Chapter 20: The Cardiovascular System: The Heart
Anatomy of the Heart
Location of the heart
o Rests on the diaphragm near midline of thoracic cavity
o Lies in the mediastinum (anatomical region that extends from the sternum
to the vertebral column, from the 1st rib to the diaphragm & in between
the lungs)
o About 2/3 of the mass of the heart lies to the left of the body’s midline
o Apex: formed by the tip of the left ventricle & rests on diaphragm—
directed anteriorly, inferiorly and to the left
o Base: opposite of apex & is its posterior aspect—formed by the atria
(upper chambers) and mostly the left atrium
o Anterior surface: deep to sternum and ribs
o Inferior surface: part of heart between apex and right surface & rests on
diaphragm
o Right surface: faces right lung & extends from the inferior surface to the
base
o Left surface: faces left lung and extends from base to apex
Pericardium
o Membrane that surrounds and protects the heart
o Confines heart to its position in the mediastinum, while allowing sufficient
freedom of movement for vigorous and rapid contraction
o Consists of 2 main parts:
Fibrous pericardium: superficial- composed of tough, inelastic,
dense irregular connective tissue
Resembles a bag that rests on and attaches to diaphragm
Open end is fused to connective tissues of blood vessels
entering and leaving the heart
Prevents overstretching
Provides protection
, Anchors heart in mediastinum
Near the apex of the heart, it is partially fused to the central
tendon of the diaphragm, so movement of the diaphragm
facilitates movement of blood by the heart
Serous pericardium: deep- thinner, more delicate membrane that
forms a double layer around the heart
Parietal layer of serous pericardium: outer layer- fused to the
fibrous pericardium
Visceral layer of serous pericardium: also called the
epicardium; adheres tightly to the surface of the heart
b/w the parietal and visceral layers of the serous
pericardium is a thin film of lubricating serous fluid
known as pericardial fluid, that reduces friction b/w
layers of serous pericardium as the heart moves
space that contains the few milliliters of pericardial
fluid is the pericardial cavity
Layers of the Heart Wall
o 3 layers
Epicardium
Composed of 2 tissue layers
visceral layer of the serous pericardium: thin,
transparent outer layer; composed of mesothelium
Adipose & fibroelastic tissue: adipose tissue
predominates & becomes thickest over the
ventricular surfaces where it houses the major
coronary and cardiac vessels of the heart
Smooth, slippery texture to the outermost surface of the
heart
Contains blood vessels, lymphatics, and vessels that supply
the myocardium
Myocardium
Middle
Responsible for the pumping action of the heart & is
composed of cardiac muscle tissue
Makes up ~95% of the heart wall
Muscle fibers (cells) are wrapped and bundled with
connective tissue sheaths composed of endomysium and
perimysium; organized in bundles that swirl diagonally
around the heart and generate the strong pumping actions
Endocardium
, Innermost, thin layer of endothelium overlying a thin layer
of connective tissue
Provides a smooth lining for the chambers of the heart and
covers the valves of the heart
Smooth endothelial lining minimizes the surface friction as
blood passes through the heart
Continuous with the endothelial lining of the large blood
vessels attached to the heart
Chambers of the Heart
o 4 chambers—2 superior receiving chambers are the atria & 2 inferior
pumping chambers are the ventricles
o paired atria receive blood from blood vessels returning blood to the heart
(veins), while ventricles eject the blood from the heart into blood vessels
(arteries)
o Auricle: wrinkled, pouchlike structure on the anterior surface of each
atrium; resembles a dog’s ear
each auricle slightly increases the capacity of an atrium so it can
hold a greater volume of blood
o Sulci: series of grooves on the surface of the heart that contain coronary
blood vessels and a variable amount of fat
Each sulcus marks the external boundary between 2 chambers of
the heart
Coronary sulcus: deep; encircles most of the heart and marks the
external boundary between the superior atria and inferior ventricles
Anterior Interventricular Sulcus: shallow groove on the anterior
surface of the heart that marks the external boundary between the
right and left ventricles on the anterior aspect of the heart
Posterior Interventricular Sulcus: continues from anterior
interventricular surface onto and around the posterior surface of
the heart, that marks the external boundary between the ventricles
on the posterior aspect of the heart
o Right Atrium
Forms the right surface of the heart and receives blood from 3
veins:
Superior vena cava
Inferior vena cava
Coronary sinus
**veins always carry blood toward the heart**
2-3 mm in thickness
, anterior and posterior walls are very different
inside of posterior wall: smooth
inside of anterior wall: rough due to the presence of muscular
ridges called pectinate muscles, which also extend into the
auricle
interartrial septum: thin partition between the right atrium and
left atrium
fossa ovalis: oval depression of the interatrial septum—remnant
of the foramen ovale (an opening in the septum of the fetal heart
that normally closes soon after birth)
blood passes from the right atrium into right ventricle through a
valve called the tricuspid valve (consists of 3 cusps); aka right
atrioventricular valve
valves of heart are composed of dense connective tissue covered
by endocardium
o Right Ventricle
About 4-5 mm in thickness and forms most of the anterior surface
of the heart
Inside contains a series of ridges formed by raised bundles of
cardiac muscle fibers called trabeculae carneae
The cusps of the tricuspid valve are connected to tendonlike cords,
called the chordae tendineae, which in turn are connected to
cone-shaped trabeculae carneae called papillary muscles
Right ventricle is separated from the left ventricle by a partition
called the interventricular septum
Blood passes from right ventricle via pulmonary valve (pulmonary
semilunar valve) into a large artery called the pulmonary trunk,
which divides into right and left pulmonary arteries and carries
blood to the lungs
**arteries always take blood away from the heart**
o Left Atrium
About same thickness as right atrium; forms most of the base of
the heart
Receives blood from the lungs through 4 pulmonary veins
Inside has a smooth posterior and anterior wall
Blood passes from the left atrium into the left ventricle through the
bicuspid (mitral) valve, which has 2 cusps; also called the left
atrioventricular valve
o Left Ventricle
Thickest chamber of the heart; ~10-15 mm and forms the apex of
the heart
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