The heart is a muscular organ located in the thoracic cavity, slightly to the left of the midline, between the lungs. It is about the size of a fist and lies within the pericardium, a protective sac. The heart functions as the central pump of the circulatory system, ensuring a continuous flow of blood throughout the body.
Externally, the heart shows four main chambers divided into two atria (upper chambers) and two ventricles (lower chambers). The atria receive blood, while the ventricles pump it out. On the surface, grooves called sulci mark the separation of chambers and contain blood vessels. Small pouch-like extensions, known as auricles, increase the capacity of the atria.
Internally, the heart is divided by septa into right and left sides. The right atrium receives deoxygenated blood from the body and passes it to the right ventricle, which pumps it to the lungs through the pulmonary artery. The left atrium receives oxygenated blood from the lungs and delivers it to the left ventricle, the strongest chamber, which pumps blood to the whole body through the aorta. Valves regulate the flow of blood and prevent backflow: the tricuspid valve lies between the right atrium and ventricle, the pulmonary valve between the right ventricle and pulmonary artery, the mitral (bicuspid) valve between the left atrium and ventricle, and the aortic valve between the left ventricle and aorta.
The heart wall consists of three layers. The innermost layer, the endocardium, lines the chambers and valves. The middle layer, the myocardium, is composed of cardiac muscle and is responsible for contraction. The outer layer, the epicardium, forms part of the protective covering. Surrounding the heart is the pericardium, a double-walled sac with fluid that reduces friction during heartbeats.
The blood supply of the heart is maintained by the coronary arteries, which branch from the aorta. The right and left coronary arteries and their branches deliver oxygen and nutrients to the heart muscle. Venous blood from the myocardium drains through cardiac veins into the coronary sinus, which opens into the right atrium.
The heart also has a specialized conduction system that regulates its rhythm. The sinoatrial (SA) node, known as the natural pacemaker, initiates electrical impulses that spread through the atria. The atrioventricular (AV) node delays the signal before passing it to the bundle of His, which branches into right and left bundle branches and Purkinje fibers, ensuring coordinated contraction of the ventricles.
Altogether, the anatomy of the heart reveals a highly organized structure where chambers, valves, vessels, and electrical pathways work in harmony to maintain life by pumping blood efficiently to the lungs and the rest of the body.
How the Heart Works Together to Pump Blood
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| Human heart |
At the center of the circulatory system lies the heart, a muscular organ roughly the size of a fist, located in the chest cavity between the lungs. The heart functions as a powerful pump, maintaining the continuous flow of blood throughout the body. It is divided into four chambers: the right atrium and right ventricle, which receive and pump deoxygenated blood to the lungs, and the left atrium and left ventricle, which receive and pump oxygenated blood to the rest of the body. The rhythmic contractions of the heart ensure that blood is propelled with enough force to reach every tissue and organ.
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| Arteries and viens system |
Arteries are the blood vessels that carry oxygen-rich blood away from the heart to various parts of the body. Their thick, muscular walls allow them to withstand the high pressure of blood being pumped from the heart. The largest artery in the body is the aorta, which branches into smaller arteries and then arterioles, delivering oxygen and nutrients to tissues.
In contrast, veins are responsible for carrying deoxygenated blood back to the heart. Their walls are thinner than arteries, and they are equipped with valves that prevent blood from flowing backward, ensuring that blood moves steadily toward the heart, even against the pull of gravity. The largest veins in the body are the superior and inferior vena cava, which return blood from the upper and lower parts of the body, respectively.
Capillaries form the link between arteries and veins and are the smallest and thinnest blood vessels in the circulatory system. Their thin walls, composed of a single layer of cells, allow the exchange of gases, nutrients, and waste products between blood and body tissues. Oxygen and nutrients diffuse out of the capillaries into the cells, while carbon dioxide and waste products move from the cells into the capillaries to be carried away.
Together, the heart, arteries, veins, and capillaries form a closed network that ensures continuous blood circulation. The heart acts as the pump, arteries distribute oxygen-rich blood, capillaries facilitate exchange at the tissue level, and veins return blood to the heart for reoxygenation. This constant cycle allows the body to function efficiently, providing energy to cells, removing waste, and sustaining life.
Basic Anatomy of the Heart (Relevant to Disease)
1. Chambers:
2. Valves (ensure one-way blood flow):
3. Major Vessels:
4. Coronary Arteries:
5. Conduction System:
Heart Diseases & Their Anatomical Correlations
1.Coronary Artery Disease (CAD) / Ischemic Heart Disease
2. Myocardial Infarction (Heart Attack)
3. Heart Failure
4. Valvular Heart Disease
5. Cardiomyopathies (Diseases of Heart Muscle)
Dilated Cardiomyopathy: LV (and/or RV) dilation + weak contraction → HF.Hypertrophic Cardiomyopathy: Asymmetric LV hypertrophy(often septum) → outflow obstruction, arrhythmias.
6. Arrhythmias (Rhythm Disorders)
7. Congenital Heart Defects
8. Pericardial Diseases
Pericardium: Double-layered sac around the heart.Pericarditis: Inflammation → chest pain, friction rub.Cardiac tamponade: Fluid buildup in pericardial space → compresses heart → reduced filling → shock.
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