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Chapter 23
The heart is a hollow muscular organ that pumps blood through the body. It is cone-shaped and weighs about 250 to 300 grams on average. The heart is ...
The heart is located in the mediastinum and spans from the first rib to the diaphragm. It lies anterior to the vertebral column, posterior to the sternum, ...
The heart wall has three layers—the epicardium, the myocardium, and the endocardium. The outermost layer, the epicardium, is the visceral layer of ...
The heart has four chambers—the right atrium, right ventricle, left atrium, and left ventricle. Externally, the coronary sulcus separates the atria ...
The heart valves open and close in response to the pressure gradients created by the contracting heart chambers. These valves regulate the blood flow by ...
The pulmonary and systemic circuits work sequentially to move blood between the heart, lungs, and peripheral tissues. Pulmonary circulation transports ...
The myocardium has its own network of blood vessels, separate from the systemic and pulmonary circuits, called the coronary circulation. The left and ...
Autorhythmicity refers to the innate ability of the heart to initiate electrical signals and trigger muscle contractions. This intrinsic conduction system ...
An electrocardiogram, abbreviated as ECG, or EKG, is a test that captures a record of the heart's electrical activity. It is performed by placing ...
The cardiac cycle comprises the contraction, or systole, and relaxation, or diastole, during one heartbeat. During atrial systole, cardiac action ...
The electrical signals recorded on an electrocardiogram (ECG) occur before the mechanical processes of contraction and relaxation during the cardiac ...
Disturbances in the heart rhythm, or arrhythmia, can cause irregular heartbeats. If the heart rate falls below fifty beats per minute, it is called ...
Heart sounds are mainly produced when valve closures cause turbulence in the blood. These are best heard at chest locations slightly away from the valves ...
Cardiac output is the blood volume ejected from the ventricles into the blood vessels each minute. It is calculated by multiplying the stroke volume by ...
The stroke volume, which is the volume of blood ejected by a ventricle with each heartbeat, is regulated by three factors: preload, contractility, and ...
The brain's cardiovascular center activates the ANS based on inputs received from sensory receptors. For example, proprioceptors in muscles and joints ...
Physical activity is beneficial for cardiovascular health. For example, the American Heart Association recommends moderate-intensity aerobic exercises, ...
Congestive heart failure, or CHF, can reduce the heart's pumping efficiency. In CHF, an increase in preload excessively stretches the myocardium, ...
Development of the heart starts on the 18th or 19th day post-fertilization from a group of mesodermal cells called the cardiogenic area. By day 20, these ...
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