Anatomy Exam 4: Heart
Direction of blood flow through the heart:
1. Superior Vena Cava, Inferior Vena Cava and Coronary Sinus 2. Right atrium 3. Tricuspid valve 4. Right ventricle 5. Pulmonary semilunar valve 6. Pulmonary trunk 7. Pulmonary arteries 8. Lungs 9. Pulmonary veins 10. Left atrium 11. Bicuspid valve 12. Left Ventricle 13. Aortic semilunar valve 14. Aorta
Pulmonary Semilunar Valve
A semilunar valve, unlike atrioventricular valves, does not possess papillary muscles and chordae tendineae. Rather, it merely exists as pocket like flaps surrounding an opening. For each semilunar valve there are 3 flaps or cusps. The free edge of each cusp has a small central thickening of fibrous tissue termed the NODULE. Extending from each side of the nodule is a narrow thin crescent area termed the LUNULA. The spaces between the cusps and the wall of the vessel are called SINUSES. When the flow of blood is from the right ventricle into the pulmonary trunk, the valve opens. If the flow is retrograde, the valve closes.
Right Atrium
A vertical muscular ridge is seen on the posterior wall of the right atrium called the Crista Terminalis. Extending from the crista terminalis are muscular, ridge like projections called Musculi Pectinati (Pectinate Muscle). The Musculi Pectinati are found in the right atrium and in the right and left auricles. There are three major venous openings into the right atrium. These are the: • Superior vena caval opening • Inferior vena caval opening • Opening of the coronary sinus.
Introduction CONT
Anteriorly, the heart is protected by the sternum. Laterally, the heart is protected by the ribs, intercostal muscles and lungs. Posteriorly, the heart is protected by the thoracic vertebrae. In addition to the previous structures, the heart is encased in a tough connective tissue sac called the pericardium.
Tricuspid Valve
Anteriorly, the right atrium opens to the right ventricle via the right atrioventricular opening. The right atrioventricular opening is guarded by the Tricuspid Valve or Right Atrioventricular Valve. A Valve is a mechanical device that will allow for flow of blood in 1 direction only, thus preventing retrograde flow (flow in the wrong direction). The heart is composed of 2 types of valves: atrioventricular valves and semilunar valves. (Semilunar valves will be discussed separately.)
Pulmonary Circulation CONT
Blood will flow through the pulmonary trunk which bifurcates into the left and right Pulmonary Arteries. The right and left pulmonary arteries carry deoxygenated blood to the right and left lungs respectively. It's important to note that the pulmonary arteries are the only arteries in the body which carry DEOXYGENATED BLOOD. Oxygenated blood will return to the heart via the four Pulmonary Veins, 2 from the right lung and 2 from the left lung. All four pulmonary veins will enter the left atrium.
External Anatomy of the heart CONT
Both the Left and Right Atria have ear-like appendages called Auricles attached to their lateral surfaces. The auricles increase the internal surface area of the left and right atria. Clinically, the term auricle is also referred to as the appendage.
Variations in the aortic branches
Bovine heart syndrome is a congenital condition which occurs when the branches of the aortic arch take on alternate configurations resembling that of a cows anatomy.
Coronary Circulation
Coronary Arteries arise from the ascending aorta and supply the myocardium of the heart itself with blood and oxygen. There are two coronary arteries aptly named the Left and Right Coronary Arteries which lead to the left and right sides of the heart respectively.
Coronary Bypass Surgery
Coronary bypass surgery involves harvesting the internal thoracic (internal mammillary) arteries or greater saphenous vein which are literally utilized to "bypass" the obstructed coronary arteries and reestablish blood flow to the myocardium. Single, double, triple or quadruple bypass surgeries are possible depending on the extent of the obstruction.
Hypertension
Due to atherosclerotic plaque build up in the arteries of the body, blood pressure will increase leading to Hypertension. The heart responds to the increased oxygen demands by increasing the force of its contractions. Prolonged hypertension can lead to Hypertrophy of the myocardium which increases the risk for myocardial infarction.
Brachiocephalic Trunk
Following the coronary arteries, the first main branch off the aortic arch is the BRACHIOCEPHALIC TRUNK.
Pulmonary Circulation
Following the pulmonary semilunar valve, blood will flow through the pulmonary trunk into the right and left pulmonary arteries, to the right and left lungs. Within the lungs, blood will give off CO2 and acquire O2. Blood will flow through the pulmonary trunk which bifurcates into the left and right Pulmonary Arteries. The right and left pulmonary arteries carry deoxygenated blood to the right and left lungs respectively.
Conduction system of the heart
Like any other muscle tissue in the body, the heart relies on nervous innervation to initiate contraction. The nerve impulse initiates at the SINUATRIAL (SA) NODE located at the base of the superior vena cava, just superior to the right atrium. The impulse is carried to the ATRIOVENTRICULAR (AV) NODE located within the membranous septum and is carried down the ATRIOVENTRICULAR (AV) BUNDLE (of HIS). From here, the impulse is carried down the LEFT and RIGHT BUNDLE BRANCHES to the PURKINJE FIBERS which radiate throughout the ventricles
Pulmonary Circulation CONT
Oxygenated blood will return to the heart via the four Pulmonary Veins, 2 from the right lung and 2 from the left lung. All four pulmonary veins will enter the left atrium. The pulmonary veins are the only veins in the body which carry OXYGENATED blood Blood flows through the pulmonary circuit as follows: 1. Right Ventricle 2. Pulmonary Semilunar Valve 3. Pulmonary Trunk 4. Pulmonary Arteries 5. Lungs 6. Pulmonary Veins 7. Left Atrium
Innervation to the heart
Parasympathetic innervation of the heart is supplied by the Vagus Nerve (CN X). Release of the neurotransmitter Achetylcholine at the SA Node will act to decrease the rate and intensity of ventricular contractions thus, slowing the heart rate. Sympathetic innervation of the heart is derived from the Sympathetic Chain Ganglion located on either side of the spinal column. The release of the neurotransmitter Norepinephrine directly to the myocardium of the ventricles will result in increased heart rate and force of contraction.
Congenital Conditions of the heart
TETRALOGY of FALLOT involves the • stenosis of the pulmonary trunk • an interventricular septal defect • displacement of the aorta • and hypertrophy of the right ventricle. Children born with Tetralogy of Fallot will exhibit bluish skin upon episodes of crying or feeding.
Aortic Semilunar Valve
The AORTIC SEMILUNAR VALVE possesses 3 cusps located at the opening of the aorta. These cusps possess nodules, lunulae and sinuses as did the pulmonary semilunar valves. The spaces between the cusps and the wall of the aorta are termed AORTIC SINUSES and differ from the pulmonary sinuses in that the right and left aortic sinuses are the sites of origin for the right and left coronary arteries respectively. Blood leaves the left ventricle and enters the aorta and then passes to all parts of the systemic circulation.
Coronary Sinus
The Coronary Sinus is a short, wide vessel that receives all 3 cardiac veins and empties directly into the right atrium. The Anterior Cardiac Veins are 2 or 3 small vessels which drain the right ventricle and end directly in the right atrium. The Venae Cordis Minimae are numerous small veins that drain the myocardium itself and empty separately into all 4 chambers of the heart.
Right Atrium CONT
The Interatrial Septum is the partition between the right and left atria. -On this septum in the right atrium lies an oval depression called the Fossa Ovalis. -The fossa ovalis is surrounded at its periphery by a ridge called the Limbus Fossa Ovalis. The fossa ovalis is a remnant of a foramen that, in the fetal stage of development, existed between the right atrium and left atrium. -This opening is called the Foramen Ovale. -Normally, the foramen ovale closes at birth and becomes the fossa ovalis in adults.
Left Coronary Artery
The Left Coronary Artery originates from the left side of the aorta and courses a short distance before giving off 2 branches. It bifurcates into the Left Anterior Descending Artery (Anterior Interventricular Branch). and the Circumflex Branch. The Circumflex Branch courses posteriorly and terminates by anastomosing with the Right Coronary Artery on the posterior surface of the heart. The Left Anterior Descending (Anterior Interventricular Branch) continues inferiorly across the anterior surface of the heart and terminates by anastomosing with the posterior interventricular branch from the right coronary artery.
Pericardium
The Pericardium is a fibrous sac that encloses the heart. Its outer layer blends with the central tendon of the diaphragm inferiorly. Superiorly, and posteriorly, the fibrous layer blends with the major blood vessels of the heart (the superior vena cava, aorta, and pulmonary trunk).
Right Coronary Artery
The Right Coronary Artery originates from the right side of the aorta, courses underneath the right auricle and continues to the posterior surface of the heart. It gives off the Right Marginal Branch and the Posterior Interventricular Branch. The right coronary artery terminates posteriorly by anastomosing with the CIRCUMFLEX BRANCH of the left coronary artery.
Major Vessels
The SUPERIOR VENA CAVA drains the head, neck and upper limbs. -It is formed as the left and right BRACHIOCEPHALIC VEINS join together and empty into the right atrium. The AORTA supplies the entire body with blood and originates at the aortic semilunar valve within the left ventricle of the heart. The aorta is divided into 3 regions: • The ASCENDING AORTA leads form the heart and courses superiorly. • The AORTIC ARCH courses posteriorly and to the left giving off it's major branches. • The DESCENDING AORTA courses posterior to the heart as it descends through the thorax. The PULMONARY TRUNK leads from the right ventricle and carries deoxygenated blood from the heart to the lungs for oxygenation.
Right Atrium CONT
The Superior Vena Caval Opening is the opening for the superior vena cava, the main vein returning blood from the upper half of the body. The Inferior Vena Caval Opening is the opening for the inferior vena cava, the main vein returning blood from the lower half of the body. The coronary sinus is a venous chamber located on the posterior surface of the heart. -It receives the cardiac veins that drain the myocardium of the heart itself. -It opens into the right atrium just anterior and superior to the inferior vena cava.
Tricuspid Valve CONT
The atrioventricular valve is characteristically composed of three parts: -CUSPS are flaps of connective tissue named according to their anatomical position. -CHORDAE TENDINEAE are connective tissue cords that attach to the lower surface of the cusps. -PAPILLARY MUSCLES are internal folds of ventricular muscle that give attachment to the chordae tendineae. The tricuspid valve functions in closing during contraction of the right ventricle. When closed, it will prevent backflow of blood from the right ventricle to the right atrium. The valve is held in a closed position via the chordae tendineae that are attached to the lower surface of the cusps, and are thus not everted into the atrium.
Right Subclavian and Right Common Carotid Arteries
The brachiocephalic trunk quickly branches into the RIGHT SUBCLAVIAN ARTERY and the RIGHT COMMON CAROTID ARTERY which supply the right upper limb and the right side of the face and head respectively.
Myocardium
The cardiac muscle itself is referred to as Myocardium.
Major Vessels CONT
The great vessels from right to left across the base of the heart can be remembered as "S.A.P." Which stands for: • Superior vena cava • Aorta • Pulmonary trunk The INFERIOR VENA CAVA receives blood from the lower limbs, pelvis and abdomen and enters the right atrium of the heart inferiorly. -It's important to note that the inferior vena cava does not attach to the base of the heart but, to it's diaphragmatic surface
Introduction
The heart is a muscle that functions in pumping blood through vessels of the cardiovascular system. The heart is composed of striated muscle, cardiac in type. The heart has 4 internal cavities called chambers, 2 atria and 2 ventricles. The atria and ventricles are further differentiated by the side of the body; thus we can speak of the 4 chambers as the right atrium, left atrium, right ventricle and left ventricle. The heart is positioned in such a way that the atria lie posterior (not superior) to the ventricles; thus, blood passing from the atria to the ventricles moves horizontally rather that vertically. The heart is located in the thorax between the lungs, resting on the diaphragm.
External Anatomy of the heart
The heart is described as having an apex, base and three surfaces: The Sternocostal surface of the heart lies adjacent to the sternum and costal cartilages. The Diaphragmatic surface of the heart is adjacent to the diaphragm. The Pulmonary surface of the heart lies adjacent to the medial surface of the left and right lungs. The Apex is a rounded projection of the heart that points inferiorly and to the left. It lies at the level of the left 6th costal cartilage. The Base is located superiorly and posteriorly. It is the area where the great vessels attach to the heart. These vessels are the Aorta, Pulmonary Trunk, and Superior Vena Cava.
Endocardium
The inner epithelium lining the chambers of the heart is referred to as Endocardium.
Right Ventricle
The internal surface of the ventricle consists of irregular ridge like projections of muscle called TRABECULAE CARNEAE. Papillary muscles are a specialized type of trabeculae carnae. Another special type of trabeculae carneae is a band of muscle that attaches to the interventricular septum and to the papillary muscle called the Moderator Band or Septomarginal Trabecula. It contains important fibers of the conduction system of the heart (the right branch of the AV bundle). The only openings of the right ventricle are the Right Atrioventricular Opening (guarded by the Tricuspid Valve) and the Pulmonary Trunk Opening. Blood will leave the right ventricle and enter the pulmonary trunk by passing through the Pulmonary Trunk Opening guarded by the Pulmonary Semilunar Valve.
Coronary Stint Placement
The left anterior descending branch of the left coronary artery has also acquired the morbid nickname "The Widow Maker" due to it's susceptibility to developing atherosclerotic plaque build up. This plaque reduces blood flow to the antero-inferior surfaces of the heart which leads to a localized area of myocardial ischemia (lack of oxygen to the myocardium). Typical treatments include coronary stint placement or if the blockage is more advanced, coronary bypass surgery.
Bicuspid Valve
The left atrioventricular opening is guarded by the Bicuspid Valve, Mitral Valve or Left Atrioventricular Valve. Being an atrioventricular valve, it has supporting papillary muscles connected to chordae tendineae which, in turn, attach to the cusps. It contains 2 cusps. Blood will flow from the left atrium into the left ventricle through the bicuspid valve.
Left Atrium
The left atrium has its musculi pectinati located within the left auricle only. The majority of the surface area of the left atrium is taken up by the 4 separate openings of the pulmonary veins. The only other opening of the left atrium is the Left Atrioventricular Opening guarded by the Bicuspid Valve, Mitral Valve or Left Atrioventricular Valve.
Left Ventricle
The left ventricle contains the internal muscular ridge like folds called TRABECULAE CARNEAE. Papillary muscles of the bicuspid valve are a type of trabeculae carneae. One major difference between the right and left ventricles is the thickness of the wall itself. The wall of the left ventricle is usually more than twice as thick as that of the right. The right ventricle must pump blood only to 1 organ, the lungs. The left ventricle must pump blood to every organ of the body with exception of the lungs. Thus, the left ventricle performs more work and is therefor larger The only openings of the left ventricle are the: • Left Atrioventricular Opening • Opening of the Aortic Semilunar Valve When the left ventricle contracts, blood will leave the heart and enter the aorta. The opening of the aorta is guarded by the Aortic Semilunar Valve.
Coronary Veins (Venous Drainage of the Heart)
The muscle of the heart is drained by the Cardiac Veins. There are three major veins that all drain into the Coronary Sinus. The Great Cardiac Vein courses with the anterior interventricular artery and circumflex branch. It continues on the posterior surface of the heart as the coronary sinus. The Small Cardiac Vein courses with the marginal branch and drains into the coronary sinus. The Middle Cardiac Vein courses with the posterior interventricular artery and drains directly into the coronary sinus.
Left common carotid artery
The next branch off the aortic arch is the LEFT COMMON CAROTID ARTERY which supplies the left side of the head and neck. The final branch off the aortic arch is the LEFT SUBCLAVIAN ARTERY which supplies the left upper limb.