Maintenance of the Body
Check Your Understanding
The heart is in the mediastinum. Just what is the
From inside to outside, list the layers of the heart wall and
the coverings of the heart.
What is the purpose of the serous ﬂuid inside the pericardial
For answers, see Appendix H.
Chambers and Associated Great Vessels
Describe the structure and functions of the four heart
chambers. Name each chamber and provide the name and
general route of its associated great vessel(s).
Te heart has four chambers
tre-ah) and two inferior
internal partition that divides the heart longitudinally is called
where it separates the atria, and the
where it separates the ventricles. Te
right ventricle forms most of the anterior surface of the heart.
Te leF ventricle dominates the inferoposterior aspect of the
heart and forms the heart apex.
±wo grooves visible on the heart surface indicate the bound-
aries of its four chambers and carry the blood vessels supply-
ing the myocardium. Te
(²igure 18.5b, d), or
, encircles the junction of the atria and
ventricles like a crown (
, cradling the anterior interventricular artery,
marks the anterior position of the septum separating the right
and leF ventricles. It continues as the
, which provides a similar landmark on the heart’s
Atria: The Receiving Chambers
Except for small, wrinkled, protruding appendages called
little ear), which increase the atrial
volume somewhat, the right and leF atria are remarkably free of
distinguishing surface features. Internally, the right atrium has
two basic parts (²igure 18.5c): a smooth-walled posterior part
and an anterior portion in which bundles of muscle tissue form
ridges in the walls. Tese muscle bundles are called
because they look like the teeth of a comb (
comb). Te posterior and anterior regions of the right atrium
are separated by a C-shaped ridge called the
In contrast, the leF atrium is mostly smooth and pectinate
muscles are found only in the auricle. Te interatrial septum
bears a shallow depression, the
marks the spot where an opening, the
, existed in
the fetal heart (²igure 18.5c, e).
²unctionally, the atria are receiving chambers for blood re-
turning to the heart from the circulation (
Te atria are relatively small, thin-walled chambers because they
need to contract only minimally to push blood “downstairs”
into the ventricles. As a rule, they contribute little to the propul-
sive pumping activity of the heart.
Blood enters the
via three veins (²igure 18.5c–e):
superior vena cava
returns blood from body regions
superior to the diaphragm.
inferior vena cava
returns blood from body areas below
collects blood draining from the myo-
, which makes
up most of the heart’s base. Tese veins, which transport blood
from the lungs back to the heart, are best seen in a posterior
view (²igure 18.5d).
Ventricles: The Discharging Chambers
±ogether the ventricles (
underside) make up most of the
volume of the heart. As already mentioned, the right ventricle forms
most of the heart’s anterior surface and the leF ventricle dominates
its posteroinferior surface. Irregular ridges of muscle called
ne-e; “crossbars of ﬂesh”) mark
the internal walls of the ventricular chambers. Still other muscle
bundles, the conelike
, which play a role in valve
function, project into the ventricular cavity (²igure 18.5e).
Te ventricles are the discharging chambers, the actual
pumps of the heart. Teir walls are much more massive than
the atrial walls, reﬂecting the diﬀerence in function between the
atria and ventricles (²igure 18.5e and f). When the ventricles
contract, they propel blood out of the heart into the circulation.
Te right ventricle pumps blood into the
which routes the blood to the lungs where gas exchange occurs.
Te leF ventricle ejects blood into the
tah), the larg-
est artery in the body.
Name the heart valves and describe their location, function,
and mechanism of operation.
Blood ﬂows through the heart in one direction: from atria to ven-
tricles and out the great arteries leaving the superior aspect of the
heart. ²our valves enforce this one-way traﬃc (²igure 18.5e and
). Tey open and close in response to diﬀerences in
blood pressure on their two sides.
Atrioventricular (AV) Valves
atrioventricular (AV) valves
, one located at each
atrial-ventricular junction, prevent backﬂow into the atria when
the ventricles contract.
Te right AV valve, the
three ﬂexible cusps (ﬂaps of endocardium reinforced by con-
nective tissue cores).
Te leF AV valve, with two cusps, is called the
tral) because it resembles the two-sided bishop’s miter or
hat. It is sometimes called the
(Text continues on p. 667.)