Ch 11 Heart Notes

Anatomy & Physiology Circulatory System – The Heart I.

Heart Anatomy A. Size & Location 1. Weighs 250 – 350 grams (about ½ to ¾ lb.) 2. Roughly the size of your fist 3. Located in the Mediastinum (the space between the lungs. 4. It is beneath the sternum (however 2/3 of it is left of the midline) 5. Between the 2nd and the 6th ribs 6. Apex – the pointed bottom portion of the heart B. Coverings of the Heart 1. Pericardium (pericardial sac) – sac that enclosed the heart. 2. Fibrous pericardium – outermost, tough layer; protects and anchors the heart. 3. Parietal or Serous pericardium – thin, slippery layer attached to the fibrous pericardium. 4. Visceral pericardium – thin, slippery layer on the surface of the heart. (AKA – epicardium) 5. Pericardial cavity – space between the parietal & visceral layers. Contains pericardial fluid that functions to lubricate the heart. C. Layers of the Heart Wall 1. Epicardium – outermost (epi) layer; thin & slippery (AKA – visceral pericardium) 2. Myocardium – middle, muscle (myo) layer; composed of the cardiac muscle. 3. Endocardium – innermost (endo) layer; thin, white, smooth tissue that is continuous with the lining of the blood vessels. D. Chamber of the Heart 1. Atria – 2 smaller upper chambers a. Pump blood into ventricles b. Auricle – ear-like flap on the edge of each atrium. 2. Ventricles – 2 larger lower chambers a. Rt. Ventricle pumps blood out the Pulmonary Artery to the lungs (pulmonary circuit) b. Lt. Ventricle pumps blood out the Aorta to the whole body (systemic circuit) c. Lt. bigger than Rt. d. Interventricular Septum – wall between the two ventricles. E. Valves of the Heart 1. Atrioventricular valves – located between the atria & ventricles a. Tricuspid – between Rt. A and Rt. V b. Bicuspid / Mitral valve – between Lt. A and Lt. V 2. Semilunar valves – located between the ventricles and the exiting arteries a. Pulmonary SL – between Rt. V and pulmonary artery b. Aortic SL – between Lt. V and aorta 3. Valves function to prevent the back flow of blood within the Heart. 4. Chordae Tendinae – string-like structures that keep the cusps from being forced backwards. 5. Papillary muscles – muscles attached at the base of each chordae tendinae to regulate their tension and maintain a perfect seal. 6. Murmur – a leaking or damaged valve that causes a back flow of blood and thus a “swishing” sound. 7. Stenosis – stiffening and narrowing of valves due to scar tissue 8. The “sound” of the heart (lubb-dubb) is actually due to the valves slamming shut. F.

Coronary Circulation 1. Coronary circ. refers to blood flow to the heart muscle itself. 2. The Rt. & Lt. coronary arteries branch directly off of the Aorta. 3. Myocardial Infarction (MI) – clogging of the coronary arteries with plaque that prevents the flow of nutrients and oxygen to the myocardium. The lack of oxygen / nutrients to part of the heart muscle causes death of the heart muscle cells. The cells in this area quit beating in rhythm with the other cells thus causing fibrillation. a. Angioplasty b. Coronary bypass surgery

II.

Heart Physiology A. Cardiac Cycle 1. Systole – contraction of the ventricles or atria 2. Diastole – relaxation & filling of the ventricles or atria 3. This is done in a coordinated fashion. The atria contract and fill the ventricles, the ventricles then contract while the atria are filling up. B. Cardiac Output 1. Stroke Volume (SV) – amt. of blood pumped by the heart in a single stroke or beat = 70 ml / beat 2. Heart Rate (HR) – number of beats per minute by the heart = 75 beats / min. 3. Cardiac Output (CO) = SV x HR = 5250 ml / min. or 5.25 L / min. 4. The blood volume of the circ. system is about 5.5 L, thus the heart pushes the entire volume of blood through the body in one minute. C. Cardiac Conduction System – series of specialized cardiac muscle fibers that distribute impulses through out the heart and maintain a coordinated rhythm. 1. Sinoatrial Node (SA node) – pacemaker. 75 bpm. Located in the upper right part of the Rt. atrium. Contractions usually originate from here. 2. Atrioventricular Node (AV node) – secondary pacemaker. 50 bpm. Located just above the tricuspid valve. Upon damage to the SA node, the AV node can keep the heart beating (albeit slowly). 3. Atrioventricular Bundle (bundle of His) – electrical path that sweeps the contraction impulse to the apex of the heart. 4. Purkinje Fibers – electrical fibers that start in the interventricular septum and turn superiorly up the ventricular walls. They cause the ventricles to depolarize from the bottom towards the top. This helps to squeeze the blood out of the heart more efficiently. D. Electrocardiogram (EKG) (Kardio = German for heart) 1. EKG is a recording of the electrical activity of the heart. 2. The characteristic wave is divided in to three parts P a. P wave – atrial depolarization b. QRS wave – ventricle depolarization c. T wave – ventricle repolarization

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E. Regulation of the Heart Rate S 1. The autonomic NS both sympathetic and parasympathetic controls heart rate. 2. HR is monitored by the cardiac center in the medulla 3. Some of the monitoring receptors include: stretch receptors or pressoreceptors in the aorta, carotid arteries, and vena cava, as well as blood chemical monitors in the heart. F.

Heart Disorders 1. Arrhythmia – uncoordinated artial & ventricular contractions due to conduction problems. 2. Tachycardia – abnormally fast HR. 100 + bpm. 3. Bradycardia – abnormally slow HR. 60 bpm. 4. Fibrillation – heart is beating completely out of rhythm. 350 – 500 bpm. a. Defibrillation – shocking the heart in order to get the heart to restart and allow the SA node to take over again. 5. Congenital heart defects – birth defects that cause mixing of oxygenated and un-oxygenated blood and / or narrowed or defective valves. (Blue baby) a. Ventricular Septal Defect – hole in the interventricular septum b. Tetralogy of Fallot – multiple defects