Page 114 - Headlines Histology2024_Neat

Heart

• The heart is a muscular, rhythmically contracting organ pumping the blood into
the vascular system.The wall of the heart consists of three main layers:
endocardium, myocardiuum and epicardium.

• The endocardium is the innermost layer corresponding to the tunica intima of
the blood vessels.It consists of endothelium, subendothelial layer and
sunendocardial layer.

• The endothelium is a single layer of flattened epithelial cells rests on a basal
lamina and is continuous with the endothelium of the vessels entering or
leaving the heart.

• The subendothelial layer is a dense connective tissue layer contains fibroblasts,
collagenous, elastic fibers and few smooth muscle cells.

• The subendocardial layer is a loose connective tissue layer binds the
endocardium to the myocardium. It contains blood vessels, nerves and
branches of the conduction system of the heart.

• The myocardium is the middle muscular layer corresponding to the tunica
media. It is made up of cardiac muscle cells embedded in loose connective
tissue that contains a dense capillary network. Three types of cardiac muscle
cells exist contractil cells, myoendocrine cells and Purkinje fibers.

• The contractile cardiac myofibers are the most numerous types. They are
striated, branched and arranged in spiral bundles.

• The Purkinje fibers represent the terminal branches of the impulse conducting
system.

• The myoendocrine cells are contractile myocardiocytes posses a well-
developed secretory apparatus within their cytoplasm. The secretory apparatus
composed of scarce rER tubules, a well-developed Golgi and large number of
secretory granules. These cells are concentrated primarily within the atrial wall
especially the right atrium. Recent studies have proved the presence of these
cells among the ventricular cardiomyocytes. Myoendocrine cells are the

114