organs and tissues and returning oxygen-poor blood to the lungs. About the size of a fist, the heart lies in the thoracic cavity in the
300 Base: Where the great vessels enter and leave the heart
The Heart Valves To ensure that blood moves in a forward direction through the heart, the heart contains four valves: one between each atrium and its ventricle and another at the exit of each ventricle. Each valve is formed by two or three flaps of tissue called cusps or leaflets . mediastinum , a space between the lungs and beneath the sternum. The heart tilts toward the left, so that
The atrioventricular (AV) valves regulate flow between the atria and the ventricles. ● The right AV valve—also called the tricuspid valve (because it has three leaflets)—prevents backflow from the right ventricle to the right atrium. ● The left AV valve—also called the bicuspid valve (because it has two leaflets), or, more commonly, the mitral valve —prevents backflow from the left ventricle to the left atrium. Fast Facts Important points related to a specific body system promote active involvement in the learning process. two-thirds of it extends to the left of the body’s midline. The broadest part of the heart, called the base , is at the upper right, while the pointed end, called the apex , is at the lower left.
Fifth intercostal space
Apex: The point of maximum impulse, where the strongest beat can be felt or heard
The semilunar valves regulate flow between the ventricles and the great arteries. There are two semilunar valves: ● The pulmonary valve prevents backflow from the pulmonary artery to the right ventricle. ● The aortic valve prevents backflow from the aorta to the left ventricle. 298 Structures of the Heart
Key structures of the heart include the pericardium, the heart wall, the chambers, and the valves.
The Pericardium Surrounding the heart is a double-walled sac called the pericardium . Anchored by ligaments and tissue to surrounding structures, the pericardium has two layers: the fibrous pericardium and serous pericardium.
The serous pericardium , which consists of two layers, covers the heart’s surface. The fibrous pericardium —a loose- fitting sac of strong connective tissue—is the outermost layer.
FAST FACT The study of the heart and the treatment of related disorders is called cardiology .
Pulmonary valve
At the heart’s base, the serous pericardium folds back on itself to form the:
Aortic valve
Skeleton of heart
• parietal layer, which lines the inside of the fibrous pericardium, and the • visceral layer, which covers the heart’s surface.
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Heart
Tricuspid valve
The human heart beats about 100,000 times in 1 day and about 35 million times in a year. During an average lifetime, the human heart will beat more than 2.5 billion times.
Mitral valve
Between these two layers is the pericardial cavity. This cavity contains a small amount of serous fluid, which helps prevent friction as the heart beats.
Ventricles relaxed Composed of a type of muscle found nowhere else in the body, the heart works to pump blood throughout the body, delivering oxygen-rich blood to The heart could be called the engine of life. This incredibly powerful organ works constantly, never pausing.
Pericardium
Ventricles contracted
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organs and tissues and returning oxygen-poor blood to the lungs. About the size of a fist, the heart lies in the thoracic cavity in the
Base: Where the great vessels enter and leave the heart
The Heart Wall The heart wall consists of three layers:
The Heart Skeleton A semi-rigid, fibrous, connective tissue called the skeleton of the heart encircles each valve. Besides offering support for the heart, the skeleton keeps the valves from stretching; it also acts as an insulating barrier between the atria and the ventricles, preventing electrical impulses from reaching the ventricles other than through a normal conduction pathway. The endocardium lines the heart’s chambers, covers the valves, and continues into the vessels. It consists of a thin layer of squamous epithelial cells. Fifth intercostal space Midline mediastinum , a space between the lungs and beneath the sternum. The heart tilts toward the left, so that two-thirds of it extends to the left of the body’s midline. The broadest part of the heart, called the base , is at the upper right, while the pointed end, called the apex , is at the lower left. Apex: The point of maximum impulse, where the strongest beat can be felt or heard
The myocardium, composed of cardiac muscle, forms the middle layer. It’s the thickest of the three layers and performs the work of the heart.
The epicardium, which consists of a thin layer of squamous epithelial cells, covers the heart’s surface. Also known as the visceral layer of the serous pericardium, the epicardium is closely integrated with the myocardium.
FAST FACT The study of the heart and the treatment of related disorders is called cardiology .
Right midclavicular line
Left midclavicular line
FAST FACT The endocardium is very smooth, an important characteristic that helps keep blood from clotting as it fills the heart’s chambers.
Pulmonary valve
Aortic valve
Skeleton of heart, including fibrous rings around valves 4/3/24 11:25 AM
Tricuspid valve
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Mitral valve
Full-color Illustrations Meticulously detailed artwork with crystal-clear explanations makes complex concepts and processes easy to understand.
The Body AT WORK Valves open and close in response to pressure changes within the heart. For example, when a ventricle relaxes, the pressure within that ventricle drops. The AV valve leaflets hang limply, allowing blood to flow through the open valve into the ventricle. As the ventricle fills, pressure in the ventricle rises. After filling, the ventricle begins to contract and the pressure rises even more. This increased pressure pushes against the cusps of the AV valve, causing it to snap closed. When pressure in the ventricle exceeds the pressure “downstream,” the semilunar valve pops open, allowing blood to flow out into the area of lower pressure.
The Body at Work Brief summaries explain physiological processes. Posterior view
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That Makes Sense Brief explanations and analogies offer tips to help students place concepts in context as a tool for remembering important ideas.
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