Exam 1 Review:  Chapter 18:  Internal Anatomy of the Heart

myocardium - The middle muscular layer of the heart wall enclosed between the epicardium and endocardium, consisting primarily of cardiac muscle contractile cells and a conduction system composed of specialized conductive or pacemaker cells; this muscular organ contracts in response to commands from the Autonomic Nervous System and to certain hormones, e.g., epinephrine = adrenalin.

endocardium - The thin serous membrane, composed of endothelial tissue, a single layer of squamous cells, which lines the interior of the heart chambers and valves and which is continuous with the inner lining of blood vessels.

endothelium - The single layer of simple squamous cells which line the walls of the heart, blood vessels, and lymphatic vessels; this tissue arises from mesoderm.

heart chambers - The four enclosed spaces or compartments, guarded by valves to prevent backflow, which receive the blood which the heart will pump through the circulatory system; they consist of two superior thin-walled atria and two inferior thick-walled ventricles.

atria - The two superior thin-walled antechambers of the heart which receive blood from the veins (vena cava and pulmonary respectively) and contract to force blood into the ventricles; the lateral ear-shaped free wall of each is referred to as the auricle; these muscles contract when stimulated by impulses from the SA node and conduction myofibers.

fossa ovalis - The closed remnant of one of the fetal heart's right-to-left shunts, the foramen ovale; it is a thin fibrous sheath forming a depression on the septal wall (interatrial septum) of the right atrium.

interatrial septum - The portion of the myocardium which forms the wall between the right and the left atria.

ventricles - (1)  In the brain, the series of four interconnecting cavities of the brain, lined by ependymal cells and with a specialized choroid plexus which produce the cerebrospinal fluid that fills these chambers.  (2) In the heart, (l) the chamber on the left side of the heart which receives arterial blood from the left atrium and contracts to force it into the aorta; and (r) the chamber on the right side of the heart which receives venous blood from the right atrium and forces it into the pulmonary artery; these cardiac chamber muscles contract when stimulated by impulses from the bundle branches and conduction myofibers.

interventricular septum - The portion of the myocardium which forms the wall between the right and the left ventricles and through which pass the bundle and bundle branches of the heart's internal conduction (pacemaker) system.

pectinate muscle - Visible raised bands of cardiac muscle, giving a comb-like surface appearance to the interior of the anterior wall of the right atrium; similar in appearance to the trabeculae carnae of the ventricular chambers; this muscle participates in atrial contraction when stimulated by impulses from the SA node.

papillary muscles - Small, cone-shaped muscles projecting from the walls of the lower heart chambers (the ventricles) to which are attached fibrous cords (chordae tendineae) stretching up to the flaps of the valves between upper and lower chambers; when the ventricles fill with blood and contract, the papillary muscles also contract and tighten the cords, allowing the valves to be pressed shut, but preventing them from being pushed back and open into the upper chambers (the atria) by the surging blood; these muscles contract when stimulated by impulses from the bundle branches and conduction myofibers.

chordae tendineae - The series of thin, branching strips or bands of dense fibrous connective tissue which connect the papillary muscles in the ventricles of the heart to the edges of the flaps of the atrio-ventricular valves (tricuspid and bicuspid/mitral) to control the position of the valves during ventricular contraction to prevent backflow of blood into the atria.

trabeculae carneae - Visible raised bands of cardiac muscle, giving a ridged surface appearance to the interior of the walls of the ventricles; similar in appearance to the pectinate muscle of the right atrium.

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