Endocardium: internal layer of endothelium and connective tissue
Myocardium: the middle, thick muscular layer of the heart
Epicardium, or visceral pericardium
The fibrous skeleton of the heart is a framework of dense collagen that encircles the orifices of the four valves (pulmonary, aortic, tricuspid
and mitral).
The functions of the fibrous skeleton are:
Maintains the patency of the atrioventricular valves
Provides a fixed site for the attachment of the leaflets and cusps of the valves
Provides a fixed site for the attachments of the cardiac muscle fibers
Insulates the atria from the ventricles so that they can contract independently
The cardiac cycle consists of
Relaxation of the ventricles (diastole) followed by
Contraction of the ventricles (diastole)
Heart sounds heard with a stethoscope:
"lub"-blood from the atria fills the ventricles
"dub"-ventricles contract and push blood out of the heartOrientation of the Heart: Border and Surfaces
[Plate 208, Heart: Base and Diaphragmatic Surfaces]The heart lies obliquely between the 3rd and the 5th ribs, mainly on the left side of the midline of the thorax, but with roughly a third of it
slightly to the right.
The base of the heart is its posterior surface, which is the left atrium.
The apex of the heart is formed from the most inferior and lateral part of the left ventricle and lies beneath the left 5th intercostal space at
approximately the midclavicular line.Borders
Right border: the right atrium between the superior and inferior vena cavae
Left border: left auricle and left ventricle
Inferior border: mainly right ventricle with some contribution from the left ventricle
Superior border (anterior view): right and left atria and their auricles