Heart

• The heart, located in the mediastinum between the second rib and the fifth intercostal space, is two-thirds to the left of the midsternal line and anterior to the vertebral column, posterior to the sternum.
• The heart is enclosed in a double-walled sac known as the pericardium, which is covered by an epithelial membrane called serosa.
• The pericardium has two layers: the visceral layer and the parietal layer.
• The pericardial cavity is filled with fluid for lubrication to reduce friction.
• The heart consists of three layers: the epicardium, the myocardium, and the endocardium.
• STEMI, or Severe Ischemia Myocardial Infarction, is usually caused by major blockage and causes extensive heart damage.
• Right heart failure leads to ankle and leg edema.
• Non-STEMI, or Non-Severe Ischemia Myocardial Infarction, is caused by partial obstruction and causes less extensive damage.
• Left heart failure leads to pulmonary edema.
• Heart Attack, also known as Myocardial Infarction (MI), is a condition where heart cells start dying due to ischemia of the myocardium.
• Heart Attack shows elevation of the S-T segment on ECG.
• Congestive Heart Failure is a condition where the heart is unable to pump blood as fast as it is returning.
• The epicardium is the visceral layer of the serous pericardium.
• The myocardium contains spiral bundles of cardiac muscle and a fibrous skeleton of the heart, made of a criss-crossing, interlacing layer of connective tissue.
• The endocardium covers the inside of the heart walls and is continuous with the endothelial lining of blood vessels.
• The atria are receiving chambers, with the right atrium receiving blood from the superior vena cava, inferior vena cava, and coronary sinus, and the left atrium receiving blood from the pulmonary vein.
• The ventricles are pumping/discharging chambers, with two types of muscles: trabeculae carneae and papillary muscles.
• The atrioventricular valves are tricuspid and bicuspid, preventing backflow of blood into the atria from ventricles, and each valve contains cusps.
• The atria have four chambers and the ventricles have two chambers.
• The atrioventricular groove, also known as the coronary sulcus, is located on the anterior and posterior sides of the heart.
• The right side of the heart is part of the pulmonary circuit, with a short, lower pressure circulation, while the left side is part of the systemic circuit, with a longer circulation and higher pressure.
• The coronary circulation is a smaller system that supplies the heart itself, with major arteries including the coronary, marginal, circumflex, and interventricular, and major veins including the small cardiac, anterior cardiac, great cardiac, and coronary sinus.
• The heart muscle is a functional syncytium, with all muscle fibers working as one big cell due to gap junctions between the muscles, allowing the action potentials to conduct from one muscle fiber to the others.
• The heart muscle has unique characteristics, including being branched to create a 3D network and anchored to each other by desmosomes, with intercalated discs formed, which prevent separation during contraction.
• The heart muscle has many more mitochondria than skeletal muscle, with one connective layer, three ion channels for Ca++, Na+, and K+.
• The action potential in the heart muscle involves depolarization of the sarcolemma, opening Na+ channels, with the membrane potential going from -90 until it reaches +20mv, Na+ channels closed, and the depolarization wave also causing the Ca++ channels to open, so Ca++ enters from the sarcoplasmic reticulum slowly, prolonging depolarization.
• Regulation of Stroke Volume, Three main factors affect SV: Preload, Contractility, Afterload.
• Congenital Defects of the Heart, Atrial Septal Defect, hole in interatrial septum, Ventricle Septal Defect (Roger’s Disease), hole in interventricular septum, Tetralogy of Fallot, VSD, Pulmonary valve problem (stenosis), Right ventricular hypertrophy, Aorta overriding.
• Autonomic Regulation, Atrial (Bainbridge) Reflex, a sympathetic reflex initiated by increased venous return, Stretch of the atrial walls stimulates the SA node, Also stimulates atrial stretch receptors activating sympathetic reflexes.
• Regurgitation, Valve does not close properly, Mitral and Tricuspid valve regurgitation leads to systolic murmur, Aortic and Pulmonic valve regurgitation leads to diastolic murmur.
• Chemical Regulation of Heart Rate, Epinephrine from adrenal medulla enhances heart rate and contractility, Thyroid Hormone increases heart rate and enhances the effects of norepinephrine and epinephrine.
• Contractility, contractile strength at a given muscle length, independent of muscle stretch and EDV, Positive inotropic agents increase contractility, Increased Ca2+ influx due to sympathetic stimulation, Hormones (epinephrine).
• Auscultation, “A PET MONKEY”.
• Heart Murmurs, Stenosis, Valve does not open properly, Mitral and Tricuspid valve stenosis leads to diastolic murmur, Aortic and Pulmonic valve stenosis leads to systolic murmur.
• Heart Disorders, Coronary Artery Disease, the most common type of heart disease, Caused by arteriosclerosis, Hardening and narrowing of arteries, Leads to inability to change size of vessels, Risk Factors: High BP, High Cholesterol, Obesity, Diabetes, Smoking, Lack of Exercise, Age, Family history, Treatments: Medication, Stent.
• Deviations from normal Heart Rhythm (Arrhythmias), Tachycardia (more than 100 bpm), Bradycardia (less than 60 bpm), Fibrillations.
• Preload, degree of stretch of cardiac muscle cells before they contract (Frank-Starling law of the heart), Cardiac muscle exhibits a length-tension relationship, At rest, cardiac muscle cells are shorter than optimal length, Increased filling  increases stretch  increases contraction force  increases SV.
• Regulation of Heart Rate, Positive chronotropic factors increase heart rate, Dopamine, epinephrine, Negative chronotropic factors decrease heart rate, Beta blockers, Acetylcholine.
• Angina Pectoris, severe chest pain that often spreads into the
• Cardiac Output, Volume of blood pumped by each ventricle in one minute, CO = heart rate (HR) x stroke volume (SV), HR = number of beats per minute (60-100), SV = volume of blood pumped out by a ventricle with each beat (70 ml).