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A comprehensive overview of the heart's anatomy and physiology, covering its structure, function, blood flow, electrical activity, and common disorders. It delves into the details of heart chambers, valves, blood vessels, and the conduction system, offering a clear and informative explanation of how the heart works. The document also discusses coronary circulation, heart sounds, and heart failure, providing valuable insights into the complexities of this vital organ.
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Location, Size, and Position of the Heart o The heart is a triangular, hollow, muscular double pump organ located in mediastinum (between two lungs) of thoracic cavity with two thirds of the mass to the left of the body midline and one third to the right; o The apex is on the diaphragm; o The shape and size of a closed fist.
Anatomy of the Heart
Heart chambers : A partition (septum) divides the heart into right and left sides. Heart has four chambers. The septum between the atrial chambers is called the interatrial septum; the interventricular septum separates the ventricles. o Two upper chambers are called atria (receiving chambers)—right and left atrium. o Two lower chambers are called ventricles (discharging chambers)—right and left ventricles. o The atria are smaller than the ventricles, and their walls are thinner and less muscular. Atria are often called receiving chambers because blood enters the heart through veins that open into these upper cavities. Eventually, blood is pumped from the heart into arteries that exit from the ventricles; therefore the ventricles are sometimes referred to as the discharging chambers of the heart.
Three layers of the heart’s wall- o Myocardium : Wall of each heart chamber is composed of cardiac muscle tissue called myocardium o Endocardium: S mooth inner lining of heart chambers. o Pericardium(covering of the heart): A two-layered outer fibrous sac that covers the heart with a lubricated space between the two layers.
The inner layer of the pericardium is called the visceral pericardium, or epicardium. The outer layer of pericardium is called the parietal pericardium. The two pericardial layers slide against each other without friction when the heart beats because these are serous membranes with moist surfaces. A thin film of pericardial fluid furnishes the lubricating moistness between the two layers of pericardium.
Types of blood vessels-
VEINS ARTERIES Carry deoxygenated blood (except pulmonary vein)
Carry oxygenated blood (except pulmonary artery) Carry blood towards the heart Carry blood away from the heart Bluish in color Bright red in color
Valves present Valves absent Veins are superficial Arteries are deep
Heart valves Valves keep blood flowing through the heart; prevent backflow. A. Atrioventricular (AV) Valv e: The two valves that separate the atrial chambers above from the ventricles below are called AV, or atrioventricular valves. The two Atrioventricular (AV) valves are: o Tricuspid valve—between right atrium and right ventricle o Bicuspid (mitral)— between left atrium and left ventricle. A number of stringlike structures called chordae tendineae attach the AV valves to the wall of the heart
B. Semilunar or SL valves are located between the two ventricular chambers and the large arteries that carry blood away from the heart when contraction occurs. The ventricles, like the atria, contract together. Therefore, the two semi-lunar valves open and close at the same time. The two semilunar valves are: o The pulmonary semilunar valve is located at the beginning of the pulmonary artery and allows blood going to the lungs to flow out of the right ventricle but prevents it from flowing back into the ventricle. o The aortic semi-lunar valve is located at the beginning of the aorta and allows blood to flow out of the left ventricle into the aorta but prevents backflow into this ventricle.
Disorder of valves A congenital defect in valve structure can result in mild to severe pumping inefficiency. o Incompetent valves leak, allowing some blood to flow back into the chamber from which it came. o Stenosed valves are valves that are narrower than normal, slowing blood flow from a heart chamber. o Rheumatic heart disease is cardiac damage resulting from a delayed inflammatory response to streptococcal infection that occurs most often in children. A few weeks after an untreated or improperly treated streptococcal infection, the cardiac valves and other tissues in the body may become inflamed—a condition called rheumatic fever. If severe, the inflammation can result in stenosis or other deformities of the valves, chordae tendineae, or myocardium. o Mitral valve prolapse (MVP), a condition affecting the bicuspid, or mitral, valve, may be genetic but can result from rheumatic fever or other factors. A prolapsed mitral valve is one whose flaps extend back into the left atrium, causing incompetence (leaking) of the valve. o Damaged or defective cardiac valves often can be replaced surgically. Animal valves and artificial valves made from synthetic materials are commonly used in valve replacement procedures.
Heart Sounds Two distinct heart sounds in every heartbeat, or cycle—"lub-dup". Disorders of the cardiac valves are often diagnosed by detecting changes in these normal valve sounds of the heart. o First sound (lub) is caused by the vibration and closure of AV valves (mitral and tricuspid) during contraction of the ventricles o Second sound (dup) is caused by the closure of the semilunar valves during relaxation of the ventricles o This first sound is of longer duration and lower pitch than the second. The pause between this first sound and the dup, or second sound, is shorter than that aft er the second sound and the lub dup of the next systole.
Blood Supply to Heart Muscle Coronary Circulation and Coronary Heart Disease o The heart muscle or myocardium requires a constant supply of blood containing nutrients and oxygen to function effectively. The delivery of oxygen and nutrient-rich arterial blood to cardiac muscle tissue and the return of oxygen-poor blood from this active tissue to the venous system is called the coronary circulation. Blood, which supplies oxygen and nutrients to the myocardium of the heart, flows through the right and left coronary arteries. o Blockage of blood flow through the coronary arteries can cause MI myocardial infarction (heart attack) resulting severe chest pain. In both coronary thrombosis and coronary embolism a blood clot occludes or plugs up some part of a coronary artery. Blood cannot pass through the occluded vessel and so cannot reach the heart muscle cells it normally supplies. Deprived of oxygen, these cells soon become damaged. In medical terms, myocardial infarction (MI), or tissue death, occurs. o Atherosclerosis , a type of "hardening of arteries" in which lipids build up on the inside wall of blood vessels) can partially or totally block coronary blood flow. o Many pathophysiologists believe the increase rate of MI results from a change in lifestyle. They cite several important risk factors associated with coronary atherosclerosis: physical inactivity, cigarette smoking, high-fat and high-cholesterol diets, obesity, hypertension (high blood pressure), and diabetes. o Angina pectoris —chest pain caused by inadequate oxygen to the heart. It is often a warning that the coronary arteries are no longer able to supply enough blood and oxygen to the heart muscle. o A therapy called coronary angioplasty , a less invasive procedure, is often attempted first to treat blockages to coronary blood flow. Angioplasty, in which a device is inserted into a blocked artery to force open a channel for blood flow. o Coronary bypass surgery is a common treatment for those who suffer from severely restricted coronary artery blood flow. In this procedure, veins are "harvested" or removed from other areas of the body and used to bypass partial blockages in coronary arteries.
Cardiac Cycle o The beating of the heart is a regular and rhythmic process. Each complete heartbeat is called a cardiac cycle and includes the contraction (systole) and relaxation (diastole) of atria and ventricles. o Each cycle takes about 0.8 second to complete if the heart is beating at an average rate of about 72
Electrocardiography The electrocardiogram or ECG is the graphic record of the heart's electrical activity. The Specialized conduction system structures generate and transmit the electrical impulses that result in contraction of the heart. This tiny electrical impulses/activity can be picked up on the surface of the body and transformed into visible tracings by a machine called an electrocardiograph. The visible tracing of these electrical signals is called an electrocardiogram , or EKG. an EGG measures the amount of the electrical activity produced by the heart and the time necessary for the electrical impulses to travel through the heart during each heartbeat A normal ECG tracing has three very characteristic deflections, or waves, called the P wave, the QRS complex, and the T wave. a. P wave—associated with depolarization of the atria b. QRS complex associated with depolarization of the ventricles c. T wave—associated with repolarization of the ventricles The recovery of the atria (atrial repolarization) is so slight; it is lost behind the strong QRS complex. Some uses of electrocardiography are to: (1) detect myocardial ischemia, (2) estimate damage to the myocardium caused by a myocardial infarction, (3) detect and evaluate cardiac arrhythmia , (4) assess effects of cardiac medication on the heart, and (5) determine if electrolyte imbalance is present.
Cardiac dysrhythmia/arrhythmia: Abnormality of heart rhythm. Various conditions such as endocarditis or myocardial infarction can damage the heart's conduction system and thereby disturb the rhythmic beating of the heart. Heart Block: One kind of dysrhythmia is called a heart block. In AV node block , impulses are blocked from getting through to the ventricular myocardium, resulting in the ventricles contracting at a much slower rate than normal. The physician may treat heart block by implanting in the heart an artificial pacemaker, a battery-operated device implanted under the skin and connected by thin wires to the myocardium. This device stimulates the myocardium with timed electrical impulses that cause ventricular contractions at a rate fast enough to maintain an adequate circulation of blood. Bradycardia : slow heart rate (less than 60 beats/min). Slight bradycardia is normal during sleep and in conditioned athletes while they are awake (but at rest). Tachycardia : rapid heart rate (more than 100 beats/min). Tachycardia is normal during and after exercise and during the stress response. Premature contractions , or extrasystoles : Contractions that occur before the next expected contraction in a series of cardiac cycles. For example, premature atrial contractions (PACs) may occur shortly after the ventricles contract. Premature contractions often occur with lack of sleep, anxiety, cold medications, too much caffeine or nicotine, alcoholism, or heart damage. Fibrillation: Frequent premature contractions can lead to fibrillation , a condition in which cardiac muscle fibers contract out of step with each other. In fibrillation, the affected heart chambers do not effectively pump blood. o Atrial fibrillation (AF or A-fib) occurs commonly in mitral stenosis, rheumatic heart disease, and infarction of the atrial myocardium. o Ventricular fibrillation (VF or V-fib) is an immediately life-threatening condition in which the lack of ventricular pumping suddenly stops the flow of blood to vital tissues. Unless ventricular fibrillation is corrected immediately by defibrillation or some other method, death may occur within minutes. o Fibrillation may be treated immediately by AED (Automated External Defibrillator) that apply an electric shock to force cardiac muscle fibers to once again contract in rhythm. o Internal defibrillators called implantable cardioverter-defibrillators (ICDs) can be implanted much like a pacemaker in patients prone to cardiac fibrillation or tachycardia. ICDs automatically monitor for fibrillation, then produce a defibrillating shock without any external intervention. Heart Failure o Heart failure is the inability of the heart to pump enough returned blood to sustain life—can be caused by many different heart diseases such as, a. Valve disorders, cardiomyopathy, or disease of the myocardial tissue, myocardial infarction , dysrhythmias, such as complete heart block or ventricular fibrillation. o Right-sided heart failure — Right-sided heart failure often results from the progression of disease that begins in the left side of the heart. Failure of the left side of the heart results in reduced pumping of blood returning from the lungs. Blood backs up into the pulmonary circulation, then into the right heart— causing an increase in pressure that the right side of the heart simply cannot overcome. Right-sided heart failure also can be caused by lung disorders that obstruct normal pulmonary blood flow and thus overload the right side of the heart—a condition called cor pulmonale. o Left-sided heart failure ( congestive heart failure )— Congestive heart failure (CHF), or simply left- sided heart failure, is the inability of the left ventricle to pump blood effectively. Most often, such failure results
