The Cardiac Muscle PDF: Structure, Function & Heart Valves

Comprehensive Overview of the Heart's Structure and Function The Heart ​ The heart is a muscular double pump ○​ Two functions ​ Pulmonary Circuit: Right side receives oxygen-poor blood from the body and pumps it to the lungs ​ Systemic C...

Comprehensive Overview of the Heart's Structure and Function The Heart ​ The heart is a muscular double pump ○​ Two functions ​ Pulmonary Circuit: Right side receives oxygen-poor blood from the body and pumps it to the lungs ​ Systemic Circuit: Left side receives oxygenated blood from lungs and pumps throughout the body Heart Location and Orientation in the Thorax ​ Position: ○​ Located between the lungs. ○​ Tilted with its apex pointing leftward from the midline. ○​ Situated within the mediastinum extending from the second to the fifth intercostal space. ​ Healthy heart typically weighs around 250-350 grams Four "Corners" of the Heart ​ Superior Right: At the costal cartilage of the third rib and sternum. ​ Inferior Right: At the costal cartilage of the sixth rib lateral to the sternum. ​ Superior Left: At the costal cartilage of the second rib lateral to the sternum. ​ Inferior Left: Lies in the fifth intercostal space at the midclavicular line. Structure of the Heart: Coverings ​ Pericardium: ○​ Fibrous Pericardium: A strong layer of dense connective tissue providing mechanical support and protection. ○​ Serous Pericardium: This is divided into the parietal layer and visceral layer (epicardium). Layers of the Heart Wall 1.​ Epicardium (most superficial): ○​ The visceral layer of the serous pericardium. 2.​ Myocardium: ○​ Composed of cardiac muscle arranged in circular and spiral patterns. 3.​ Endocardium: ○​ A simple squamous epithelium resting on a layer of connective tissue, which lines the interior of the heart chambers. Chambers of the Heart ​ Right and Left Atria: ○​ Upper chambers that receive blood. ​ Right and Left Ventricles: ○​ Lower chambers responsible for pumping blood. Internal Divisions ​ Interventricular Septum: Divides the two ventricles. ​ Interatrial Septum: Divides the two atria. External Markings ​ Coronary Sulcus: Encircles the heart, separating atria from ventricles. ​ Anterior and Posterior Interventricular Sulci: Run along the boundaries between the left and right ventricles. Right Atrium ​ Function: Forms the right border of the heart and receives deoxygenated blood from the systemic circuit via the superior vena cava, inferior vena cava, and coronary sinus. ​ Internal Features: ○​ Pectinate Muscles: Rigid muscles on the anterior wall. ○​ Crista Terminalis: A landmark used to locate vein entries. ○​ Fossa Ovalis: A depression in the interatrial septum, remnant of the fetal foramen ovale. Right Ventricle ​ Function: Pumps blood into the pulmonary circuit via the pulmonary trunk. ​ Internal Features: ○​ Trabeculae Carneae: Irregular muscular ridges. ○​ Papillary Muscles: Anchor chordae tendineae. ○​ Chordae Tendineae: Prevent valve prolapse. ○​ Pulmonary Semilunar Valve: Located at the opening to the pulmonary trunk. Left Atrium ​ Function: Receives oxygenated blood from the lungs via pulmonary veins. ​ Internal Features: Opens into the left ventricle through the left atrioventricular valve (bicuspid or mitral valve). Left Ventricle ​ Features: ○​ The apex of the heart. ○​ Internal Walls: Similar to the right ventricle but with thicker myocardium (cardiac muscle) due to the higher force required to pump blood through the systemic circuit. ​ Trabeculae Carneae: Irregular muscular ridges. ​ Papillary Muscles: Anchor chordae tendineae. ​ Chordae Tendineae: Prevent valve prolapse. ○​ Aortic Semilunar Valve: At the opening to the aorta. Heart Valves ​ Atrioventricular (AV) Valves: ○​ Tricuspid Valve (Right): Between the right atrium and ventricle. ○​ Bicuspid (Mitral) Valve (Left): Between the left atrium and ventricle. ​ Semilunar Valves: ○​ Aortic Valve: Between the left ventricle and aorta. ○​ Pulmonary Valve: Between the right ventricle and pulmonary trunk. Cardiac Skeleton ​ Composed of dense connective tissue that surrounds all four valves, providing structural support. ​ Functions: ○​ Anchors valve cusps prevents overdilation of valve openings ○​ Main point of cardiac for cardiac muscle ○​ Blocks direct spread of electrical impulses Function of the AV Valves ​ Purpose: Prevent backflow into the atria during ventricular contraction. ​ Mechanism: ○​ As ventricles fill, the valve flaps hang limply. ○​ When ventricles contract, papillary muscles contract and chordae tendineae tighten to prevent prolapse. Function of the Semilunar Valves ​ Purpose: Prevent backflow from arteries into the ventricles. ​ Mechanism: ○​ Valves open due to ventricular contraction. ○​ Valves close as ventricles relax and blood tries to flow back into the ventricles. Heart Sounds ​ "Lub-Dup": The sound of valves closing. ​ "Lub": Closure of AV valves. ​ "Dup": Closure of semilunar valves. Pathway of Blood Through the Heart 1.​ Oxygen-poor Blood: ○​ Enters the right atrium via superior and inferior vena cavae. ○​ Flows into the right ventricle and is pumped to the lungs through pulmonary arteries. 2.​ Oxygen-rich Blood: ○​ Returns from the lungs to the left atrium via pulmonary veins. ○​ Flows into the left ventricle and is pumped through the aorta to the systemic circuit. Heartbeat ​ Normal Rate: 70–80 beats per minute at rest. ​ Phases: ○​ Systole: Contraction phase. ○​ Diastole: Expansion (relaxation) phase. Structure of Heart Wall ​ Walls differ in thickness ○​ Atria- Thin walls ○​ Ventricles- thick walls ○​ Systemic Circuit ​ Longer than pulmonary circuit ​ Offers greater resistance to blood flow Cardiac Muscle Tissue ​ Characteristics: ○​ Striated and contracts via the sliding filament mechanism. ○​ Cells are short, branching, with one or two nuclei. ​ Connections: ○​ Intercalated Discs: Form complex junctions with adjacent cells. ○​ Fascia Adherens and Gap Junctions: Facilitate synchronous contraction. Mechanism of Contraction ​ Initiated by the influx of calcium ions into the sarcoplasm. ​ Signals the sarcoplasmic reticulum to release more calcium, triggering contraction. ​ Not all cardiac cells are innervated ○​ Will contract in rhythmic manner without innervation ○​ Inherent rhythmicity ​ Is the basis for rhythmic heartbeat Conduction System ​ Cardiac muscle tissue has intrinsic ability to: ○​ Generate and conduct impulses ○​ Signal these cells to contract rhythmically ​ Conducting System: ○​ A series of specialized cardiac muscle ○​ Sinoatrial (SA) node sets the inherent rate of contraction Disorders of the Heart ​ Coronary Artery Disease: Includes conditions such as atherosclerosis, angina pectoris, and myocardial infarction. ​ Heart Failure: Progressively weakened heart that can lead to congestive heart failure. ​ Arrhythmias: Abnormal heart rhythms including atrial and ventricular fibrillation. Blood Supply to the Heart ​ Coronary Arteries: Arise from the base of the aorta and supply the heart muscle. ​ Coronary Veins: Carry deoxygenated blood from the myocardium to the right atrium. Innervation of the Heart ​ Parasympathetic Fibers: Decrease heart rate (vagus nerve). ○​ Restricted to: ​ SA node, AV node, coronary arteries ​ Sympathetic Nerves: Increase heart rate and contraction strength from the cervical and upper thoracic chain ganglia. ○​ Innervate SA node, AV node, coronary arteries- same as parasympathetic ○​ Also innervate cardiac musculature throughout the heart ○​ Increase heart rate and strength of contraction ​ Autonomic input: ○​ Controlled by cardiac centers in reticular formation of medulla ​ Cardioinhibitory center- influences parasympathetic ​ Slows it down ​ Cardioacceleratory center- influences sympathetic neurons ​ Increase