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# The Heart ## Pericardium The pericardium is a loose-fitting covering that surrounds the heart and functions to protect it from trauma and infection. It has three layers: 1. **Fibrous pericardium**: A tough, inelastic fibrous connective tissue. It prevents overstretching of the heart and provid...

# The Heart ## Pericardium The pericardium is a loose-fitting covering that surrounds the heart and functions to protect it from trauma and infection. It has three layers: 1. **Fibrous pericardium**: A tough, inelastic fibrous connective tissue. It prevents overstretching of the heart and provides protection and anchors the heart in place. 2. **Parietal pericardium**: A serous membrane that lines the fibrous pericardium. 3. **Visceral pericardium (epicardium)**: A serous membrane on the surface of the heart. The pericardial cavity is the space between the visceral and parietal layers, containing about 5-10 ml of pericardial fluid. This fluid lubricates the surfaces to prevent friction. ## Layers of the Heart Wall 1. **Endocardium**: The innermost layer consisting of simple squamous epithelium. It lines the chambers of the heart and covers the heart valves. 2. **Myocardium**: The middle layer, which is the thickest. It is responsible for pumping blood. It is the actual contracting muscle of the heart. 3. **Epicardium (visceral pericardium)**: The thin, transparent outermost layer of the heart wall. ## Special Feature of the Myocardium Cardiac muscle cells are branched cells with light striations and have specialized partitions (intercalated discs) between the cells. These intercalated discs allow for rapid transfer of electrical impulses between cardiac muscle cells. ## Chambers of the Heart Each side of the heart has two chambers: * **Atria**: The two upper chambers, known as the "receiving chambers." They receive blood from veins. * **Ventricles**: The two lower chambers, known as the "pumping chambers." They push blood. The chambers are separated by septa: 1. **Interatrial septum**: The upper portion that separates the right and left atria. 2. **Interventricular septum**: The larger lower portion that separates the right and left ventricles. ## Four Chambers 1. **Right Atrium**: A thin-walled chamber that receives deoxygenated blood returning from the body tissues. This blood is carried through the superior vena cava from the upper body and Inferior vena cava from the lower body. 2. **Right Ventricle**: Receives blood from the right atrium and pumps it to the lungs (via pulmonary artery). 3. **Left Atrium**: Receives oxygenated blood (high in oxygen content) from the lungs via the four pulmonary veins. 4. **Left Ventricle**: The heart's largest, most muscular, and thickest chamber. It pumps blood to all parts of the body through the aorta. ## Valves of the Heart **Atrioventricular (AV) Valves:** These valves lie between the atria and ventricles, preventing backflow of blood into the atria when ventricles contract. 1. **Tricuspid Valve (Right AV valve)**: Made of three cusps (leaflets or flaps). When open, blood flows freely from the right atrium into the right ventricle. When the ventricles contract, the valve closes to prevent backflow to the atrium, ensuring forward flow into the pulmonary artery. 2. **Mitral Valve (Bicuspid valve or Left AV valve)**: Made of two heavy cusps. It allows free flow from the left atrium to the left ventricle. When the left ventricle contracts, the valve closes to prevent backflow and ensures forward flow into the aorta. ## Chordae Tendineae Strands of fibrous connective tissue that connect the flaps of the AV valves to the papillary muscles. They help stabilize the flaps when the ventricles contract, preventing the valves from inverting. ## Papillary Muscles Cardiac muscle projections from the floor of a ventricle. They anchor the flaps of the AV valves via the chordae tendineae, preventing the valves from inverting during ventricular contraction ## Semilunar Valves Half-moon-shaped flaps growing out of the lining of the pulmonary artery and aorta. These prevent blood from flowing back into the ventricles from the aorta and pulmonary artery.