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PART 4 Regulation and Maintenance

are mainly flat, but the interior of both auricles and a part of theright atrial wall contain muscular ridges called pectinate (pek ′ ti-n ā t) muscles. The pectinate muscles of the right atrium are sepa-rated from the larger, smooth portions of the atrial wall by a ridgecalled the crista terminalis (kris ′ t ă ter ′ mi-nal ′ is; terminal crest).The interior walls of the ventricles contain larger, muscular ridgesand columns called trabeculae (tr ă -bek ′ ū -l ē ; beams) carneae (kar ′ n ē - ē ; flesh).

External Anatomy and CoronaryCirculation

The heart consists of four chambers: two atria ( ā ′ tr ē - ă ; sing. atrium ) and two ventricles (ven ′ tri-klz). The thin-walled atria formthe superior and posterior parts of the heart, and the thick-walledventricles form the anterior and inferior portions (figure 20.5). Auricles (aw ′ ri-klz; ears) are flaplike extensions of the atria thatcan be seen anteriorly between each atrium and ventricle. Theentire atrium used to be called the auricle, and some medical per-sonnel still refer to it as such.Blood enters the atria of the heart through several large veins.The superior vena cava (v ē ′ n ă k ā ′ v ă ) and the inferior vena cava carry blood from the body to the right atrium. In addition, the

smaller coronary sinus carries blood from the walls of the heartto the right atrium. Four pulmonary veins carry blood from thelungs to the left atrium.Blood leaves the ventricles of the heart through two arteries:the pulmonary trunk and the aorta. The pulmonary trunk carriesblood from the right ventricle to the lungs. The aorta carries bloodfrom the left ventricle to the body. Because of their large size, thepulmonary trunk and aorta are often called the great arteries.The coronary circulation consists of blood vessels that carryblood to and from the tissues of the heart wall. The major vesselsof the coronary circulation lie in several grooves, or sulci, on thesurface of the heart. A large coronary (k ō r ′ o-n ā r- ē ; circling likea crown) sulcus (sool ′ k ŭ s; ditch) runs obliquely around the heart,separating the atria from the ventricles. Two more sulci extendinferiorly from the coronary sulcus, indicating the division betweenthe right and left ventricles. The anterior interventricularsulcus ( groove ) is on the anterior surface of the heart, extend-ing from the coronary sulcus toward the apex of the heart(figure 20.5 a,b ). The posterior interventricular sulcus ( groove )is on the posterior surface of the heart, extending from thecoronary sulcus toward the apex of the heart (figure 20.5 c ). In ahealthy, intact heart, the sulci are covered by adipose tissue, andonly after this tissue is removed can they be seen.

Aortic arch

Left pulmonary artery

Superior vena cava

Aorta

Branches of rightpulmonary artery

Right pulmonary veins

Left atrium

Right atrium

Coronary sulcus

Right coronary artery

Great cardiac vein(in anterior interventricular sulcus)

Anterior interventricular artery(in anterior interventricular sulcus)

Left ventricle

Branches of leftpulmonary artery

Pulmonary trunk

Left pulmonary veins

Right ventricle

Inferior vena cava

(a) Anterior view

FIGURE 20.5 Surface View of the Heart

( a ) The two atria (right and left) are located superiorly, and the two ventricles (right and left) are located inferiorly. The superior and inferior venae cavae enterthe right atrium. The pulmonary veins enter the left atrium. The pulmonary trunk exits the right ventricle, and the aorta exits the left ventricle.