossa ovalis: On the lower part of the septal wall of the atriuOn the lower part of the septal wall of the atrium there is an oval depression, called the m there is an oval depression, called the fossa fossa ovalisovalis, which is the remnant of the oval foram, which is the remnant of the oval foramen of the fetal heart.en of the fetal heart. The anterior inferior part of the right atrium is The anterior inferior part of the right atrium is the the right atrioventricular orificeright atrioventricular orifice. Blood from . Blood from the right atrium goes into the right ventricle ththe right atrium goes into the right ventricle through this orifice.rough this orifice.

ⅡⅡ) The Right Ventricle) The Right Ventricle It constitutes the right inferior portion of the hIt constitutes the right inferior portion of the heart. Its anterosuperior surface forms a large peart. Its anterosuperior surface forms a large part of the sternocostal surface of the heart. Thart of the sternocostal surface of the heart. The wall of the right ventricle is thinner than that e wall of the right ventricle is thinner than that of the left, the proportion between them being of the left, the proportion between them being as 1:3. as 1:3. The interior of the right ventricle is separated iThe interior of the right ventricle is separated into thento the inflowinflow and and outflow tractsoutflow tracts by a muscul by a muscular ridge, the ar ridge, the supraventricular crestsupraventricular crest, situated , situated between the atrioventricular and pulmonary obetween the atrioventricular and pulmonary orifices.rifices.

1. 1. Inflow tract of the right ventricleInflow tract of the right ventricle The inflow tract has rough walls due to the preThe inflow tract has rough walls due to the presence of trabeculae carneae. It receives the blsence of trabeculae carneae. It receives the blood from the right atrium through the ood from the right atrium through the right atright atrioventricular orificerioventricular orifice.. The right atrioventricular (tricuspid) valve guaThe right atrioventricular (tricuspid) valve guards the right atrioventricular orifice, and consirds the right atrioventricular orifice, and consists of three somewhat triangular cusps, namests of three somewhat triangular cusps, named d anterioranterior, , posteriorposterior, , medial medial oror septal cuspsseptal cusps..

A number of delicate, tendinous cords, termed the A number of delicate, tendinous cords, termed the chchordae tendineaeordae tendineae, are attached to the apices, margins , are attached to the apices, margins and ventricular surfaces of the cusps.and ventricular surfaces of the cusps. The The trabeculae carneaetrabeculae carneae are irregular muscular colum are irregular muscular columns which project from the whole of the inner surface ons which project from the whole of the inner surface of the ventricle. Some of them are merely elevated ridgf the ventricle. Some of them are merely elevated ridges, others form conical projections, the es, others form conical projections, the papillary muspapillary musclescles, which give origin to the chordae tendineae. The , which give origin to the chordae tendineae. The chordae tendineae of each papillary muscle are connechordae tendineae of each papillary muscle are connected with the contiguous margins of two cusps, hence, cted with the contiguous margins of two cusps, hence, there are 3 papillary muscles on th eright side.there are 3 papillary muscles on th eright side.

A muscular band termed the A muscular band termed the moderator bandmoderator band or or septomarginal trabeculaseptomarginal trabecula, which extends fr, which extends from the interventricular septum to the base of om the interventricular septum to the base of the aterior papillary muscle. It serves to convethe aterior papillary muscle. It serves to convey the right bundle branch of the atrioventriculy the right bundle branch of the atrioventricular bundle.ar bundle. Tricuspid valve complexTricuspid valve complex: The rings and apex: The rings and apexes of tricuspid valve, chordae tendineae, and pes of tricuspid valve, chordae tendineae, and papillary muscles constitute the tricuspid valve apillary muscles constitute the tricuspid valve complex.complex.

2. 2. Outflow tract of the right ventricle, conus arteriosus or infundibulum It has smooth walls and leads upwards to the opening of the pulmonary trunk, termed the pulmonary orifice. The pulmonary valve consists of three semilunar cusps, which are attached to the pulmonary orifice, their free borders being directed upwards into the lumen of the vessel. The semilunar valves are constructed to permit the flow of blood in only one direction.

ⅢⅢ) The Left Atrium) The Left Atrium It constitutes the most part of the base oIt constitutes the most part of the base of the heart.f the heart. It is divided into two portions, an anterioIt is divided into two portions, an anterior part (the left auricle), and a posterior pr part (the left auricle), and a posterior part (left atrial sinus or atrium proper). art (left atrial sinus or atrium proper).

1. Left auricle1. Left auricle A small somewhat conical pouch, termed the A small somewhat conical pouch, termed the lleft auricleeft auricle, projects forwards from its upper le, projects forwards from its upper left corner and overlaps the root of the pulmonaft corner and overlaps the root of the pulmonary trunk. The pectinate muscles, fewer and smry trunk. The pectinate muscles, fewer and smaller than those in the right atrium, are confinealler than those in the right atrium, are confined to the inner surface of the auricle. d to the inner surface of the auricle.

2. 2. left atrial sinusleft atrial sinus or or atrium properatrium proper The interior side of left atrial sinus is smooth.The interior side of left atrial sinus is smooth. The The pulmonary veinspulmonary veins, four in number, open in, four in number, open into the upper part of the posterior surface of thto the upper part of the posterior surface of the left atrium, two on each side; their orifices are left atrium, two on each side; their orifices are not provided with valves.e not provided with valves. The The left atrioventricular orificeleft atrioventricular orifice is the apertur is the aperture between the left atrium and ventricle.e between the left atrium and ventricle.

ⅣⅣ) The Left Vertricle) The Left Vertricle It constitutes the left inferior portion anIt constitutes the left inferior portion and the apex of the heart. Inferiorly, it formd the apex of the heart. Inferiorly, it forms a large part of the diaphragmatic surfas a large part of the diaphragmatic surface of the heart.ce of the heart. Inflow tract.Inflow tract. Left atrioventricular (or bicuspid, mitral) Left atrioventricular (or bicuspid, mitral) valvevalve Anterior cusp.Anterior cusp. Poterior cusp.Poterior cusp.

Mitral valve complexMitral valve complex: : The rings and apThe rings and apexes of bicuspid valve, chordae tendineaexes of bicuspid valve, chordae tendineae, and papillary muscles constitute the te, and papillary muscles constitute the tricuspid valve complex.ricuspid valve complex. Outflow tractOutflow tract.. Aortic vestibule.Aortic vestibule. Aortic orifice.Aortic orifice. Aortic sinuses.Aortic sinuses.

ⅣⅣ. The Structure of Heart. The Structure of Heart The wall of the heart comprises three layers, named frThe wall of the heart comprises three layers, named from within outwards endocardium, myocardium and eom within outwards endocardium, myocardium and epicardium.picardium. (1) The (1) The endocardiumendocardium is a thin, smooth, glistening me is a thin, smooth, glistening membrane which lines the chambers of the heart, and is mbrane which lines the chambers of the heart, and is continuous with the lining of the large blood vessels.continuous with the lining of the large blood vessels. The valves are formed by duplications of the lining enThe valves are formed by duplications of the lining endocardium of the heart, strengthened by intervening ldocardium of the heart, strengthened by intervening layer of fibrous tissue.ayer of fibrous tissue. (2) The (2) The myocardiummyocardium consists of the ordinary cardiac consists of the ordinary cardiac muscle and specially differentiated cardiac muscle (thmuscle and specially differentiated cardiac muscle (the conduction system).e conduction system).

(3) The (3) The epicardiumepicardium is the visceral layer of the is the visceral layer of the serous pericardium.serous pericardium. It consists of a layer of the mesothelium and a It consists of a layer of the mesothelium and a delicate layer of connective tissue.delicate layer of connective tissue. The interatrial septum and interventricular seThe interatrial septum and interventricular septumptum:: The The interatrial septuminteratrial septum is placed so obliquely is placed so obliquely that the right atrium lies in front and to the rigthat the right atrium lies in front and to the right of the left atrium. It is formed by two layers ht of the left atrium. It is formed by two layers of the endocardium, strengthened by fibrous tof the endocardium, strengthened by fibrous tissue and containing a few muscular fibers.issue and containing a few muscular fibers.

The The interventricular septuminterventricular septum slops obliquely f slops obliquely from before backwards and towards the right, rom before backwards and towards the right, and is curved with the convexity towards the riand is curved with the convexity towards the right ventricle. Its margins correspond with the ght ventricle. Its margins correspond with the anterior and posterior interventricular grooves anterior and posterior interventricular grooves on the surface of the heart, it is so called the on the surface of the heart, it is so called the mmuscular partuscular part of the interventricular septum. In of the interventricular septum. In its upper part, there is a thin, fibrous area, whiits upper part, there is a thin, fibrous area, which is termed the ch is termed the membranous partmembranous part..