Mitral Valve

Aortic Valve

Papillary Muscle


FIGURE 4-1 Anatomy of the heart. SVC, superior vena cava; RA, right atrium; IVC, inferior vena cava; PA, pulmonary artery; PV, pulmonary veins; LA, left atrium; LV, left ventricle; RV, right ventricle.

papillary muscles located on the respective ventricular walls. The papillary muscles contract when the ventricles contract. This generates tension on the valve leaflets via the chordae tendineae, preventing the AV valves from bulging back and leaking blood into the atria (i.e., preventing regurgitation) as the ventricles develop pressure. The semilunar valves (pulmonic and aortic) do not have analogous attachments.

Autonomic Innervation

Autonomic innervation of the heart plays an important role in regulating cardiac function. The heart is innervated by parasympathetic (vagal) and sympathetic efferent fibers. (See Chapter 6 for details on the origin of these autonomic nerves.) The right vagus nerve preferentially innervates the sinoatrial (SA) node, whereas the left vagus nerve innervates the AV node; however, significant overlap can occur in the anatomical distribution. Atrial muscle is also innervated by vagal efferents; the ventricular myocardium is only sparsely innervated by vagal efferents. Sympathetic efferent nerves are present throughout the atria (especially in the SA node) and ventricles and in the conduction system of the heart.

Vagal activation of the heart decreases heart rate (negative chronotropy), decreases conduction velocity (negative dromotropy), and decreases contractility (negative ino-tropy) of the heart. Vagal-mediated inotropic influences are moderate in the atria and relatively weak in the ventricles. Activation of the sympathetic nerves to the heart increases heart rate, conduction velocity, and inotropy. Sympathetic influences are pronounced in both the atria and ventricles.

As Chapter 6 describes in more detail, the heart also contains vagal and sympathetic afferent nerve fibers that relay information from stretch and pain receptors. The stretch receptors involve feedback regulation of blood volume and arterial pressure, whereas the pain receptors produce chest pain when activated during myocardial ischemia.

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Blood Pressure Health

Blood Pressure Health

Your heart pumps blood throughout your body using a network of tubing called arteries and capillaries which return the blood back to your heart via your veins. Blood pressure is the force of the blood pushing against the walls of your arteries as your heart beats.Learn more...

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