The Chambers

The heart has four chambers (see fig. 19.4). Blood returning to the heart is received by two superior chambers, the right and left atria (AY-tree-uh; singular atrium6). These are mostly posterior in position, so only a small portion of each is visible from the anterior aspect. Each atrium has a small earlike extension called an auricle7 that slightly increases its volume. The two inferior chambers, the right and left ventricles,8 are the pumps that eject blood into the

5endo = internal eatrium = entryway

7 auricle = little ear

Bventr = belly, lower part + icle = little

Saladin: Anatomy & I 19. The Circulatory System: I Text I I © The McGraw-Hill

Physiology: The Unity of The Heart Companies, 2003 Form and Function, Third Edition arteries. The right ventricle constitutes most of the anterior aspect of the heart, while the left ventricle forms the apex and inferoposterior aspect.

The heart is crisscrossed by sulci (grooves) that mark the boundaries of the four chambers. The sulci are occupied largely by fat and coronary blood vessels. The atrioventricular (coronary9) sulcus encircles the heart near its base and separates the atria from the ventricles. The anterior and posterior interventricular sulci extend vertically, from the coronary sulcus toward the apex, externally marking the boundary between the right and left ventricles.

The four chambers are best seen in a frontal section (fig. 19.6). The atria exhibit thin flaccid walls corresponding to their light workload—all they do is pump blood into the ventricles immediately below. They are separated from each other by a wall, the interatrial septum. The right atrium and both auricles exhibit internal ridges of myocardium called acoron = crown + ary = pertaining to

Chapter 19 The Circulatory System: The Heart 721

the pectinate10 muscles. A thicker wall, the interventricular septum, separates the right and left ventricles. The right ventricle pumps blood only to the lungs and back, so its wall is only moderately thick and muscular. The left ventricle is two to four times as thick because it bears the greatest workload of all four chambers, pumping blood through the entire body. Both ventricles exhibit internal ridges called trabecu-lae carneae11 (trah-BEC-you-lee CAR-nee-ee).

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