Chapter 18: The Cardiovascular System
Heart Anatomy
Size, Location, Orientation
-superior surface of diaphragm (on top)
-left of the midline, from 2nd rib to 5th intercostal (between ribs) space
-anterior (in front) to the vertebral column; posterior to the sternum
-mediastinum (middle of chest)
Coverings of the Heart
-the heart is enclosed in a double-walled sac called the pericardium
-the loosely fitting superficial part of this sac is the fibrous pericardium
-protects the heart
-anchors it to surrounding structures
-prevents overfilling of the heart with blood
-below the fibrous pericardium is the serous pericardium
-a thin, slippery, 2 layer serous membrane
-the parietal layer of the serous pericardium lines the internal surface of the fibrous
pericardium; it attaches to the large arteries exiting the heart and then turns and
continues over the external heart surface of the visceral layer (epicardium)
-between the parietal and visceral layers is the pericardial cavity (look at pg. 663) which
contains a film of serous fluid; this allows the heart to work in a relatively friction-free
Layers of the Heart Wall
-the heart wall consists of the epicardium, myocardium, and the endocardium
-the superficial epicardium is the visceral layer of the serous pericardium and is often
infiltrated with fat especially in old people
-the myocardium is the middle layer and is composed mainly of cardiac muscle and forms
the bulk of the heart
-it is the layer that contracts
-branching cardiac muscle cells are tethered to one another by crisscrossing
connective tissue fibres and arranged in a spiral or circular bundles
-the fibrous skeleton of the heart forms a dense network and reinforces the
myocardium internally and anchors the cardiac muscle fibres
-it also limits the direct spread of action potentials across the heart to
specific pathways
-the endocardium (inside the heart) is a glistening white sheet of endothelium (squamous
endothelium) that rests on a thin connective tissue layer
-it lines the heart chambers and covers the fibrous skeleton of the valves
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-endocardium is continuous with the endothelial linings of the blood vessels
leaving and entering the heart
Chambers and Associated Great Valves
-the heart has 4 chambers
-2 superior atria and 2 inferior ventricles
-the internal partition that divides the heart longitudinally is called the interatrial
septum where it separates the atria and the interventricular septum where it
separates the ventricles
-the right ventricle forms most of the anterior surface
-the left ventricle dominates the inferoposterior aspect of the heart and forms the apex
-two grooves visible on the heart surface indicate the boundaries of its 4 chambers and
carry the blood vessels supplying the myocardium
-the coronary sulcus or atrioventricular groove encircles the junction of the atria
and ventricles like a crown
-the anterior interventricular sulcus marks the anterior position of the septum,
separating the right and left ventricles and continues as the posterior
interventricular sulcus
Atria: The Receiving Chambers
-except for protruding appendages called auricles (little ear) which increase atrial volume
somewhat, the right and left atria are remarkably free of distinguishing surface features
-the right atrium has 2 basic parts:
-a smooth-walled posterior part and an anterior portion where the walls are ridged
by bundles of muscle tissue that look like the teeth of a comb and are called
pectinate muscles (pectin = comb)
-the posterior and anterior of the right atrium are separated by a C-shaped ridge
called the crista terminalis (terminal crest)
-the left atrium is mostly smooth and pectinate muscles are found around the
-functionally, the atria are receiving chambers for blood returning to the heart from
-small and thin-walled chambers since they contract minimally
-contribute little to the propulsive pumping activity of the heart
-blood enters the right atrium via 3 veins:
1) the superior vena cava returns blood from body regions superior to the
diaphragm (above the diaphragm)
2) the inferior vena cava returns blood from body areas below the diaphragm
3) the coronary sinus collects blood draining from the myocardium
-4 pulmonary veins enter the left atrium which transport blood from the lungs back to the
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Ventricles: The Discharging Chambers
-the ventricles make up most of the volume of the heart
-trabeculae carneae (crossbar flesh) mark the internal walls of the ventricular chambers
and are irregular ridges of muscle
-the cone-like papillary muscles play a role in valve function and project into the
ventricular cavity
-the ventricles are the actual pumps of the heart
-ventricular walls are much thicker than atrial walls
-when the ventricles contract, blood is propelled out of the heart into the circulation
-the right ventricle pumps blood into the pulmonary trunk which routes the blood to the
lungs where gas exchange occurs
-the left ventricle ejects the blood into the aorta, the largest artery in the body
Pathway of Blood Through the Heart
-the heart is made up of 2 side-by-side pumps, each serving a separate blood circuit
-the blood vessels that carry blood to and from the lungs form the pulmonary circuit
which serves gas exchange
-the blood vessels that carry functional blood supply to and from all body tissues constitute
the systemic circuit
-the right side of the heart is the pulmonary circuit pump
-blood returning from the body is relatively oxygen-poor and carbon dioxide-rich
-it enters the right atrium and passes into the right ventricle which pumps it to the
lungs via the pulmonary trunk
-in the lungs, the blood unloads carbon dioxide and picks up oxygen
-the oxygenated blood is carried by pulmonary veins back to the left side of the
-typically, veins carry oxygen-poor blood to the heart and arteries transport
oxygen-rich blood from the heart
-this is the opposite in the pulmonary circuit
-the left side of the heart is the systemic circuit pump
-freshly oxygenated blood leaving the lungs is returned to the left atrium and
passes into the left ventricle, which pumps it into the aorta
-the blood is transported via smaller systemic arteries to the body tissues where
gases and nutrients are exchanged across capillary walls
-once the blood is loaded with carbon dioxide and depleted of oxygen, it returns
through the systemic veins to the right side of the heart, where it enters the right
atrium through the superior and inferior vena cavae
-the 2 ventricles have unequal workloads but pump equal volumes of blood
-the pulmonary circuit, served by the right ventricle is a short, low-pressure
-the systemic circuit, served by the left ventricle, takes a long pathway through
the entire body and encounters 5 times as much resistance in blood flow
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