PowerPoint Lecture Outlines. Chapter 15. ANATOMY OF THE HEART. ANATOMY OF THE HEART. Size of Heart. Size 12 - 14 cm x 8 - 9 cm x 6 Weight, M – 280 to 340 g F – 230 to 280 g The heart continues to increase in weight and size up to an advanced period of life
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PowerPoint Lecture Outlines Chapter 15
Size of Heart • Size • 12 - 14 cm x 8 - 9 cm x 6 • Weight, • M – 280 to 340 g • F – 230 to 280 g • The heart continues to increase in weight and size up to an advanced period of life • This increase is more marked in men than in women.
Size of Heart • The wall of the right ventricle is thinner than that of the left, the proportion between them being as 1 to 3; it is thickest at the base, and gradually becomes thinner toward the apex. The cavity equals in size that of the left ventricle, and is capable of containing about 85 c.c.
Size of Heart • The left ventricle is longer and more conical in shape than the right, and on transverse section its concavity presents an oval or nearly circular outline. It forms a small part of the sternocostal surface and a considerable part of the diaphragmatic surface of the heart; it also forms the apex of the heart. Its walls are about three times as thick as those of the right ventricle.
Myocardial Thickness and Function • The thickness of the myocardium of the four chambers varies according to the function of each chamber. • The atria walls are thin because they deliver blood to the ventricles. • The ventricle walls are thicker because they pump blood greater distances (Figure 20.4a). • The right ventricle walls are thinner than the left because they pump blood into the lungs, which are nearby and offer very little resistance to blood flow. • The left ventricle walls are thicker because they pump blood through the body where the resistance to blood flow is greater.
Thickness of Cardiac Walls Myocardium of left ventricle is much thicker than the right.
Location of Heart • posterior to sternum • medial to lungs • anterior to vertebral column • base lies beneath 2nd rib • apex at 5th intercostal space • lies upon diaphragm
Heart Chambers • Right Atrium • receives blood from • inferior vena cava • superior vena cava • coronary sinus • Left Atrium • receives blood from pulmonary veins • Right Ventricle • receives blood from right atrium • Left Ventricle • receives blood from left atrium
Chambers and Sulci Anterior View
Chambers and Sulci Posterior View
Right Atrium • Receives blood from 3 sources • superior vena cava, inferior vena cava and coronary sinus • Interatrial septum partitions the atria • Fossa ovalis is a remnant of the fetal foramen ovale • Tricuspid valve • Blood flows through into right ventricle • has three cusps composed of dense CT covered by endocardium
Right Ventricle • Forms most of anterior surface of heart • Papillary muscles are cone shaped trabeculae carneae (raised bundles of cardiac muscle) • Chordae tendineae: cords between valve cusps and papillary muscles • Interventricular septum: partitions ventricles • Pulmonary semilunar valve: blood flows into pulmonary trunk
Left Atrium • Forms most of the base of the heart • Receives blood from lungs - 4 pulmonary veins (2 right + 2 left) • Bicuspid valve: blood passes through into left ventricle • has two cusps • to remember names of this valve, try the pneumonic LAMB • Left Atrioventricular, Mitral, or Bicuspid valve
Left Ventricle • Forms the apex of heart • Chordae tendineae anchor bicuspid valve to papillary muscles (also has trabeculae carneae like right ventricle) • Aortic semilunar valve: • blood passes through valve into the ascending aorta • just above valve are the openings to the coronary arteries
Heart Valves Tricuspid Valve Pulmonary and Aortic Valve
Atrioventricular Valves Open • A-V valves open and allow blood to flow from atria into ventricles when ventricular pressure is lower than atrial pressure • occurs when ventricles are relaxed, chordae tendineae are slack and papillary muscles are relaxed
Atrioventricular Valves Close • A-V valves close preventing backflow of blood into atria • occurs when ventricles contract, pushing valve cusps closed, chordae tendinae are pulled taut and papillary muscles contract to pull cords and prevent cusps from everting
Semilunar Valves • SL valves open with ventricular contraction • allow blood to flow into pulmonary trunk and aorta • SL valves close with ventricular relaxation • prevents blood from returning to ventricles, blood fills valve cusps, tightly closing the SL valves
Valve Function Review Ventricles contract, blood pumped into aorta and pulmonary trunk through SL valves Atria contract, blood fills ventricles through A-V valves
Skeleton of Heart • fibrous rings to which the heart valves are attached
Fibrous Skeleton of Heart • (Figure 20.5). Dense CT rings surround the valves of the heart, fuse and merge with the interventricular septum • Support structure for heart valves • Insertion point for cardiac muscle bundles • Electrical insulator between atria and ventricles • prevents direct propagation of AP’s to ventricles
Heart Actions Atrial Diastole/Ventricular Systole Atrial Systole/Ventricular Diastole
Cardiac Cycle • Atrial Systole/Ventricular Diastole • blood flows passively into ventricles • remaining 30% of blood pushed into ventricles • A-V valves open/semilunar valves close • ventricles relaxed • ventricular pressure increases
Cardiac Cycle • Ventricular Systole/Atrial diastole • A-V valves close • chordae tendinae prevent cusps of valves from bulging too far into atria • atria relaxed • blood flows into atria • ventricular pressure increases and opens semilunar valves • blood flows into pulmonary trunk and aorta
Heart Sounds • Lubb • first heart sound • occurs during ventricular systole • A-V valves closing • Dupp • second heart sound • occurs during ventricular diastole • pulmonary and aortic semilunar valves closing Murmur – abnormal heart sound
Cardiac Muscle Fibers • Cardiac muscle fibers form a functional syncytium • group of cells that function as a unit • atrial syncytium • ventricular syncytium
Muscle Bundles of the Myocardium • Cardiac muscle fibers swirl diagonally around the heart in interlacing bundles
Electrocardiogram • recording of electrical changes that occur in the myocardium • used to assess heart’s ability to conduct impulses P wave – atrial depolarization QRS wave – ventricular depolarization T wave – ventricular repolarization
Electrocardiogram • Impulse conduction through the heart generates electrical currents that can be detected at the surface of the body. A recording of the electrical changes that accompany each cardiac cycle (heartbeat) is called an electrocardiogram (ECG or EKG). • The ECG helps to determine if the conduction pathway is abnormal, if the heart is enlarged, and if certain regions are damaged. • Figure 20.12 shows a typical ECG.
Electrocardiogram---ECG or EKG • EKG • Action potentials of all active cells can be detected and recorded • P wave • atrial depolarization • P to Q interval • conduction time from atrial to ventricular excitation • QRS complex • ventricular depolarization • T wave • ventricular repolarization
ECG • In a typical Lead II record, three clearly visible waves accompany each heartbeat It consists of:. • P wave (atrial depolarization - spread of impulse from SA node over atria) • QRS complex (ventriculardepolarization - spread of impulse through ventricles) • T wave (ventricular repolarization). • Correlation of ECG waves with atrial and ventricular systole (Figure 20.13)
ECG • As atrial fibers depolarize, the P wave appears. • After the P wave begins, the atria contract (atrial systole). Action potential slows at the AV node giving the atria time to contract. • The action potential moves rapidly through the bundle branches, Purkinje fibers, and the ventricular myocardium producing the QRS complex. • Ventricular contraction after the QRS comples and continues through the ST segment. • Repolarization of the ventricles produces the T wave. • Both atria and ventricles repolarize and the P wave appears.
THE CARDIAC CYCLE • A cardiac cycle consists of the systole (contraction) and diastole (relaxation) of both atria, rapidly followed by the systole and diastole of both ventricles. • Pressure and volume changes during the cardiac cycle • During a cardiac cycle atria and ventricles alternately contract and relax forcing blood from areas of high pressure to areas of lower pressure.
One Cardiac Cycle - Vocabulary • At 75 beats/min, one cycle requires 0.8 sec. • systole (contraction) and diastole (relaxation) of both atria, plus the systole and diastole of both ventricles • End diastolic volume (EDV) • volume in ventricle at end of diastole, about 130ml • End systolic volume (ESV) • volume in ventricle at end of systole, about 60ml • Stroke volume (SV) • the volume ejected per beat from each ventricle, about 70ml • SV = EDV - ESV