3. internal structure of the heart
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The document summarizes the internal structure of the heart, including its four chambers, septa that divide them, and valves that regulate blood flow. It describes the conduction system that controls heart contractions, including the sinoatrial node that initiates impulses, the atrioventricular node that relays them to ventricles, and Purkinje fibers that conduct impulses through the ventricles. It also reviews the heart's blood supply, innervation by the autonomic nervous system, and roles of the sympathetic and parasympathetic fibers.
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3. internal structure of the heart
- 1. Internal structure of the heart Dr. Mohammed Mahmoud Mosaed
- 2. THE HEART • The heart is divided by vertical septa into four chambers: 1. the right and left atria 2. the right and left ventricles. • The right atrium lies anterior to the left atrium, and the right ventricle lies anterior to the left ventricle
- 3. Internal structure of the right atrium • The right atrium consists of cavity and small auricle • The cavity of the right atrium is divided by cresta terminalis into; • 1. Posterior smooth part is derived embryologically from the sinus venosus • 2. Anterior rough part is roughened or trabeculated by bundles of muscle fibers, the musculi pectinati, which run from the crista terminalis to the auricle. • This anterior part is derived embryologically from the primitive atrium.
- 4. Openings into the Right Atrium • 1.The superior vena cava opens into the upper part of the right atrium; it has no valve. • 2.The inferior vena cava opens into the lower part of the right atrium; it is guarded by a rudimentary, nonfunctioning valve. • 3. The coronary sinus, which drains most of the blood from the heart wall. opens into the right atrium between the inferior vena cava and the atrioventricular orifice. It is guarded by a rudimentary, nonfunctioning valve. • 4. The right atrioventricular orifice lies anterior to the inferior vena caval opening and is guarded by the tricuspid valve. • 5. Many small orifices of small veins also drain the wall of the heart and open directly into the right atrium
- 7. Fetal Remnants in the right atrium • 1. The rudimentary valve of the inferior vena cava. • 2. The fossa ovalis and anulus ovalis. These structures lie on the atrial septum, which separates the right atrium from the left atrium. • The fossa ovalis is a shallow depression, which is the site of the foramen ovale in the fetus. • The anulus ovalis forms the upper margin of the fossa. • The floor of the fossa represents the persistent septum primum of the heart of the embryo, and the anulus is formed from the lower edge of the septum secundum.
- 8. Internal structures of the right ventricle • The walls of the right ventricle show several internal projecting ridges formed of muscle bundles known as trabeculae carneae. • The trabeculae carneae are composed of three types. • The first type; the papillary muscles, which project inward, being attached by their bases to the ventricular wall; their apices are connected by fibrous chords (the chordae tendineae) to the cusps of the tricuspid valve. • The second type is attached at the ends to the ventricular wall, being free in the middle. One of these, the moderator band, crosses the ventricular cavity from the septal to the anterior wall. It conveys the right branch of the atrioventricular bundle, which is part of the conducting system of the heart. • The third type is simply composed of prominent ridges
- 11. The tricuspid valve • The tricuspid valve guards the atrioventricular orifice and consists of three cusps: anterior, septal, and inferior (posterior) cusps. • The bases of the cusps are attached to the fibrous ring of the skeleton of the heart, whereas their free edges and ventricular surfaces are attached to the chordae tendineae. • The chordae tendineae connect the cusps to the papillary muscles. The chordae tendineae of one papillary muscle are connected to the adjacent parts of two cusps.
- 14. The pulmonary valve • The pulmonary valve guards the pulmonary orifice and consists of three semilunar cusps; one posterior (left cusp) and two anterior (anterior and right cusps). • The curved lower margins and sides of each cusp are attached to the arterial wall this attachment prevent the cusps from prolapsing into the ventricle. • No chordae or papillary muscles are associated with these valve cusps; • At the root of the pulmonary trunk are three dilatations called the sinuses, and one is situated external to each cusp
- 17. The internal structure of the left atrium • The interior of the left atrium is smooth, but the left auricle possesses muscular ridges as in the right auricle • Openings into the Left Atrium • 1. The four pulmonary veins, two from each lung, open through the posterior wall and have no valves. • 2. The left atrioventricular orifice is guarded by the mitral valve
- 20. Left Ventricle The walls of the ventricle show internal projecting ridges formed of muscle bundles known as trabeculae carneae. The trabeculae carneae are composed of two large papillary muscles, which project inward, being attached by their bases to the ventricular wall and their apices are connected by the chordae tendineae to the cusps of the mitral valve. There is no moderator band.
- 22. The mitral valve • The mitral valve guards the atrioventricular orifice. • It consists of two cusps, one anterior and one posterior. • The anterior cusp is the larger and intervenes between the atrioventricular and the aortic orifices. • The attachment of the chordae tendineae to the cusps and the papillary muscles is similar to that of the tricuspid valve.
- 24. The aortic valve • The aortic valve guards the aortic orifice. • It has 3 cusps: One cusp is situated on the anterior wall (right cusp) and two are located on the posterior wall (left and posterior cusps). • Behind each cusp the aortic wall bulges to form an aortic sinus. • The anterior aortic sinus gives origin to the right coronary artery, and the left posterior sinus gives origin to the left coronary artery
- 26. Conducting System of the Heart • The pumping action of the heart (heart beat) is controlled by the heart’s electrical system or the cardiac conduction system. This is a group of specialised cells located in the wall of the heart which send electrical impulses to the cardiac muscle causing it to contract. • The rhythmic contractile process originates spontaneously in the conducting system and the impulse travels to different regions of the heart, so the atria contract first and together, to be followed later by the contractions of both ventricles together.
- 27. The conducting system of the heart The conducting system of the heart consists of: the sinuatrial node, the atrioventricular node, the atrioventricular bundle and its right and left terminal branches the subendocardial plexus of Purkinje fibers (specialized cardiac muscle fibers that form the conducting system of the heart).
- 29. Sinuatrial Node • Site: located in the wall of the right atrium in the upper part of the sulcus terminalis just to the right of the opening of the superior vena cava. • The node spontaneously gives origin to rhythmic electrical impulses that spread in all directions through the cardiac muscle of the atria and cause the muscle to contract.
- 30. Atrioventricular Node • Site: on the lower part of the atrial septum just above the attachment of the septal cusp of the tricuspid valve. • From it, the cardiac impulse is conducted to the ventricles by the atrioventricular bundle. • The atrioventricular node is stimulated by the excitation wave as it passes through the atrial myocardium.
- 31. Atrioventricular Bundle • The atrioventricular bundle (bundle of His) is the only pathway of cardiac muscle that connects the myocardium of the atria and the myocardium of the ventricles • At the upper border of the muscular part of the ventricular septum it divides into two branches, one for each ventricle. • The right bundle branch (RBB) reach the moderator band, where it crosses to the anterior wall of the right ventricle. Here it becomes continuous with the fibers of the Purkinje plexus • The left bundle branch (LBB) pierces the septum and passes down on its left side beneath the endocardium. It usually divides into two branches (anterior and posterior), which eventually become continuous with the fibers of the Purkinje plexus of the left ventricle.
- 32. Arterial Supply to the Conducting System • The sinuatrial node is usually supplied by the right but sometimes by the left coronary artery. • The atrioventricular node and the atrioventricular bundle are supplied by the right coronary artery. • The RBB of the atrioventricular bundle is supplied by the left coronary artery; • The LBB is supplied by the right and left coronary arteries
- 33. Nerve Supply of the Heart • The heart is innervated by sympathetic and parasympathetic fibers of the autonomic nervous system via the cardiac plexuses situated below the arch of the aorta. • The sympathetic supply arises from the cervical and upper thoracic portions of the sympathetic trunks • The postganglionic sympathetic fibers terminate on the sinuatrial and atrioventricular nodes, on cardiac muscle fibers, and on the coronary arteries. Activation of these nerves results in cardiac acceleration, increased force of contraction of the cardiac muscle, and dilatation of the coronary arteries. • the parasympathetic supply comes from the vagus nerves. • The postganglionic parasympathetic fibers terminate on the sinuatrial and atrioventricular nodes and on the coronary arteries. Activation of the parasympathetic nerves results in a reduction in the rate and force of contraction of the heart and a constriction of the coronary arteries. • Afferent fibers running with the sympathetic nerves carry nervous impulses that normally do not reach consciousness. However, should the blood supply to the myocardium become impaired, pain impulses reach consciousness via this pathway. Afferent fibers running with the vagus nerves take part in cardiovascular reflexes