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HEART
The heart is a muscular organ that is responsible for pumping blood throughout the body. It is located in the chest, behind the sternum, and between the lungs. Position The heart is located in the chest, slightly to the left of the center of the chest, between the lungs and behind the sternum (breastbone).The top of the heart is called the base and the bottom is called the apex. The heart is surrounded by a protective sac called the pericardium. Organs Associated with the heart Inferiorly —the apex rest on the central tendon of diaphragm Superiorly —the great blood vessels,i.e.the aorta, superior vena cava, pulmonary artery and pulmonary veins Posteriorly—the oesophagus,trachea,left and right bronchus, descending aorta, inferior vena cava and thoracic vertebrae Laterally—the lungs-the left lung overlaps and left side of heart Anteriorly —the sternum,ribs and intercostal muscles
Structure The heart is composed of three layers: the epicardium, myocardium, and endocardium. Epicardium: This is the outermost layer of the heart and is also called the visceral pericardium. It is a thin layer of connective tissue that covers the heart and also contains blood vessels and nerves. Myocardium: This is the middle layer of the heart and is responsible for pumping blood throughout the body. It is composed of cardiac muscle fibers and is the thickest of the three layers. Endocardium: This is the innermost layer of the heart and is in direct contact with the blood that is being pumped. It is made up of a layer of endothelial cells and connective tissue.
1.)Deoxygenated blood enters the right atrium of the heart through two large veins called the superior vena cava and inferior vena cava. These veins bring blood from the body that has already circulated through the tissues and given up oxygen. 2.)From the right atrium, the blood flows through the tricuspid valve into the right ventricle. The tricuspid valve is a one-way valve that prevents blood from flowing back into the atrium. 3.)The right ventricle then contracts, pumping the blood through the pulmonary valve and into the pulmonary artery. The pulmonary artery carries the deoxygenated blood to the lungs, where it picks up oxygen and releases carbon dioxide. 4.)The oxygenated blood returns to the heart through the pulmonary veins, entering the left atrium. 5.)From the left atrium, the blood flows through the mitral valve into the left ventricle. Like the tricuspid valve, the mitral valve is a one-way valve that prevents blood from flowing back into the atrium. 6.)The left ventricle contracts, pumping the blood through the aortic valve and into the aorta, the body's largest artery. The aorta carries the oxygenated blood to the rest of the body.
Pulmonary and systemic circulation
The coronary arteries are the blood vessels that supply the heart muscle with oxygen-rich blood. They arise from the base of the aorta, which is the largest artery in the body, and branch out into smaller vessels that penetrate the heart muscle. The right coronary artery supplies blood to the right side of the heart, while the left coronary artery divides into two branches: the left anterior descending artery and the left circumflex artery, which supply blood to the left side of the heart. The coronary arteries are surrounded by small blood vessels called capillaries, which allow for the exchange of oxygen and nutrients between the blood and the heart muscle cells. The deoxygenated blood is then collected by the cardiac veins and returned to the right atrium of the heart through the coronary sinus. The heart also has its own network of blood vessels, called the coronary collateral circulation, which provides an alternative route for blood flow in case of blockage or narrowing of the main coronary arteries Proper blood supply to the heart is essential for maintaining its normal function, and any disruption in this blood flow can lead to serious cardiovascular problems.
Conducting system of heart The conducting system of the heart is responsible for coordinating the contractions of the heart muscle, which allows for efficient pumping of blood throughout the body. The conducting system consists of specialized cardiac muscle cells that are capable of generating and conducting electrical impulses. The major components of the conducting system include the sinoatrial (SA) node, atrioventricular (AV) node, bundle of His, and Purkinje fibers. 1.)The SA node is located in the right atrium and serves as the natural pacemaker of the heart. It generates an electrical impulse that spreads across the atria and stimulates them to contract. 2.)The AV node is located at the junction between the atria and ventricles. It receives the electrical impulse from the SA node and delays it briefly before passing it on to the bundle of His. 3.)The bundle of His is a bundle of specialized fibers that extends from the AV node down the septum (the wall that divides the right and left ventricles).
4.)The Purkinje fibers are specialized cardiac muscle fibers that spread throughout the ventricles and transmit the electrical impulse rapidly, causing the ventricles to contract and pump blood out of the heart. The coordinated activity of the conducting system ensures that the atria and ventricles contract in a synchronized manner, allowing for efficient blood flow through the heart. Any disruption or damage to the conducting system can result in abnormal heart rhythms or arrhythmias, which can be dangerous and may require medical
The sympathetic nerves to the heart originate from the thoracic spinal cord (T1-T4) and travel through the sympathetic chain to reach the heart. These nerves release the neurotransmitter norepinephrine, which activates beta-1 adrenergic receptors on the cardiac muscle cells, resulting in increased heart rate and contractility. The parasympathetic nerves to the heart originate from the vagus nerve, which is a cranial nerve that originates in the brainstem. These nerves release the neurotransmitter acetylcholine, which activates muscarinic receptors on the cardiac muscle cells, resulting in decreased heart rate and contractility.
